Motorsport Composite Fundamentals: Surface Finishing
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Surface Finishing
04.33
| 00:00 | In this module we'll discuss the tools involved in surface finishing our composites. |
| 00:04 | These discussions won't include any coatings or fillers as we've already discussed these in the previous section of the course. |
| 00:11 | Check back if you need a refresher. |
| 00:13 | Rather we'll be focusing on the process of removing material, which is somewhat of a continuation of the previous module on material removal. |
| 00:21 | However, the aim here is to increase the surface finish rather than shape the part. |
| 00:26 | Generally, for this work though we'll use much finer grit abrasives. |
| 00:30 | At the coarsest end of the spectrum this will be sandpaper around 120 grit and we might work all the way up to around 2000 grit wet sanding. |
| 00:39 | So, it's important we're using waterproof sandpaper. |
| 00:42 | Random orbital or dual action sanders speed up this process significantly and are particularly useful on larger more simple surfaces. |
| 00:51 | To be clear the grit required is going to largely depend on the quality of the surface out of the mould. |
| 00:57 | We wouldn't expect to use 120 grit on a part straight out of the mould for example if everything has gone to plan. |
| 01:04 | It's more likely we'll turn to something this aggressive for a repair where flatting is required on the excess resin or top coat to match the original surface shape. |
| 01:13 | It's also common to use these more coarse grits on patterns during construction. |
| 01:18 | The surface finish on these patterns translates to that of the mould and then onto the part. |
| 01:24 | Ideally if we've done enough prep work the part out of the mould will have a surface finish good enough that it doesn't need any work. |
| 01:31 | It's unlikely we'd call it perfect though so we're always looking for an improvement and this is where we turn to polishing. |
| 01:38 | Polishing as you're likely aware as car enthusiasts involves rubbing the surface with an abrasive compound with the aim of removing a fine layer and with it any scratches or swirl marks for a smooth and glossy finish. |
| 01:51 | Generally, this process will be used on parts with clear gel coats as far as composites are concerned because we have a thicker layer of material to cut down before getting into the reinforcement layers. |
| 02:02 | There are many compounds on the market designed specifically for composites. |
| 02:06 | Certain resins like epoxy and vinyl ester form relatively hard surfaces so these compounds are formulated with those in mind. |
| 02:14 | That said I'd recommend using your favourite compound that you also use for your car's paint and kill two birds with one stone. |
| 02:21 | As you'd expect more aggressive cutting compounds will work faster on deeper scratches like those from a thousand grit sandpaper but fall short of an optimal finish. |
| 02:31 | Following this with a less abrasive polishing compound will get rid of any remaining swirl marks and give the highest gloss finish. |
| 02:38 | While polish application pads are a budget friendly option, an orbital polisher is again going to help with efficiency of this process. |
| 02:46 | To be clear, although very similar power tools, these generally aren't the same as sanding machines as a sander will be too aggressive to provide a good finish and often feature some form of dust recovery system, unnecessary for this work. |
| 03:00 | A good middle ground is using a drill with special attachments for polishing pads. |
| 03:05 | On that note a fine wool or medium heavy foam pad will be suitable for heavier cuts whereas a softer foam pad is good for finishing up for the best possible finish. |
| 03:16 | It's important not to overdo it with aggressive compounds or pads, running the polisher on too high a speed or simply pressing too hard on one area for too long as this can burn the surface. |
| 03:28 | After application a clean microfiber towel is used to remove the leftover compound and we'll be left with a glossy finish. |
| 03:35 | With that let's wrap up this module with the key points to remember. |
| 03:39 | Flattening, cutting and polishing the surface of our parts is a common finishing step, usually when we've used a gel coat as this provides material thickness to cut flat. |
| 03:48 | The pattern surface will transfer to the mould surface and then this to the part surface so each step needs to be considered here. |
| 03:56 | At the more aggressive end of the spectrum we'll use sandpaper grits under 1000 grit dry and then work all the way up to something like 2000 grit wet sanding. |
| 04:05 | So, make sure you're buying waterproof sandpaper. |
| 04:08 | Past this we'll move to polishing using cutting and polishing compounds designed specifically for hard resin on our composite parts along with an orbital polisher. |
| 04:17 | Or for a more budget friendly option you could use a drill with a special attachment as well as car paint polish. |
| 04:24 | After we're finished a microfiber towel is the go-to for wiping off the leftover compound. |
