Free 173 Best Homemade Tools eBook:  
Remove advertisements
Page 1 of 2 1 2 LastLast
Results 1 to 10 of 11

Thread: Centroid CNC12 Screw Mapping on a RF-30 Mill/Drill

  1. #1
    rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    437
    Thanks
    113
    Thanked 696 Times in 250 Posts

    rgsparber's Tools

    Centroid CNC12 Screw Mapping on a RF-30 Mill/Drill

    The intent of Screw Mapping is to take near perfect ball screws and make them even closer to perfect. What happens when Screw Mapping is applied to the lowly leadscrew on a RF30 Mill/Drill? Leadscrews are far from perfect yet do benefit. The advantages and limitations of trying to turn a sow's ear into a silk purse are presented.

    If you are interested, please see

    http://rick.sparber.org/CSMX.pdf


    Your comments are welcome. All of us are smarter than any one of us.


    Thanks,

    Rick
    Rick

  2. The Following 2 Users Say Thank You to rgsparber For This Useful Post:

    Seedtick (10-22-2017), tonyfoale (10-23-2017)

  3. #2
    [email protected] tonyfoale's Avatar
    Join Date
    Nov 2016
    Location
    Spain
    Posts
    502
    Thanks
    211
    Thanked 864 Times in 266 Posts

    tonyfoale's Tools
    Rick,
    That's very interesting.
    I note from the graph on p13 that if you remove the "random" errors there is a well defined increasing error which looks to be roughly linear at 3.5 thou/ft. That would seem to indicate a similar error in the machine used to cut your lead screw. If the screw was cut on a geared lathe that could be explained by either; the lead screw on that lathe was far from perfect or maybe it was of the wrong units (inch to metric or vice versa) and compound gearing was used in place of a 127 tooth gear. It might be interesting to compare the error that would occur with the commonly used compound ratios to the 3.5 thou/ft value.

    BTW I am thinking of getting an Acorn for a lathe conversion. Also the Oak appeals as a conversion for my mill which has servos and linear optical slides. I currently use a Galil card for control. It is a very capable controller but it confines me to using Mach3 which I hate with a vengence, despite its popularity.
    I'd fit ball screws and open loop steppers to the lathe and I'd follow your example and map those. The mill doesn't need the ball screws mapping but maybe I should map the slides?

  4. #3
    rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    437
    Thanks
    113
    Thanked 696 Times in 250 Posts

    rgsparber's Tools
    Quote Originally Posted by tonyfoale View Post
    Rick,
    That's very interesting.
    I note from the graph on p13 that if you remove the "random" errors there is a well defined increasing error which looks to be roughly linear at 3.5 thou/ft. That would seem to indicate a similar error in the machine used to cut your lead screw. If the screw was cut on a geared lathe that could be explained by either; the lead screw on that lathe was far from perfect or maybe it was of the wrong units (inch to metric or vice versa) and compound gearing was used in place of a 127 tooth gear. It might be interesting to compare the error that would occur with the commonly used compound ratios to the 3.5 thou/ft value.

    BTW I am thinking of getting an Acorn for a lathe conversion. Also the Oak appeals as a conversion for my mill which has servos and linear optical slides. I currently use a Galil card for control. It is a very capable controller but it confines me to using Mach3 which I hate with a vengence, despite its popularity.
    I'd fit ball screws and open loop steppers to the lathe and I'd follow your example and map those. The mill doesn't need the ball screws mapping but maybe I should map the slides?
    Tony,

    It never occurred to me to think about the source of the leadscrew's constant error. See the bottom of page 4 where my uncorrected leadscrews measured 20.02 rev/inch including my 2:1 gearbox. so just the leadscrew is 10.01 rev/inch or .39409 rev/mm. Multiply this by (13 + 0.0043)/13 for the residual error and I get 0.39436. A ratio of 101:256 yields 0.39453. So it is likely the constant error is due to re-gearing a metric lathe to cut imperial.

    When I used Mach3 for small jobs, it worked good enough as long as I avoided those functions that were not reliable. But my last project had a 12 hour run time and Mach3 went nuts near the end and ruined the part. My theory, therefore, is that people's satisfaction with Mach3 is a function of the complexity of their part. Mach3 is a very impressive hobby quality CNC program. Centroid's CNC12 is commercial grade and has run multi-million dollar machines for decades. It is not fair to compare the two.

    If you mapped the linear optical slides, it would certainly be interesting to see how they compare to gage blocks and a finger DTI.

    Rick
    Rick

  5. #4
    rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    437
    Thanks
    113
    Thanked 696 Times in 250 Posts

    rgsparber's Tools
    I have reworked this article with more measured data and more theory.

    Rick
    Rick

  6. The Following 2 Users Say Thank You to rgsparber For This Useful Post:

    Jon (11-21-2017), tonyfoale (11-21-2017)

  7. #5
    [email protected] tonyfoale's Avatar
    Join Date
    Nov 2016
    Location
    Spain
    Posts
    502
    Thanks
    211
    Thanked 864 Times in 266 Posts

    tonyfoale's Tools
    Quote Originally Posted by rgsparber View Post
    I have reworked this article with more measured data and more theory.
    great stuff, very interesting.

  8. #6
    rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    437
    Thanks
    113
    Thanked 696 Times in 250 Posts

    rgsparber's Tools
    Thanks Tony. You are looking at 8 weeks for work. I spent a lot of time stumbling around.
    Rick

  9. #7
    [email protected] tonyfoale's Avatar
    Join Date
    Nov 2016
    Location
    Spain
    Posts
    502
    Thanks
    211
    Thanked 864 Times in 266 Posts

    tonyfoale's Tools
    Quote Originally Posted by rgsparber View Post
    Thanks Tony. You are looking at 8 weeks for work. I spent a lot of time stumbling around.
    I am an inveterate tester and measurer so I understand only too well the effort that your work required.

  10. #8
    Responsible's Avatar
    Join Date
    Feb 2017
    Posts
    10
    Thanks
    0
    Thanked 7 Times in 4 Posts

    Responsible's Tools
    Hi Rick;

    That is interesting. I wonder if a quick note about cosine error with DTI's might be a good addition. It could be a problem with larger error measurements, or if someone doesn't carefully implement their DTI in the setup.

    Pete

  11. #9
    rgsparber's Avatar
    Join Date
    Nov 2012
    Location
    Phoenix, AZ
    Posts
    437
    Thanks
    113
    Thanked 696 Times in 250 Posts

    rgsparber's Tools
    If I understand you correctly, I only use the DTI to indicate 0 so there is no cosine error.
    Rick

  12. #10
    Responsible's Avatar
    Join Date
    Feb 2017
    Posts
    10
    Thanks
    0
    Thanked 7 Times in 4 Posts

    Responsible's Tools
    Ah Ok! I initially misunderstood the section I had read where I thought it might be a concern. My mistake, you're right, it should be no problem.

    Pete

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Tags for this Thread

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
  •