Bevel Gear Set-up 2

[artbuc]

Power is transmitted to my Ariens mower through a gearbox mounted on the mower deck. Ariens has been using this design for at least 25 years and before that it was used by New Holland. The mower is no longer in production but Ariens will build one for you from parts which is what I just did. Unfortunately, the new gearbox had excessive endplay on the output shaft (0.028" vs spec of 0.003/0.008")which could not be fixed. Usually there are shims which can be removed to reduce endplay but this unit had excessive endplay with no shims. The replacement gearbox was the same. My dealer did a non-Ariens approved modification to reduce endplay (something he has done many times over the years) but now the box has a high pitch whine at full speed and an intermittent scraping noise at half-speed.

Ariens Engineering Department has set-up another gearbox and is sending it to the dealer. They are not forthcoming about what caused the original problem other than saying it was due to an accumulation of tolerances. This doesn't strike me as plausible.

The box design is somewhat crude. It is aluminum diecast with the bearing races for the vertical output shaft located by non-machined shoulders in the diecast. The horizontal input shaft bearing races on either side of the input gear are adjustable to set input shaft endplay and gear backlash. The gears are straight bevel and have no markings to set mounting distance or to identify mating teeth. The service manual does not specify gear mounting distance but says backlash should be 0.005/0.015".

Unfortunately, I think all of the new Holland/Ariens engineers who know about this box have retired and Ariens says they will obsolete the part instead of investing much effort to find the problem. I am expecting the third box will not be much better than the first two.

Can someone give me some suggestions on how to set-up this box? Or, where can I find a person or shop that can set this box up for me? Thanks for your help.

PS I will try to post a drawing of the gearbox although I think you all can probably visualize it.

 

[tbuelna]

artbuc,

Nice job with the gearbox. I think it's great seeing someone with limited knowledge of gears take a structured approach to gain an understanding of a problem.

Per your latest "test report", anytime you have displaced metal (smearing or galling) on your gear flanks, it's due to contact pressures in excess of what the material can take. The smearing may be the result of excessive torque loads, load concentrations due to misalignment or geometry errors, loss of mechanical properties due to overheating, or low mechanical properties due to a manufacturing defect.

Getting a specific answer would likely entail more test work than you want to undertake. Maybe when you're done though, you can get Ariens to hire you as a consultant to redesign their gearbox.

Regards,
Terry