Bent tubing question

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I am working on my friends drag-bike (he spent probably 250k on this thing), question, I am looking at the frame and at the bends, directly after the radius on the bend I am seeing and feeling dents in the tube, on the inside radius the tube is squished...quite unlike I have ever seen on a bent piece of 4130 when a proper tubing bender.Initially I thought that the tube was over bent then the material was held in something then bent back leaving a divot in the tubing, however I am seeing these identical marks in each tube directly after the radius.What kind of bender will leave this type of damage to the tubing after bending? I am thinking either a hydraulic bender (H.F. type) or maybe an electrical conduit bender.  If I need to I will take some pictures. Thanks.
Reply:Are they bite marks from a tubing bender?  Like pock marks in a pattern layout?
Reply:It is kinda hard to get a good picture, here are a couple. Attached Images
Reply:yuck.  it's probably safe but certainly not high grade work.
Reply:If you've ever use a Harbor Freight bender, you've seen picture one before. Not saying that's what was used because it would probably be much worse. Just saying it looks the the tubing was bent with a low quality bender.
Reply:I can tell is was from a cheap bender, not having any first hand experiance with what it would look like with a conduit or HF bender I am searching for a reason.Yes, I agree not a high of quality as the rest of the bike.
Reply:It is not easy to tell from the pictures, but there will still be a slightly raised or depressed area right at the bend when using a rotary draw bender if a mandrel is not used. It is unavoidable. Depending on the material thickness and alloy will either hide this or make it more pronounced. I seriously doubt someone is building a 1/4 million dollar bike with $100 pipe benders...I have been bending tube for some time and you need to consider a few things before you jump to conclusions.A tight radius in many materials WITHOUT a mandrel WILL kink the tube as what it sounds like is happening above.Granthttp://jackalopefab.com/MM210Synchrowave 200DXMiller XMT350 w/60series feederMiller Bobcat 250 with SGA 100 and spoolgunHTP PlasmaFull Machine shop with everything
Reply:On the same topic, a fella on the offroadfabnet site was building a mandrel bender and one of his dies he made LOOKED beautiful but every piece of tube he tried to bend it kinked and would not even bend aithout ruining the tube. His CLR (center line radius) was miscalculated and he thought he machined the radius to 6" when in fact it was the diameter which left him with a 3" CLR!!!! All the work for nothing on that die!!His bender build at that point was not fully mandrel and was still a rotary draw bender (like a jd2 or protools).Granthttp://jackalopefab.com/MM210Synchrowave 200DXMiller XMT350 w/60series feederMiller Bobcat 250 with SGA 100 and spoolgunHTP PlasmaFull Machine shop with everything
Reply:The condition of the bends don't look like any of the tubing I have bent with my JD2, on the tight radius places there is kinking in the tubing, rules dictate that the tubing is at least .058" this particular tubing is 1.25" If you look at picture 2 the kink in the middle of the bend appears like it is following the radius of the die, however it is a very small radius.All of the bends if they are light or not remind me of an exhaust pipe bent up at the local muffler shop.
Reply:Riceburner,   JD2 is referring to wall thickness being at least 0.o58" not the diameter. You just confirmed my belief with your comment of the tight radius in the bend. THAT will cause tube to kink without a mandrel, and YES, it will appear as though a pipe bender created it. I'd put money on it;-)GrantLast edited by jackalope; 04-06-2011 at 07:24 PM.http://jackalopefab.com/MM210Synchrowave 200DXMiller XMT350 w/60series feederMiller Bobcat 250 with SGA 100 and spoolgunHTP PlasmaFull Machine shop with everything
Reply:Here's the thread on the ofn forum I was referring to. Read ithttp://offroadfabnet.com/forums/showthread.php?t=1661Start reading page 4 of the thread and you will see the problem MUCH more clearly. On page 6 you can see where he made a bend in the tube. Yeah, there is a crease, but if he had stopped before the crease there would be the very obvious kink in the tube that you can also see in his pics.GrantLast edited by jackalope; 04-06-2011 at 07:50 PM.http://jackalopefab.com/MM210Synchrowave 200DXMiller XMT350 w/60series feederMiller Bobcat 250 with SGA 100 and spoolgunHTP PlasmaFull Machine shop with everything
Reply:Yes, a larger diameter thin wall tube when bent too far without a mandrel (like an exhaust pipe) will bend and kink when bent too far, however in the areas that I am concerned the bends are not tight, I have kinked 4130 in the past but you have to work at it.There are kinks in some 1" that is bent less than 90 degrees, my experience is that the 1" x .058 you can almost bend into a 10" circle without a kink using a regular tube bender.Last edited by riceburner; 04-06-2011 at 08:21 PM.