andrew-theasby
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| posted on 28/10/10 at 10:21 PM |
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how smooth should a mould be?
Just having a play at making some parts, ive made a mould, with a surface of filler and primer, but theres a few imperfections in it still. Not
bothered about them being transferred to the component, but will it release or does it need to be like glass? Plan to wax it then a few coats of PVA.
Its a one off so dont want to waste too much time if its not necessary. Thanks
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stevebubs
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| posted on 28/10/10 at 10:24 PM |
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It should still release....
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andrew-theasby
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| posted on 28/10/10 at 10:26 PM |
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Thanks. Is pva suitable for epoxy too as the descriptions ive seen all say for polyester.
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twybrow
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| posted on 28/10/10 at 11:06 PM |
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quote:
Originally posted by andrew-theasby
Thanks. Is pva suitable for epoxy too as the descriptions ive seen all say for polyester.
Yes, but you would still typically use a was first (it will help to physically fill those little bumps you have!).
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BenTyreman
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| posted on 28/10/10 at 11:19 PM |
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I have been doing a bit of this recently. Unless the shape is particularly hard to release, the surface finish doesn't have too much effect.
However, the shinier the mould, the shinier the part.
The mould should be waxed several times. General consensus is around 5 times. This is not to build up a thicker layer of wax, but to ensure that the
entire surface is waxed with no missed spots.
I have been using 1 thin layer of PVA (I presume you are using the alcohol, not the glue) on top of the wax. I have been having a lot of difficulty
applying the PVA by hand and still getting a good finish. However, the PVA is an essential step for the first couple of pulls using polyester resin,
as the resin put down for the part can bond to the approx. 5% of the still active resin (including car body filler) in the mould.
Why are you using epoxy resin? It is more expensive, and the catalyst needs adding in a much more accurately controller ratio. Also, epoxy resin will
not dissolve the binder in certain kinds of chop-strand mat.
Obviously it depends on the kind of glass you are using, but I would say a roller is essential for CSM. I have tried just stippling, but the roller
definitely creates a much more consolidated part.
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BenTyreman
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| posted on 28/10/10 at 11:58 PM |
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Incidentally, this is what I was doing:
sidescreens / half doors
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Fred W B
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| posted on 29/10/10 at 06:12 AM |
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quote:
I have been having a lot of difficulty applying the PVA by hand and still getting a good finish.
This is apparently the problem with PVA, although i have never tried it.
I use only wax, applied 10 times.
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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BenTyreman
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| posted on 29/10/10 at 07:25 AM |
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quote:
Originally posted by Fred W B
quote:
I have been having a lot of difficulty applying the PVA by hand and still getting a good finish.
This is apparently the problem with PVA, although i have never tried it.
I use only wax, applied 10 times.
Cheers
Fred W B
Are you using polyester? The longer the mould has to mature, the less of an issue it is. After 1 or 2 pulls, the active resin is mostly gone from the
mould, so I might try just wax next time.
From what I have read, mostly about boat construction, on a large, expensive mould, they do a splash pull, where they layup the gelcoat and a couple
of layers of cheap glass on top of the PVA. This is then pulled off and thrown away. They can then use just wax to get a better finish.
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twybrow
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| posted on 29/10/10 at 12:14 PM |
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Try spraying the PVA on. you can use a plant mister, to apply a light mist of PVA to the tool. A damp sponge is useful to ensure even coverage....
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andrew-theasby
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| posted on 29/10/10 at 04:49 PM |
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Im only thinking of using epoxy if i make one out of carbon too, but the first will probably be glass and polyester. Can you see the pva before you
do the lay up to tell whether it is even or not? The mould surface will form the inside of the part, so not too critical, and most of it is tapered
so should be a good shape to release.
[img][/img]
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BenTyreman
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| posted on 29/10/10 at 05:28 PM |
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So that shape is the mould? I presume you will doing the parts in 2 pieces then and joining after the mould is removed. The flanges could be tricky to
do. The square sides will make it hard to get the glass to sit down properly without leaving voids.
The PVA is very thin. The stuff I have has a blue colour to it, so you can see where you have been. If you have access to spray equipment, then that
would definitely be preferable than applying it by hand, although if you apply it with a cloth then it certainly won't be any rougher than the
existing mould finish.
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andrew-theasby
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| posted on 29/10/10 at 05:34 PM |
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ok ta, thats not the finished mould by the way, its had a few more coats of filler since then, and yes it will be 2 halves. Ill see how it goes then
maybe have to vacuum bag it if it wont cling to the mold. Thanks for all the pointers
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