Fred W B
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| posted on 16/1/09 at 06:01 PM |
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Epoxy verses poly resin, for moulds?
Hi All
Regular browsers will know what I am trying to do, otherwise see here - CANAMSA body
thread
I would appreciate some help on the following, various sources seem to differ.
Do I need epoxy resin for the molds, or will I get away with poly?
Any of the resident GRP experts want to discuss?
Cheers
Fred W B
[Edited on 16/1/09 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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twybrow
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| posted on 16/1/09 at 06:09 PM |
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What are you making the parts out of?
Unless you are using high temperature systems, polyester will be adequate. I assume you are planning on using gelcoat/tooling gel, which typically is
only in polyester. You can get epoxy gelcoats, but it is not widely used.....
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Echidna
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| posted on 16/1/09 at 06:12 PM |
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It will cost you a fortune if you use epoxy resin for the molds! And epoxy can be used only in conjunction with fabrics (fiberglass, carbon, kevlar)
and not chopped strand mat. This is because the "needles" chopped strand mat (which is super cheap and ideal for molds) are kept together
by a chemical which is dissolved when mixed with polyester resin. If you use CSM with epoxy this chemical will never dissolve.
kitCARBON is the new carbon composite parts company specialising in kitcar parts. We can make parts to order in carbon, carbon/kevlar, kevlar,
texalium and more!
For any question, just U2U or email me at
theodragonas@gmail.com
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Hugh Paterson
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| posted on 16/1/09 at 06:15 PM |
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Poly resins are fine for molds, especially for ease of use, I would recommend u you use tooling gelcoat for the mould rather than standard general
purpose gelcoat. Its formulated for its hardness and suitability for machine finishing to get a high quality finish on your mould tooling. All handy
if u want to use the tooling for multiple "pulls" Fred.
Epoxy is a lot more expensive and is even more hazardous to use especially in large quantities, more suited to structural and marine applications. I
manufacture commercial structural mould tooling for a living, some to a large scale, 90% of our moulds are polyester based some of them are over 15
years old and still working commercially.
regards
Shug
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Fred W B
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| posted on 16/1/09 at 06:15 PM |
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Thanks Twy for quick response.
I had been planning to use tooling gel in the molds and Poly for the parts. I read that Epoxy is the better option, but this is locost
builders.....
I supose the question is, will mold shrinkage really be a problem?
Fred W B
[Edited on 16/1/09 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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Fred W B
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| posted on 16/1/09 at 06:19 PM |
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Wow, two more responses while I was typing above. Thanks guys, you have confirmed what I have been thinking.
And, apparently we all need a life, sitting on here on a Friday evening
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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twybrow
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| posted on 16/1/09 at 06:28 PM |
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I don't know what parts you are making, but I would bet good money, the accuracy of your moulds, and whatevery you are outting these parts onto,
will be further out than the changes caused by resin shrinkage. More likely is you will see 'print through' off the CSM onto the surface
of your tool as it cures. To avoid this, use glass tissue on the backside of the tooling gel, or even a barrier paste if surface finish is really
important to you. Otherwise, you may be able to see the slight impression of the CSM in your final part....
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clairetoo
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| posted on 16/1/09 at 06:48 PM |
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quote:
Originally posted by Fred W B
Thanks Twy for quick response.
I had been planning to use tooling gel in the molds and Poly for the parts. I read that Epoxy is the better option, but this is locost
builders.....
I supose the question is, will mold shrinkage really be a problem?
Fred W B
[Edited on 16/1/09 by Fred W B]
Never heard of `tooling gel` ? (and I've been doing fibreglass for over twenty years.........)
I've allso never had such a thing as `print through` - the gel would have to be extremly thin for that to occur .
Provided the molds are fairly thick and well braced , I doubt you will have major troubles with shrinkage - it usually happens if the mold is too thin
, or you use heat to speed up curing .
Good to hear you are close to making your molds - cant wait to see the finished body
Its cuz I is blond , innit
Claire xx
Will weld for food......
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Fred W B
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| posted on 16/1/09 at 06:52 PM |
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Thanks, WRT laying up the molds, I have 600 density CSM for the bulk of the molds, and have planned to put surface tissue benind the gell. I'm
thinking I must get some much lighter CSM as a first layer over the tissue, to get into the radia and other details.
Another question - Once I lay up the first couple of layers of the molds, and let it go off, what prep if any do you do before you start again with
more layers?
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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Hugh Paterson
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| posted on 16/1/09 at 07:25 PM |
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Depends on the quality of your inital surface finish/consolidation, small spikes especially on a tight radius are common, a quick despike to these
with a bit of 80 grit is not unusual, just enough that the next layer of csm does not have to lie on a high point and allow a void to form. Its
important to try and get the inital 2-3 layups after the tissue surface on in one day to maintain the primary bond, the back-up layers and stiffeners
can go on in day two if its beyond your capability in the first 24 hours. Most modern general purpose gelcoats especially the lloyds approved ones
allow for inital consolodation within 24 hours of application. Its standard practice however to get at least the surface tissue and inital layer on
larger plugs on before stop of play. Preperation is the key to success, cut and tailor all your matt prior to lay-up and have it close to hand. Avoid
buildup of all the joins by staggering them across the surface of the mold, and dont butt straight edges of the roll to straight edges, better to have
torn joints slightly overlapping with your csm than cut edges.
Oh and a couple of flunkys/trainees to fetch and carry help, feed em beer on completion not before
Shug
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Mave
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| posted on 16/1/09 at 07:42 PM |
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For my new body I'm considering using epoxy for the body itself (poly for the moulds). My reason behind this is the shrinkage of the poly, often
seems to result in surfaces that are not really smooth (especially after some time). Flat panels don't appear 100% flat anymore, if you know
what I mean (look at the poly sidepanels on a Seven for instance, and compare them to a (painted) alloy panelled Seven. I heard that when using epoxy,
over the years the body will stay better in shape.
What are your thoughts on this?
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twybrow
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| posted on 16/1/09 at 07:52 PM |
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quote:
Originally posted by clairetoo
Never heard of `tooling gel` ? (and I've been doing fibreglass for over twenty years.........)
I've allso never had such a thing as `print through` - the gel would have to be extremly thin for that to occur.
Tooling gel is widely used. I am very surprised you have not heard/used it if you have been doing grp for so long....
Try a quick google, and you will plenty of hits, with products from SP, Scott-BAder, Cray Valley etc. Print through is a huge problem in the marine
industry. Yacht owners pay a lot of money for a mirror finish on their yacht. The company I worked for (the largest private yacht builder in the
world!) spent a small fortune trying to solve it. Not so much to do with gel coat thickness (this should be checked when applying anyway), more to do
with what is behind the gelcoat. Have a look
here for some more info on surface
finish, and possible solutions.... Everyday is a school day on Locostbuilders!
Look closely at the GRP work on our cars, and I can pretty much guarantee, you can see the CSM pattern in the gelcoat surface.
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