Too much backlash between gears
Too much backlash between gears
(OP)
I am working on a gear box using a worm and worm gear. (boston gear HDSH-1 and bostonGear D1124). In the manual it says to have the center distances be 1/2 the pitch diameter of the worm plus 1/2 the diameter of the worm gear. In this case the distance was 0.792" and when I assembled the gearbox together there was still a good amount of backlash between the gears. Is there a different way to calculate the center distance or a better way of aligning them? Thanks





RE: Too much backlash between gears
RE: Too much backlash between gears
All gears should have some backlash for a free running and a space for the oil film. The backlash and tolerances on the center distance are function of the gears accuracy. If you need less backlash you need to specify more accurate gears. If Bostom gears uses the AGMA gear system then they should specify the AGMA accuracy class for the worm and the worm gear.
RE: Too much backlash between gears
Have you considered the play in your bearings? How accurately was the housing machined to this center distance?
Don
Kansas City
RE: Too much backlash between gears
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Too much backlash between gears
RE: Too much backlash between gears
I don't understand how you can claim that cdeane44s' calculations are correct because the worm gear's diameter is being used and not the worm gear's pitch diameter. I must be missing something as I have never seen a center distance equation that uses the diameter of a gear.
From Dudley's Gear Handbook second edition, page 2.45, table 2.10; to find the center distance of a worm and gear having the pitch diameters of both parts; C = (D + d) / 2.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Too much backlash between gears
In the manual it says to have the center distances be 1/2 the pitch diameter of the worm plus 1/2 the (PITCH) diameter of the worm gear.
RE: Too much backlash between gears
cdeane44 is correct and he was asking a good question he just missed the word "pitch" for the worm gear. A quick check in Boston gear catalog shows that the worm pitch diameter is 0.333" and worm gear pitch diameter is 1.25" therefore, the theoretical center distance is 0.7915". Your debate is off course. The gears diametral pitch is 48.
Here is a note from Boston gear catalog "Note: Worm & Worm Gears do not have AGMA Class listings,
however Boston Gear manufacturing tolerances relate to
AGMA 8"."
RE: Too much backlash between gears
Chris
RE: Too much backlash between gears
I'm guessing that the center distance is not ending up exactly .792", or varies, either due to machining tolerances, bearing play, or bearing-to-housing/bearing-to-shaft fit (or a combination of these factors). If you really need precision, I would recommend using precision bearings (not needle bearings or cheapies). Put some tighter tolerances on your hole centers and ensure that the bearings fit snugly in the housing and on the shaft, according to the manufacturer's recommended tolerances. And, as israelkk said, you want a little backlash in a worm-gear pair since they rub rather than roll.
Don
Kansas City
RE: Too much backlash between gears
Don
Kansas City