Welded rod and bar bowed??

[22george]

I stitch welded a 4 foot long 3/8 inch diameter rod to a 1/4 inch by 1 inch 4 foot long rectangular bar on the 1/4 inch side. I welded it up one side and down the other side. It did not bow from side to side. When I put a 4 foot straight edge across the top of the round rod, it is bowed about 3/16 down in the center from end to end. ( touches at both ends and a tapered gap from each end to 3/16 inch in the center. ) I did the same thing using a 1/2 inch round rod welded to the same size rectangular bar with no bowing. The stitch welds are about 3/4 inch long and 1-1/2 inch apart. Why did the one bow and how do I fix it. I tried heating up the bottom side to orange at each end hoping that as it cooled that side would shrink some straightening it out with no luck.

Thanks for your help

 

[joe49]

Peen your welds. Not a easy process to get right with out experiance. If you have none try using a drift punch and drop your hammer on to the punch, don't swing to strike. The impacts will be more uniform. Work each weld alternating sides.

 

[American Locomotive]

Metal expands when heated, and shrinks when it cools down. When you weld something, you obviously make it extremely hot, so it expands. Think of that rod you're welding as if it were a rope tied to each end of your bar. When you first weld it, everything is molten hot, and it only has to cool down a little bit before it "locks" together. As the rod cools down, it starts to shrink, pulling very hard on the top ends of the bar, bending it upwards.

The 1/2" rod likely didn't bend as much, because it had much higher mass. This means the rod didn't get as hot, so it didn't expand as much as your smaller rod.

Your options are:
1) Preheat the pieces some to help equalize out temperatures
2) Pre-bend the pieces in the opposite direction and hope they flatten out enough once welded
3) Smaller,shorter stitch welds & more patience.

 

[Walkers]

Just use a couple of 2x4s and a hammer, or hold one end and flex it toward the bench, or hold it in a vise and bend it.

 

[kerrynzl]

I stitch welded a 4 foot long 3/8 inch diameter rod to a 1/4 inch by 1 inch 4 foot long rectangular bar on the 1/4 inch side. I welded it up one side and down the other side. It did not bow from side to side. When I put a 4 foot straight edge across the top of the round rod, it is bowed about 3/16 down in the center from end to end. ( touches at both ends and a tapered gap from each end to 3/16 inch in the center. ) I did the same thing using a 1/2 inch round rod welded to the same size rectangular bar with no bowing. The stitch welds are about 3/4 inch long and 1-1/2 inch apart. Why did the one bow and how do I fix it. I tried heating up the bottom side to orange at each end hoping that as it cooled that side would shrink some straightening it out with no luck.

Thanks for your help

Heat straighten it.
Clamp it straight , then gently reheat both pieces together then let them cool while still clamped [It doesn't need to be too hot]

If you clamp it straight and only heat one piece it will bow the other way when cools [after the clamps are released]

 

[22george]

Thanks for the responses

 

[e015475]

A couple of videos I found helpful in understanding distortion-

 

[22george]

A couple of videos I found helpful in understanding distortion-

Thanks

 

[Gunfixr]

Heat bending involves rapid cooling.
You heat the high side, then rapid cool it, and it shrinks back past where it was, and so removes the warp. You measure how much you move it with heat, to move it the other way accurately. It often will not work multiple times in the same place.
As might be guessed, this has a learning curve.
I used to straighten dredge boat driveshafts by this method.

Prob easier to just press it straight.

 

[csp]

Heat bending involves rapid cooling.
You heat the high side, then rapid cool it, and it shrinks back past where it was, and so removes the warp. You measure how much you move it with heat, to move it the other way accurately. It often will not work multiple times in the same place.
As might be guessed, this has a learning curve.
I used to straighten dredge boat driveshafts by this method.

Prob easier to just press it straight.

I worked in a hot rod shop in college that also built driveshafts for locals, as it wasn't a large enough town for a driveline shop. The owner never balanced shafts, just used a torch and wet rag to eliminate runout. Never had one come back for vibration problems.

 

[nadogail]

Amazing what can be done by determined people.

 

[Gunfixr]

I worked in a hot rod shop in college that also built driveshafts for locals, as it wasn't a large enough town for a driveline shop. The owner never balanced shafts, just used a torch and wet rag to eliminate runout. Never had one come back for vibration problems.

I used a torch and a water sprayer, with an indicator on the shaft close by, to measure how much I drew it.
But, I was working on 6" solid stainless shafts. They were 20-25 ft long, and had to have less than 010" runout over the entire length.

 

[corn chip]

that guy jody probly has the best videos on youtube if you ask me. i been watching them atleast 5yrs. still watching them to this day. his distortion video is great but doesnt apply to many situations. theres also welding books with tips to combat distortion.
depending what your working on ,distortion can be irrelevant. the part can be machined straight or flat afterward ,again distortion is mostly irrelevant. you can weld apposing sides where possible. use clamping jigs. stitch welding techniques. use heat sinks. theres alot of ways to go about it depending what your working on . this is alittle info from lincoln https://www.lincolnelectric.com/en/...source-Center/Welding-How-Tos/Weld-Distortion

 

[22george]

Thanks