Page 1 of 5 123 ... LastLast
Results 1 to 10 of 49

Thread: Question about Leveling to a Primary Datum -A-

  1. #1
    Member
    • Additional Information
      • Years CMM Experience:
      • 8
      • Software Version:
      • 3.7 MR2
      • Machine Type:
      • DEA Mistral
      • Location:
      • Vermont
      • Job Function:
      • Senior Metrologist

    Join Date
    Apr 2006
    Location
    Vermont
    Posts
    74

    Default Question about Leveling to a Primary Datum -A-

    Hello everyone...

    We are currently having a discussion about leveling to a primary plane, (Datum A). The discussion concern is whether we should be leveling to a "high point plane" or if we should be leveling to a "best-fit" plane using every point that is probed.

    I am currently probing a planar surface that is approximately 150mm diametrically in 3 seperate rings that are 5 degrees apart so there are a total of 216 points. I have an overall flatness of approximately 0.3mm with a total tolerance of 0.8mm.

    As I stated before the disussion is whether we should be finding the high points of the plane and then be leveling to that plane or not (high point plane). I guess my feeling is that you would not level to the high point plane but in certain applications you may want to set the "Z" origin to that plane.

    What are your most common approaches of leveling to the primary Datum plane? Thanks for your replies!

    Mike

  2. #2
    PC-DMIS Guru
    • Additional Information
      • Years CMM Experience:
      • Since 1981
      • Software Version:
      • v3.7
      • Machine Type:
      • B&S One
      • Location:
      • Central NC
      • Job Function:
      • CMM Software Programming & Training; Inspection Fixture Design & Build Measure Max programming and Training PCDMIS programming and Training CMM Automation. CMM Parametric programming. Programming for the shop floor is a specialty.
    cmmguy's Avatar
    Join Date
    Feb 2006
    Location
    Central NC
    Posts
    3,351

    Default

    The high point plane is not repeatable. just like the max insc or min circ. diameters.

    Also, it would be difficult to set origin on a plane without leveling to it first.

    I think by definition the plane should be the high point plane but it is very difficult to achieve on a CMM and much less repeat.

    Most commonly used is best-fit. If you guys think that "high-point" is required then a datum simulator is needed.
    Last edited by cmmguy; 01-08-2007 at 09:39 AM.

  3. #3
    has received PC-DMIS total consciousness
    • Additional Information
      • Years CMM Experience:
      • Since 1988
      • Software Version:
      • V3.7 MR3 (have V3.2063 to V2012)
      • Machine Type:
      • B&S Validator
      • Location:
      • He||
      • Job Function:
      • Inspector - Programmer - all around flunky
    Matthew D. Hoedeman's Avatar
    Join Date
    Feb 2006
    Location
    He||
    Posts
    11,169

    Default

    Well, if you level to the 'high-points' of the plane, then you have just cut your tolerance zone in half, if it is bi-lateral, you are forcing all the 'non-plane' points to one side of your origin. Bad.

    Quote Originally Posted by AndersI View Post
    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

  4. #4
    former user
    • Additional Information
      • Years CMM Experience:
      • 3.5
      • Software Version:
      • 3.7 MR3
      • Machine Type:
      • Brown & Sharpe Xcel 7107
      • Location:
      • Cognito
      • Job Function:
      • QA Calibration Technician

    Join Date
    May 2006
    Location
    Cognito
    Posts
    3,237

    Default

    It would certainly take an enourmous ammount of points to find the actual high points.

    I can see applications for both depending on the function of the part. I would say...

    I would think if datum targets are defined then use them. If no datum targets are specified, I would say average unless otherwise specified.

    I always do the average and have never had anyone ask about high points.

  5. #5
    Member
    • Additional Information
      • Years CMM Experience:
      • 8
      • Software Version:
      • 3.7 MR2
      • Machine Type:
      • DEA Mistral
      • Location:
      • Vermont
      • Job Function:
      • Senior Metrologist

    Join Date
    Apr 2006
    Location
    Vermont
    Posts
    74

    Default

    I couldn't agree more cmmguy... Any more thoughts. I need to gather as much information as possible so that I can provide facts and logic to this conversation because these guys are talking in a theoretical world where every point would be analyzed and all that conceptual stuff. I'm dealing with a plastic part that is 6 inches in diameter and do not have the luxury of analyzing every point on the part nor could I do that in the first place.

  6. #6
    Member
    • Additional Information
      • Years CMM Experience:
      • 8
      • Software Version:
      • 3.7 MR2
      • Machine Type:
      • DEA Mistral
      • Location:
      • Vermont
      • Job Function:
      • Senior Metrologist

    Join Date
    Apr 2006
    Location
    Vermont
    Posts
    74

    Default

    I think that so far all of us are on the same page here. The methods that you have mentioned are how I was "taught" orginally but my methods are being questioned so I need to explain why I do the things I do. Thanks a bunch for your replies I really appreciate it!!!

    Mike

  7. #7
    PC-DMIS Guru
    • Additional Information
      • Years CMM Experience:
      • Since 1981
      • Software Version:
      • v3.7
      • Machine Type:
      • B&S One
      • Location:
      • Central NC
      • Job Function:
      • CMM Software Programming & Training; Inspection Fixture Design & Build Measure Max programming and Training PCDMIS programming and Training CMM Automation. CMM Parametric programming. Programming for the shop floor is a specialty.
    cmmguy's Avatar
    Join Date
    Feb 2006
    Location
    Central NC
    Posts
    3,351

    Default

    Quote Originally Posted by Matthew D. Hoedeman View Post
    Well, if you level to the 'high-points' of the plane, then you have just cut your tolerance zone in half, if it is bi-lateral, you are forcing all the 'non-plane' points to one side of your origin. Bad.
    ???
    The y14 (pg60) definition of the datum plane is exactly that - to the high points. It is just too difficult to achieve on a CMM. How are you cutting your tolerance in half?

  8. #8

    Default

    What everyone else says -

    There's only one way to repeat the high point plane and that's if you use a fixture, probing the fixture to simulate the contact points which would be the highest points on the datum surface.

    If the surface stays within the form tolerance then it's probably good enough to level and assign as origin.
    PC-DMIS CAD++ 3.7 from 4.2 MR1

  9. #9
    has received PC-DMIS total consciousness
    • Additional Information
      • Years CMM Experience:
      • Since 1988
      • Software Version:
      • V3.7 MR3 (have V3.2063 to V2012)
      • Machine Type:
      • B&S Validator
      • Location:
      • He||
      • Job Function:
      • Inspector - Programmer - all around flunky
    Matthew D. Hoedeman's Avatar
    Join Date
    Feb 2006
    Location
    He||
    Posts
    11,169

    Default

    Quote Originally Posted by cmmguy View Post
    ???
    The y14 (pg60) definition of the datum plane is exactly that - to the high points. It is just too difficult to achieve on a CMM. How are you cutting your tolerance in half?
    Everything has a tolerance. Everything. In sheet metal (and plastic too, I would imagine) every surface has a tolerance. I would imagine his print calls out a tolerance for that surface, either flatness or position or both. Now, do you want to shoot yourself in the foot by turning your 1mm tolerance band into 0.5 by choosing the highest points of the surface? If the surface is allowed (toleranced) to move 0.5mm in each direction, shouldn't you use the average plane to place both + and - points on the plane?

    Quote Originally Posted by AndersI View Post
    I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

  10. #10
    PC-DMIS Guru
    • Additional Information
      • Years CMM Experience:
      • Since 1981
      • Software Version:
      • v3.7
      • Machine Type:
      • B&S One
      • Location:
      • Central NC
      • Job Function:
      • CMM Software Programming & Training; Inspection Fixture Design & Build Measure Max programming and Training PCDMIS programming and Training CMM Automation. CMM Parametric programming. Programming for the shop floor is a specialty.
    cmmguy's Avatar
    Join Date
    Feb 2006
    Location
    Central NC
    Posts
    3,351

    Default

    Quote Originally Posted by Matthew D. Hoedeman View Post
    Everything has a tolerance. Everything. In sheet metal (and plastic too, I would imagine) every surface has a tolerance. I would imagine his print calls out a tolerance for that surface, either flatness or position or both. Now, do you want to shoot yourself in the foot by turning your 1mm tolerance band into 0.5 by choosing the highest points of the surface? If the surface is allowed (toleranced) to move 0.5mm in each direction, shouldn't you use the average plane to place both + and - points on the plane?
    Flatness is a moving band - so that doesnt apply
    Dont think position would apply either since it is the primary datum. Why would you apply anything beyond flatness to a primary datum anyway?

    So I still dont see where you are robbing yourself of any tolerance - sheetmetal, plastic, or machined parts.

Similar Threads

  1. Slot as Primary datum
    By dwade in forum PC-DMIS for CMMs
    Replies: 1
    Last Post: 09-12-2007, 11:47 AM
  2. Another Datum Question
    By RussL in forum PC-DMIS for CMMs
    Replies: 5
    Last Post: 03-13-2007, 01:53 PM
  3. Datum Question
    By RussL in forum PC-DMIS for CMMs
    Replies: 5
    Last Post: 03-13-2007, 10:01 AM
  4. Leveling 2 planes
    By cmmmike in forum PC-DMIS for CMMs
    Replies: 2
    Last Post: 08-15-2006, 07:59 AM
  5. Leveling a cylinder
    By RICHIE RICH in forum PC-DMIS for CMMs
    Replies: 19
    Last Post: 06-14-2006, 09:20 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •