Simple Fab Alignment problem

[BikerDad]

So, I'm building another mobile base, this one for Uncle Max, my jointer/planer.

The base is a simple rectangle (roughly 28" x 22") with two additional interior members running the long way, overbuilt using 2" square tubing.

I've got the first corner done, and the first interior member, everything is happy. When welding the other long side piece on, it ended up about 3/16" - 1/4" out of plane at the short side that hasn't been welded, i.e. when placed on the floor, the blasted thing has some rockin' going on. (I'm thinking it may have been heat distortion....)

So, other than cutting it out and trying to reweld, what's the best way of coaxing it into position?

 

[Jzkudzin]

I think you are fiureing out that tack welding may have been a good start if you have some rigid angle or extra tube. Clamp the assembly into submission and see if a few tack welds hold and straighten it out. If this does not work than reconsider cutting and refitting or if you are careful slightly bend where the problem is.

 

[kerrynzl]

Try hammer welding.

When the weld is cooling and shrinks, you peen it with a hammer.
Otherwise heat shrink it back into shape

 

[jhelrey]

Add adjustable feet...

The kind that looks like a bolt.

 

[jimgood]

I don't know much about fabrication in general but it seems to me the way to approach an assembly like that would be to tack the outer perimeter first; tacking the outside of each corner at the mid point. I'd say blow it apart and start over.

 

[gte718p]

I don't know much about fabrication in general but it seems to me the way to approach an assembly like that would be to tack the outer perimeter first; tacking the outside of each corner at the mid point. I'd say blow it apart and start over.

That will will help, but it will still try to pull out of square if you put a lot of heat in one corner. It is best to clamp it solidly in shape. A good fixture table is incrediably helpful. Seeing as how most people don't have one, check the alignment often while welding and use a large hammer to convince the metal to be where you want it to be. It is best to make small adjustments along the way then big corrections at the end.

 

[b_bueno]

Always tack your pieces before finish welding.

 

[JJThrasher]

Get the hammer and straighten it.

 

[bdbecker]

As others have already said, clamp the **** out of it. Tack and weld as much as you can with clamps on. Let it cool with the clamps on if you can.

Also, tack and weld strategically. The material is going to pull towards the heat. If you tack/weld on the inside corner of a 90 degree frame first, its going to pull to be 87 degrees. Tack/weld on the outside first, 93 degrees (just example measurements to illustrate my point). Tack/weld on the top face first? It'll want to pull out of flat. Try to work with the heat, not against it.

Also, make sure you have good, solid tacks before welding. Unless you are in a production environment where cycle times are king, there is no reason to not over-tack your projects. Nothing better than hearing a pop midway through a weld and finding out the other end of the tube popped free.

How do I these things? Repeated failure to heed my own advice...