Restoration - Perspex windows, heat forming, help

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m1nder

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I am restoring an old boat. I need to form new windows for the front. As you can see they curve around. I am wondering if any of you can give me any advice about this? It looks like I need to DIY as the costs of plastic fabricators are prohibitive.

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My latest plan is to fashion a stiff backing from cardboard and masking tape behind the window, then fill it with a pollyfilla or car filler. Smooth it to the profile of the window and let it harden. That will give me a mold, then I need to somehow heat my piece of perspex over that. Am I on the right track here?

Many thanks as always
 
m1nder said:
I am restoring an old boat. I need to form new windows for the front. As you can see they curve around. I am wondering if any of you can give me any advice about this? It looks like I need to DIY as the costs of plastic fabricators are prohibitive.

attachment.php


My latest plan is to fashion a stiff backing from cardboard and masking tape behind the window, then fill it with a pollyfilla or car filler. Smooth it to the profile of the window and let it harden. That will give me a mold, then I need to somehow heat my piece of perspex over that. Am I on the right track here?

Many thanks as always
Click to expand...
They are a lovely shape - and I see your problem.
I have no experience, so can only offer my gut instinct, but I would start with the cardboard to make a pattern, cut the perspex to shape and pre-drill the fixing holes, then fix to the outside edge of the window.
Next heat and bend the perspex fixing as you go to the centre of the boat.

Is that Lough Derg in the background?
 
I remember an article from a couple of years ago about a chap who was restorng one of those Messerschmit bubble cars. He had the same problem, as I recall he made a former and place it and the sheet of perspex in an oven on a very low temp. I'd look around for a potter or a Heat treatment company who might let you use their oven/kiln for a couple of hours.
I'd also suggest a trial run first - I take it you've seen the cost of perspex lately?
 
@BGW - The windows will be fitted with rubber seals, no screwing etc. Also I will cut an oversized piece first, then form it and then trip it to size as I suspect it will deviate during heating. Not Lough Derg, Lough Arrow (Co Sligo).

@dgadee, I cant imagine how one might make such a 3d template from mdf. I'd either need to bend mdf around the inside of the profile or get a piece of mdf several inches thick and carve/sand it to shape.

@wot, yes I was quoted €70 for a sheet of 6x4 4mm yesterday. Crazy! Why is a simple common polymer so expensive?
 
Just an idea but why not add a fibregalss strip into the window to take out the curve as per a very simply edited photo attached
 
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I've tried this before for some car headlight covers. It's not easy!

You're biggest problem will be finding an oven big enough. It looks like it's only single plane curvature, so I'd be inclined to make yourself a thin sheet of fibreglass and bend it round to the right shape for the "glass". Self-tapper it to the boat to hold the curve. Whilst in situ, lay up more fibreglass on the back and laminate some plywood stiffeners on to the back in an "egg box pattern". When it's all set, take the self-tappers out and fill the hollows that they're bound to have left with car body filler.

You then need to get your sheet of Perspex and heat it UNIFORMLY until it goes like a slice of processed cheese on a burger. It's a long time ago but I think that was just over 100 degrees C. BE CAREFUL! IF you get it just SLIGHTLY too hot, you start to get little tiny bubbles forming in it and the job is scrap. Too cold, and it just springs back to shape as it cools. You may have to pre-heat the fibreglass former. If you get the temperature right, it's just a sinple case of "draping" the rubbery sheet of hot Perspex over the former and leaving to cool. It won't follow the curve exactly but you'll be able to pull it that last bit into shape with the rubber seal (or self tappers or adhesive or whatever you're going to use). I don't know if there are any similar materials that you could use these days, which can be "cold formed" though. Might be worth asking some suppliers of acrylic and polycarbonate.
 
m1nder said:
@dgadee, I cant imagine how one might make such a 3d template from mdf. I'd either need to bend mdf around the inside of the profile or get a piece of mdf several inches thick and carve/sand it to shape.
Click to expand...

sorry for my rubbish description. I mean to make a framework from mdf which gives the outline shape in 3d (think of a framework for a model boat hull) and cover it in chicken wire/plaster to get a surface. It's a lot of work (since two forms are needed) but I presume that was how the original windows were made.
 
dgadee said:
sorry for my rubbish description. I mean to make a framework from mdf which gives the outline shape in 3d (think of a framework for a model boat hull) and cover it in chicken wire/plaster to get a surface. It's a lot of work (since two forms are needed) but I presume that was how the original windows were made.
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Yea that's kinsa what I have in mind except, I think I'll tape cardboard to the back of the windows, then wire over the card, then polyfilla it out to the window profile and smooth that off, then sand it when dry. I might use thin ply instead of card.
 
We mould plastic in a large specially made fan oven at school. The kids find it a nightmare. As others have said the sheet comes out like a large sheet of jelly and cools very quickly. As long as you don't overheat it you can just have another go and re-heat as many times as you like. We use 3mm sheets of acrylic but I think this would be too thin for you job. Another thing to bear in mind is that you will get some distortion of you view from inside, you may well feel drunk, best solution is to get drunk, it may all even out!!!
 
Better with polycarbonate Even 4 mm will take a hammering . It wont require heat to bend more expensive than acrilic and perspex but B&Q sell. Screw on, every 1 1/2 or 2 inches , bedding on sealant.
edit : you will struggle to break poly' can hit it with an 2 ld hammer! Might have to put closer screw in places
 
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fergie_mac66 said:
Better with polycarbonate Even 4 mm will take a hammering . It wont require heat to bend more expensive than acrilic and perspex but B&Q sell. Screw on, every 1 1/2 or 2 inches , bedding on sealant.
edit : you will struggle to break poly' can hit it with an 2 ld hammer! Might have to put closer screw in places
Click to expand...

I can't read this.

Either way, I am planning on making the mould, resting the glass on it and then heating, thus letting the glass rest on the mould before cooling.
 
Haven't we just had a thread on this?

Make an oven big enough for the mould and flat sheet. I used tin roughly folded up. Insulate with blankets or old rockwool.(from the tip?) Heat with an element from an oven. I used a spare 1500wt electric one. Put in a small fan to even out the heat. (computor cooling fan? I used one from a refridgeraton unit) Temp needs to be 120deg C and it will droop over the mould by itself. Allow it to cool off before you remove it. Make it over size and trim to fit. Cutting with a sharp wood blade in the jigsaw and some dilute washing up liquide in a squeezy bottle to cool/lube it. Alt. use an angle grinder and thin disc, very effective and quick.
I was using 10mm perspex, thinner will heat up quicker.

Any idea of using a heat gun will lead to blisters and (expensive) tears.

Good luck.

Edit: You could put a tin oven on top of a domestic burner for a heat source, just put a second bit of metal inside the 'oven' so as not to have direct heat radiating up.

This is assuming you do not have a domestic oven big enough. The average one does not look big enough for them.
 
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About 20 years ago I helped someone with a calum craft very similar to that
similar to this

http://cgi.ebay.co.uk/17ft-NORMAN-p...0583513?pt=UK_Power_Boats&hash=item2a0f9d25d9

After making a patten from cardboard to get the shape we screwd the polycarb down starting at the middle of the bend top and bottom self tap screw top then bottom at 1 and a 1/2 space it wasnt easy but with 2 off us it went down without heat the polycarb we used was 3 mm If you can tape cardboard over the window the poly carb will go
 
Minder I have done this before, on a boat I keep in Ireland (Co Cork) funnily enough. You need to make a former as you say, either in the way you describe or out of 3mm MDF bent around "frames" cut from 15mm mdf

Then put the perspex on the former and heat it evenly with a hot air gun. Be very patient and careful, obviously. If you get the right temp it will go very soft and form easily around the curve. I'd suggest bend the perspex as a rectangle and cut out the window trapezium shape afterwards. Took me a few hours but mine worked fine, in 5mm perspex iirc. Make sure to use perspex not polycarbonate. Good luck.
 
Thanks guys, some god info there. If I do have a go, I will photo log it and post the method and results. Gonna order either 4 or 5.5mm perspex tomorrow and cheap ply to make mould and oven. Then gotta borrow a 2 bar heater somewhere. Also does anyone know if it is possible to get a cheap thermostat / thermometer to monitor temp in an oven?
 
Just bought this little beauty, it was one of the few decent ones that had a decent probe, worth it for me as I have 2 windows and a windscreen to do. I can always sell it afterwards.
 
DownWest said:
M1inder,
Any good cook will have an oven thermometer, check your friends.
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IMHO, the oven is way over the top and you will not get the control you want or the close eyeball view to monitor the process

Much better to set up the former as described above, place a weight on the cantilvered and of the sheet of perspex or have an assistant apply a bending force, then waft hot air along he start of the curve and working a "bending front" along till you get to the end. The cantilevered part of the perspex will just nicely droop over the former, and that will tell you you have the right temp. You wont get that with the oven

And i repeat, use perspex (acrylic) not polycarbonate. Polyc is more impact resistant (hence used for riot shields) but you don't need that. The trouble with it is it is way softer than acrylic so it'll be scratched into a right mess within a year. None of the big boat builders use polyc; they all use acrylic like perspex, for this reason

Good luck
 
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