I'm working on some CNC cut foam patterns, and after some advise on which products/methods to use to get a suitably surfaced pattern for taking the mould...

The surface isn't perfectly smooth, with many small pockets from the machining process - see attached image (slightly worse in places)

My original plan - (and have ordered these bits) was to use your epoxy coating resin with glass bead & silica and then brush/spray onto the surface - do you think that will be sandable to a suitable surface finish? should I be looking at adding some 163g woven glass over the part? These are largish parts for car bodywork...

Many Thanks,
James

Hi James,

Yes, I think what might be significant here is what you were expecting from this scrim cloth. When you're working on a soft pattern material like the low density foam then the expectation is that you're really just using the foam for the general shape and that your fine detail you will put into whatever you coat the pattern with. The glass cloth and first coat of resin are just there to add considerable stiffness to the shape, you'll then add another coat or resin (and microballoons probably) which will give you the surface into which you'll put all your effort (defining the detailed shape and getting a really smooth, flat finish.

For this reason, if you've got a bit of 'wobble' in the glass or even a few problems where it's not gone down exactly as you wanted then anything like this will soon be knocked off when you give the pattern a first flat (with a really coarse paper) before you apply the pattern coat. It sounds to me like you were expecting a more perfect finish at this stage which is why it came as a dissapointment; in fact it was probably fine and ready (once cured) for a good flat to knock it into shape and then a coat of resin/balloons ready to take it up to its fine finish.

I hope this helps, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales