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Questions about DCC accuracy after initial manual alignment setup.

Hello everyone!

So, I've been lurking for some time on these forums, and finally feel I am experienced enough to post. I'm relatively new to programming and using our CMM in day-to-day use, but I've been familiar with them since about 2012. I work in aerospace, and work is getting to the point where I need to have more output from our CMM (I work in a small shop and am the only QC person here). I've been told by QC guys that I know from a few local businesses that it is NOT acceptable to use DCC to inspect parts after a Manual alignment is ran. Basically, I have a small fixture where the X and Y of the part does not move much if at all. I run the manual alignment on the first part for the day/ if I am just setting this part number up, let the program run the DCC and then the rest of the program. After I get the results, I record/save the .PDF file for our records, and then I clear execution list, slap another part on the table and bolt it down, and run the program from where the DCC starts. Essentially, the QC guys I know say that the repeatability on this is atrocious, and not good calibration practices. I've been doing some snooping around on this forum and it seems that quite a few experienced users here think the opposite: that as long as the fixture is good and your probes are calibrated after every change that things should be smooth sailing. I keep my touch and move speeds the same as cal too. I'm super new to all of this, and I'm not *exactly* sure about all the values either, and even though I've looked through this forum, don't really know the difference between LF/SF/MF/EF type probes or the differences between touch speed and all that. I try to read up on as much of this stuff as I can, but changing some of those small parameters doesn't seem to change much...but then again I'm a rookie here, so I probably wouldn't know the difference. If anyone could point me towards a guide where it might help me understand the small nuances it would be greatly appreciated. This is especially important because we have many parts that have Total Positioning tolerances of as tight as .010, so repeatability is my biggest concern. (well, that and getting off as many parts as humanely possible from our CMM)

Also, I looked around for an answer for this next question...but how do I change parameters for to automatically calibrate a single tip in the program? I finally figured out how to change probe tips in a program, the user has to manually change it (we don't have an auto changer), and then the program can calibrate the newly inserted tip. It took me FOREVER to figure out that I had to draw the sphere because info was kinda scarce/confusing. When I insert the Calibrate Single tip command, it works great..but how do I change the settings for the auto-cal? Changing any values in the very first probe loadout in the program does nothing to change the values for the auto-cal. The auto-cal always takes 13 hits from my sphere, and then stops without going up which I find odd. I just add in +6 inches for an incremental move after that just to be on the safe side.

Thank you for any information that y'all can provide. This place is awesome, thanks for having me!

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  • Repeat what was done with the manual alignment in DCC, and you have essentially left the manual alignment behind and moved on under DCC.

    By the sound of it, you'd be good to locate the part the same every time with mounting/work instructions. Then you can run 100% DCC.

    Also, research READPOINT alignments.

  • If you record the location and set up the same next time, you don't need a manual alignment at all. You can start the probe in the air over the part and drop right into the alignment features. Part has to be where the program says its going to be. This is easiest to do using some manual programming at the machine. A readpoint alignment is the best of both worlds and can be programmed completely offline. It can run 100% DCC after manually moving the probe into the starting spot, 'the readpoint'. So with a readpoint alignment, you can mount it anywhere, as long as the volume of the program movement doesn't go outside the measuring envelope of the CMM.
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  • If you record the location and set up the same next time, you don't need a manual alignment at all. You can start the probe in the air over the part and drop right into the alignment features. Part has to be where the program says its going to be. This is easiest to do using some manual programming at the machine. A readpoint alignment is the best of both worlds and can be programmed completely offline. It can run 100% DCC after manually moving the probe into the starting spot, 'the readpoint'. So with a readpoint alignment, you can mount it anywhere, as long as the volume of the program movement doesn't go outside the measuring envelope of the CMM.
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