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Ola, I am about to design a 4/6 points rollover bar for my 4A and I want it to match closely the curve of the back light and door posts. To do this I need to prepare a template/pattern of the bar. I thought about using plumbing PVC tubing and elbows and heat them with a Bunzen to give them the right shape before sending the template to the workshop for fabrication. Anyone tried to use this method or is there another method that would give similar result with less work ?

Thanks as always

 

 

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I'd be very surprised if rigid PVC could be heated and bent successfully into a template for your roll bar -- the radii are likely to be too tight.

 

Here's a writeup by one of the companies big in plastic tubing that may have some tips:

http://www.harvel.com/piping-systems/gf-harvel-clear-pvc-pipe/installation/heat-bending

 

Maybe consider using flat profiles from light plywood or corrugated paperboard. One could imagine the full three-dimensional tube but working with a flat "cross section" would be much easier. It would still provide a layout template for your fabricator.

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Thanks Don and Pete, Yes I want to work 3D @ 1/1 scale and leave no room for mistakes at the workshop. The advantage of PVC or whatever plastic is that I can cut-shape the bar from AtoZ including the brackets. The top of the bar will sit just under the backlight glass seal and follow that shape.

 

Edit: Perhaps I could use aeration flex tubing 40mm, stick it with masking tape at the right shape and then stuff the tube with polyurethane foam and let it harden for a while ?

post-11469-0-04717000-1413991411_thumb.jpg

Edited by Geko
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Hi Stef,

Given your location I would have thought that the guys who are hopefully skilled fabricators and therefore know their way round a pipe bender could get the basic shape more accurately to fit with the car in front of them. Get the basic shape right from the "get go". Let them decide also where the mounting points will tie up with chassis mounts. As has been said the hood frame may be lower than the surrey back frame so perhaps now is the time to sort that out and not after it is made.

Not sure if you use the rear seat for passengers ( even those of a small disposition) but a diagonal will negate that possibility. You need a stronger roll bar if not using a cross diagonal or horizontal brace and seat belt mount.

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Tks Rod, several critical points have been thought of already:

1/ Top of the bar will be below clearance for the hood frame if located under the seal

2/ Top of the bar will be behind the head of the driver/passenger so as to prevent the driver/passenger's head from hitting the bar in case of bumps

3/ Sides of the bar will be well behind the driver/passenger shoulders so as to prevent hitting the bar with the head in case of lateral shock and enable to fit the mounts for the roller seat belts.

4/ No diagonals but 2 perpendiculars will be bolted on either side of the fuel tank and shall/should not prevent using the rear seat for whatever purpose.

Edited by Geko
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+1 with Rod, leave the fabricators see the rabbit !

 

When we buy roll cages in the UK it's not unusual to take the car and leave with the specialist roll cage manufacturers for a couple of days for much measuring twice, cutting once and bending sometimes by increments until the cage fits snugly. They do offer preformed roll cages but I'm not sure the fit can be as good as a "tailored" one.

 

Mick Richards

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Stef an alternative may be to use a sheet of 50mm polystyrene and a hot knife/ wire to cut it. I believe it can be glued together to create the struts/ braces

 

Good luck with it

 

Graze

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