Broken gear - Calling all machinists/ welders

[CT_Tree_Guy]

Andy -

Thanks a million - he sounds like a great contact. I will definitely give him a call and pick his brain about Powers cranes etc. I think I'll also be on the lookout for other trucks with this crane to pick up for spare parts for the future.

Thanks again for the excellent lead, John

 

[markct]

tree guy, northfield is a part of litchfield. what does this gear actualy do, is it the gear that rotates the crane around, if so its relatively low speed so if it were mine i would not be affraid to weld it up then grind it out with a die grinder and or small angle grinder, make a template of one of the other teeth and grind till it matches, for a low speed gear thats fine. often times when you weld up a gear the weld has hard spots and machining is difficult and ya end up cleaning it up with a grinder anyhow. even tho i have a lathe and milling machine here often stuff like this comes out just as good and easier if you do it freehand and match it to a template

 

[CT_Tree_Guy]

Howdy neighbor -

I'm still amazed I've never heard of Northfield, especially since it's so close.

Yes, this is the gear that rotates the crane around. Quite low speed, but a lot of torque, 37,000 ft. lbs. The repair just calls for strength and halfway decent tolerances. Maybe I could even let Gilligan himself take a shot at it.

We'll see what the local shops have to say, or maybe that guy in Franklin.

Thanks for the help, John

 

[markct]

you would be surprised sometimes what will hold up with a bit of luck, you wont be likely to get a repair as strong as original, but strong enough to work is whats needed, probably some kinda shock load was what broke it in the first place

 

[AndyMA]

</font><font color="blue" class="small">( Yes, this is the gear that rotates the crane around. Quite low speed, but a lot of torque, 37,000 ft. lbs. The repair just calls for strength and halfway decent tolerances. Maybe I could even let Gilligan himself take a shot at it.
)</font> Now I'll put my engineers hat on. The forces on that gear are huge and things like hand grinding have a very slip chance of working. If one point on the gear meshws first and their is not uniform contact (and at the correct point) the point forces will clearly tear off the repaired gear. I suspect that the tooth could be welded up, but the grinding would have to be very accurate.

Andy

 

[CT_Tree_Guy]

Andy - Thanks for the reality check. I believe you are absolutely correct in your assessment of the forces involved and how the tolerances must be right on if I want the repair to last. Ditto on the strength. Just from what you've said I'm leaning toward having a new gear made and having it heat treated. Thanks for rescuing me from Gilligan's Island. (I'll send a chopper back to pick up the others).

John

 

[markct]

andy, i understand your point about forces and the need for acuracy, but i will say that if you make a template acuratly outa sheetmetal and then also use a straightedge and stone along with some machinist blue or even magic marker you can infact do a job that would get very close to the original profile, its not something you would do in 15 minutes with an angle grinder, but with and angle grinder to rough it out, then move on to a finer wheel like a cuttoff wheel in a die grinder then onto a sanding disk in the die grinder, and then some touch up with a fine stone will yield a gear tooth that you would be hard pressed to tell different from the others once it gets some oil on it. it takes a steady hand and some patience, but i have done a few different gears, even a few helical, and have had pretty good results

 

[philshel]

I'll jump in here as i was a machinist in a previous life. the part would be simple to make as long as the the tooth is a standard pitch. that is, if it can be cut with off the shelf tooling. it is likely surface hardnened and the new part would need to be also. it is likely just 4140 that has been case hardened down to .010 or so. it could be welded, but i would not suggest it as it will not hold up as well and will cause a mismatch with its mate before long, when that happens, you could end up replacing both gears. any decent job shop should be able to handle this as long as the gear is a standard, if not a cutter will need to be either fabed or possibly a standard cutter could be reground. hope this helps

 

[CT_Tree_Guy]

Phil - Thanks, that does help a lot, and makes perfect sense. I'm heavily leaning toward having the gear made from scratch, and your input reinforces the merits of going that way.

I apologize to all that I haven't ripped the old gear out yet, I haven't needed the crane lately but I will.

Pictures, progress and final resolution to come.

John D.

 

[AntrimMan]

Given my druthers I would choose E4340 heat treated to Rc 32 for toughness and Ion Nitrided for wear, or 8620 carburized and heat treated Rc 58-60 at .005 deep. The 4140 lacks Ni, the addition of which promotes long torsional life in a 4point alloy.
The nice thing about the E4340 is it can be heat treated, have all the diameters turned and ground then wire cut the spur teeth and Ion Nitrided. Finished, no scale or smut to remove.

It just has to be a lot easier and less costly to find an existing gear, new or used. I would surely try finding one before making one.

Keep us informed if you will. This sort of thing interests me.

Martin