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roll bar thoughts
Miks15 - 26/4/08 at 09:41 PM

Just a quick thought.
Could you take a premade rollbar for a standard car, chop a section out the middle and weld it back up to get the right width for mine? Or is this a big nono?

Dont need one soon but thinking ahead and as always trying to keep costs down. Car wont be used on the track and roll bar will be purely aesthetical(although will be nice to know it wont snap if somehow i do manage to go upside down.

Am i being completly ridiculous?

clairetoo - 26/4/08 at 09:45 PM

quote:
Originally posted by Miks15

Am i being completly ridiculous?

Um.......................

carlknight1982 - 26/4/08 at 09:51 PM

and roll bars are sprung steel so no it wouldnt work

Miks15 - 26/4/08 at 09:55 PM

fair enough, probs one of things i wouldnt mind spending a little more anyway, if it saves my live later on then mabye worth it
ta

nitram38 - 26/4/08 at 09:56 PM

quote:
Originally posted by carlknight1982
and roll bars are sprung steel so no it wouldnt work


He said Roll bar, not Anti-roll bar.
They are two different things!

Miks15 - 26/4/08 at 09:58 PM

so it would be possible then?

Mr Whippy - 26/4/08 at 10:00 PM

oh you bad man, if you insist on doing this I'd say get a heavy walled bit of tube (scaffold about 2ft long) and insert it inside before welding it up. Make sure you are welding to both the tube and the other half of the bar by leaving about a 10mm gap between the two bar half’s.

This is how I shortened my buggy’s bar.

Miks15 - 26/4/08 at 10:02 PM

ahh right i got ya whippy!
Thats sounds like a good idea, so basically plug it to put the strength back into it!
Sounds good cheers

Mole - 26/4/08 at 10:54 PM

I suppose since theres no requirement to have one you can do as you wish. Would have thought it would be less safe than a one piece bar though. Also ignoring the safety consideration you would have a visible weld in the midde of your bar.

[Edited on 26/4/08 by Mole]

mark chandler - 26/4/08 at 11:13 PM

Correct CDS tube £60, two mandrell bends put in @ £15 each and weld it up. Not worth mucking around.

Miks15 - 27/4/08 at 07:53 AM

the weld can be smoothed over so it isnt noticeable

Mole - 27/4/08 at 08:05 AM

Your better at dressing welds than I am then. Out of interest why won't a standard roll bat fit?

Edited because I've just looked in your photo archive. Another option would be to ask one of the roll bar manufacturers to turn out one to a different spec. Cannot imagine it would be much more expensive if any, almost the same work involved.

[Edited on 27/4/08 by Mole]

Fred W B - 27/4/08 at 08:21 AM

In addition to Mr Whippy's tip, I would drill some holes into the cut bar some distance out from the join so you can plug weld through onto the insert tube.

Cheers

Fred W B

MikeR - 27/4/08 at 08:56 AM

why would this approach be that much weaker?

You've got potentially double the thickness of steel spread through out the top section of the bar, yeah you've got a heat affected zone in the middle - but would it really be weaker?

Ok, if you just cut and welded or cut and welded with a 4" bar inside, but if you go to something like 24" or even better the whole length of the top section, i would have thought it would be heavy but strong.

delboy - 27/4/08 at 10:00 AM

mikeR, your spot on, I used to repair the front bumper of my saloon stock in a similar way. We sleeved the main 40x40x4 bar with a 30x30x3 inside for only about 200mm and they didn't fail at the joint. We usually managed to bend it at a point beyond the joint if the hit was big enough.

NeilP - 27/4/08 at 10:12 AM

quote:
Originally posted by MikeR
yeah you've got a heat affected zone in the middle...


If you've got a blow torch around then preheat the weld until it's too hot to touch - stops some of the worse effects of local heating through welding...

RazMan - 27/4/08 at 10:59 AM

Personally if it was my car, I wouldn't bother modding anything and just make a real one. Dressing the welds might make it look pretty but it won't do anything to improve strength.

Mark Allanson - 27/4/08 at 12:09 PM

quote:
Originally posted by RazMan
Personally if it was my car, I wouldn't bother modding anything and just make a real one. Dressing the welds might make it look pretty but it won't do anything to improve strength.


Dressing the welds will increase the strength of the weld as any local stress risers will be eliminated. The important thing is not to undercut the weld in the first place, or to over dress the profile. Probably best done on MMA using low hydrogen rods, E7018 from memory.

RichardK - 27/4/08 at 04:19 PM

I got mine done at MNR, gave Marc the diamentions I needed, they bent the main hoop and gave me the rear stays for me to cut and weld up, all out of cds really pleased with it and didn't cost an arm or a leg either as it was like a roll bar kit, just need to decent weather so I can paint the bugga

Just a thought

Rich

Miks15 - 27/4/08 at 06:48 PM

do you know how much it cost in total rich?

82 Locost - 27/4/08 at 08:47 PM

Never scrimp safety. In my opinion all roll bars should be triangulated (front or rear) so it doesn't fold when (if) the car flips.

Griffo - 28/4/08 at 08:25 PM

A good weld is usually as strong as the material it is joining so would there be a need for an inner tube (although it wouldn't hurt)?

RichardK - 28/4/08 at 09:47 PM

Here is the link to the jobbie, third item down £100

LINKY

Its now blue, surprise, surprise



Cheers

Rich

[Edited on 28/4/08 by RichardK]

MikeRJ - 30/4/08 at 05:14 PM

That seems rather tall!

chriscook - 30/4/08 at 05:47 PM

quote:
Originally posted by MikeRJ
That seems rather tall!


To be honest I think everyone gets used to seeing roll bars that are too short - which make the ones that are the right height seem tall.

To get the right height you should draw a straight line from the highest solid point at the front of the chassis to the top of the roll bar. The top of your head (with helmet on) should be below this line with a bit of a gap to allow for movement under the harnesses.

MNR seem to be one of the few companies that do it right from what I've seen - I noticed someone else on here had an MNR roll bar that was tall enough in my eyes. (edit: it's coozer's car)

[Edited on 30/4/08 by chriscook]

MikeR - 3/5/08 at 07:04 PM

i've often wondered how safe the roll bars with ears welded on are. any thoughts ?