# How to calculate bending from welding a long object?

• posted
We have to fab some caster track, the kind made from angle iron welded upside
down onto flat stock. The casters on the rolling unit have V grooves to ride on
the angle. I think that when we weld the angle to the flat stock, our long
track is going to have an upward curve to it due to the shrinkage from the
stich welding. Perhaps it will simply pull flat when we bolt it down, but I
would like to try and keep it flat. We have no means of rolling it after
assembly.
The plan is to prebend the pieces in the opposite direction and clamping them
to hold a slight reverse curve. The stock is flexible enough that we can do
this easily by letting it drape over some blocks. But, how to calculate how
much bend we need?
The flat stock is 3/8" x 6" hot rolled steel, the track will be 18' long. The
angle is 2" x 2" x 1/4". Right now I'm planning on a stich weld every 12".
Dennis
• posted
Do you have some material to do a test weld, using the same materials and conditions of the real product? Maybe do a 3' piece and calculate from there.
Richard
• posted
The track may move either way according to proportions. For example if you were welding four inch angle 1/4 thick to a 1/8 by six inch flat bar likely the "short side" would be the flat bar. If you were welding two inch angle onto a 1/2 by 6 inch flat bar likely it would go the other way. To minimize any possible bending take two sections of track that you have tacked up. Tack them together back to back, flat bars against each other. Do your stitch welding, let it cool and then break apart. This tactic will not remove all bending but will reduce it. If you have an arc then measure how much it is in the middle. On the next pair you weld tack the pieces back to back but with spacers to oppose the arc you had on the first pair. If the arc is say one inch high then use a one inch spacer in the middle. Longitudinal shrinkage is difficult to predict whereas angular/transverse on a fillet is more consistent. Randy
We have to fab some caster track, the kind made from angle iron welded upside down onto flat stock. The casters on the rolling unit have V grooves to ride on the angle. I think that when we weld the angle to the flat stock, our long track is going to have an upward curve to it due to the shrinkage from the stich welding. Perhaps it will simply pull flat when we bolt it down, but I would like to try and keep it flat. We have no means of rolling it after assembly.
The plan is to prebend the pieces in the opposite direction and clamping them to hold a slight reverse curve. The stock is flexible enough that we can do this easily by letting it drape over some blocks. But, how to calculate how much bend we need?
The flat stock is 3/8" x 6" hot rolled steel, the track will be 18' long. The angle is 2" x 2" x 1/4". Right now I'm planning on a stich weld every 12".
Dennis
• posted
If the bend is up heat it with a rosebud tip down perhaps every 12", consistant with your stitch welding intervals. Then there's always the sledgehammer, clamping techniques................
• posted
Your main concern is to tack it up straight Forget about weld shrinkage If you can , mount the flat bar to the floor where you need them . Now place the angle on top of them . make a jig for setting the distance or spread of the tracts . Get a grinder and Remove the radius part inside the angle that you will use for your jig , now it will sit flat on your rails . They use this type of system to align the sections of aircraft during assembly . The angle that you use will have "bow" and "run-out" . You may need to grout and grind the floor flat before you mount the flat bar . You know your tolerances . And now you know how much the floor is off . Even if you are going to ship the rails somewhere else mount them to the floor . A good way to use a "straight line" is to use a spacer or gage to set it up off the surface so that high spots don't interfere with the line , then use another spacer to check it with . You will want to set one angle down first , Hold it against the flat bar to take out the bow and use a string line along the top corner to eliminate the run out . You will be tacking as necessary to keep it straight . This is the most important dimension , this is what keeps your thing from binding . Use 1/8" fillets with 1/2" long tacks you don't need many at all . The angle should be strong enough to keep from spreading open and the floor should be grouted as to keep the rails from bowing as the weight rolls back and forth . After the welds have cooled it can be unbolted and transported wherever they are needed but don't forget that the floor will have to be prepared for mounting .
Over the years I spent a lot of time trying to find the best weave, only now that I have a constant shake do I feel content !

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