Gear Runout vs. Space Width Error

[[Sy...]]

How does gear pro differentiate between a pitch diameter runout and tooth thickness/space width variation? I should add that the gear pro output shows that tooth thickness variation increases as the out of roundness condition increases. I don't necessarily believe my tooth thicknesses are varying very much but rather the part is out of round. How does gear pro essentially take tooth thickness measurements as a tooth caliper would (regardless of a datum or pitch out of round error).

[[Ri...]]

Please sign in to view this quote.

You can see the case now for using the double-flank pitch evaluation vs the single-flank pitch evaluation. With the single-flank pitch evaluation you will see more error in the tooth thickness as you go around the part if you have concentricity error in the part as the probe is not contacting where it should be. If you use the double-flank pitch evaluation, you typically don't have this problem as the probe self-centers between two teeth.

[[Mi...]]

I have some programs that only have one flank or the other that you can select and both Flanks tab is greyed out. Where is it that turns self centering off. I have used self centering before but they were all on the Feed In Tab.

Thanks

[[Ma...]]

Please sign in to view this quote.

Richard, I find your line of thinking interesting and worth further discussion. Tooth thickness and its various surrogates seem to be one of the most contentious and least understood areas of gear metrology and design despite it being so fundamental. The latest standard on the topic I am aware of is ANSI/AGMA 2002-D19. It contains a wealth of pertinent information. It does a very good job of explaining all the different representations of tooth thickness (chordal thickness, dimension over one or two balls, span etc.) and breaks them into two basic groups "nominal" and "functional" depending on if they are influenced by location of the teeth relative to the axis of the part or not.
Assuming the original poster meant Normal Circular Space Width, the individual measured values should by definition vary with the amount of runout in the part. A CMM with a small stylus in single flank contact is probably the most direct way to measure this. This would also be the most direct way to measure pitch fp and cumulative pitch Fp deviations. Radial runout Fr, and the other tooth thickness parameters can then be calculated from index measurements. Similarly, the two flank index test you recommend would be the most direct method to determine radial runout Fr and Dimension over a single ball, while the pitch and other tooth thickness parameters can be calculated from the results. If the physics and the math were all perfect either method would yield the exact same results. As most gears operate with only single flank contact, my tendency is to prefer single flank measurements. However, there is a considerable speed advantage to the 2-flank method you recommend but this may be diminished somewhat by the need to use a different stylus for helix and profile measurements.
End Rant. 😃

[[Ro...]]

Tooth thickness and runout are two completely different things. For example, the teeth can be ideal, with a deviation of zero, but their pitch to each other are nonuniform distributed around the gear. Now, when you insert the ball for the runout measurement, it has different distances to the axis because the gaps have different widths.The manufacturing method of the gear essentially determines how the individual defects on the real part are related to each other (eg. molding vs. hobbing).

[[Na...]]

Please sign in to view this quote.