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carrey
science forum beginner
Joined: 23 May 2006
Posts: 4
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 Posted: Tue May 23, 2006 9:43 am Post subject:
gear
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i have got a machine part on which i got a sector of gear welded. the
issue now is i m not able to find the diameter and diametrical pitch of
the gear. please help in the matter.
regards,
carrey |
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eromlignod
science forum addict
Joined: 02 May 2005
Posts: 68
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| Posted: Tue May 23, 2006 2:25 pm Post subject:
Re: gear
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carrey wrote:
| Quote: | i have got a machine part on which i got a sector of gear welded. the
issue now is i m not able to find the diameter and diametrical pitch of
the gear. please help in the matter.
regards,
carrey
|
You can usually tell the pitch P by laying the gear on a tooth-size
chart (there is one in Machinery's Handbook, p. 1769 in the 23rd ed.,
and some gear catalogs have them). If there's any chance that it's a
metric module gear, be careful that you use the right chart.
To find the diameter is a little trickier. Does the machine part, or
the mating parts of the machine, have a center that your gear teeth
pivot about? You can measure the radius from this. Otherwise you can
calculate it geometrically. The addendum (distance from the pitch
circle to the outer diameter of the gear) is basically the reciprocal
of the pitch. So, for example, a 16-pitch gear would have an addendum
of about 1/16 inch. If you trace a pitch line along the existing teeth
and then measure the chord length c between the ends and the and the
height h from the center of the chord to the center of the arc, then
you can calculate the diameter D from
D = (c^2 + 4h^2) / 4h
Recall that the theoretical whole gear must have an integral number of
teeth N and that D = N/P, so see what integer value of N gives the
closest value of D to your calculation and use that as your pitch
diameter.
Determining the pressure angle is really tricky. There are charts for
checking gears by putting rods of a known diameter between teeth on
opposite sides of the gear and measuring the outside dimension, but the
difference between the measurements of a 14-1/2 deg. gear and a 20 deg.
gear is so small that it is really difficult to determine the angle
without a doubt, especially on used gears. Short of meshing the gear
with another gear of known pressure angle, I've never really found a
foolproof method of determining this. Perhaps someone else in the
group has a clever method?
Don
Kansas City |
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carrey
science forum beginner
Joined: 23 May 2006
Posts: 4
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| Posted: Wed May 24, 2006 6:37 am Post subject:
Re: gear
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thanks don
carrey |
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