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torsional capacity of rock drill steel

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Wardner

11-19-2007 17:46:10

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I am making something like a 3pt hitch rock shaft. The material is an extension section of a rock drill. It is 1.5" diameter with a 1/2" air hole.

When I cut the 3/8" keyways on both ends, I missed the alignment by maybe 1 degree. I could cut a special offset key but I am wondering whether I can heat the steel and twist the keyways back into alignment without damaging the steel.

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Ryan - WI

11-22-2007 06:34:27

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Re: torsional capacity of rock drill steel in reply to Stan in Oly, WA, 11-19-2007 17:46:10

You wouldn't necessarily have to have the arms rebroached. You could always file down a shoulder into a key to make a custom fit.

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Johnski

11-21-2007 23:12:27

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Re: torsional capacity of rock drill steel in reply to 36 coupe, 11-19-2007 17:46:10

If you are going to use 2 hyd. cylinders the I think I would try to cold bend the rod by piping the cylinders opposite each other and twisting it with the hydraulics. You would have to extend the cylinders to about mid stroke and then reverse the piping on one cylinder. HTH Jf

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markct

11-21-2007 15:08:32

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-19-2007 17:46:10

if it were mine, and i have made these sorta mistakes a few times, making two lefts of a pair of brackets etc lol, i think i would either make the keyway the next size wider and in the right location, or turn the piece 180 and cut a keyway on the opposite side

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Wardner

11-21-2007 16:27:26

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Re: torsional capacity of rock drill steel in reply to markct, 11-21-2007 15:08:32

The drill rod is hard. I don't feel like wrecking any more endmills.

I am not going to widen the key because the arms are already broached by another and I'll have to send that job back to the machine shop. In retrospect, I should have let the machine shop that did the broaching cut the keyways on the rod.

I could have avoided my mistake if I had two vises. The piece is long enough so that holding it in the center would have cause a vibration and a sloppy fit. I had to reposition the rod and that is where I screwed up.

As I indicated below, I have discarded the idea of using the drill steel as a torsion rod. I will use two cylinders and align the keyways with the help of some heat.

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markct

11-22-2007 08:12:13

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-21-2007 16:27:26

just a few thoughts to add, you can widen the keyway and use a stepped key which are readily available, or can be made quick. i understand not wanting to recut the whole keyway, i too have done alot of those type jobs that cost an endmill but get done. as for cutting them without repositioning the shaft to cut the other, i often lay the shaft right into the t slot of the mill and put a couple strap clamps on it to hold it in place, works well and fast, and accurate unless your t slots were extremely worn i suppose. i know thats not a help now, but just thought i would mention it for the future

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GPWT

11-20-2007 09:41:41

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-19-2007 17:46:10

The drill rod is almost certainly cold drawn stock, and it might be heat treated. In either case heating it enough to twist the keyways into alignment would weaken it quite a bit. How much depends on the alloy and initial heat treatment and it sounds like these things are not known.

If the drill rod is an air hardening steel heating it might make it too hard and brittle and it could break without warning. Is it worth taking this chance?

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Coloken

11-20-2007 06:49:33

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-19-2007 17:46:10

Don't think I would hest it. Might reduce its strength. No more that you need I think I would try bending it cold. I knoe what you mean..that would bug me too.

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CENTAUR

11-19-2007 20:45:19

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-19-2007 17:46:10

Will one degree make a difference.Perhaps there is somthing I do not understand.Would you consider explaining why this is important.CENTAUR

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Wardner

11-19-2007 21:37:23

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Re: torsional capacity of rock drill steel in reply to CENTAUR, 11-19-2007 20:45:19

Well, the pins at the end of the arms are 3/8" off. It bugs me.

I'll only be using one 3.5" x 8" hydraulic cylinder. It will be attached to one of the arms. The piece of drill steel will be under a torsional load and the offset is negative. If it were positive, I might test it under load and see if it levels out. If the drill steel can't handle the torque load, I will have to use two smaller cylinders; one on each side. That's another $150 I don't want to spend.

I am trying it this way because IH did something similar on their fast hitch.

I am concerned that if I heat the drill steel, it may permanently affect its torsional capacity. Why don't I whack off another piece of drill steel and cut new keyways? It's because I dulled two endmills with the first piece.

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nballen

11-20-2007 07:56:06

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-19-2007 21:37:23

I don't know enough about rock drills to know if the drill extension has been hardened or heat-treated.

Did you saw-cut or flame-cut the shaft? If the shaft has never been hardened, or if you (partially) annealed the ends by flame-cutting the shaft, you would probably be ok to torque the shaft and get your alignment.

Nathaniel

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Wardner

11-20-2007 11:49:07

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Re: torsional capacity of rock drill steel in reply to nballen, 11-20-2007 07:56:06

I cut it with an abrasive saw. There is no feed back with that kind of cut.

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nballen

11-20-2007 12:31:37

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Re: torsional capacity of rock drill steel in reply to Wardner, 11-20-2007 11:49:07

Yeah...with an abrasive saw you might have heated up the first 1/4"...no way you would have annealed enough to make that twist like (and where) you are talking about.

Nathaniel

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Wardner

11-20-2007 15:26:49

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Re: torsional capacity of rock drill steel in reply to nballen, 11-20-2007 12:31:37

I just found a matching 3.5" x 8" IH tie-rod cylinder and that gives me a pair. So I guess I will heat the drill steel, make the alignment, and not worry about the torsion capacity.

I'd rather use the smaller 2.5" x 8" IH cylinders but I can wait till one or a pair shows up on eBay.

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