Failed Bandsaw Gearbox Shaft, Material Recommendation
Failed Bandsaw Gearbox Shaft, Material Recommendation
(OP)
Hello everyone,
Just had a main gearbox shaft failure (torsional bending fatigue?) in a production horizontal saw. It's been in service 19+ years (daily use) and is still in production by its original manufacturer. We may be in a situation where we have to machine our own replacement shaft just because of the time involved in getting a factory part.
The OEM part is a mystery steel at this point, induction hardened from both ends toward the center stopping right at a snap ring groove where the stresses concentrated to propagate the failure. I am proposing to machine our temporary replacement out of 4340, through harden, oil quench and temper to 42-46 RC, with a little radius in the snap ring groove and key seats. The gearbox is put together like a brick shothouse, massive bearings, worm and gear like new condition, oil bath, etc. I don't want to put an inherently flawed part back in and we may end up using our temp replacement long term. (we did discuss with the factory the perceived shortcoming of the original design, even though 19 years of hard use is pretty good)
Any pitfalls that anyone can think of concerning the potential next weakest link or my proposed material selection?
Thanks.
Just had a main gearbox shaft failure (torsional bending fatigue?) in a production horizontal saw. It's been in service 19+ years (daily use) and is still in production by its original manufacturer. We may be in a situation where we have to machine our own replacement shaft just because of the time involved in getting a factory part.
The OEM part is a mystery steel at this point, induction hardened from both ends toward the center stopping right at a snap ring groove where the stresses concentrated to propagate the failure. I am proposing to machine our temporary replacement out of 4340, through harden, oil quench and temper to 42-46 RC, with a little radius in the snap ring groove and key seats. The gearbox is put together like a brick shothouse, massive bearings, worm and gear like new condition, oil bath, etc. I don't want to put an inherently flawed part back in and we may end up using our temp replacement long term. (we did discuss with the factory the perceived shortcoming of the original design, even though 19 years of hard use is pretty good)
Any pitfalls that anyone can think of concerning the potential next weakest link or my proposed material selection?
Thanks.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.





RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
Thanks again!
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
Most likely, rotating bending fatigue based on the fracture surface appearance. See if you can introduce a larger radius at the snap ring corners to reduce stress concentration in addition to the above suggestions.
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
Given the relatively simple design of the shaft and the long lead time/cost involved in procuring a replacement, it may indeed be cost effective to purchase a piece of heat treated 4340 bar and have your local machinist make the new shaft.
Good luck to you.
Terry
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation
I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)
RE: Failed Bandsaw Gearbox Shaft, Material Recommendation