# Re: first helical gear

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Posted by BillS on April 24, 2012 at 10:31:35:

In Reply to: Re: first helical gear posted by Jim Pollock on April 23, 2012 at 17:53:14:

Based on the CC distance and the gear specs, I get an angle = 32.82 Deg for tight mesh at 5.100 CC (Is the 5.100 CC correct or an approximation?):

(48 + 12)
-----------------   =  2 x 5.100
(7 x COS HA)

Does that sound about right to you? I know you saw 32 deg on your tool grinder, but wonder if you were approximating?

Your 32 deg HA would yield tight mesh at 5.054 CC:

CC  =  (48+12) / (7 x COS(32))  =  5.054

I would approximate the backlash this way:

Separation of pitch circles = 5.100-5.054 so that approximate backlash is:

(5.100-5.054) x TAN (20)  =  0.016

Does .016 backlash sound OK to you?

If you can assemble and, with dial, measure actual Backlash by clicking back and forth, we could confirm or revise the HA - of course, this assumes like new gear and pinion.

Notice that the calcs above never find either pitch circle diameter - we just use the sum of both.

When cutting the 12T pinion, use the recommended pin diameters (on the CPC-HOB printout) to get a measurement over wires (MOW) on your sample. Use the sample's MOW to check and adjust your cutting depth. This should get your mesh right at assembly.

Finally, you want to roll together at assembly with blueing to see where the contact is. From that you will know if your pinion angle is correct. Of course, if this is a high torque app (tractor pulling? yep) then you may want to bias the contact by slightly biasing the HA according to expected shaft deflection.

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