I'm currently making a buck to make a mould for a diffuser. Based around a wooden construction with a fibre board to get a good curve. I am wondering what a good sealer for this would be.

Hi, Tango.

I use polyester filler (2k) and it never disappointed me. It builds thickness fast, can be shot with a "standard" spray gun (I have a 30euros  1.4 mm tip gun and thats enough) and polishes to a very very decent gloss.

I reduce it with acetone, or else it's too thick for my 1.4mm tip. It works pretty good. By using acetone, you can still build a good thick coat, but I would suggest in that case that you apply two lighter coats (that would still be thicker than regular paint) to allow acetone to evapore. From my experience, working in "high temp" room, like 25°C, would allow acetone to evapore (part would turn to mat color rather than its glossy state when you spray it) in like 12-13 mins, so you would skip a few gun cleanings, and then spray all your coats in one operation. I usually prepare a new batch of filler while the part is curing.

Dont be tempted by rattle can fillers, It could react with heat or chemicals. I had those troubles, so did a friend of mine, and with a different brand.

In any case, remember to wear a respirator, this stuff is not cool to your body.

I hope it helped.

 



 


    A $1000 electronic device will always protect a 10 cents fuse

ok... so i've now got the curve on and I've softened the edging with newplast. 

I know we've just spoken on the phone about this but I'll put the same reply on the forum so it might assist others.

Generally, the way we seal our patterns (on our manufacturing side) is using 2k polyurethane filler primer sprayed liberally all over them and then flatting them back and sometimes spraying and flatting again. If you have access to a spray-gun (and a place to do the spraying) then this is the fastest way to seal a pattern. It also covers a multitude of sins (like polyester body filler!) that may have been used on the pattern.

Shellac sealer works really well on MDF (and just about any wood) and is a great option for those without spray facilities or who don't fancy the idea of spraying a 2k paint even if they do! - It's a much more friendly way to seal a wood pattern but it needs to be built up in several coats and flatted between each coat, making it slower going than an instant result filler/primer.

Never be tempted to user primers out of a rattle can (cellulose) 1-part type sprays. They just don't work right, the solvent leaches out of them for a long time and their bond to the pattern is so bad that if they don't ruin the release agent with their solvents they will still probably end up coming off the pattern and sticking to the mould anyway.

We did talk about the fact that you've put Plasticine fillets in the corners for your radiuses and the fact that I really wouldn't endorse spraying a primer (or any other mould sealer) over the top of a soft clay like this. The primer is almost guaranteed to crack through when you try to flat it. What I recommended was scraping the Plasticine (modelling clay) away and then replacing it with radiuses made from polyester body-filler. This will give you something much more sturdy underneath to seal over the top of.

I hope this helps and look forward to seeing some more updates!

All the best, Matt

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Maybe a little cheap but useful tip to apply body-filler:

Use a rubber rectangle that you fold so that it forms a radius. Or you can even cut the radius you want on one corner of this rectangle. Applying filler with finger only can be done too, but it might be messier around the radius (and... on the finger too). Plastic scraper would not be pliable enough if you want a tight radius.

Plus, rubber would leave a clean surrounding area around your radius, or at least move excess far enough from the radius for you to remove it without risks of touching your radius.

 



 


    A $1000 electronic device will always protect a 10 cents fuse

Thanks Guys... 

a slightly pointy spoon can be great for making variable fillets. Go in the direction of the back of the spoon (convex side). The angle you hold the spoon at changes the radius of the fillet