Polyester mold for epoxy foils

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MCR
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Polyester mold for epoxy foils

Post by MCR » Sat Mar 07, 2009 1:42 am

Hi all building gurus

I'm about to start the molds for my foils and I was thinking about doing the mold out of polyester resin as I've heard that Epoxy has a hard time bonding to it, and this would be an added bonus for releasing the foils. Has anyone done anything like this and what are the pros & cons of this method? As I'm doing parallel leading and trailing edge shapes to start with I use a method where you drag a template of the foil shape through some thickened resin which leaves the impression in the surface once it goes off. I've built foils this way before for my moth and it works OK, as long as you only want parallel edges. I've contacted some CNC people but haven't had any luck with anyone who will do foil molds for me so I'm looking at my options right now.
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Christian AUS
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Re: Polyester mold for epoxy foils

Post by Christian AUS » Sat Mar 07, 2009 2:30 am

MCR wrote:Hi all building gurus

I'm about to start the molds for my foils and I was thinking about doing the mold out of polyester resin as I've heard that Epoxy has a hard time bonding to it, and this would be an added bonus for releasing the foils. Has anyone done anything like this and what are the pros & cons of this method? As I'm doing parallel leading and trailing edge shapes to start with I use a method where you drag a template of the foil shape through some thickened resin which leaves the impression in the surface once it goes off. I've built foils this way before for my moth and it works OK, as long as you only want parallel edges. I've contacted some CNC people but haven't had any luck with anyone who will do foil molds for me so I'm looking at my options right now.
Speak to Geoff Harman about how he is knocking up the foils for the Flatpack boats. Tim Wilson also builds foils, and could probably make or assist you with foils.

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Re: Polyester mold for epoxy foils

Post by Chris Maas » Sat Mar 07, 2009 7:44 pm

MCR wrote:Hi all building gurus

I'm about to start the molds for my foils and I was thinking about doing the mold out of polyester resin as I've heard that Epoxy has a hard time bonding to it, and this would be an added bonus for releasing the foils. Has anyone done anything like this and what are the pros & cons of this method? As I'm doing parallel leading and trailing edge shapes to start with I use a method where you drag a template of the foil shape through some thickened resin which leaves the impression in the surface once it goes off. I've built foils this way before for my moth and it works OK, as long as you only want parallel edges. I've contacted some CNC people but haven't had any luck with anyone who will do foil molds for me so I'm looking at my options right now.
The template dragging method sounds okay. Used to be a common method using plaster in pattern making.

Don't rely on the poor bond between poly and epoxy as a form of mold release. It will still bond well enough to ruin your mold and/or part. I use Partall #2 wax and spray on a good coat of PVA film. I'm sure you guys have something similar. That works well on rough molds.

A western red cedar or what you call oregon core is a good way to go for a one-off board.

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MCR
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Re: Polyester mold for epoxy foils

Post by MCR » Sat Mar 07, 2009 10:33 pm

Hi Chris

Yes, I'll definitely use release agent in the mold as well. Below is a photo of one of the foil sides for the last Moth. You can kind of see the mold and how it ended up. I did them as carbon skins with a carbon strut down the max thickness point. Other that that they are hollow.
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Re: Polyester mold for epoxy foils

Post by Phil Stevenson » Mon Mar 09, 2009 6:58 am

Geoff.
Did you try Ian Dixon: http://www.dixonboats.com/ for CNC molds?
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Re: Polyester mold for epoxy foils

Post by MCR » Mon Mar 09, 2009 9:12 am

Hi Phil

Yeah, I tried email but no answer. I might have to resort to that old "telephone" technology to make contact. :lol:
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Re: Polyester mold for epoxy foils

Post by GBR242 » Mon Mar 09, 2009 6:23 pm

Hi MCR or indeed Chris M,

could you give me a few more words on how you use the template to create the mould.

It sounds like a good way....but I can't quite visualise what you are doing.

cheers

eib
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Re: Polyester mold for epoxy foils

Post by MCR » Mon Mar 09, 2009 9:03 pm

Hi Ed

I hope you can see what I'm talking about from the two photos below. I make up a board with channel from a plank about 150mm longer and 100mm wider than the longest foil. It is very important that the walls are parallel and straight as these are the guides for the foil template. I them make up a paddle with the foil template attached from a piece of about 20-25mm ply. This width helps you hold the paddle at 90 degres to the mold and stops you from rocking it around as you drag it. If it rocks in the mold it will change the foil shape. The foil template sits inside the rails so that it tracks straight and the handle sits on top to keep it at a constant depth. For these foils I was planning on filling the channel with builders bog (cheap polyestrer car filler) and you then drag the shape through it. It is important to use something that won't sag before it goes off as this will also change the shape.

Some little personal additions I made are the groove you can see under the paddle. I lay some 3 strand silver polyethylene (cheap plastic anchor rope) into the grove to allow the vacuum to travel down the length of the mold. I them drill down through the groove at each end and in from the end so I have a hole to put the vacuum hose into, you can kind of see this in the photo above.

Hope this explains things, if you need some more info I can help...
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Re: Polyester mold for epoxy foils

Post by Steve Clark » Mon Mar 09, 2009 11:40 pm

I have done stuff like this as well. I like to fill up as much of the mold as I can with bits of wood cut to shape to make the amount of bog heating up, sagging, shrinking and otherwise misbehaving down to a minimum.
I also have been known to make sanding blocks that are the shape of the section and which follow the rails so I can sand back with some assurance that I am getting the right shape.
If I had hands as smart as Chris' this wouldn't be a problem. But as a spaz I have to compensate.
SHC
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