Maybe some of the mandrel bending guys like CRMB can help me out. Im use to doing bends like a main hoop where they are all on the same plane. I have stepped up my challenge and have 3 bends (12, 21, and 67 IIRC) for my a pillar bar and all of the bends are on a different plane. I have already bent up a mock up piece of tubing out of some cheap steel where i cut about half way in between the bends and places an insert inside so i can rotate the tubing. So i have a mock up piece that fits great im just worried when i go to bend it in one piece out of 1.625 x.090 4130 it might be a little off and i won't be able to tweak it like you can with a thinner nhra style main hoop.

How do you bend consistent bends?

 

http://www.vansantent.com/angle_find...indicators.htm

 

My roommate used to work at a local exhaust shop with a mandrel bender making custom exhausts. Basically they would tack together a template from scrap tube and then use that as a guide to bend the exhaust on the bender.

 

Lay the piece on some flat ground, measure the degrees that each bend is off axis, then use this (pic below) to measure it while on the bender. Easy as pie. I use a digital one for the ability to reset to 0 degrees on various surfaces and for accuracy while on the bender, but you can use a regular oil filled type.

 

I will try to make a bracket like that for my digital mitutoyo. I think i will try to better level the table, and weight it down with some engines. Wish i could get the bender to be a little more sturdy.

 

We don't commonly do this anymore, but when we had manual mandrel bends I would train my guys to reset the POB between bends. That way they are always rotating to an absolute value, as opposed to subtracting angles from their previous bends. So as soon as a tube is clamped up and ready to bend, I have my guys reset to a 0 plane.

 

/\ wouldn't that result in stacking of differences?

 

Are you asking about how to calculate the rotation, or how to replicate it?

 

I don't have a hydraulic bender, every time i go to bend my bender flexes. My table bends and lifts a leg off of the ground. I understand how to measure the bend axises but im just worried that everything that's flexing/moving will throw off my accuracy.

 

You dont have to worry about the bender flexing, or a leg lifting off. Those factors dont twist the tube in the die. The only thing that could throw off your plane of bend/axis rotation is the tube twisting in the die from something. But you could always test it by getting the level attached to the tube like my pic, bend a piece of tube and see if the angle is the same or if it did indeed twist and throw off the plane of bend while bending.

 

Thanks for the pointers, i will try mounting the level on the tubing next time i go to the garage. I will test on some cheap stuff first.

 

Got it bent up but it was not easy. I figured out my bender is flexing and i was getting about a degree and a half rotation from the tubing relaxing and twisting while i was using the "ratcheting" part of the bender. Once i was done the final piece was only about a 1/4" off from the mock up one which i think is acceptable for a roof/a-pillar bar.

 

I use a JD2 tube bender and usually when trying to do the a-pillar bars I level one end and the use and angle finder to degree in my rotation. The tubing wont be level in the bender until tension is on the piece so too get the right angle I always level the piece. This seems to work fairly well with keeping to my calculated bends. But with the a-pillar for the rotational axis is sorta a one shot deal or the tube needs to be scrapped. So make sure everything is perfect before you bend and that your rotating the tubing the right way depending on if its the passenger or driver side.

 

Yea i figured out that the bolt that holds the tubing in place could be tightened and it wasn't long before i had a heavy adjustable wrench hanging off of it to "auto tighten". Its a nice bender but i think i may do some mods to it and the mounting table in the future.

 

Mine is anchored too the floor using 4 1/2 concrete anchor bolts. I think they have a rating of 6800lbs each in any direction. That is really the best way to securely anchor the bender too not allow for any movement.

Also before I started bending the first time with the bender. I calculated my length to the center line of the bend with a piece of scrap from 5*-75*. So I can get the center line of the bend exactly where I want it on a piece.

Without having a cnc bender it can be really hard to replicate bends unless you have a really good system planned out too keep your bends as precise as possible.