Posted by Ron V on February 05, 2006 at 20:34:05:
In Reply to: Re: Helical Gear Problem posted by Azher Shahzad on February 05, 2006 at 16:51:52:
Stuart,
I'm sorry but there must either be a mistake in your calculations or the data you’re taking from the samples is flawed.
How did you measure the helix angle? Was it taken with a protractor or was the sample set up in a hobbing machine and the diff’s change gears set up until a zero trace was given on a dial indicator (mounted on the hobbing head) in contact with a tooth face while traversing the entire tooth length?
Do your calculations account for the possibility that the samples are corrected?
How have you come up with the pitch and pressure angle? Was it calculated or have you measured the base pitch of the samples? Are you working in the transverse or normal plane? There are standards where the pitch and pressure angles are in the transverse plane.
You have to be very careful when reverse engineering helicals. There are many variables, which if not correct, can through out your calculations.
Don’t forget that if you are calculating the center distance based on the operating/working P.C.D.s you’ll end up with incorrect results if the corrections are not equally inverse to each other.
I would suggest you first measure the base pitch (in the normal plane) of the samples, preferably in an area with the least amount of wear.