Problems bending thin walled tube

[DaveB]

I am trying my hand at building a custom exhaust collector and have been bending thin walled tubing. I am using a ProTools air over hydraulic tubing bender and when I bend the thin stuff I get wrinkles on the inside curves. I even tried packing one bend with dry sand and sprayed the dies with WD40 which helped a bit but still wrinkled. Any thoughts on what I need to do to stop the wrinkles ? I see that mandrel bent exhaust places can do it wrinkle free so what am I doing wrong ?

 

[TJDukit]

I think the non-mandrel bent part is the worst culprit. If you look at exhaust systems not bent on a mandrel they are pinch in the bend or even wrinkled. I'm not an expert though so maybe someone can help more.

 

[I Lean]

Thin-wall tubing is hard to do well without a mandrel bender. For "our" style benders, the only way to do it is to use a larger radius die. (the larger the radius, the thinner wall you can successfully bend)

 

[DaveB]

I'm using the largest radius die that I have so maybe I'll have to live with the wrinkles or use thicker walled tube.

 

[Tacoma]

I think without a mandrel you're just gonna have to live w/wrinkles..

 

[I Lean]

I've heard (but never tried) filling the tube with water and freezing it, then bending can work. Obviously you'll be into some work capping the ends and stuff.....but if it works that'd be kinda neat.

 

[neagtea]

I never had much luck with it. I resorted to buying pre bent u bends, j bends and elbows.