David A's New 2x3 Bench Top CNC - Page 29


Page 29 of 35 FirstFirst ... 1926272829303132 ... LastLast
Results 337 to 348 of 414

Thread: David A's New 2x3 Bench Top CNC

  1. #337
    Member
    Join Date
    Oct 2004
    Location
    USA
    Posts
    44
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by davida1234 View Post
    Thank you Outlawtaz.

    The short answer would be that I just was curious.
    I don't know if there are any benefits or drawbacks.


    Following are my personal thoughts and relates only
    to the lower-cost equipment we generally use here:

    Option #1:
    If you put a servo on a CNCRP drive, you get additional
    speed or, with lower gearing, torque. All happening at the
    pulley side.

    The final gear side, pinion with pressure spring on the rack,
    stays the same. Some noise, wear and minute cogging.
    Protruding servos. Weight of servos on carriage.

    Option #2:
    A direct rack drive with a gear box and pinion is expensive
    for a good gear box. Can select appropriate speed/torque
    combination. Requires perfect gear mesh or pressure. Some
    noise, wear and minute cogging. Protruding servos.
    Weight of servos on carriage.

    Option #3:
    With traditional ball nut and screw application, everything is
    happening at the nut/screw side. With xx05 nuts, you get
    more torque, with xx10 nuts, you get speed. Just two fixed
    ratios. Less noise, wear and almost no cogging. Speed limit
    due to whipping and/or larger screw inertia. Possible
    backlash in coupling. Protruding servos.

    Option #4:
    With a powered ball nut, everything is happening at the
    nut/screw side as well, not the pulley. Less noise, wear and
    almost no cogging. With xx05 nuts, you get more torque, with
    xx10 nuts, you get speed. Limited speed/torque combinations.
    Less inertia than #3. No whipping but possible harmonics noise.
    Weight of servos on carriage.

    From all four options, #4 seemed the least explored to me. I
    prefer ball nuts over rack drive, so I wanted to see what's possible
    in that setup.
    .
    #4, servos and xx05 screws may give better speed than xx10 screws with steppers.



  2. #338
    Member
    Join Date
    Oct 2009
    Location
    United States
    Posts
    282
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    That's what I have here, numbers are slightly
    better for servos and can go even higher.

    1204's (not xx05) with servos give about 450 ipm @ 3,000 rpm

    1610's with steppers give about 400 ipm @ 1,000 rpm.



  3. #339
    Member
    Join Date
    Oct 2009
    Location
    United States
    Posts
    282
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    .
    Before I do the final install of power ball nuts
    and drive line, I am going to tram the Z-axis.

    All Z ball bushings freshly greased, Z-slide
    balanced by the springs. Just having some fun:





  4. #340
    Member
    Join Date
    May 2018
    Location
    United States
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Hey David,

    Thanks for the reply and thanks for sharing the knowledge. I think it's great that you are taking the road less traveled. I will definitely have to go back and reread all your posts in detail.

    Another question: how many hours would you expect the belts to hold repeatability/tolerance before stretching and having to be adjusted?

    I've always wondered this, not necessarily for your design specifically, but for all machines that use a belt drive system. The machines I worked on as a tech used belt drives on alot of the rotary axes and I had to adjust them a couple times a year to ensure repeatability. Granted, that was production runs but I've always been curious if it smaller machines / smaller belts would degrade at about the same rate.

    Thanks again and good luck on the test runs!!



  5. #341
    Member
    Join Date
    Oct 2009
    Location
    United States
    Posts
    282
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Hey Outlawtaz, thank you.

    I do not know enough about belts to give you an educated answer.
    However, I did talk to an engineer with the Belt Corporation of America some
    time ego and he told me that most belts have the majority of stretch within the
    first 10 hours of use. Then it tapers down and stretches little for a long time
    until material degradation starts and then it picks up again until the belt breaks.

    One of the main reasons I wanted to explore the power nut system is that I think that it is
    much less effected by belt stretching and belt backlash than other conventional systems.

    Let me give you an example:

    I am going to compare a standard pinion/rack drive system which most people
    use here and which is basically an industry standard. All numbers are rounded.

    Let's say there is a 0.01" of belt 'looseness' in the rack and pinion drive.
    The big pulley (60T) has a pitch diameter of 2.256" which equates to a circumference of 7.1".

    0.01" relative to 7.1" would be a 0.00141 ratio (0.01 ÷ 7.1).

    So, 0.01" of belt backlash produces a backlash at the big pulley at a factor of 0.00141 of circumference.

    The pressed-in steel pinion has a pitch diameter of 1" which equates to a 3.142" circumference.

    3.142" circumference at a factor of 0.00141 equals to a backlash of 0.0044" at the rack.


    Let's say there is a 0.01" of belt 'looseness' in the power nut drive.
    The nut pulley (40T) has a pitch diameter of 1.5" which equates to a circumference of 4.7".

    0.01" relative to 4.7" would be a 0.002 ratio (0.01 ÷ 4.7).

    So, 0.01" of belt backlash produces a backlash at the nut pulley at a factor of 0.002 of nut lead.

    The 1204 ball nut has a 4mm lead which equates to 0.158".

    0.158" of lead at a factor of 0.002 equals to a backlash of 0.0003" at the screw.


    I just hope I am not wrong with my math and, if I am not, a rack and pinion drive seems to have
    at least ten times more backlash than a power nut drive for a given belt looseness.

    Another possible advantage would be the pulley ratio. A 1:3 reduction (20T to 60T) means that
    the small stepper pulley just provides the necessary minimum amount of tooth engagement and
    the belt has to be fairly tout to avoid belt jumping.

    For the power nut, there really is no need for a gearing (38T to 40T) and the belt can be run
    looser to minimize friction and wear without belt jumping.

    Somehow, your questions always seem to require elaborate and lengthy answers.

    Last edited by davida1234; 03-14-2019 at 08:02 PM.


  6. #342
    Member
    Join Date
    May 2018
    Location
    United States
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Quote Originally Posted by davida1234 View Post

    Somehow, your questions always seem to require elaborate and lengthy answers.
    Yea, I'm pretty good at asking questions like that... I spent close to 10 years working in Quality Assurance/Control.

    As for your math, I went over it a few times my head and it appears sound. Of course, unless I had an example of each sitting on the test bench in front of me, I wouldn't be 100% sure.

    The reason I asked is because thinking back, the backlash was paradoxical on the machines I worked on. The rotary axes all used a belt driven worm gear and planetary setup. Interestingly, the smaller the overall rotary, the more belt stretch and adjustments that had to be done to the belt. Conversely, the bigger and heavier the rotary axes, the more I had to play with the adjustments in the physical gear meshing. Unfortunately, I really have no idea where the forces amounts would be at the break even point (meaning equal adjustment on the gears and the belt).

    Then again, I'm not even sure my observations are even germane to your machine... I just drive alot for my job and so I sit there and ponder stuff that I find interesting...



  7. #343
    Member
    Join Date
    Oct 2009
    Location
    United States
    Posts
    282
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Hah, bored you are. Keep coming with your QA/QC questions. They are all somewhat germane.



  8. #344
    Member
    Join Date
    Oct 2004
    Location
    USA
    Posts
    44
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by davida1234 View Post
    Hah, bored you are. Keep coming with your QA/QC questions. They are all somewhat germane.
    I don't know what the Germans have to do with this.



  9. #345
    Member
    Join Date
    Jan 2005
    Location
    USA
    Posts
    9306
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Quote Originally Posted by Arjay View Post
    I don't know what the Germans have to do with this.
    That's not what the word means

    Mactec54


  10. #346
    Member
    Join Date
    May 2018
    Location
    United States
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    Quote Originally Posted by Arjay View Post
    I don't know what the Germans have to do with this.




  11. #347
    Member Ntl's Avatar
    Join Date
    Aug 2018
    Posts
    383
    Downloads
    0
    Uploads
    0

    Wink Re: David A's New 2x3 Bench Top CNC

    Quote Originally Posted by Arjay View Post
    I don't know what the Germans have to do with this.
    Funny guy gotta love those $2 words.



  12. #348
    Member
    Join Date
    Oct 2009
    Location
    United States
    Posts
    282
    Downloads
    0
    Uploads
    0

    Default Re: David A's New 2x3 Bench Top CNC

    I am sure the method shown here is old news for many
    members. Please let me know if there are better ones.

    TRAMMING:

    Holes for linear trucks are slightly elongated on
    upper and lower plates of X-carriage for tramming:
    David A's New 2x3 Bench Top CNC-1-img_7366-jpg

    David A's New 2x3 Bench Top CNC-2-img_6710-jpg



Page 29 of 35 FirstFirst ... 1926272829303132 ... LastLast

Tags for this Thread

Posting Permissions

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


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

David A's New 2x3 Bench Top CNC

David A's New 2x3 Bench Top CNC