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What weight cloth for Cowl?

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Erfolg11/02/2020 17:38:17
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11749 forum posts
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I am about to lay up a cowl from glass cloth and polyester resin. There is a problem, I do not remember or have a feel what weight cloth will produce a useful moulding.

I know that most of us no longer do this sort of thing, i am hoping that some peoples memories are better than my own. sadOr may be they have a note book in which they recorded what they have done.

Here's hoping.smiley

Callsign Tarnish11/02/2020 17:41:38
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How big is the cowl Erflog, that will have a bearing? Personally I'd start with 2 layers of 200g twill and go from there, maybe some additional local reinforcement where the mounting screws go. Also, why polyester? It's heavy, brittle and poor working time. Epoxy all the way

McG 696911/02/2020 17:56:09
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Hi Carl,

It depends indeed a bit on the size of your cowl.

You seem to be wanting to make a mould from a plug.

In that case, I would opt to start with a lighter glass tissue (something between 50 and 100gr/m2) and work up to different layers of 200gr as Callsign T stated.

The final cowl should be lighter, of course. Two (max. 3) layers of 100gr or equivalent if you use lighter grammage tissue.

Use preferably epoxy resin for the reasons already stated...

... and of course don't omit a few layers of wax (polished) before you start any work.

Cheers

Chris

Graham R11/02/2020 18:30:35
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26 photos

Keep a check on the amount of resin you use. Ideally weight of resin = total weight of glass. anything more is just adding weight but no strength.

As everybody else had said use epoxy rather than polyester.

Erfolg11/02/2020 20:09:27
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11749 forum posts
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Polyester is available where I live, epoxy resin needs me to send away.

Callsign Tarnish11/02/2020 20:18:12
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103 forum posts
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I'd recommend sending away for it, better results and easier working. It's the one consistent theme in the advice.

Martin McIntosh11/02/2020 20:35:03
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We need to know the size of the cowl first. For a finished product of 6" or so then a first layer of 25-50gm then one or two at 80gm will be quite enough. Don`t even think about polyester (I expect you are thinking of the Halfrauds car repair stuff) because for one reason it is very brittle. You must use 24hr epoxy made for the job. I have to send away for my materials too.

Braddock, VC11/02/2020 21:09:40
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1654 forum posts
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Is the model likely to need noseweight, if you can assess what the amount is likely to be sheet lead can be laminated into the cowl.

I've had good results with the lost foam method of laying up, make the cowl from white foam so that its final shape includes the thrustline, spinner position etc and paint with emulsion, dark green or whatever colour you fancy.

Lay up your glass cloth or chopped strand mat and paint your resin on around the foam, polyester is the better of the choices for this. Try to get the outside as near to the outline as possible. Don't get the resin on bare foam btw.

Once the resin goes off, about 15 minutes iirc, start filing the outside to your final shape. Use cellulose filler to make up any low areas and keep reducing the coarseness of your abrasive until the finish is acceptable to you.

Whilst doing this please wear a face mask as not only will it keep the dust out but also the bits of sputum that pass coronavirus on.

You can then paint on a thin layer of gelcoat and sand that back until it suits you. when you're finished sprinkle cellulose thinners on the foam inside the cowl and watch it shrivel up cut and scrape the last knockings out, the paint will remain stuck to the resin and will show you when all the foam is gone.

It's probably going to take about as long as making a plug and mold to lay up a conventional cowl. It's smelly and dusty but the results can be stunning.

HTH, remember Brian Taylor used to use polyester for the cowls he supplied and I have two, one's been around since the mid 80s in the last century, the other is 10 years younger and still in use. They are solid and easy and quick to repair btw.

Edited By Braddock, VC on 11/02/2020 21:10:55

Edited By Braddock, VC on 11/02/2020 21:14:26

Andy Stephenson11/02/2020 23:45:23
169 forum posts
28 photos

I made quite a deep a cowl for a patternship by taking the original ABS one and filling it and sanding it to a fine finish with filler primer. I cast this in 2 part silicone supported in a plywood box as the silicone sets quite floppy. This resulted in a negative mould. After several attempts and some success I found the combination of the first layer (outer) 81g twill GF with the second one of 180g this gave the best results. I used a good quality laminating epoxy. You can't actually paint a gel coat on to silicone as it doesn't stick. I layered overlapping strips of GF and stippled on the epoxy with a brush then using a miniature roller on a long handle I rolled the epoxy through the weave to give a smooth surface when set. To de-mould the cowl I removed the silicone from the supporting box, peeled it away round the edges and with some soapy water eased it out.

Former Member12/02/2020 07:28:10

[This posting has been removed]

Erfolg12/02/2020 11:45:25
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11749 forum posts
1337 photos

Back again

I have now measured the cowl, it is approx 5" dia and 3" deep.

wp_20200122_11_39_36_pro.jpg

As can be seen there two of them.

I have waxed the mould and polished 6 times.

I will paint with the blue PVA before I start to lay up.

Just a few more pictures.

wp_20200210_16_32_45_pro.jpg

wp_20200212_11_16_27_pro.jpg

As can be seen I have made some patterns and the cut some cloth. The cloth works out at approx 200 grm M^-2. I have some 1.5 oz stuff which I have toyed with using to pick up the fine detail. I had not intend to show them here as they more appropriately belong on an other thread.

Once upon a time I did quite a lot of laying up for both polyester and epoxy resins, from canoe to fuz, to wings. The trouble is I have forgotten much of how I did things, the bits and pieces lost or just binned. I am talking 40 years ago, in some cases.

You are correct in thinking that I had intended using the Halfords, Davids resin. I will reconsider, particularly as the temperature is a little low for working in the garage. IMO these are not materials to use in the house, particularly with carpeted model room. I would be dead if I got any gunge on any of the other house carpets.

I will be looking for no more than 500ml, ideally with a long shelf life, as i will probably not use again for some time if ever. Some ideas please, remembering I know little of the current products.

Callsign Tarnish12/02/2020 12:28:13
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103 forum posts
2 photos

There are many options so expect different answers. East Coast Fibreglass do several and their service is excellent. My preferred choice at the moment is from EasyComposites and can be had in small quantities:

https://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/epoxy-resin/EL2-epoxy-laminating-resin.html

Erfolg12/02/2020 15:12:17
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11749 forum posts
1337 photos

I have gone for 500 ml of easy composites.

Like others I have both cowls and models made from Polyester resin.

Probably what has decided me is the smell from polyester, with an integral garage, I do not wish to upset the better half.

Another consideration is that the rear cowl may not fit without some persuasion and maybe cutting etc.

Then there is the issue of getting the mouldings out of the mould. I am hoping that the rear moulding can be persuaded out, Using propellor blades, so if need be I can make an other. I do not think there is any hope with the front moulding, as there is no taper at all. If it were strictly scale, I think there should be a reverse taper, making the cowl barrel like.

Anyway, the weather is against me at present, being to cold by far. It was just hail stoning a few minutes ago, mountainous waves are crashing onto the nearby beach, where the residual water runs up the beach for hundreds of yards. Helped along by very strong wind. The weather is nasty right now.

Edited By Erfolg on 12/02/2020 15:12:47

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