[polkat]

Thanks much for the welding advice!! How about using heat to bend tubes? I have two 14" long rear vertical frame tubes (1" .125 wall mild steel) that I want to cut at one end, bend down about 4" and reweld. I was thinking maybe heat the still welded end and just push it down.

There's no room to use a bender this way and I don't want to kink the tubes, but if I use heat, will it weaken the bend area? This is part of a partial "konging" I'm doing to my KZ750. Below is a rough drawing of what I'm talking about.

 

[StarGate]

I think the temper of the metal might be a concern doing that but I've never tried anything like that so can't speak from experience.

 

[kawpaul]

Since your drawing does not show a curve but rather a straight pipe that is just reattached a bit lower at one end why not just cut both ends and reweld?

 

[zoro]

Thanks much for the welding advice!! How about using heat to bend tubes? I have two 14" long rear vertical frame tubes (1" .125 wall mild steel) that I want to cut at one end, bend down about 4" and reweld. I was thinking maybe heat the still welded end and just push it down.

There's no room to use a bender this way and I don't want to kink the tubes, but if I use heat, will it weaken the bend area? This is part of a partial "konging" I'm doing to my KZ750. Below is a rough drawing of what I'm talking about.

Polcat, Im a certified tube welder (Boilermakers Local 83 and Ironworkers local 10) and unlimited thickness certs in all position plate, its what Ive done for well over 32 years now. I repair anything from boiler tubes in powerhouses to structural steel in bridges and highrises and am proficient in stick(SMAW)(FCAW)(MIG)and (TIG) so I hope you'll take this advise carefully! Make your bends prior to welding the tubes. The diagram is very doable if you dont overheat the tubes. When you use heat to bend the tubes, never heat beyond (dull red) and heat only the compression (inside) of the bend, you never want to stretch the wall thickness, only increase it by compressing the inside radius of any bend. Allow the metal to cool (slowly)! DANGER Will Robinson!!! I advise against heating and bending any frame tubing for the obvious safety reasons! I know thats not going to deter you, the warning will allow me to sleep when your welds fail and kill you! A-36 or mild steel is not the alloy to use in frame welding applications! Chromoly is the stuff of choice! One more thing, any bike frame is engineered to handle to various loads and distribute those loads evenly throughout the frame itself. Any design changes will compromise the integrity of that frame! And no frame is "over engineered" especially the KZ frames! Bring the bike to me and Ill help you at no charge to save your life! Good Luck!

 

[Bob Myers]

As doomsday warning as it sounds, and contrary to what you are going to hear later,,, Zoro is right. Do not heat and stretch the outer radius of the tube, if you must do what you propose then either cut and TiG weld back into your propose configuration or heat the entire underside of the tube you wish to move and allow it to cool and pull (shrink) to the point you want it reattached.
If I were doing it I would cut it at the right side, and cut partially through from the bottom on the left, drop it down and reweld both ends via TiG
I too base my voice on this from 35+ years in metal working industries, from working as a welder in boiler field to being a tool maker, and most everything in between except farrier work.

 

[polkat]

This last post by Bob Myers1 is interesting in that it sort of reminds me of how necks are often raked. Cut one end off and cut partially on the other end at the inside of the bend, and then do the bend. Might be a good idea.

I was thinking that keeping one weld intact might result in a stronger result, but I'm beginning to think that the best approach is to cut the tube entirely out and then weld in a new piece at the angle I want. Bob and zoro, no, I'm not a very experienced welder though I have some wire welder experience. I understand that heating a tube to bend it can weaken it, but then does not the actual act of welding also weaken the tube?

Also, if I cut out the tube, what's the best way to clean up the remains of the weld? Die grind it off? Chisel it off? Thanks for the good advice!

 

[bretsk2500]

I was thinking that keeping one weld intact might result in a stronger result, but I'm beginning to think that the best approach is to cut the tube entirely out and then weld in a new piece at the angle I want. Bob and zoro, no, I'm not a very experienced welder though I have some wire welder experience.

Then you absolutely should not be attempting this, frames are not things to screw up.... building welding tables is good practice, modifying a frame is not.

I understand that heating a tube to bend it can weaken it, but then does not the actual act of welding also weaken the tube?

It can weaken it, but typically a stronger filler is used than the base material.... The actual explaination is quite a bit longer and more complex, but this works for your question.

Also, if I cut out the tube, what's the best way to clean up the remains of the weld? Die grind it off? Chisel it off? Thanks for the good advice!

grinder. chisels are good for spot welds though.

 

[polkat]

I understand, though I'll never learn to weld without trying. For now I'll farm it out if I can find someone good.

 

[bretsk2500]

It's not a matter of trying to learn without trying... it's a matter of learning without DYING....

 

[650hardtail]

I understand, though I'll never learn to weld without trying. For now I'll farm it out if I can find someone good.

go buy some tubing..or find a scrap frame ya can cut up and practice welding/fitting on

 

[polkat]

Yea, I've done a lot of welding on scrap and such. I might get a good welder to walk me through it.