Worm Drive Center Distance tolerance.

[JSlippy]

I am designing a worm drive consisting of a worm driving an internally threaded wormgear to move a concentric non-rotating acme threaded rod. The gear is loaded predominantly in the axial (thrust) direction, so I am considering using thrust roller bearings for the thrust loads and simple bushings for the radial loads, which are light. The issue is that I need to know what tolerance is required on the center distance of the worm/gear set. I have not found any resources containing this information. If a good design book exists (with real usable information -- not just theory) or if you have experience in this area please let me know.

 

[shopguy]

Traditionally, the min. standard backlash allowance in the gear set is .030 / DP. The maximum standard backlash is .050 / DP. This is a rule of thumb that will probably work for your needs. If you need specific backlash requirements because of special operating or loading conditions, there are AGMA specs that you can order through the American Gear Manufacturers Association.
Good Luck.

 

[shopguy]

The backlash is directly affected by the center distance. Don't allow any more center distance tolerance than half the difference between the min and max backlash.

 

[omer2000]

hi
please center distance tolerances dependes on what is center distance and what is the quality degree of manfacturing
for more information you can go to APPENIX L in HANDBOOK OF GEAR DESIGN
TataMcGraw-Hill Publishing Company Limited
NEW DELHI

 

[JSlippy]

Thank you for the input! This little bit of information is really helpful.
-J

 

[JSlippy]

My situation has a DP of about 20 (D=1.5, 30 teeth on worm gear). According to the above tolerances, I would need a center distance tolerance of about 1/2 of a thousanth. This seems a little bit tight to me, considering the components that need to stack up between the two shafts of the worm and gear. Is this the kind of tolerance range you would expect to see? How much will the wear-in of the gears account for larger tolerances? Any tips you might be able to share would be appreciated.
--J