Thread: Heating, Bending,... and Breaking a Steel Rod (Where did I go wrong?...)

not enuff heat...high carbon steels need to be near white heat, otherwise they seem to have a tendency to snap like that...

I tried bending a worn chainsaw file last week to make a probe but my first attemot was a failure as it snapped even though it was red.....I got it hotter and it bent properly on the second attempt..

.R.C is right. no where near enough heat. In fact I think you will be struggling with a small butane torch to get enough heat into it. I'm assuming your torch is one that just uses Butane or LPG as a fuel gas and gets its oxygen from the atmosphere? Do you know anyone with an oxy-acetylene set? With enough localised heat from an oxy you will be able to bend it by hand. The oxy is hot enough that you can heat up a relatively small area to white heat before the heat spreads to the rest of the bar. The smaller Butane/LPG - air torches just can't put the heat in fast enough.

regards
bollie7

Dear Chaps,

Okay, I hear both of you. But I'm starting to form the opinion that even more heat may not be the answer, because I've got a sneakin' suspicion that the flattened "stamped" area might well be - for all intents and purposes - now unbendable.

Consider this: there was already a slight bend in the axle before I started any work on it whatsoever, but the bend was where the rod was round (ie. where it had been purely "drawn", rather than "stamped"). It should have been the other way around, because the wider flat area has a lesser "Moment of Inertia" than the taller round part of the rod, so it should have bent there, instead of where the rod is still round. The only explanation for this would be that the flat area is now "harder" than the round area. If you have a good look at the close-up of the two broken ends, you can see that they have a very random-fractured-crystalline appearance very unlike what you'd perhaps expect something that was "drawn" to have. I suspect that this is the result of the "stamping" having "disorientated" any organised pattern to the crystalline structure that may have been brought about by the earlier "drawing" of the rod.

In becoming "random" in its crystalline structure, the flat area (which is where the break occurred) is perhaps now behaving much more like something that was "cast" (ie. hard and brittle), compared to the round drawn area which is perhaps still more ductile and tougher (and therefore still able to be bent...)

Maybe I am therefore expecting too much of the piece to try to bend it where it has been stamped flat - even with the addition of red-heat. The solution might well be to have a think about bending it where it is still round and drawn (ie. tougher and still ductile), and then grinding a flat face on the bent bit so that I can then drill the required hole through it...

Many Thanks Gentlemen ,
Batpig.

To me, from the photos, it looks like a fatigue break - it was probably ready to break anyway, and your trying to bend it was the 'last straw'.

If you are having trouble reaching a good colour when heating, make sure you have some 'back up' to the area you are heating - a couple of old bricks, some sand, coke or BBQ heat beads will work - something to make a small sheltered area around the bit being heated that the hot gases can swirl around in, and take your time.

Oxy is wonderful in the right place - you can case harden rod with Oxy by blasting away at the rod until it is red to yellow on the outside, but the heat hasn't had time to get to the core of the rod, so when you quench the rod it goes very hard on the outside and stays soft in the middle - or it can snap when you try to bend it I've had some hammer heads delaminate when I heated them up to reshape as the outside had heated to red and the core was still cold - and that was in a coke forge.

batpig, you are onto something when you say it must have been harder at the flat part than the round part because it most likely was.
if, as you suggest, it has been stamped it is most likely done cold, cold forming of metals makes them become harder and in turn more brittle.
take a piece of ordinary flat steel say 2-3mm think and bend it back and forth repeatedly, eventually it will break because it work hardens at the point you bend it, hardens to a point where it is no longer maleable (soft and bendy).
work hardening is a result of the change in molecular structure of the material.
this may explain the different crystal structure you saw.

case hardening is also a change in molecular structure, effectively when you get the material white hot all the molecules of the material start spinning around quickly, when you quench it you freeze the outer layer which has a hardening effect.

often in the past where I have welded something or heated and formed and do not want to weaken it as it is critical, I have had to bury it in cement dust, lime or sand to give an even gradual cooling process to give the material the best chance of returning to its orginal molecular form.

what also didnt help you was it had holes in it, this immediately caused a weak spot in the material.

to bend it, try doing it cold on it round part, or if you want to bend the flat part get it hot, really hot and bend it at a point not directly where the hole is, it should work ok either way.

hope this explains a little what happened the first time.

Dear Chaps,

Thank-you to all four replies so far. I don't have Oxy gear, but I've certainly got some Heat Beads and Bricks lying around (a'la Bsrlee's excellent suggestion), and I've got nothing to lose by having another go at the other end of the flattened zone (ie. where it's still attached to its half of the round axle...). If she goes and breaks again in the circumstances, well - I can just revert to bending it cold somewhere along the round part (albeit after maybe 10mins in the Toaster Oven, since the ambient temperature is starting to crispen a bit...), and then giving it a slight grind to give me a nice flat face to at least start drilling from.

I'll try to do it sometime over the next couple of days and post the results .

Many Thanks,
Batpig.

Dear Guys,

Well, I had another go bending the other half of the Axle on Saturday morning. This time I made sure to give it as much heat first as I practically could, by first giving it a good "baking" amongst some Heat Beads, followed by a nice butane-torching whilst it was still over the hot Beads. Try as I might, I couldn't get much of a glow out of it, though.

Attachment 104256

Unfortunately, the result when bending was much the same as the first effort, except:

1) The thing bent a little further this time before it broke:

Attachment 104252

and,
2) This time the fractured ends had no pretty colours to them:

Attachment 104253

It's not the end of the world, because I can just weld the little bit of flat plate that I need onto the end of the rod at right angles anyway. I'm still formulating the exact layout of the Depth Stop; a successful bend in the Axle would have given me a handy little "Design Hard Point" that could have formed a nice starting point from which to evolve the rest of the device. Now, after another breakage: well, I just have to make a few more decisions, and do a little more work to achieve the same result (I'll get there...)

Many Thanks again,
Batpig.

Is there some compelling reason why it must be bent at this location for the design objective? The flat-formed element, weakened by two pre-existing holes, seems like the worst candidate for bending, except as a challenge.

I know from experience, that a legitimate question, answered with "Why don't you do this instead?" can be frustrating, so I've tried to be more cordial. One of my best mentors mostly suggested that I think about it a while longer.

I've amassed a collection of metal orphans, some bent professionally, from which I can design components of DIY contraptions. Might be worth consideration.

Cheers,
Joe

Dear Joe,

Originally Posted by joe greiner

Is there some compelling reason why it must be bent at this location for the design objective?

Mainly because she was already flattened and widened at that point, with a reasonably-sized threaded-hole already drilled in (which would have been perfect for the proposed Height-Adjustment Screw/Bolt...). If I have to grind a flat area into the Rod and then drill it to accomodate the said Screw, the decrease in available width compared to the existing stamp-flattened area would dictate the use of a smaller-diameter Screw (which will be more difficult to get a Spanner around the head of...).

In addition, each Axle-half by itself is not all-that-much longer than what appears to be the bare-minimum required to give me clearance at the top for the Knob, as well as some length up there for a Spring and a couple of Washers, and roughly the same setup at the bottom. So bending it at the "Flat" would have been ideal...

Still, it's not the end of the world. I'll just have to weld a little flat bit at 90deg to the end of the Rod now (after I finalise in my mind the exact layout of the thing, that is...)

Anyhow, Best Wishes to Y'all over there Joe!
(and make sure you slap our F-35's together properly for us too!... I hope we're getting "Mate's Rates"! )
Batpig.