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Need help stylii & speed selection, prehit/ retract & probe modules selection.

Hello everyone again!
This community is so awesome, I just wanna say thank you everyone. :-) I've already had so many questions answered by y'all just from reading here and learning. So, over the weekend, after taking y'alls advice and retweaking even more of my program, I ran into a little bit of a snafu. Basically, what happened is that some parts that were consistently checking good all of a sudden started checking bad. I traced the problem down to a portion of the program where I had re-tooled it to use a different size probe to take points on a smaller hole. (I went from probing the hole with a 1mm to a 4mm ruby) . The hole sizes are .290 inches and .286. I am also using the 1mm ruby to measure a hole that is .100 inches in diameter. The .100 inch hole has always measured really well on this part, even though the 1mm ruby barely fits in the hole. I only have 2 probe modules right now (we are currently in the process of buying more modules and looking at a tool changer). I have an SF probe module and an MF probe module. The 1mm ruby is in the green/MF module, and the 4 mm ruby is in the yellow/SF module. I am fairly confused here too. I thought that since the 4mm ruby was in the Standard force module, that it would actually be more sensitive in this case than the 1mm ruby because the 1mm ruby was in the MF module...??? Also, the data when using the 4mm ruby is so bad, it scared everyone in production. Some of the values were 6 or 7 thousandths off, but whenever we checked it with the 1mm ruby that error went down to the tenths, like .0002 off and such. I just don't understand, because I thought that CMM operators generally tried to use the biggest ruby within reason to cut down on time wasted (the ruby having to travel a big distance). I was having trouble with the 1mm ruby when I had the touch speed jacked up to 3mm/sec in the small .100 holes. When I changed that touch speed to 1mm/sec, the ghost and double hits in the hole went away. Which really confused me because you think I would have many, many more problems with the 1mm probe exploring a .100 hole. Nope! For some reason the 4mm ruby just does not like the .286 holes.

In general, I just need more experience with the ins and outs of CMM operation. I just really don't have enough experience here and am humbly asking anybody for more information for all these nuances/ if any of y'all have a really down and dirty guide for the behind-the-scenes data that doesn't seem to be talked about very much. i don't really understand the difference between the probe modules either (LF/SF/MF/, and EF). I don't really understand the relationships between accuracy and prehit distance and retraction either. I get that the slower the touch speed is the more inherent accuracy the operator will get. I'm just really stumped by the 1mm ruby outperforming the 4mm one. Especially since I was told from the beginning that the smaller probes can be finicky and unreliable, yet in this instance it is quite the opposite, and the smaller probes have been great. Selecting the right stylii and all the little accessories was not something that was explained to me very well. We used generic stuff at the Hexagon training labs, and it seems that every QC lab I've toured just has their own preferences, and when I've queried about different stuff in their operations, they just respond "it's what works/what we do and we just haven't changed it). I've found that a lot of the settings/preferences/data seems many times to be set by someone before the current operator/they just use what they always do and don't have an explanation.
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  • Make sure your touch speed is the same in your program as it is in your calibration for each probe. You can also experiment with different touch speeds for each probe to see which one gives the best stddev. You might notice you're not gaining much by setting the touch speed that low.
  • I typically use 2mm/sec for my 1mm probes, but they are only 20mm long. 1mm/sec might be good for yours since its twice the length, but like I said that's something you will need to experiment with. I've never gone below 1mm/sec even with my 0.3mm probe, at that point it's more important to use the correct module (low force).
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  • I typically use 2mm/sec for my 1mm probes, but they are only 20mm long. 1mm/sec might be good for yours since its twice the length, but like I said that's something you will need to experiment with. I've never gone below 1mm/sec even with my 0.3mm probe, at that point it's more important to use the correct module (low force).
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