Hey Guys,
I’m making a fiberglass mold off of an old plastic part that has a pretty rough surface but I’d like the mold to have a smooth surface. Normally I’d go over the plug with a surfacing primer and sand it smooth but the catch is that I can’t ruin the plug in this case. Anybody have any suggestions as to what I could coat this thing with that would take out some of the roughness but leave the part intact?
How bad is sanding the mold surface an option after pulling the mold
Sanding the mold is definitely an option. I’m just a bit worried about sticking the plug due to the rough surface. But since its a plastic part with some flexibility maybe I shouldn’t be so worried about that.
Pva is your best friend.
Yeah that’s what I’m thinking as well. I’ll probably just go that route.
Definitely PVA. I’ve pulled rough moulds off 60 grit surfaces when in a bind, so I’m sure you won’t have any issues.
OK. PVA it is then. Thanks for the advice.
ive pva’d MDF and then applied wax … the PVA stays on the mould and the part comes out clean. I would imagine you could do the same and then wash the plastic piece after ?
I have found that the yellow fillet wax can be nicely smeared film like with your fingers to fill and smooth a surface. You could then PVA that too.
Another option if dimensions aren’t an issue is sheet wax. This would give a much smoother surface to start with.
It’s a lot of work but if it’s super critical you can pull a splash off the part, lay up an extra rigid part and then modify that for your smooth plug (plus add features, etc). That’s how complicated molds are made where you need tricky parting lines and such.
I actually made the mold this past weekend. A healthy coat of wax and PVA and all went well. Thanks for the suggestions everybody.