interestedparty
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| posted on 9/8/10 at 05:41 PM |
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Making GRP moulds
I want to have a go at making some bodywork from GRP, and will obviously need to make moulds.
I'm ok with the patterns, but I would like to get some opinions on the thickness of the moulds (expressed in terms of how many layers of a
particular weight of chopped strand matt) and of the body parts I hope to make.
I reckon a finished thickness of 2.5 to 3mm will be ok for the body parts, but all the advice (mostly from people who sell the materials  ) is that
the moulds need to be much thicker.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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PSpirine
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| posted on 9/8/10 at 05:47 PM |
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5-6mm for parts moulds
If you haven't got strengthening ribs already, then I suggest doing the following.. lay 3-4mm, then use balsa sticks (you can prebend them
roughly by scalding them with boiling water, then let them dry in the bent position) as ribs, then put 3mm on top of that, laminating the ribs in
place.
What I used to do was then just put filler/CSM to build up thickness in corner areas.
Having said that, if you're only going to take one part from it, you can get away with a 3mm mould (it'll be flexible, but shouldn't
matter too much). If you're going this way, I suggest having one woven layer, not all CSM
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Humbug
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| posted on 9/8/10 at 05:47 PM |
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I don't know what body parts you are planning to make, but my off the shelf panels are at least 5mm thick, if not more. I suppose it depends on
weight, strength, flexibility considerations etc.
Can't help you on the moulds
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interestedparty
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| posted on 9/8/10 at 06:07 PM |
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quote:
Originally posted by PSpirine
5-6mm for parts moulds
If you haven't got strengthening ribs already, then I suggest doing the following.. lay 3-4mm, then use balsa sticks (you can prebend them
roughly by scalding them with boiling water, then let them dry in the bent position) as ribs, then put 3mm on top of that, laminating the ribs in
place.
What I used to do was then just put filler/CSM to build up thickness in corner areas.
Having said that, if you're only going to take one part from it, you can get away with a 3mm mould (it'll be flexible, but shouldn't
matter too much). If you're going this way, I suggest having one woven layer, not all CSM
Any thoughts on what that would amount to in terms of weight/ number of layers of matt?
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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PSpirine
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| posted on 9/8/10 at 06:16 PM |
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if using chunky stuff (450-600g), probably 3-5 layers, followed by the same again. Depends how liberal you are with resin application
I always tended to beef up corners and curves by just laying more mat (as you can get sloppy on the outside, I'd just pile 2-3 layers in at a
time and soak it in resin).
Like I said, it depends on how much use you're going to get out of it.
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twybrow
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| posted on 9/8/10 at 08:46 PM |
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450gsm will give you a thickness of between 0.75-0.95mm (approx) depending upon how well consolidated and how much resin you flood it with. Aim for
5mm minimum for a one off mould, and thicker (anywhere up to 10mm+) for moulds you want to make more parts from. Apply gel, let it go tacky to the
touch (ie no gel on your finger if you touch it with a rubber glove). Then layup a very light glass tissue, or as light a CSM as you can get. Let that
go off, then build up your layers to the thickness you need. Just dont build too much thickness in one go, or it will exotherm and potentially
pre-release and/or shrink.
As said above, add ribs etc to add stiffness. If you can get it, vinyl ester resins tend to work better for tooling (low shrinkage). Also make sure
you use gelcoat (preferably tooling gel) and apply plenty of releases to your plug before you start gelling up.
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interestedparty
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| posted on 9/8/10 at 09:03 PM |
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If a thin mould (comparatively) is ok for one part, why does it needs to be thicker for several parts?
I'm not trying to suggest it shouldn't be, just trying to understand as much as I can about this before I start. What is it that changes
as more parts are taken from the mould- if moulding a part adversely affects the mould in some way, isn't it the surface of the mould that would
be affected rather than its thickness?
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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aabrams
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| posted on 9/8/10 at 09:25 PM |
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Hi I've made a number of moulds.
I like to use a layer of 300grm matting all over the plug/pattern first. Then 3 layer3 of 600grm matting. Make sure that you have enough material on
corners and edges. If you need to use some more 300grm matting on areas which will not conform.
I also like to use 2 layers of gelcoat aswell which are different colours. This is because if you need to do any repair work or flatting of the mould
then you know when you have gone through the first layer and then you know when to stop.
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twybrow
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| posted on 9/8/10 at 09:54 PM |
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quote:
Originally posted by interestedparty
If a thin mould (comparatively) is ok for one part, why does it needs to be thicker for several parts?
I'm not trying to suggest it shouldn't be, just trying to understand as much as I can about this before I start. What is it that changes
as more parts are taken from the mould- if moulding a part adversely affects the mould in some way, isn't it the surface of the mould that would
be affected rather than its thickness?
Its more a case that a thicker mould will last longer in terms of distortion (ie it will distort less and will stand up to more abuse/repair!). If you
brace it well, then going thinner is usually fine. As others said, corners are your usual area to beef up.
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interestedparty
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| posted on 10/8/10 at 04:29 AM |
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Just one more quick question-
when laying up, if I run out of catalysed resin, can I make up some more and carry on, or is it better to wait until what I've already done has
gone off?
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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twybrow
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| posted on 10/8/10 at 05:48 AM |
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You can make up more and carry on, but you should not aim to build up too much in one hit - 3-4mm in one hit is ok.
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Fred W B
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| posted on 11/8/10 at 06:20 AM |
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I have just been researching the same question and making a mould
I used two coats of tooling gel, 1 x surface tissue, 1 x 300 gram and 5 x 600 gram layers. Double thickness on the flanges. You can see what I did a
little down the page
HERE
I was advised to put any bracing right on the outside of the full layup, to hopefully reduce "print through". Seemed to work for me.
l
Cheers
Fred W B
[Edited on 11/8/10 by 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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