I have searched the forum extensively on this topic and found a lot of good information but I am still not completely satisfied.
I use TP20's with a wide variety of tip configurations at multiple index angles. I have gathered that different probe configurations may require different calibration parameter settings (i.e. Number of Hits, Touch Speed, Number of Levels, etc) in order to get the best calibration. I have been told this is especially true for miniature probe tips and tips on the long end of what a module is rated for.
The one piece of advice that I am struggling with the most is in regards to the Number of Hits to use. I have heard lots of opinions that span from 5-25 hits and from multiple sources that the number of hits needs to be odd. I have also heard that the number of hits needs to be prime. I can not rationalize why this matters and I have in fact only seen evidence to the contrary. I accept that there may not be a "good" answer to this but I was hoping someone out there may have some information that would give me the confidence to go one way or the other when deciding how many hits to use.
If anyone has any advice on how to pick the other parameters I would love to hear it as well.
The 'analytical' way to determine required number of points is to remeasure with more points, and as long as the form error increases you need even more points...
For example, if a circle is two-lobed (oval) you may completely miss the form deviation with four equidistant measuring points if you place them 'unlucky',
independent of the actual form error!
For a three-lobed circle (very common) you may completely miss the form deviation with six measuring points. With seven, you're mathematically guaranteed to find at least 79% of the actual form error (Assuming the surface is perfect, only error is form).
In a way, it's a pity that we have the autofeatures in PC-DMIS, as they always generate equidistant mp:s, while it is statistically better to divide the measured surface into equidistant areas and place an mp randomly inside each area.
The 'analytical' way to determine required number of points is to remeasure with more points, and as long as the form error increases you need even more points...
For example, if a circle is two-lobed (oval) you may completely miss the form deviation with four equidistant measuring points if you place them 'unlucky',
independent of the actual form error!
For a three-lobed circle (very common) you may completely miss the form deviation with six measuring points. With seven, you're mathematically guaranteed to find at least 79% of the actual form error (Assuming the surface is perfect, only error is form).
In a way, it's a pity that we have the autofeatures in PC-DMIS, as they always generate equidistant mp:s, while it is statistically better to divide the measured surface into equidistant areas and place an mp randomly inside each area.