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Author Topic: Bending Perspex  (Read 3863 times)

ukmike

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Bending Perspex
« on: November 30, 2018, 10:38:17 am »

I need some advice as to permanently bending the sheet to form the windscreen on my current build.
The plastic is 2mm thick and although quite pliable it isn't enough to get the fairly tight curves needed.
I only get 1 go at this so the more information as to how to do it all be most helpful.


I have made a template from thickish card which is 600mm long X 100mm wide at the centre then tapering to
nothing at the ends. The double frame, one inside and one outside, is from 1mm Aluminium strip which isn't
stiff enough to hold the plastic in shape. The rake of the screen at the front is 45 degrees.


The photo shows what I am aiming for. Any advice will be most helpful.


Mike.









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Martin (Admin)

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Re: Bending Perspex
« Reply #1 on: November 30, 2018, 10:42:32 am »


 I have no experience of this but I wonder if you make a negative mould of the shape you need, heat the Perspex in the oven and lay it on the mould, if that would work. ( May take some of trial-and-error! )

Also:
https://youtu.be/Y5Za7N87qI4  -  https://youtu.be/wXAQe57gmsA

( NB: Great Photo! )
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canabus

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Re: Bending Perspex
« Reply #2 on: November 30, 2018, 11:39:13 am »

Hi Mike
Martin has the right idea.
I had done a few with Perplex including right angles and curves.
I use a heat gun on low and warmed the Perplex up slowly.
It will bend with its own weight on curves and if you use gloves you can hold it in place.
It cools down very quickly with the heat off.
Right angle ones cover the area that you do not wish to bend and apply heat slowly.

Canabus
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tonyH

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Re: Bending Perspex
« Reply #3 on: November 30, 2018, 11:41:50 am »

One thing I tried, fairly successfully, when I wanted green tinted windows for a patrol boat was using plastic 2litre 7up bottle material in the oven on a template. It's free and once you get the temperature right with a bit of trial and error then you can do as many as you want. BUT BUT BUT you must cut it well oversize and then trim back because it does shrink substantially, thickening in the process.
Tony
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aeronut

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Re: Bending Perspex
« Reply #4 on: November 30, 2018, 12:28:22 pm »

ukmike - what type of plastic are you actually using?  Everyone seems to have assumed Perspex, which would not be my first choice for that, as it is tricky to work.
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Re: Bending Perspex
« Reply #5 on: November 30, 2018, 12:35:24 pm »

how about using a motorcycle helmet visor, that should fit to your curves
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ukmike

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Re: Bending Perspex
« Reply #6 on: November 30, 2018, 12:39:41 pm »

ukmike - what type of plastic are you actually using?  Everyone seems to have assumed Perspex, which would not be my first choice for that, as it is tricky to work.
As the heading says... Perspex


Mike.





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Martin (Admin)

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Re: Bending Perspex
« Reply #7 on: November 30, 2018, 12:49:27 pm »


 What other / better choices are there,  rather than Perspex?   :-)
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aeronut

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Re: Bending Perspex
« Reply #8 on: November 30, 2018, 12:54:38 pm »

I only asked because many people call any clear plastic sheet Perspex.  True Perspex can be quite brittle, cracks easily and can be quite tricky to work.  Clear PETG sheet is a better choice if you want to bend it.
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Re: Bending Perspex
« Reply #9 on: November 30, 2018, 12:57:56 pm »

I also agree with the petg also lexan, polycarbonate are flexible.
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TailUK

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Re: Bending Perspex
« Reply #10 on: November 30, 2018, 01:07:10 pm »

Perspex is the trade name used by ICI for their brand of Acrylic which is always Cast Acrylic  The name became synonymous with the product, Like calling a vacuum flask a Thermos. 
While cast acrylic does heat bend it is also prone to blistering if you get it too hot.  PETG is a better option as it cuts more easily and isn't as prone to blistering.
 Failing that try getting hold of extruded acrylic which a bit more forgiving than the cast.  A wooden former lined with good quality paper will help prevent marks an a fabric "scarf" which covers the entire piece of plastic and can be used to push the plastic down around the mould.
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Neil

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Re: Bending Perspex
« Reply #11 on: November 30, 2018, 01:23:13 pm »

if it is true Perspex it is moulded when still "hot" and you will just shatter it unless you have an autoclave to slowly reheat through uniformly...…the molecules change within the plastic when it cools down, to make it flexible but not bendable...…….you see often what happens when a vandal takes exception to a bus stop shelter or phone box..…..if it is any of the other clear plastics, as already stated then a hot air gun or hair dryer for slow heat, and bent around a wooden plug...…...but your best bet is to make a wooden plug, find someone with a vac former, make a tool for vac forming and do that way.
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justboatonic

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Re: Bending Perspex
« Reply #12 on: November 30, 2018, 02:56:57 pm »

Doesn't perspex tend to go white when you try and bend it even if gently heated? Personally Id investigate using clear lexan what they use for RC car body shells. Given it is quite 'bendy' you shouldn't need to heat it to get the right shape. Plus, it is relatively easy to cut (best with small curved nail scissors) and file if your cuts get a little wobbly.
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Baldrick

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Re: Bending Perspex
« Reply #13 on: November 30, 2018, 03:11:24 pm »

I'm going back about 60 years now when Perspex was new on the market but my memory says we used to bend it by putting it in a tray of very hot water.
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Neil

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Re: Bending Perspex
« Reply #14 on: November 30, 2018, 03:54:35 pm »

I'm going back about 60 years now when Perspex was new on the market but my memory says we used to bend it by putting it in a tray of very hot water.



it can do on very tight corners, because of its molecular structure, but there are so many better products on the market these days readily available in model and craft shops that are easier and more flexible I wouldn't even consider something that is brittle and needs to be heated...…...but you can only offer advice, can't change minds already set upon a course.
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ukmike

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Re: Bending Perspex
« Reply #15 on: November 30, 2018, 04:02:06 pm »

I'm going back about 60 years now when Perspex was new on the market but my memory says we used to bend it by putting it in a tray of very hot water.


Thanks for that Baldrick ... Good news at last.
Have spoken to the tech. dept. at ICI and after explaining what I needed to do they say warming in hot water or gentle heating with a heat gun should work. After all it's a quite large screen at 600mm so the curved portion is relatively gentle and the sides are straight.
Seems that your 60yr. old information is indeed correct


Mike.
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BrianB6

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Re: Bending Perspex
« Reply #16 on: December 01, 2018, 12:10:23 am »

I love using Perspex.   It is so easy to work and gives a really smooth finish either clear or painted.I have made the superstructures of 3 warships from it.
Generally I use 1.5 mm. clear ordered from a signwriting firm.   They normally use 3 mm. but ordered a sheet of 1.5 mm for me.   The proper glue is expensive and evaporates very quickly so I use Araldite where I want it to remain clear and superglue where it will be painted as superglue makes it go white.
I know the windscreen in the photo below is broken but it is over 50 years old and rather dirty!   It was heated in a gentle domestic oven and bent by hand as the exact curve was not critical.   I cannot remember if the paper was left on.

Dorina was built in the 1980's but all the joints are still sound.  The rear superstructure wall was bent with a heat gun and is all in one piece.

Ararat shows that it can be bent to gentle curves without heating as long as there is a former to keep the bend.   I used 3 mm. for the bridge as that was the only thickness that the signwritters had in the colour I needed and they did not charge for the offcut!

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ukmike

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Re: Bending Perspex
« Reply #17 on: December 01, 2018, 05:52:27 am »

Many thanks for that BrianB6, you have you have helped me make my mind up. Perspex it's going to be.
Mike.

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ukmike

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Re: Bending Perspex
« Reply #18 on: December 01, 2018, 03:01:04 pm »


 It seems that Perspex needs 170deg.C for cast and 155degC for extruded, both of which well above boiling point so I will have to use a heat gun.
I have no idea which type of the plastic will be supplied, but fortunately, I have an R.S. supplied Steinel professional heat gun, old but in good working order so will use that.
The temperature is selectable from 50 to 650 degrees in 50 degree steps and the flow rate is fully controllable.


I will post pictures of all the results, good or bad, but no video, not possible as I don't have one.


If it's of any interest to anyone here a some pictures of the heat gun.


Mike.

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TailUK

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Re: Bending Perspex
« Reply #19 on: December 01, 2018, 06:02:19 pm »


Quote removed - Admin


Cast Acrylic usually has printing on the protective film which should be on both sides.  Extruded usually has no printing and the film is clear blue or green plastic.  You minimise problem by pre-drying the acrylic to prevent the formation of blisters if it gets too hot warm the plastic too about 120 degrees for a couple of hours and let it cool slowly.  This will make it less prone to blisters, solvent cracking and stress cracks.
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Onetenor

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Re: Bending Perspex
« Reply #20 on: December 01, 2018, 07:09:02 pm »

Come on guys let's not fall out over a little bit of plastic please. I used to bend plastics quite a lot using the element for an electric fire. Position the required bending   point about an inch above the element until it softens and remove from heat and quickly make the required angle bend. For more general bends use 3 bars and a bigger distance away and a longer time   gently flexing the sheet 'til it moves then remove from the heat  and set and hold the curve until set. A former is best to use for accuracy. As I always say EXPERIMENT.  Time and distance are the factors to keep in mind. .Happy bending.
John
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Martin (Admin)

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Re: Bending Perspex
« Reply #21 on: December 01, 2018, 08:25:37 pm »


'Clean up on aisle two!'   :police:
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ukmike

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Re: Bending Perspex
« Reply #22 on: April 20, 2019, 10:44:29 pm »

As promised, here is the result of my Perspex windscreen.
Bent around a former using a 2500 watt heat gun which is only just enough to bend a piece of this size.
Fortunately, all went well at the first attempt.
A couple of photos.


Mike.



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Peter Fitness

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Re: Bending Perspex
« Reply #23 on: April 21, 2019, 04:08:44 am »

That's worked a treat Mike, it looks great.


Peter.
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TugCowboy

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Re: Bending Perspex
« Reply #24 on: April 23, 2019, 09:08:02 am »

Great results and a new string to the bow.
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