On this page I will describe the process that each component goes through after being produced using additive manufacturing technologies, and what it takes in order to turn it into a fully finished component ready for assembly. I will also talk about the main post-processing challenges that I have encountered while working on this project.
MAIN CHALLENGES
The first problem that I've encountered after I've decided to use additive manufacturing technologies in my project was the complete lack of any sort of relevant literature or sources on post-processing even the basic MJF or SLS nylon (PA12) components, let alone the more exotic and rare Graphite or Carbon Fiber reinforced materials. In fact, even many of the companies who were developing these technologies and dealing with the actual component production, didn't offer any post-processing services. That meant I was stuck in a situation where I could get my components manufactured out of extremely advanced and high quality materials, but nobody knew how to make them look nice. I genuinely felt like not a lot people ever bothered finishing parts manufactured this way to a high standard, at least not publicly. It makes sense in a way, since most of the applications of MJF and SLS printing in the industry are either related to prototyping or for use with mechanical parts, where visual aspects of the components are irrelevant. Most companies don't spend a lot of money and time on making the prototype components look nice, since that is not their priority, they are mainly looking at the function, the fitting and the mechanical properties, before using the same designs for mass production of the parts afterwards. At the same time, using additive manufacturing for mass production is still economically inefficient. In addition, even to this day, most people, even those who are familiar with basics of 3D printing, often aren't familiar with SLS and MJF technologies or have very limited experience in that field, so getting advice from people with first-hand experience was more than difficult. There were a few sources out there on various forums, but they managed to only achieve very low levels of finishing quality and didn't manage to hide the fact that the parts were manufactured using 3D printing. The same is true for several of the more mainstream oriented companies who deal with additive manufacturing and do offer post-processing services. They over-charge for their services massively and deliver mediocre results because they haven't developed proper procedures.
The main reason for that is the fact that MJF and SLS manufactured components require quite a lot of effort to post-process properly and require a very hands-on approach. I imagine it would be very difficult to automate the process I'll describe here, and therefore make it profitable on a large scale. MJF and SLS manufactured components have a slightly porous surface, and their surface is not perfectly smooth. It's slightly textured, sometimes with stepping lines from the printing layers still visible. This is both a disadvantage and an advantage. It's a disadvantage because it requires more effort and more steps in order to make the components look great. It's an advantage because the surface to which paint products are being applied to is rough and the products manage to soak into the surface layers of the components, so the adhesion between them is very good, much better than when applying them to perfectly smooth plastic surfaces for example. This means that the results achievable aren't only visually great, but also very durable, especially when using professional and high quality automotive paint products.
Considering my goal from the beginning was achieving an absolutely perfect finish on my headphones, as good or better than on any high end headphone on the market, I knew I'd have to figure out how to do it on my own. That meant I had to go through a lot of trial and error in order to figure out exactly how to achieve a proper high quality finish on the components. I've tested countless products and methods until I finally developed a reliable step-by-step procedure that leads to satisfactory results every time, without any need for expensive equipment or special tools, just patience and precision.
The main reason for that is the fact that MJF and SLS manufactured components require quite a lot of effort to post-process properly and require a very hands-on approach. I imagine it would be very difficult to automate the process I'll describe here, and therefore make it profitable on a large scale. MJF and SLS manufactured components have a slightly porous surface, and their surface is not perfectly smooth. It's slightly textured, sometimes with stepping lines from the printing layers still visible. This is both a disadvantage and an advantage. It's a disadvantage because it requires more effort and more steps in order to make the components look great. It's an advantage because the surface to which paint products are being applied to is rough and the products manage to soak into the surface layers of the components, so the adhesion between them is very good, much better than when applying them to perfectly smooth plastic surfaces for example. This means that the results achievable aren't only visually great, but also very durable, especially when using professional and high quality automotive paint products.
Considering my goal from the beginning was achieving an absolutely perfect finish on my headphones, as good or better than on any high end headphone on the market, I knew I'd have to figure out how to do it on my own. That meant I had to go through a lot of trial and error in order to figure out exactly how to achieve a proper high quality finish on the components. I've tested countless products and methods until I finally developed a reliable step-by-step procedure that leads to satisfactory results every time, without any need for expensive equipment or special tools, just patience and precision.
STEP-BY-STEP POST-PROCESSING GUIDE
STEP 1) PREPARATION - After the parts get manufactured using AM technologies, they have to be prepared for painting. That means three things:
SUMMARY:
- Sanding - Every surface of every MJF and SLS printed part has a slightly rough appearance which has to be lightly sanded using 320 grit sanding paper, just enough to make the surfaces scuffed and help with paint adhesion. Making surfaces perfectly smooth at this stage is unnecessary, but the smoother they are, the easier the next steps will be. It's important to sand all surfaces evenly, applying even pressure and always with an X pattern, which means sanding in two perpendicular directions for an equal amount of time, with equal pressure. This is especially important on curved surfaces, as it helps to retain the original shape. Flat surfaces can be sanded using flat sanding blocks. Certain surfaces on printed parts have stepping lines visible on them. These are 0.05 - 0.1 mm steps present on the "underside" of the part, on surfaces which are at low angles relative to the horizontal plane in the additive manufacturing machines during production. Whenever possible, the part printing orientation is set so that the printing lines are avoided, or that the side with printing lines will not be visible on the assembled headphone. However, when it's visible and has to be painted, it's advisable to sand the part until the steps are barely felt with a fingernail. It's not necessary to completely remove them. Sanding until the steps no longer feel rough is enough, and generally a very small amount of material is sanded off in this step, less than 0.1 mm.
- Cleaning and de-greasing - In order for paint products to adhere to the surface of a printed part properly, all the residual dust from the manufacturing process, as well as from the sanding, has to be removed. The best way to do that is to simply use a hard brush or a similar tool, and brush the surface of the parts under running water. After the components are thoroughly washed, they have to be de-greased. In my opinion and experience, pure acetone is the best option for this step. Components are soaked in an acetone bath for a couple of minutes, completely submerged. They can be additionally brushed at that point if necessary. After a couple of minutes in an acetone bath, they are removed and placed somewhere to completely dry up. This will usually take a couple of hours and can be sped up by leaving the parts next to a source of reasonable heat in a well ventilated area. Handling the parts with bare hands should be avoided after this point in order to prevent smearing them with finger oils, dirt, etc.
- Masking - This is an optional step for certain parts that have features on them that aren't supposed to be painted, or sides that won't be visible on the final product. Whenever possible, parts are masked using masking tape which is precisely taped and cut with a scalpel in order to protect certain surfaces. This is done in order to preserve certain assembly tolerances, to reduce the consumption of expensive paint products and to reduce the weight of the parts. Once the masking tape is added, it usually won't have to be removed until the end of the painting process, so it's important to be accurate at this stage. At this point, parts are also attached to various holders, such as pieces of wire, wooden skewers or similar items, in order to handle them more easily during the next steps. IMPORTANT: When parts need to be masked, the "B) PLASTIC PRIMER" step is done BEFORE masking in order to intentionally overshoot the plastic primer beyond areas that will later be painted. Masking tape can still be used to protect the bulk of the areas that won't be painted, but it's important to overshoot the plastic primer by at least 2-3 mm beyond the edge where the final masking tape will be placed. This will prevent the edges of paint from chipping off or peeling off in the future.
SUMMARY:
- Sand 3D printed parts with 320 grit sanding paper in order to remove any obvious surface imperfections.
- Sand curved surfaces in an X-pattern, and use flat sanding blocks or rigidly folded sanding paper while sanding flat surfaces.
- Sand only the areas that will be painted, making sure to sand each continuous surface separately, avoiding edges between them.
- As soon as the surface of the parts feels smooth to the touch, stop sanding in order to prevent excess plastic removal or surface deformation.
- Finish the sanding process by gently sanding the edges in continuous passes all around the plastic part.
- Clean and de-grease the part with pure acetone and a brush. Don't touch the part with bare hands after this point.
- If required, mask the areas that won't be painted with masking tape, precisely cutting the masking tape along the edges, ensuring that a few millimeter wide gap is left between the masking tape and the actual edges that will be visible on the assembled headphone.
- Attach the part to something that will allow you to manipulate it during painting without touching the painted surfaces.
STEP 2) APPLYING PLASTIC PRIMER - After the parts have been properly prepared for painting, they have to be covered with a plastic primer, also known as an adhesion promoter. The plastic primer application is one of the most crucial steps in the entire process. That is because the plastic primer serves a dual purpose. It improves the adhesion between the plastic and the filler, but also acts as a surface sealer. As I've mentioned previously, MJF and SLS components have a slightly porous surface, which means that all liquids, including paint products, are absorbed into the upper layers of the plastic surface. Proper application of the primer will prevent products applied onto the parts after the primer from soaking in excessively. For that reason, the plastic primer has to be applied in multiple very thin coats, with 5 to 10 minutes of drying time between each coat. The drying period between coats may vary from product to product, but the purpose of applying the primer in multiple coats remains the same. It's important not to wait for too long between coats, as the primer might dry to such an extent that the next coat applied to it won't adhere optimally anymore. At the same time, applying the next coat too soon, while the previous coat is still too wet, won't lead to a desired effect because too much of the product will soak into the porous plastic. It's a fine balance which ensures that the first coat, which will be fully absorbed by the surface of the part, is fairly dry by the time the second coat is applied. Then when the second coat is applied, it won't be absorbed by the porous surface as much as the first one. The third coat will be absorbed to even lesser degree, and so on. Usually it takes 4 to 5 such thin coats of plastic primer to seal the surface properly. It's easy to notice the point at which the surface is properly sealed, because the plastic primer makes the surface of the plastic part slightly glossy after it dries up, as opposed to soaking into the plastic entirely and leaving a completely matte surface before an appropriate amount of coats are applied. Once the parts are sealed properly, they'll look as if they're covered by a thin coat of semi-gloss lacquer. After that's been achieved, the primed parts are left to dry and cure as per instructions of the product manufacturer. Usually that is around 30 to 60 minutes, and within that time window, it's recommended to apply the high build filler, as the adhesion between the primer and the filler will be optimal in that case. After the plastic primer dries sufficiently, it's recommended to lightly scuff the surfaces using a grey (600 grit) Scotch-Brite pad, using very light pressure, until an even, matte surface is achieved. This will additionally improve the adhesion between the primer and the high build filler. Any residual dust is wiped off using a damp cloth, and once the parts are clean and dry, we can move on to the next step.
SUMMARY:
SUMMARY:
- Shake the plastic primer spray can for at least 3 minutes.
- Apply the first coat onto the surface of the part from 25-30 cm of distance, very lightly, in short, even bursts, always keeping the spray nozzle moving. Cover the contact edges first, followed by smaller continuous surfaces and finally finishing a single coat with the largest continuous surface.
- After drying the part for 5-10 minutes, apply a second coat using the same technique, until a semi-gloss wet surface is achieved.
- Wait for 5-10 minutes, and repeat the previous step in order to apply the third coat.
- Wait for 5-10 minutes, and repeat the previous step in order to apply the fourth coat.
- Wait for 5-10 minutes, and apply the fifth coat more heavily, until a fully wet and glossy surface is achieved, try to avoid runs or primer build-up.
- Let the primer dry for 30-60 minutes, or as recommended by the primer manufacturer.
- Before applying the filler, lightly scuff the semi-gloss and dry surface of the primer with an abrasive pad, until the surface turns matte.
- Wipe any residual dust off with a damp cloth, let the part dry, and then move onto the high-build filler application.
STEP 3) APPLYING HIGH-BUILD FILLER - The next step in the post-processing is applying a spray high-build filler onto the surface of the parts. The purpose of applying a filler is to cover the still uneven and rough surfaces of the parts with a product that can be easily sanded to a perfectly smooth finish. A special automotive type of product is used in this step, which can be applied in much thicker layers than the primer or the base coat and is specifically designed for this exact purpose. On top of that, because it's meant for automotive applications, it's especially tough, resistant to temperature and humidity changes, and has a decent level of flexibility and impact resistance. After it's applied, it's sanded until a perfectly smooth surface ready for applying the base coat is achieved. This can be done in one step, but usually two steps are required for 3D printed parts. This means that the first layer of filler is sanded as much as possible, almost reaching the plastic underneath it, leaving only the thinnest possible layer of filler necessary for achieving a smooth surface. The plastic can even get exposed on some areas by the time the surface becomes perfectly smooth, this usually happens around edges. Because of that, a second, thinner layer of filler is then applied on top, in order to cover the exposed parts of the plastic again. This way, the thinnest possible layer of filler is left on the components before applying the base coat.
The filler is sprayed onto the surface in several coats after shaking the can for at least 3 minutes in order to ensure an optimal mixture is applied to the parts. The first coat is applied very lightly, just dusting the surface without covering it entirely. The second coat is applied a bit more heavily, now fully hiding the surface of the components, while the following coats are applied heavily, until a fully wet finish is achieved. It's important to let the filler dry for at least 10 minutes between two coats. Certain fillers leave a slightly textured finish after they're applied, but once they dry up, the surface tightens up and has a fairly smooth, matte finish. This method can be modified depending on the application, sometimes less filler will be sufficient, other times more coats will be required, it all depends on the complexity of the parts, as well as their roughness. Most of the time three to four coats are enough. The basic idea is to apply a thick enough layer of filler to be able to sand it and achieve a perfectly smooth surface finish, but without sanding all the way through to the raw plastic. Filler products are very flexible in the way they function and how they can be applied, and therefore it's not very easy to mess up when working with them, in the worst case scenario the filler can be sanded off and reapplied. The most important thing to remember is to not start sanding the filler until it's fully dried and cured. After the filler has been applied, it's left to dry and cure for at least 24 to 48 hours, depending on the thickness applied, as well as the specific product used. Certain 2K fillers can dry in a couple of hours, but there's no harm in leaving them to cure for longer than that. An easy way to tell whether the filler is ready for sanding is to simply try sanding a small surface area. If it feels dry, like the surface of a chalk, and leaves a lot of dry, dusty residue, then it's ready. If it feels rubbery and as if the sanding paper is sticking to it, then it needs more drying time. Another thing to remember is that the high-build filler, once cured, doesn't require the base coat to be applied to it immediately, in fact, a lot of automotive paint experts claim that a properly cured filler essentially won't degrade with time at all, so rushing towards the base coat phase is not necessary, which means that a lot of time can be devoted to sanding the surfaces properly and re-coating with a new layer of filler if necessary.
SUMMARY:
The filler is sprayed onto the surface in several coats after shaking the can for at least 3 minutes in order to ensure an optimal mixture is applied to the parts. The first coat is applied very lightly, just dusting the surface without covering it entirely. The second coat is applied a bit more heavily, now fully hiding the surface of the components, while the following coats are applied heavily, until a fully wet finish is achieved. It's important to let the filler dry for at least 10 minutes between two coats. Certain fillers leave a slightly textured finish after they're applied, but once they dry up, the surface tightens up and has a fairly smooth, matte finish. This method can be modified depending on the application, sometimes less filler will be sufficient, other times more coats will be required, it all depends on the complexity of the parts, as well as their roughness. Most of the time three to four coats are enough. The basic idea is to apply a thick enough layer of filler to be able to sand it and achieve a perfectly smooth surface finish, but without sanding all the way through to the raw plastic. Filler products are very flexible in the way they function and how they can be applied, and therefore it's not very easy to mess up when working with them, in the worst case scenario the filler can be sanded off and reapplied. The most important thing to remember is to not start sanding the filler until it's fully dried and cured. After the filler has been applied, it's left to dry and cure for at least 24 to 48 hours, depending on the thickness applied, as well as the specific product used. Certain 2K fillers can dry in a couple of hours, but there's no harm in leaving them to cure for longer than that. An easy way to tell whether the filler is ready for sanding is to simply try sanding a small surface area. If it feels dry, like the surface of a chalk, and leaves a lot of dry, dusty residue, then it's ready. If it feels rubbery and as if the sanding paper is sticking to it, then it needs more drying time. Another thing to remember is that the high-build filler, once cured, doesn't require the base coat to be applied to it immediately, in fact, a lot of automotive paint experts claim that a properly cured filler essentially won't degrade with time at all, so rushing towards the base coat phase is not necessary, which means that a lot of time can be devoted to sanding the surfaces properly and re-coating with a new layer of filler if necessary.
SUMMARY:
- Shake the filler spray can for at least 3 minutes.
- Apply the first coat onto the surface of the part from 25-30 cm of distance, very lightly, in short, even bursts, always keeping the spray nozzle moving. Cover the contact edges first, followed by smaller continuous surfaces and finally finishing a single coat with the largest continuous surface. The first filler coat should be so thin it doesn't even cover the plastic entirely.
- After drying the part for 10 minutes, apply a second coat more heavily, from 15-20 cm of distance, until a slightly textured, but fully wet surface is achieved and the plastic is completely covered.
- Wait for 10 minutes, and repeat the previous step in order to apply the third coat.
- Wait for 10 minutes, and apply the last coat relatively lightly, similar to the first one, in order to give the surface a finer texture and make the sanding process easier.
- Let the filler dry for 24-48 hours before sanding, or as recommended by the filler manufacturer.
- OPTIONAL: About 30 minutes before sanding, apply a very light guide coat onto the part in order to make the sanding process easier.
STEP 4) SANDING THE FILLER - Filler is first dry sanded using a 320 or 400 grit sanding paper, with medium pressure, until a smooth and even surface is achieved. A neat trick that can be used here is to apply a guide coat onto the parts, which means lightly dust spraying some black spray paint onto them before sanding, leaving the black guide coat to dry for a couple of minutes, and then sanding the filler until the black guide coat is fully removed. The guide coat will hopefully fill up all the low spots on the surface, so when the last trace of it is removed, the low spots should be gone as well, and the surface of the filler should be smooth and even. In addition, the visibility of the guide coat is a clear indicator of the amount of filler that's already been sanded off at any given moment. Sanding curved surfaces in an X-pattern and using sanding blocks for flat surfaces is crucial here in order to maintain the original surface shapes. Every continuous surface should be sanded separately, while edges between them should be avoided until the very end, when they should be carefully sanded and shaped to a desired roundness,. The layer thickness of filler tends to be lower in areas around and on the actual edges, meaning the plastic will be exposed more easily during the sanding process. Scotch-Brite and foam backed sanding papers can be used on curved surfaces in order to even out the pressure and make the sanding process easier. The entire purpose of sanding with 320 or 400 grit paper is to remove excess filler, leaving behind a fairly even, but not necessarily a perfectly smooth surface. The surface is sanded until the thinnest possible amount of filler is left on it. Usually, the plastic will gradually become visible through the filler, near edges of the components first, as the filler is thinner in those areas. Once that happens, it's time to move onto a finer grit of sanding paper. Sanding the visible plastic surfaces should be avoided, in order to not damage the plastic primer layer.
Once most of the filler has been removed, it's time to move onto sanding the surface with an 800 grit sanding paper. The purpose of this step is to make the surface of the filler perfectly smooth, while removing as little of it as possible. At this stage, attention to detail and patience are most important. Once again, using a foam backed sanding paper makes this process easier, while all of the previously mentioned sanding rules should be followed. The surface achieved now will have the actual base coat or the second coat of filler applied to it, so it has to be perfectly smooth, without any low or high spots, scratches, cracks, etc. This is necessary in order make sure the next coat of product applied to it can dry to a perfectly smooth surface. All imperfections left behind at this stage will be further amplified by the successive coats. It's best to imagine that the surface achieved at this stage will be the actual surface of the finished component and should be treated accordingly. Very light pressure should be used, starting off with one pass of dry sanding, followed by one pass of wet sanding for the final finish. The wet sanding paper should be soaked in water for a couple of minutes before use and washed every few seconds during sanding. Soaking or washing the actual components in water should be avoided, but some wetness is not a big deal, as the fillers are designed to be wet sanded. In cases when a second filler layer is necessary, the wet sanding part can be skipped before applying it, as there is no need for it. Dry sanded surface is perfect for application of another layer of filler, which can then be finished with 800 grit wet paper for a final finish ready for the application of a base coat. Once the surfaces are sanded, they need to be wiped with a damp cloth in order to remove all the residue, and then they need to be left to dry for a couple of hours. The safest practice is to just leave them to dry in a fairly warm room overnight.
Second filler layer: As mentioned previously, if at any point the filler layer is sanded through and the plastic is revealed, which will almost always happen on components with curved geometries and sharp edges, another coat or two of filler can be sprayed over the entire component, left to dry for at least 24 hours again, and then very lightly sanded with wet 800 grit paper following the same rules as before. The purpose of this step is to avoid issues with base coat application. I've purposefully decided to show how this is done in this guide, even though it won't always be necessary. Because the new coats of filler are applied onto an already sanded and smooth surface, only a minimal amount of sanding will be required, just enough to scuff the surface and prepare it for base coat application. If the plastic is just slightly visible through the filler because the filler layer is very thin, but the plastic isn't fully exposed, then the base coat can be sprayed onto it. Spraying the base coat onto fully exposed plastic will cause uneven settling and drying of the base coat, which will be visible once the base coat dries, especially on metallic paints. Therefore, it should be avoided.
SUMMARY:
Once most of the filler has been removed, it's time to move onto sanding the surface with an 800 grit sanding paper. The purpose of this step is to make the surface of the filler perfectly smooth, while removing as little of it as possible. At this stage, attention to detail and patience are most important. Once again, using a foam backed sanding paper makes this process easier, while all of the previously mentioned sanding rules should be followed. The surface achieved now will have the actual base coat or the second coat of filler applied to it, so it has to be perfectly smooth, without any low or high spots, scratches, cracks, etc. This is necessary in order make sure the next coat of product applied to it can dry to a perfectly smooth surface. All imperfections left behind at this stage will be further amplified by the successive coats. It's best to imagine that the surface achieved at this stage will be the actual surface of the finished component and should be treated accordingly. Very light pressure should be used, starting off with one pass of dry sanding, followed by one pass of wet sanding for the final finish. The wet sanding paper should be soaked in water for a couple of minutes before use and washed every few seconds during sanding. Soaking or washing the actual components in water should be avoided, but some wetness is not a big deal, as the fillers are designed to be wet sanded. In cases when a second filler layer is necessary, the wet sanding part can be skipped before applying it, as there is no need for it. Dry sanded surface is perfect for application of another layer of filler, which can then be finished with 800 grit wet paper for a final finish ready for the application of a base coat. Once the surfaces are sanded, they need to be wiped with a damp cloth in order to remove all the residue, and then they need to be left to dry for a couple of hours. The safest practice is to just leave them to dry in a fairly warm room overnight.
Second filler layer: As mentioned previously, if at any point the filler layer is sanded through and the plastic is revealed, which will almost always happen on components with curved geometries and sharp edges, another coat or two of filler can be sprayed over the entire component, left to dry for at least 24 hours again, and then very lightly sanded with wet 800 grit paper following the same rules as before. The purpose of this step is to avoid issues with base coat application. I've purposefully decided to show how this is done in this guide, even though it won't always be necessary. Because the new coats of filler are applied onto an already sanded and smooth surface, only a minimal amount of sanding will be required, just enough to scuff the surface and prepare it for base coat application. If the plastic is just slightly visible through the filler because the filler layer is very thin, but the plastic isn't fully exposed, then the base coat can be sprayed onto it. Spraying the base coat onto fully exposed plastic will cause uneven settling and drying of the base coat, which will be visible once the base coat dries, especially on metallic paints. Therefore, it should be avoided.
SUMMARY:
- Sand flat surfaces with a sanding block or rigidly folded sanding paper, sand curved surfaces in an X-pattern and avoid sanding the edges directly.
- First evenly sand the surface with 320 grit dry sanding paper in several even passes, in order to remove as much filler as possible, making sure most of the guide coat is removed.
- Once most of the guide coat is removed, and plastic becomes slightly visible in some areas, continue sanding with 800 grit sanding paper until all guide coat spots are removed and the surface is perfectly smooth.
- Sand the edges by lightly pressing the sanding paper directly onto them with a fingertip and moving the paper in one direction along each edge.
- OPTIONAL: Apply another coat or two of filler, let it dry for 24 hours.
- Sand the new filler layer with 800 grit sanding paper until a perfectly smooth surface is achieved, making sure not to expose the plastic.
- Finish the sanding process by very lightly wet sanding the part with 800 grit paper in order to additionally smooth-out the surface.
- Clean the surface with a damp lint-free cloth and then allow it to dry completely.
STEP 5) APPLYING THE BASE AND CLEAR COATS - The base coat and the clear coat have to be applied together, within a certain time window of each other. After the filler has been dried completely, the part is wiped off with a lint-free cloth to remove dust, and it's ready for painting. I'm using a Dupli Color professional automotive base coat in this guide, but the painting process is pretty much identical regardless of the product used. Recommended drying times may differ from product to product though, so that has to be taken into consideration.
The application of the base coat starts by shaking the can for at least 3 minutes, which is especially important when using metallic paints. Following that, the base coat is applied in 3 coats. While painting the base and clear coats, it's crucial to apply them in quick bursts, always moving the spray nozzle across the surface of the part. The first coat is very light, with the paint just dusted onto the surface of the part from 25-30 cm away, in order to improve the adhesion of the following coats and prevent runs. It's important to paint the edges first in order to ensure a proper base coat thickness over them. Smaller continuous surfaces of the parts are painted next, finishing off with larger areas, in order to ensure a proper spread and blending of metallic particles. After approximately 5 minutes of drying, the second coat is applied, from the same distance, but a little bit more heavy than the first coat, covering the surface of the part entirely with a semi-gloss finish. After drying for 5 minutes again, the third coat is applied, more heavy than the previous one again. It's important to apply a fully wet and glossy third coat, with an even spread of metallic particles, while avoiding runs or product build-up. Only a fully wet base coat will dry to a smooth surface, a semi-wet coat will usually lead to an orange peel effect, which will result in more work later on. It's important to practice painting on a different surface in order to get a hang of how much paint should be applied in order to achieve a wet coat and avoid runs. It's a fine balance that varies from product to product, but generally speaking a short burst of paint should be sprayed onto a surface, followed by another one after a 1-2 second pause, followed by another burst after another 1-2 seconds of pause, etc. Paint needs a second or two to settle and become glossy, so it's important to gradually build it up to that stage, instead of attempting to achieve a wet coat with a single long burst. That usually leads to runs. Ideally, while applying a wet coat, it should be sprayed just until the surface becomes very glossy, but still with a very slight orange peel effect, which then evens out in a few seconds as the paint flows over the surface and becomes perfectly smooth. This exact same principle applies to the clear coat as well.
After the base coat has been applied, it has to dry for 30 minutes, and then the clear coat has to be applied to it. This time window may vary from product to product, and it's extremely important to follow it. If the clear coat is applied too soon, before the base coat has dried and degassed sufficiently, it may cause blisters and small bubbles in the clear coat. On the other hand, if the clear coat is applied too late, and the base coat has dried too much, the chemical bond between the two will be weak and the clear coat could crack or chip off very easily in the future.
The clear coat is applied in 5 coats, because it's going to be wet sanded and polished after it dries, so quite a thick layer has to be achieved. Just like with the base coat, it's important to properly shake the can before use and spray in relatively short bursts, never keeping the spray nozzle still. The first coat is applied very lightly, just dusted onto the surface from 25-30 cm. It's important to cover the contact edges of the component first in order to build a thick enough layer of clear coat over them to avoid chipping or cracking in the future. After that, the rest of the part is sprayed, following the principles listed for the base coat application. Because the goal is to build quite a thick layer of clear coat, it's important to apply each coat evenly, gradually building the thickness with adequate drying periods between coats. Each clear coat has a different recommended drying time between coats, but 5-10 minutes is good in most cases. The second coat is applied a bit more heavily than the first, until a semi-gloss surface is achieved, followed by 5-10 minutes of drying. The exact same process is repeated for the third and the fourth coats. It's important to note that while applying the clear coat, at first the surface of the part is finely textured and matte, but in a few seconds, as the newly applied coat blends with the previously applied coats, the surface turns glossy and becomes smoother. This effect gradually becomes more extreme as the number of coats grows. Finally, the fifth coat is applied until a fully wet, almost perfectly smooth surface is achieved. In order to avoid runs and excessive build-up of clear, the wet coat technique mentioned in the base coat paragraph should be used. Since the surface of the clear coat will be wet sanded and polished, it's not crucial to achieve a perfectly glossy mirror finish at this stage. In fact, it's important to realize that it's almost entirely impossible to spray a clear coat and not end up with a slight orange peel effect once it fully dries, but getting close to a perfect surface will greatly reduce the amount of wet sanding and polishing required later on. After the clear coat has been applied, the part can be left to dry in a dust-free area, at room temperature, for an amount of time recommended by the clear coat manufacturer. Usually, that means 5 to 10 days. I always dry the parts for at least a week to be on the safe side. It's easy to check whether the clear coat is completely dry by trying to gently push the tip of a fingernail into the surface of the clear coat. If the surface feels completely hard and solid, then it's dry. If it still has some give and feels rubbery, it needs more drying. It's crucial not to sand and polish it before it's completely dry.
SUMMARY:
The application of the base coat starts by shaking the can for at least 3 minutes, which is especially important when using metallic paints. Following that, the base coat is applied in 3 coats. While painting the base and clear coats, it's crucial to apply them in quick bursts, always moving the spray nozzle across the surface of the part. The first coat is very light, with the paint just dusted onto the surface of the part from 25-30 cm away, in order to improve the adhesion of the following coats and prevent runs. It's important to paint the edges first in order to ensure a proper base coat thickness over them. Smaller continuous surfaces of the parts are painted next, finishing off with larger areas, in order to ensure a proper spread and blending of metallic particles. After approximately 5 minutes of drying, the second coat is applied, from the same distance, but a little bit more heavy than the first coat, covering the surface of the part entirely with a semi-gloss finish. After drying for 5 minutes again, the third coat is applied, more heavy than the previous one again. It's important to apply a fully wet and glossy third coat, with an even spread of metallic particles, while avoiding runs or product build-up. Only a fully wet base coat will dry to a smooth surface, a semi-wet coat will usually lead to an orange peel effect, which will result in more work later on. It's important to practice painting on a different surface in order to get a hang of how much paint should be applied in order to achieve a wet coat and avoid runs. It's a fine balance that varies from product to product, but generally speaking a short burst of paint should be sprayed onto a surface, followed by another one after a 1-2 second pause, followed by another burst after another 1-2 seconds of pause, etc. Paint needs a second or two to settle and become glossy, so it's important to gradually build it up to that stage, instead of attempting to achieve a wet coat with a single long burst. That usually leads to runs. Ideally, while applying a wet coat, it should be sprayed just until the surface becomes very glossy, but still with a very slight orange peel effect, which then evens out in a few seconds as the paint flows over the surface and becomes perfectly smooth. This exact same principle applies to the clear coat as well.
After the base coat has been applied, it has to dry for 30 minutes, and then the clear coat has to be applied to it. This time window may vary from product to product, and it's extremely important to follow it. If the clear coat is applied too soon, before the base coat has dried and degassed sufficiently, it may cause blisters and small bubbles in the clear coat. On the other hand, if the clear coat is applied too late, and the base coat has dried too much, the chemical bond between the two will be weak and the clear coat could crack or chip off very easily in the future.
The clear coat is applied in 5 coats, because it's going to be wet sanded and polished after it dries, so quite a thick layer has to be achieved. Just like with the base coat, it's important to properly shake the can before use and spray in relatively short bursts, never keeping the spray nozzle still. The first coat is applied very lightly, just dusted onto the surface from 25-30 cm. It's important to cover the contact edges of the component first in order to build a thick enough layer of clear coat over them to avoid chipping or cracking in the future. After that, the rest of the part is sprayed, following the principles listed for the base coat application. Because the goal is to build quite a thick layer of clear coat, it's important to apply each coat evenly, gradually building the thickness with adequate drying periods between coats. Each clear coat has a different recommended drying time between coats, but 5-10 minutes is good in most cases. The second coat is applied a bit more heavily than the first, until a semi-gloss surface is achieved, followed by 5-10 minutes of drying. The exact same process is repeated for the third and the fourth coats. It's important to note that while applying the clear coat, at first the surface of the part is finely textured and matte, but in a few seconds, as the newly applied coat blends with the previously applied coats, the surface turns glossy and becomes smoother. This effect gradually becomes more extreme as the number of coats grows. Finally, the fifth coat is applied until a fully wet, almost perfectly smooth surface is achieved. In order to avoid runs and excessive build-up of clear, the wet coat technique mentioned in the base coat paragraph should be used. Since the surface of the clear coat will be wet sanded and polished, it's not crucial to achieve a perfectly glossy mirror finish at this stage. In fact, it's important to realize that it's almost entirely impossible to spray a clear coat and not end up with a slight orange peel effect once it fully dries, but getting close to a perfect surface will greatly reduce the amount of wet sanding and polishing required later on. After the clear coat has been applied, the part can be left to dry in a dust-free area, at room temperature, for an amount of time recommended by the clear coat manufacturer. Usually, that means 5 to 10 days. I always dry the parts for at least a week to be on the safe side. It's easy to check whether the clear coat is completely dry by trying to gently push the tip of a fingernail into the surface of the clear coat. If the surface feels completely hard and solid, then it's dry. If it still has some give and feels rubbery, it needs more drying. It's crucial not to sand and polish it before it's completely dry.
SUMMARY:
- Shake the spray cans for at least 3 minutes before use.
- Apply a very thin, dusted first layer of base coat over the part from around 25-30 cm of distance, in short bursts, making sure to always keep the spray nozzle moving. Cover the contact edges first, followed by smaller continuous surfaces and finally finishing a single coat with the largest continuous surface. The first base coat should be so thin it doesn't even cover the filler entirely.
- After drying for 5-10 minutes, apply the second coat a bit more heavily than the first one, from 20-25 cm of distance, until a semi-gloss, slightly textured surface is achieved and the filler is entirely covered.
- Apply the third coat after 5-10 minutes of drying, slightly heavier than the second coat, until a fully wet and glossy surface is achieved.
- Let the base coat dry for 30 minutes.
- Apply a very thin, dusted first layer of clear coat over the part from around 25-30 cm of distance, in short bursts, making sure to always keep the spray nozzle moving. Cover the contact edges first, followed by smaller continuous surfaces and finally finishing a single coat with the largest continuous surface.
- After drying for 5-10 minutes, apply the second coat a bit more heavily than the first one, from 20-25 cm of distance, until a semi-gloss, slightly textured surface is achieved while spraying, with the surface gradually becoming more glossy as the new coat blends with the previous ones.
- Repeat the same process for the third and the fourth coat, making sure that the clear coat build-up or runs are avoided.
- Let the previous coat dry for 10 minutes, then apply the fifth coat heavily, until a fully wet and glossy surface is achieved.
- Let the part dry and cure at room temperature for a recommended period of time before wet sanding and polishing, usually between 5 to 10 days.
STEP 6) WET SANDING AND POLISHING - Finally, after drying the clear coat for 5 to 10 days, we've arrived at the last step of this guide, a step that defines the difference between a good finish, and an absolutely flawless one. This is what sets some post-processed parts apart from the others, taking that final step that most manufacturers don't bother taking, because it takes too much time, effort and hand work. For me, it's the only way to do it, and the only way to achieve a finish that is worthy of a high-quality product. As can be seen on the photos below, the clear coat has a very slight orange peel effect on the surface. That's pretty much unavoidable, regardless of how well the clear coat has been applied. From some distance, it looks good and it's not noticeable, but it's still not perfect from close-up. In order to make it perfect, the surface has to be wet sanded until the low and high spots are removed, and then polished to a perfect glossy finish. Low and high spots are terms that refer to the peaks and dips in the texture of the clear coat. The goal of the sanding process is to completely remove them, while using at least 2500 grit sanding paper. Finer grits aren't necessary, but they can speed up the polishing process. The polishing compound I'll be using is designed to remove 2500 grit sanding marks and create a perfectly glossy finish, all in a single step. Samples of it will be included in LTS DIY post-processing kits, in an amount sufficient to polish an entire headphone.
Before the wet sanding begins, the sanding paper needs to be soaked in water mixed with a few drops of soap for a couple of minutes, in order to become softer. Water softens the surface of the paper and leads a smoother finish. While sanding, it's important to regularly rinse the sanding paper in order to remove the debris from it. The actual sanding process is very simple, with all of the previously mentioned sanding rules applying here as well. That means the curved surfaces are sanded in an X-pattern, edges are avoided until the end, and all continuous surfaces are sanded separately. Low pressure is used at all times, just enough to ensure the paper is in contact with the surface. It's also extremely important to distribute the pressure over the surfaces as evenly as possible, in order to remove the same amount of clear coat from all areas.
As the sanding begins, the surface of the clear coat turns from glossy to partially matte. The matte spots on the surface are the high spots that have been sanded off, while the still glossy spots are the low spots, or the parts of the clear coat that have not been sanded yet. The goal is to continue sanding until low spots are no longer visible, and no more than that. As soon as low spots are gone from the surface, the sanding should stop in order to keep the clear coat as thick as possible. It's very important to dry and inspect the surface every few seconds in order to ensure an even clear coat removal. If there are more matte spots in certain areas than in others, it means those areas are being sanded more quickly, which should be avoided. After some practice, the whole process becomes very quick and easy, and can actually be done mostly be feel, without even seeing the surface of the clear coat. At first, there's some resistance to moving the sanding paper across the surface, but as the surface becomes smoother, the sanding paper begins to glide over the clear coat with no resistance at all, like over wet glass. At that point, the surface is usually nearly perfect. After all of the continuous surfaces are finished, the edges are gently sanded as well, by pressing the sanding paper onto the tips of the edges, and gently moving the paper along them, until all low spots are removed. Special care should be taken in this step, because the thickness of the clear coat is lower on the edges.
In cases where the orange peel effect is more extreme, the sanding can start with rougher grits, such as 2000, or even 1500, in order to more quickly remove the imperfections, and then gradually switch to higher grits in order to end up at 2500. However, it's important to remember that 1500 grit paper is far more aggressive than 2500 grit paper, removes much more material and leaves deeper scratches. Therefore, it's important to sand the surface with 2500 grit paper for a longer amount of time than it's been sanded with 1500 grit paper. For example, for every 5 passes over the same area with 1500 grit paper, 10 passes should be completed with 2500 grit paper, otherwise 1500 grit scratch marks will be visible after polishing.
After the entire part has been sanded, and no low spots are visible, the surface of the part should be thoroughly washed with soap. Removing absolutely all of the sanding residue is crucial here, otherwise it's impossible to polish the surface, as the sanding dust just mixes with the polishing compound and keeps scratching the surface. If there are any traces of white dust or white smears on the surface of a dried part, it means it hasn't been washed properly.
Once the part is dry, the polishing can start. All that's required for this step is a high quality polishing compound and a microfiber cloth. Electric polishers could be used, but headphone parts are small enough to be finished by hand. The polishing process is actually very straight-forward, it just takes time and patience. A small amount of polishing compound is applied onto a microfiber cloth, spread over the surface of the part in order to create a thin layer, and then the surface is rubbed with the microfiber cloth using medium to high pressure until the compound is removed, and a glossy and dry surface is left behind. The high pressure and friction warm up the surface of the clear coat as well, making the polishing process quicker. After one application of the polishing compound has been buffed off, the surface should be thoroughly wiped with a clean part of the microfiber cloth, and then inspected under a bright light. If the surface is not sufficiently glossy yet, or small scratches are visible, the whole process should be repeated. Usually two to three passes over the same area are required for a perfect finish, at least with the polishing compound I use. This may vary with other products. The only two rules to remember is to not use too much pressure while polishing the edges, and to avoid circular motion at all times. That's pretty much it, the entire surface of the part is treated in much the same way, until the entire part is perfectly glossy. It usually takes around 20 minutes for a part such as the one used in this guide. Once the entire part has been polished, it should be thoroughly wiped with a clean part of the microfiber cloth, and inspected once again in order to ensure the surface is absolutely perfect. Finally, the part should be washed with some dish or car washing detergent, in order to completely remove all polishing compound residue.
SUMMARY:
Before the wet sanding begins, the sanding paper needs to be soaked in water mixed with a few drops of soap for a couple of minutes, in order to become softer. Water softens the surface of the paper and leads a smoother finish. While sanding, it's important to regularly rinse the sanding paper in order to remove the debris from it. The actual sanding process is very simple, with all of the previously mentioned sanding rules applying here as well. That means the curved surfaces are sanded in an X-pattern, edges are avoided until the end, and all continuous surfaces are sanded separately. Low pressure is used at all times, just enough to ensure the paper is in contact with the surface. It's also extremely important to distribute the pressure over the surfaces as evenly as possible, in order to remove the same amount of clear coat from all areas.
As the sanding begins, the surface of the clear coat turns from glossy to partially matte. The matte spots on the surface are the high spots that have been sanded off, while the still glossy spots are the low spots, or the parts of the clear coat that have not been sanded yet. The goal is to continue sanding until low spots are no longer visible, and no more than that. As soon as low spots are gone from the surface, the sanding should stop in order to keep the clear coat as thick as possible. It's very important to dry and inspect the surface every few seconds in order to ensure an even clear coat removal. If there are more matte spots in certain areas than in others, it means those areas are being sanded more quickly, which should be avoided. After some practice, the whole process becomes very quick and easy, and can actually be done mostly be feel, without even seeing the surface of the clear coat. At first, there's some resistance to moving the sanding paper across the surface, but as the surface becomes smoother, the sanding paper begins to glide over the clear coat with no resistance at all, like over wet glass. At that point, the surface is usually nearly perfect. After all of the continuous surfaces are finished, the edges are gently sanded as well, by pressing the sanding paper onto the tips of the edges, and gently moving the paper along them, until all low spots are removed. Special care should be taken in this step, because the thickness of the clear coat is lower on the edges.
In cases where the orange peel effect is more extreme, the sanding can start with rougher grits, such as 2000, or even 1500, in order to more quickly remove the imperfections, and then gradually switch to higher grits in order to end up at 2500. However, it's important to remember that 1500 grit paper is far more aggressive than 2500 grit paper, removes much more material and leaves deeper scratches. Therefore, it's important to sand the surface with 2500 grit paper for a longer amount of time than it's been sanded with 1500 grit paper. For example, for every 5 passes over the same area with 1500 grit paper, 10 passes should be completed with 2500 grit paper, otherwise 1500 grit scratch marks will be visible after polishing.
After the entire part has been sanded, and no low spots are visible, the surface of the part should be thoroughly washed with soap. Removing absolutely all of the sanding residue is crucial here, otherwise it's impossible to polish the surface, as the sanding dust just mixes with the polishing compound and keeps scratching the surface. If there are any traces of white dust or white smears on the surface of a dried part, it means it hasn't been washed properly.
Once the part is dry, the polishing can start. All that's required for this step is a high quality polishing compound and a microfiber cloth. Electric polishers could be used, but headphone parts are small enough to be finished by hand. The polishing process is actually very straight-forward, it just takes time and patience. A small amount of polishing compound is applied onto a microfiber cloth, spread over the surface of the part in order to create a thin layer, and then the surface is rubbed with the microfiber cloth using medium to high pressure until the compound is removed, and a glossy and dry surface is left behind. The high pressure and friction warm up the surface of the clear coat as well, making the polishing process quicker. After one application of the polishing compound has been buffed off, the surface should be thoroughly wiped with a clean part of the microfiber cloth, and then inspected under a bright light. If the surface is not sufficiently glossy yet, or small scratches are visible, the whole process should be repeated. Usually two to three passes over the same area are required for a perfect finish, at least with the polishing compound I use. This may vary with other products. The only two rules to remember is to not use too much pressure while polishing the edges, and to avoid circular motion at all times. That's pretty much it, the entire surface of the part is treated in much the same way, until the entire part is perfectly glossy. It usually takes around 20 minutes for a part such as the one used in this guide. Once the entire part has been polished, it should be thoroughly wiped with a clean part of the microfiber cloth, and inspected once again in order to ensure the surface is absolutely perfect. Finally, the part should be washed with some dish or car washing detergent, in order to completely remove all polishing compound residue.
SUMMARY:
- Soak the 2500 grit sanding paper in water with a little bit of soap for at least 10 minutes before sanding.
- Keep the sanding paper and the surface of the clear coat wet at all times, and rinse the paper every few seconds.
- Sand the clear coat with even and low pressure. Sand every continuous surface separately, curved surfaces in an X-pattern, and avoid edges.
- Dry and inspect the surface every few seconds in order to ensure the clear coat is being removed evenly.
- Pay attention to the removal of high and low spots. Already sanded off high spots are matte, while low spots are still glossy. Make sure all areas are sanded evenly, and pay attention to the distribution of matte and glossy areas. If certain areas are considerably more matte than others, it means they're being sanded too quickly.
- Once the low spots are gone, and the surface of the clear coat has an even, completely matte surface, stop sanding. The wet sanding paper should glide over the surface with no resistance at that point, like over wet glass.
- Repeat that process for every continuous surface separately, while avoiding edges.
- Finally, sand the edges by gently pressing the sanding paper onto the tip of an edge, and pulling the sanding paper along the entire length of the edge until all glossy low spots are removed.
- Once the entire part has been sanded, wash it with some dish or car washing detergent in order to remove sanding debris, and then dry it.
- Apply a small amount of polishing compound onto a clean microfiber cloth, spread it over a small area in order to create a thin layer of it.
- Rub or buff the surface with medium to high pressure, in linear motion. Avoid circular motion at all time, especially if combined with high pressure.
- Keep buffing the surface until the compound is completely removed and only a dry and more glossy surface than before is left behind. The surface of the clear coat will get warm during polishing, that's a good thing.
- Wipe the surface with a clean part of the microfiber cloth and inspect it under a light.
- If it's not sufficiently glossy or scratches are visible, repeat steps 10 to 13. Usually 2 to 3 passes are required over the same area for a perfect finish.
- Repeat the process for the entire part, ensuring not to apply too much pressure onto the edges and to avoid circular motion.
- Once the part has been polished, it should be wiped clean and inspected for the last time in order to make sure the surface is perfect.
- Wash the part, preferably with a car washing detergent, in order to completely remove all polishing compound residue.
- Wipe it and dry it with a completely clean microfiber cloth.
IN CONCLUSION...
With that, the post-processing of a single part is at the end. It's a long process, with a lot of steps, but the final results are worth it. Hopefully, this also highlights how much work and effort needs to be put into making a single LTS headphone, and illustrates the difference between custom hand-built and mass-produced products. Usually, 8 to 10 hours of hand work is required just to post-process parts for a single headphone, not counting in the drying times, various preparations or the actual headphone assembly and testing. With that included, the number goes up to around 20 hours of work for a single headphone spread over a period of about two weeks. On top of that, around €40 worth of various products and consumables alone are spent during the process, not counting in the value of time. When I build headphones, I treat them as small works of art, therefore, I don't settle for anything less than perfection in every detail, from the first line drawn in the design process, to the last step of the post-processing, and that requires a certain amount of time and determination. However, I believe the results speak for themselves, and make all the effort worthwhile. It's a fun process, and the quality of the outcome entirely depends on the attention to detail and the amount of effort invested into it.