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Renishaw SP25

Big John
Hello,
At the moment we have a couple of CMM's with Renishaw PH10M heads and either a TP20 or a TP200 module.
We are thinking about buying a new CMM. We are planning to scan some products.
Hexagon recommended their own rotating head type HP-L. This looks quite fancy, except that I have heard that for calibration it needs 25 hits for each angle being used. If that is so, then we will lose plenty of time calibrating instead of measuring. At the moment we calibrate using 5 hits on the calibration sphere. (Minimal I know, but it seems to work for us)
The difference is 5 times longer!!

I have 3 questions:

Is the 25 hits correct?

If we were to buy a Renishaw SP25 how many calibration hits are needed on the sphere? I asked Renishaw, they replied that it is up to the software.

Concerning the HP-L or the SP25

Is it not possible to calibrate the first position with 25 hits, then the other angles scan the sphere?

Regards
John
  • Yes 25 is correct.

    The SP25 takes less hits, but then does a series of scans around and over the sphere, which takes much longer than the Hexagon offering.


    Obviously what you loose in calibration you would typically make up more than in use, scanning diameters and surfaces rather than taking touch hits.
  • If you are scanning then you do need to take 25 hits over at least 3 levels and perform a scnrdv calibration as well (scans once around the equator of the sphere). However, if you only want to take discreet hits and use it like a touch trigger probe then you only need 15 hits, again spread over 3 levels. is correct about the SP25. It takes an initial 5 hits on the sphere an then (from memory) does at least 8 scans in multiple positons & directions around the sphere taking around 2.5 to 3 minutes per tip angle which is considerably slower than the LSPX1 (HP-S-X1) - even if it's taking 25 hits.
  • in reply to Neil Challinor
    Another thing to take into consideration when comparing the SP25 to an LSPX1-H is that the LSPX1-H can handle styli up to 240mm long and, for star probes, up to 100mm horizontal. To achieve the same range with an SP25, you would need SP25-1 (20mm - 50mm), SP25-2 (50mm - 105mm) & SP25-3 (120mm - 200mm) modules.
  • Hello Ninja Badger and Neil,

    Thank you both for your reactions.
    From your answers I would say that the HP_L was the better choice.

    John
  • in reply to Big John
    Another consideration with the SP-25M, which we use, is that depending on the release version of PC-DMIS you use, the later versions have a tick box option to use partial scan only. That being said, once an initial calibration for a new tip has been completed you can check that box and a calibration will be completed with only 5 touch hits on the sphere. The software stores and remembers the scan data and ties it to the touch hit data during calibration For us, once I upgraded from V4.2 to 2009, I was able to reduce our calibration time from 6.5 hours to 1.5 for our rack of probe tips. Hope this information helps.
  • in reply to Big John
    It is true, you can use the reduced calibration method that only takes 5 points but this only updates the calibration values for touch trigger probing. If you are performing any type of scanning operation within your programs you need to do the longer calibration or the scanning parameters will not get updated.
  • in reply to Neil Challinor

    I guess it's time for me to wake a zombie thread... (but hey, I searched the forum!) (sorry, no actual advanced search options exist here)

    We are in the process of coming back online with our machine, which uses a SP-25...
    Managment has asked some questions about our calibration process, since we have a "new and different" machine now. Rather than move forward with the default "that's how it's always been done" answer I shall humble myself here on these great forums and hopefully get something more in depth to report. 

    Seems that the response above is what I was looking for, but just to be clear... (assuming after round 1 new probe calibration has been performed)

    To use the system with the best accuracy for scanning features, you must run the default calibration of 5 TTP hits and 8 or so scans per tip angle. 
    To use the system with the best accuracy for TTP measurements, running a "patrial calibration" that skips the scans and uses 13-25 TTP hits per tip angle will be best. 
    And these two forms of "calibration" only ever add to each other, not cancel each other out by choosing the wrong option? 

    99.9999999995% of our programs are TTP only so they understandably care most about that function of the machine. 

  •  5 hits?  Is that top center and 4 hits around?

  • in reply to RobOntario

    Pretty much, it finds the sphere and starts scanning. 

  • Why are you so concerned with calibrating tips, instead of the bigger question of whether or not you have a BUSINESS NEED for a more expensive higher accuracy tool?

    You can always change your probe calibration frequency. 

    We calibrate our tips arbitrarily once a month, unless someone breaks a probe or crashes a machine which is super rare (<15/year with 4 machines running 24/7).  If we wanted to, we could study probe accuracy and justify a longer probe calibration interval.  Most organizations and regulatory agencies we operate within allow justified extension of calibration intervals, so stop shooting yourself in the foot over the probe calibration stuff and make a Big Boy decision, Big John :D

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