fabricating tips?

I have to fabricate a stand out of 2x3 rect tubing, .1875 wall. This will be a simple rectangular frame, but required to be extremely square. Any time I have ever built something like this, I usually get it warped, or unsquare a bit. In this case, I have to shape up my habits. Would building a wooden jig be worthwhile? Or am I simply going too fast, or not making the proper spot welding techniques? Any positive guidance or input is very welcome.

Ryan

Reply to
Ryan
Loading thread data ...

Your description is pretty vague. Is it aluminum or steel? How square is extremely square? By spot welding do you mean tack welding? By frame, do you mean 4 pieces of tubing in a square or does it also have legs?

Given my welding skills and the fact that I only have an oxy/ace torch, I'd try welding brackets on the ends of the tubing and then bolting it together at the brackets. Rigidity will be an issue if you can't have at least one diagonal brace.

Reply to
Jim Stewart

Clamp the pieces everywhere so they can't move. Skip weld so that your welds pull in opposite directions. If it warps, don't be afraid to heat up the weld area red-hot and use a hammer to move the joint to square.

To do this job right, you need your most important tool, the one between your ears. Just be aware of how shrinking weld metal pulls, and deal with it. There are lots of ways.

Are you making a rectangular square to which will be attached 4 legs? Nothing is ever perfect, by the way. My tolerance when I built my lathe stand (fabricated from angle iron) was 1/16" out of square over 30". I was able to do that, but I had many years of experience fitting angle iron on Navy ships, and I was only barely able to do it.

Grant

Ryan wrote:

Reply to
Grant Erwin

Frames like this have a nasty habbit of warping all over, as you have noticed. Normal approach is to tack weld the thing together, and square it up with a big hammer. Then start welding 1" stitch welds on opposite sides. Left then right, top then bottom, back then front, etc. Check often with a square, use a hammer, wedges, com-a-long, hydraulic jack, etc to pull it back to shape as the welding progresses.

I doubt if a wooden frame will help much.

The big boys weld something like this while clamped to a several ton welding table. Then it goes off to the annealing oven to soak at 1000 degrees F for 12 hours, then for another round of straightening.

If you need real accuracy, (like mounts for a lathe)weld some

1/4" pads on the critical surfaces, grind or machine these after welding.

Cheers.

Ryan wrote:

Reply to
Roy

Ryan wrote: (clip) Any positive guidance or input is very welcome. ^^^^^^^^^^^^ Any time you make a weld, the shrinking metal tries to pull the corner from

90 degrees to a slightly smaller angle. To prevent this from happening, it is important to clamp everything in place in such a way that the sides of the rectangle support each other before they are welded. Then, do little tacks, going around the piece, so no single weld is strong enough to overcome the resistance of the entire structure.

And check for movement as you go, so you don't wind up with a problem that's to big to fix. An acetylene torch is useful for undoing distortion. However, electric welding is probably better for doing the actual welding, since there is much less heating of the metal, and therefore less shrinkage--so less distortion.

Reply to
Leo Lichtman

A wood jig would help.

I made a metal jig out of some 1/4 inch steel and some 2 by 2 angle that works pretty well. I C-clamp the angle or square tubing to the jig and know that it is square while I am welding it and while it is cooling.

Dan

Reply to
Dan Caster

Brazing with standard bronze rod would eliminate most of the warpage problems and would be nearly as strong as welding. If you took the time to fit the joints tightly, silver brazing would eliminate all the warpage problems and also be very strong.

Randy

Reply to
Randal O'Brian

What Roy said...with one extra.

If it REALLY has to be square, don't rely on welding. Design your frame so you have mechanical connections that can be squared after the fact. You can probablly get close by taking care with the welding not better than about 1/16" and that is with skill.

Koz

Roy wrote:

Reply to
Koz

I see you didn't get any replies so far on the newsgroup to your question about making a really square table. Did you get any good direct responses? I am a novice-to-amatuer at this stuff and can always use some help, but here are a few things that I was taught:

-Leave a slight gap at ALL joints (even .020 can help). This is so when you tack you have some room to correct for the distortion that ALWAYS occurs.

-You need a flat place to assemble and weld up stuff. The guy that taught me uses 2 1" square solid bars about 4 or 5 feet long sitting on saw horses as the "flat spot". He has one of them painted safety orange and the other painted white. He kneels down and sights across them. Because of the color diferences, he can easily see where he needs to shim to get them exactly level. Then he builds the job on those two bars.

-I heard recently that at Caterpillar Tractor they now just press things into shape, realizing that there will always be distortion! Not something I am likely to be able to do!

-Tack opposite corners as lightly as possible. Straighten. Turn over. Tack the other sides. Check again. Don't be afraid of the angle grinder to cut an offending weld loose to correct.

-My son is a welder of many years. He says that a BIG gap is always your firend. I have trouble with that because I have a machinist's sense of accuracy (although I'm not on of those either). I want the dry fit up to be dead on.

-So, when I had to do some pretty accurate rectangular work recently (with 1" square solid mild steel), I cut a large number of .025 BRASS shims about 1/2" X 1 1/2", and used them to maintain the gaps I needed for tacking. I laid a 4 foot square sheet of steel on my two flat bars. I laid out my component on the sheet. I placed two or three of the shims at each joint, chcking for squareness USING DIAGONALS and then tack welded as mentioned above. I would then turned the aseembly over, checked and adjusted for square and TWIST and made any corrections. Then tack, check and weld 2 diagonals. Turn it over, weld the other two diagonals, final check, turn over, weld last two diagonals, turn over once more and finish up.

Hope this helps, Pete Stanaitis

Ryan wrote:

Reply to
Pete & sheri

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.