# Re: Helical Gear Problem

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Posted by Ron V on February 01, 2006 at 21:38:05:

In Reply to: Helical Gear Problem posted by Stuart on February 01, 2006 at 16:27:34:

Based on the O.D.s you've quoted the pinion is corrected +0.38 and the gear +0.363. With a helix angle of 14 deg this works out to a center distance of 318.76. This is not a well designed set, something is not right. Either the helix angle or center distance is wrong. The amount of plus correction you would have to introduce to the pinion to make 320mm centers would create a very inefficient gear set. Are you working from samples or drawing?
Doing some quick calculations at a fixed center distance of 320mm you'd be better off to have a helix angle of 18deg with a plus correction to the pinion of 0.28 and minus correction to the gear of 0.305. (OD for the pinion would be 179.845mm and for the gear would be 488.145mm). This would give a Balanced Specific Sliding Ratio of 0.964 and Recess/Approach angles of 15 deg/10 deg making the gear set have an efficiency of 97.12%. These results yield a reasonably well designed gear train as B.S.S.R. is close to 1 and you've got a "recess action" gear train making it run smoother and quieter. All this is of course assuming the bearings can handle the increase in axial loading due to the increase in helix angle.
In answer to your questions: when calculating centre distance, along with the information you have already mentioned, remember to take into account the correction factors and the operating P.C.Ds, not the standard P.C.D.s. The operating P.C.D. takes into account the amount of correction

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