# Re: True Position versus Timing of Spline teeth

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Posted by Dan O on June 10, 2002 at 09:50:26:

In Reply to: Re: True Position versus Timing of Spline teeth posted by Zachary Young on June 08, 2002 at 16:19:05:

I think we're making this harder than is needed.
It is unfortunate the customer is not using the centers
from which the spline datum is created, however using
the "v" blocks will be ok depending on how it is treated.
Yes, unequivocally, measuring from a pin, the correct
pin for measuring tooth size is 'the' best way to determine
where the center of the space is located. We can
manage the errors mentioned in the email through the
setup for checking. First, the part must be located in
such a way as to 'fix' the location of the datum 'B' at
the height of the centerline of the spline orienting it
exactly 90 degrees to the right (at 3:00 position looking
at the clock) and by using jo-blocks. The center of this
datum is oriented on the height of the center of the
spline. With this setup, any measurements, and any
subsequent part measurements are taken from the
datum established from this hard position location.
The variation on any of the measurements over the
measuring pin of subsequent parts are all strictly
the variation of the location of the center of the space
to the (hard) datum point. Flipping from side to side
and getting the same measurement verifies you have
the center of the datum on the center of the spline.
We often orient spline teeth or spaces to datum
points through spline rolling, and have a couple of
tools to help us find the centerline quickly, a piece
with a flat ground to the exact center of the bar for
example. We feel by fixing the datum on a hard
position and measuring the variation of the pin
directly that we're eliminating many of the errors
you've mentioned. For a case a space is located at
a given anglular orientation from the datum, we compute
the theoretical 'height' off the reference setup for the
angular offset, and measure the variation from this
'target height' off the granite table.

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