Thread: RHS Welding Distortion

Hi,
There's a couple of ways to straighten it. It depends on access to the back of the frame. Its just the frame so far? No other bodywork?

Firstly how much is a couple of MMs ? 3, 5 or 20 and over what distance.
After that you can consider:

• Heating and cooling ? - leave it for people who understand what they are doing.
  
• Striking with a BFH - again maybe only if you have the said hammer and know where and how hard to strike.
  
• What about a hydraulic jack over the opposite face to the spring hangers pushing against some chain attached to a pair of pull plates that are tacked to the frame - steady and controllable if done in small increments and can be gauged with the length of the frame against a string line.

does this help?

Grahame

Hi Grahame

The rails are 2900 long, and the distance between the hangers is about 870, I'm calling this the straight bit. The front and back drop 5mm from this. I've got full access to all sides, it's just a chassis frame with some wheels bolted on at the moment.

Heating and cooling make sense to me, after all, that's what got me into this mess to start with. I just have no experience with it.

I do have a BFH, but I don't know that I want to go down that path!

I like the idea of the controlled bending back into shape though, just need to get myself a hydraulic jack, they're not too expensive, and rig up some sort of bending arrangement.

You say that it's a chassis at this stage, are you planning on welding sides or anything on top and finally where abouts in Melbourne are you?

I can straighten it back up for you using oxy/acet or chains and jacks or show you what you need to do, but if you're planning on more welding, it may pay to take some pics with descriptions of further work planned.

If you're going to be welding sides etc on, you can use this to straighten it back out.

Originally Posted by Acco

You say that it's a chassis at this stage, are you planning on welding sides or anything on top and finally where abouts in Melbourne are you?

I can straighten it back up for you using oxy/acet or chains and jacks or show you what you need to do, but if you're planning on more welding, it may pay to take some pics with descriptions of further work planned.

If you're going to be welding sides etc on, you can use this to straighten it back out.

Thanks for the offer, much appreciated. I'll have a go at straightening it with a jack on the weekend and see if I can get it right.

It's just a frame at this stage, and I'll be welding sides on it eventually, so, as you say, I can use that to pull it just that little bit further.

No worries Anthony

Sing out if you'd like some hints or help if you get stuck etc

Hi ,
If you cut some 6mm plate with slots to take chain the vertical plates can be tack welded - say 25mm long - to frame. No tack needed on chains.

The jack pushes on the chain which drags the frame up.

MS Paint diagram attached.

Grahame

Must have been some fair old welds to warp a 75 x 50 x 3. Normally a spring hanger is welded at two points on the chassis, a bead either side longitudinally along the chassis rail. Then, when the drawbar is attached, a bead down the end of the drawbar where it meets the leading edge of the hanger.
For me, 10mm over 2.9Mts wouldn't be a huge concern. For all the mucking around trying to straighten the 4 bend points, and get them all even, you could pull it back when you do the sides. Are you using off the shelf trailer sides? You're going to need an upright in each corner to support the flat sides. Make them 50 x 50 x 3mm, weld them at each corner (they're welded to the top of each front & rear cross rail, and their inside edge needs to line up with the outside of each chassis rail). Make sure they're exactly 90* to the ends of the chassis rail. Cut a piece of 25/30/40/50mm SHS exactly to length of the measurement between the bottom of the front & rear uprights (theoretically should be the cut chassis length). Using a ratchet strap attached to the top of each upright, pull them together until the SHS piece is a neat fit & tack in place level with the top of the uprights.
While that alone wont relieve the stress in the chassis from the bend, it should straighten it enough for your fit out. And if you apply a heat source to the top sides of the chassis rails, even a heat gun will do, it should stop the chassis from being a loaded spring.

Thanks Graham, that makes perfect sense. I'll have a crack at it on the weekend, seems very simple.

You're right Yonnee, I may have sightly overwelded the rear shackle hangers a little . If I can't get it spot on using Graham's method, I'll tweak the rest in to place as you have suggested.

Once I have it straightened out, do you think it would be worth welding some gussets on the side of the rail to strengthen it a little?

Originally Posted by atregent

Once I have it straightened out, do you think it would be worth welding some gussets on the side of the rail to strengthen it a little?

No. It needs to flex. If it's not allowed to flex, it will lead to cracks.

Thank you all for your advice, I've managed to get it almost spot on. I'm only out my a couple of mm over the whole length now, and with a little more tweaking, I should be able to get that out too.

I've learned a valuable lesson, not to go too gung-ho with the welding, and also picked up a very handy tip for straightening things out.

Now I can get back to the far more enjoyable and rewarding task of designing and building this thing!

Before you go too far with your trailer it might pay to hit the achives and have a look at some of the camper trailer stuff that has been posted previously. Stuff like tailgate clearance etc.........

Now is the time to decide on your choice of tent (if u havent already), cause the floor drop is not something that can be easily changed once its made, or mod height of trailer sides. Recently knocked back a job cause the guy didnt do his homework in this regard and it was gunna be an absolute PIA to try and fix.

Beware of the Chinese stuff. Most of the regulars know I have a interest in this, so I not try to repeat myself too much.

Feel free to ask heaps of questions. Fotos of course help.

Jatt.

Thanks Jatt, will do!

I'm actually embarking on the, perhaps rather ambitious, task of building a no-canvas pop top camper, similar to a kimberley karavan.

When I get a few spare minutes, I'll get my photos together and start a build thread (I don't want the bad omen of having my build documented under the welding distortion title!)

I don't want the bad omen of having my build documented under the welding distortion title
I don't want the bad omen of having my build documented under the welding distortion title!) 27th Feb 2012 06:40 PM
I don't want the bad omen of having my build documented under the welding distortion title!) 27th Feb 2012 06:40 PM

fair call