# Re: True Position versus Timing of Spline teeth

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Posted by Zachary Young on June 08, 2002 at 16:19:05:

In Reply to: Re: True Position versus Timing of Spline teeth posted by Phil Rockwell on June 08, 2002 at 12:43:13:

Phil,
In response to your posting, personnel in my company all seem to feel that we are looking at several different variables which are complicating the verification method which the customer is using to attempt to inspect this feature. Since the datum features are unfinished (complication #1), the customer is asking us to use the ground surfaces adjacent to the -A- datum, which has an axis perpendicular to centerline of the spline and the secondary datum -B-. The customer is placing the part in a v-block along the length of the shaft which is over 12" in length and is straight only within .002 on average. The are not mounting the part on either of the datums (complication #2). Then they are leveling the ground surfaces on top of the -A- datum and placing a pin in the valley of the spline teeth. Then they are placing the v block on it's side, rotating the part 90 degrees, and zeroing an indicator on top of the pin. Then flipping the v block over, 180 degrees and indicating the pin again. The difference in the readings is up to .005. I'm attampting to explain to them that by checking the part in this way, they are introducing a host of other errors into the equation. Would not the straightness of the shaft, the lead error of the tooth (which is allowed by the spec, and would be multiplied by two with this method) and the parallelism of the sides of the v block all be accumulated in this method? They vehemently deny that those factors have any influence on the indicated readings over the pin. They suggest that we level pins adjacent to the timed valley and indicate the ground surfaces within .0003. Since the ground surfaces are spaced 1.460 apart, and the opposite leg of that right triangle calculation is .0003, this gives us an angle of 46 seconds. I'm trying to explain to them that this is impossible to achieve. I basically don't know what else to tell them at this point.

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