Ok.... another mould question

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#1

I’m new on this site and must say there is a lot of good information here!!

And as many others I also have a problem that I can’t fix. I’ve already destroyed 2 models so it starts to get a bit expensive :smiley:

This is what I have

I’m willing to make this (and other things) out of carbon.

This is an polyster fender for my motorcycle. The problem is the mould won’t come out… Should the mould be in pieces, and what is the best way to do?
The parts that came of, where not in one piece, especialy the edges…

This is what I’ve done:

  • waxed the polyester fender (there was nothing on the fender, pure polyester) 4 or 5 times
  • put a PVA in the wax layers
  • painted some gelcoat on it
  • let the gelcoat dry
  • added polyster on the gelcoat
  • let the polyster dry

What is the best way for the edges? The brake down fast… I can’t get the mould from the fender in one good piece… Anybody any tips??

#2

It looks like you will need to make a 3 part (bolt together with flanges) mold to make this item. You will should be able to mold it in all in one piece but then unbolt and remove each mold part to get the part out.

I have a photo of a 3 part Honda front air dam, but I’ll try and locate it and post it here later today or tonight as I have a lot to do today…

#3

her is a link to show basic mold making process, They did a street rod body, I think parting flanges is on page 3
http://www.hotrodder.com/32Blowpar/page10.html

#4

Some pics would be nice yes!

#5

My technical English is not so good (I’m from Holland) but 'there is one thing I don’t understand here. The make the mould in pieces, deviding it with some cley. When you remove the clay, there will be a part missing in your mold (the polyester doesn’t come under the clay though?) How do they solve that?

#6

you build dams with the clay, then make one part of the mold. WHen that part is done you remove the clay but leave that part of the mold and make the next part of the mold. you have to but some bumps or keys on the flanges so you can line them up again when you take them apart . when you are done you can take alll the peices off seperately.
make sure you click on all the pictures on pages 3 thru 5, it will become pretty clear.

#7

Ok, thanks it’s clear now!

Got another polyster frontfender today, and willing to start with it. What do I have to do to the polyster? Just wax it?? And should I make the mould in pieces on the same way with cley?

#8

:frowning:

It’s just not my project… Made a seperation with the cley, but it’s hard to get a straight line, so how am I gonna connect it to the othe mould part??

The first part I made wasn’t a succes… The mould wouldn’t come of right the polyster even came thrue the gelcoat and attached to the polyster part… What the *%^$ am I doing wrong??

#9

if you ae having sticking problems use som PVA parting film after you wax, It acts as a barrier. If you used enough wax and buff it should not stick. it doesnt matter if the clay line is straight, just peel the clay once the first of the mold part cures, wax the parting line and brush on some pva, let it dry and add the next part of the mold. Once you have all the peices done, take the mold apart so you can remove teh peice. now bolt or clamp the mold pieces back together and you have a mold. It may take a couple of attempts to get it all to come together right.

#10

Correct me if I am wrong, but do you spray or brush on a releasing agent (like PVA) after the waxing? If not that may be part of your problem. I usually brush/spray on a couple of thin layers of PVA to make sure there are no dry spots.

For the parting flange, I use a deck of cards tape togetherand backed by clay. This way the flange is straight and easy to peel away.

I hope this helps. Keep at it, you’ll only get batter with time!

Harv

#11

Thanks for the 2 tips!

I wax the part 3 or 4 times, I put on the pva with a brush.

I will repait the original part tomorrow (little damage from the failed mould… :() and try again with these new tips

#12

Another failure…

The gelcoat sticks on to the edges, and damaged the fender again… :frowning: :frowning: :frowning:

Painted the fender again (in black this time) and spraying the
2-c lack on it tonight.

Tomorrow I will put on the gelcoat again, but how to handle the edges? Should I put on the polyester while the gelcoat is still a bit wet or when it’s complete hardend out?

#13

Are you waxing the edges and backside of the part? Look for any spots gelcoat or resin may get on, and apply mold release.
Also, after applying the gelcoat, put some of that gelcoat on a piece of carboard or something, so you can check on it as it cures without touching the actual mold. Wait until the gelcoat is almost dry, but you can leave a fingerprint on it. If no gelcoat gets on your finger, the next resin can be applied.

#14

Should there be more then one layer of gelcoat then, or do you mean the polyester with the next resin? I do wax the edges, but not the backside.

#15

You can do that fender in two part mold. That part that makes it look like a 3 part is a little tricky, but if you pull the parts in the right direction, pulling the the part of the fender that mounts to the forks first, the rest will fall out.

as far as the edges, there are certain losses that you will have to accept or take the time to account for when making a mold of OEM plastic. since they are round edges, you’ll have to grind down until the round no longer binds the part in, OR you’ll have to build square edges alllll the way around the fender to keep the EXACT size of the fender. To me, loosing 1/16-1/8" of the part that doesn’t meet up with ANY other parts is acceptable.

#16

Finally, I found these pictures:

#17

Another picture…

#18

Here’s a 1 piece mold and a 3 piece mold…

#19

But with a mold split you will have this:

#20

Scotch tape the mold at the seams. You won’t see the parting line nearly as bad.