Question about tube bending

[Nick]

We are trying to bend 1 in diameter steel tubing with a JD Squared model 32 tube bender but every time we bend a tube it creases in the center of the bend. We are using all the proper dies and have tried various ways of preventing this from happening such as oiling the tubes and dies applying pressure along the tube as we bend it and different techniques of applying the bending force (fast, slow...) Does anyone have any idea how to prevent this? Were considering sand packing but that is a lot of work so any other suggestions would be much appreciated. Thanks

 

[itsid]

Easiest way is to
fill the tube with sand.

'sid

 

[KartFab]

Dumb question... Are you using tube or pipe?
Another question... Thin wall tubing? That's the most susceptible to creasing but you should be able to lock the tube/die in place through the bending process. If you don't lock it, it will release tension and cause spring back, which will crease the next time you move the arm.

 

[landuse]

Easiest way is to
fill the tube with sand.

'sid

Thats the way I know

 

[supermanotorious]

mandrel?

 

[rmm727]

I have the same bender. You shouldn't have to pack it full of sand. Are you using the anti springback mechanism?

 

[Nick]

mandrel?

We're looking into that now.

I have the same bender. You shouldn't have to pack it full of sand. Are you using the anti springback mechanism?

That is the circled pin right? If so yes we have been but we havent been putting big enough bends into the tube for that to even engage...

 

[rmm727]

That is to hold the die in place when you max out the travel. You have to use the lower toothed plate to keep the die from springing back in between strokes of the handle. Did you watch their youtube video? I'll post up a like in a few.

Here you go.

http://www.youtube.com/watch?v=I1cAaOkuvRs

 

[Nick]

Yes we have been using that as well. Yesterday we took a few of the tubes to a local race shop and used their bender which creased it even more than ours had been. We found last night that we can make the bend by bending a very small amount then moving the tube a little and bending a little further. Its not nearly as precise or quick as doing one bend but at least it is smooth.

 

[andrewmacc]

What is the CLR of your die? The website should state the rated minimum wall thickness for their die. The smaller the CLR of the die, the more susceptible thin-walled tubing is to wrinkling along the bend. This is why mandrels are used for high quality exhaust tubing, and why cheap exhaust pipe is wrinkled along the inner-side of the bend.

IE my bender has a 1.5" die on it currently, with a CLR of 4.5", and the minimum wall thickness is .095". The 6" CLR has a minimum wall thickness of .078 with the possibility of bending .065 with a 12% OD pull-in.

 

[OzFab]

What is the CLR of your die?

Just to clarify, for anyone who is unsure: CLR = Centre Line Radius, meaning, the radius of the bend through the centre of the tube

 

[Nick]

Thanks for the help. We eventually solved the issue by just making composite bends. By that I mean we bent the tube about 8-10 degrees then moved the tube further into the die by about 1/4 in or so and bent again till we had the desired angle. Then since the bend radius did not match our model we compared the point to point distance between the two ends and adjusted our bends till that distance matched our Solidworks model.