Bending Acrylic Sheet

[davidpbo]

I am replacing my windows Jeanneau Tonic 23.5.

The front window has a curvature on it. It appears to be a simple curve, the discrepancy between the top and bottom of the window is probably caused by measurement error and the fact that the window tapers slightly towards the top.

The radius of the curve appears to be about 2800mm (2.8M) Window is 1240mm at top and 1294mm at bottom and 406mm high

Thickness 10mm

I think this has been bent into shape as it was fitted using inter screws rather than heat formed prior to fitting. Am I likely to be right?

 

[VicS]

I think it might be difficult to pull material that thick to shape as you fit it.

I think it would bee sensible to discuss it with the supplier and if necessary get them to pre-form it by "drape moulding" using the old windows as the moulds.

I had the front windows shaped like that for my Sea Wych although I was able to bend the main windows without. They are only 5mm thick, IIRC, but in rubbers

 

[Dave100456]

My thoughts would be that it could be cold formed, however, you may be on the limit for the min cold forming radius. If the boat manufacturer had gone to the expense and trouble of needing and producing a mould/former then I think they would have done something more exotic with the shape.
If you have a plastics supplier go in and try to bend a 10mm sheet over the length and deflection you state.
The rough calculation I use when working with acrylic is 200 times the thickness gives the minimum radius of bend and this is borne out by the guide on this website
http://www.eplastics.com/Plastic/Plastics_Library/PLEXIGLASS-SHEET-COLD-FORMING
Note their mix of units!

Your deflection and radius is within the limit but as ever check with the supplier.

Good luck
Dave

 

[Avocet]

I agree with Vic. That's quite a thickness! I think it might end up being of similar stiffness to the surrounding fibreglass! I have "drape-formed" clear acrylic once before (making headlight covers for a car, and it's possible to do but there's a temperature at which the acrylic will become floppy enough to allow it but you don't have to go much higher than that before you start seeing small bubbles start to form inside the clear plastic. It took me quite a lot of Perspex before I got a good pair! Definitely worth talking to the supplier. At work, we use an "impact modified acrylic" (Tradename "Resist 65") which I know can be cold-formed. Ours is only 4mm thick though. I'm not sure it can be got in thicknesses about 6mm.

 

[Davegriff]

Are you sure its 10mm thick? That seems way over the top to me.

 

[Tranona]

!0mm is far too thick for that application and don't think it would cold bend and stay put just using screws. My choice would be 6mm polycarbonate.

 

[peteK]

I am replacing my windows Jeanneau Tonic 23.5.

The front window has a curvature on it. It appears to be a simple curve, the discrepancy between the top and bottom of the window is probably caused by measurement error and the fact that the window tapers slightly towards the top.

The radius of the curve appears to be about 2800mm (2.8M) Window is 1240mm at top and 1294mm at bottom and 406mm high

Thickness 10mm

I think this has been bent into shape as it was fitted using inter screws rather than heat formed prior to fitting. Am I likely to be right?

I was thinking of replacing windows on a Leisure 23 sl which are 10mm thick but a lot flatter than the above,the original were tinted but which is hard to obtain,so thought of using tinted plastic film which is used for car windows.
Did get a price from a sign maker for £350 plus vat in clear 10mm ,Whats it like to cut and drill if I made them myself?

 

[davidpbo]

Are you sure its 10mm thick? That seems way over the top to me.

!0mm is far too thick for that application and don't think it would cold bend and stay put just using screws. My choice would be 6mm polycarbonate.

Front window is definitely 10mm thick. Sides are 8 but without much curve.

 

[GrahamM376]

Can be bent once the first screws are in place using a hot air gun but grp has to be masked off well with something heat resistant.

 

[Dave100456]

Be very careful if using a heat gun which will do localised heating and expansion of the acrylic leading to physical and optical distortion. I would advise against this method.

 

[davidpbo]

Having had a conversation yesterday with a very helpful man from a local injection moulding, I removed the winidow.

Putting it on a table (admittedly a warm sunny day) it bend back flat very easily, I don't it was heat formed and that the curvature that remained was the result of being in that position for the last 25 years. What others think pleaser?

http://i1205.photobucket.com/albums/bb425/17234/20140610_145109_zps9f925eae.jpg

 

[Rigger Mortice]

As said earlier, some sites talk about being able to bend cold acrylic by up to 200 times it's thickness, so it should be Ok. TBH it seems quite a lot to me.

It may also be worth checking that the existing window really is acrylic. Polycarbonate appears to be better able to take a cold bend. Personally though, I prefer acrylic for windows.

 

[davidpbo]

I am looking at a bend radius of over 280 times is thickness. I am fairly sure it is acrylic.

 

[Rigger Mortice]

I am looking at a bend radius of over 280 times is thickness. I am fairly sure it is acrylic.

If you want to be sure what plastic it is something like this can be very helpful,
http://www.modernplastics.com/how_to_identify_plastics.htm

I had to find out what a lump of plastic was on my boat. It was for the swinging keel pin so I didn't want to get it wrong. A simple test showed me that it was delrin.

 

[ReefMagnet]

Just went through this exercise recently with 10 mm (unsuccessfully, but the bend radius was much greater) and you should be able to cold bend to that shape without major issues. You need to use cast acrylic sheet as opposed to extruded (which probably isn't in 10 mm t size anyway). The higher the ambient temp when you do it the better. The acrylic will eventually take a "set" once in place for a while.