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echnidna
22nd Nov 2005, 04:47 PM
How do I weld up a rhs frame without distortion.
see the pic for the frame shape.
I need the 3 x 2 rhs to stay straight along its length.

Ivan in Oz
22nd Nov 2005, 05:13 PM
Being a Sprayer of Chicken 5417 [Numberplate Lingo for the Clean minded and Uneducated];) :confused:
I'd say tack each and every corner, then tack between and keep on doing a Divide and Conquer.
MIG it if you can.

ozwinner
22nd Nov 2005, 05:22 PM
If you want to keep the 3x2 straight dont weld across the box, you can weld along the edge without too much distortion, but once you weld the box section all is lost.

It will still distort welding along the edge but nowhere near as much.

Unless you plan to clamp the box, and heat treat, then you can get away with it.

Al :)

echnidna
22nd Nov 2005, 05:37 PM
Thanks Al, thats what I thought.

Next question
If I put another 3 x 2 on top of the 2 x 2 crosspieces (straight above the first 3 x 2) can I shorten the crosspieces so they only go halfway across the 3 x 2 then weld the ends of the 2 x 2 crosspieces along both the 3 x 2's ?.

I'm making up the rails for a slabbing mill and I need them to stay nice and straight.

echnidna
22nd Nov 2005, 05:40 PM
I suppose I could bolt the whole lot together and then weld it up.

ozwinner
22nd Nov 2005, 05:45 PM
I suppose I could bolt the whole lot together and then weld it up.

If you bolt and weld, it will still distort.
Dont forget molten metal in the liquid state ie:- weld, will shrink, as it shrinks so does everything else in contact with it...

:) Im amazed.:) All them years ago at Ballarat School of Mines doing a DLI welding course seems to have stuck.

Al :D

echnidna
22nd Nov 2005, 06:11 PM
I suppose a combination of bolts at the ends of the 2 x 2's in the centre of the 3 x 2's plus welds only on the corners of the 3 x 2's.

dazzler
22nd Nov 2005, 06:28 PM
Are you using a mig or stick welder?

echnidna
22nd Nov 2005, 06:42 PM
stick, don't do enough welding to justify a mig

ozwinner
22nd Nov 2005, 06:51 PM
It wont matter what you use, mig, tig, manual, 3000 degrees molten metal is 3000 degrees, no matter what method you use.

Al :)

Harry72
22nd Nov 2005, 08:45 PM
Tack/stitch weld another 3 x 2 rhs(or bigger)on the back side of your rails, this will stay cold while you weld across the rail and stop it distorting while it cools... make sure the welds between rail and support rail are easily accesable with a angle grinder for removal.

DanP
23rd Nov 2005, 09:14 AM
Call me silly, but I reckon if you can get an RHS 3X2 to distort, you're either using too thin a gauge of RHS or you're doing something very strange.

Dan

Schtoo
23rd Nov 2005, 11:21 AM
Dan, yer silly. :D

I've seen that size (and bigger) distorted on structural stuff that was doing what it was supposed to be doing, ie: holding up a building. Not serious twists, but enough to notice it. Usually a little ripple in the surface, but no bends or anything like that. And always an on site add-on.

Only happens what you start whacking bits on with reckless abandon though. Proper flange plates and things don't do much to it.

Bob, does the 2x2 have to sit on top pf the 3x2? If you can butt it into the sides, might have a better chance of keeping it all straight. That, and a porta-power might help. ;)

Just seems to me that sticking it together the way you have shown is asking for trouble. Might be worthwhile asking somewhere to throw one together, depending on what you need as 'straight'.

Or, rethink the thing until you can get it together without too much trouble nor too much twisting. Maybe flange plates on the ends of the cross pieces, a piece of RSJ as the sides, or vice-versa.

DanP
23rd Nov 2005, 01:53 PM
In five years of welding RHS (both MIG and ARC) I never had any distortion.

If you use the right thickness of RHS and weld it in the right sequence, you would have to be pouring the amps into it to get it to distort.

Dan

Schtoo
24th Nov 2005, 01:46 AM
Diesel powered arc, and on site so it was nothing 'professional'. ;)

Seen it a couple of times, usually some kinda bracket tacked onto something to hold guttering or whatever. Nothing special, just a little out of kilter.

With this mill thing, if it had to be straight and true I know I'd blow it with my level of welding. Lots of practise, but I'm no great shakes at it.

I must admit, when a proper welder type did the job at work, you could tell. ;)

echnidna
24th Nov 2005, 10:41 AM
Schtoo, I'm not stuck with the original configuration but I need to run wheels on top of the top tube and a keeper underneath 1 bottom edge so the carriage (not shown) cannot lift or tilt

I don't have any spare 3 x 2, but I might run a few welds on a couple of 2 x 2 shorts just to see how much distortion there is.

Eastie
26th Nov 2005, 09:13 PM
Mig brazing would do it if you have it available - runs a couple of hundred degrees below the fusion point of steel so it won't distort.

echnidna
28th Nov 2005, 08:54 PM
I've been chewing all this over and I think I'll bolt the whole lot together including top and bottom rails, both sides.
Then I'll weld it up sequentially in stages.
If it comes out ok wonderful but if its distorted too much I'll bolt a top rail made of angle on using the same bolt holes used to bolt it all together intially,
this way I can pack the angle so its perfectly straight.

In fact I might put the angle on regardless as a 1/4" width of angle (web pointing up) will have a lot less tendency for sawdust buildup and possibly eliminate a need for sawdust wipers that I would need if I track the carriage wheels on a 2" flat surface.

Thanks everyone for all your comments

Schtoo
29th Nov 2005, 11:30 PM
You can get wheels that run on angle too. At least around here you can.

Used them on a gate that's surrounded in dirt, and they keep on ticking, save having to dig the rail out every 6 months or so.

I'd go for it. :)