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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Kelly's Machine Tool Warehouse - MD001
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  1. #1
    Join Date
    Mar 2011
    Posts
    525

    Kelly's Machine Tool Warehouse - MD001

    OK guys here we go.

    The MD001 should arrive in a few days and I need to start thinking about the servo's drives. I have been really pleased with the DMM Tech AC servo's and I would like to go with them again.

    The motors are rated at 3000 RPM and I would like to go with a 2 to 1 gear ratio on the X and Y and maybe 3 or 4 to 1 on the Z if it is needed.

    Ball Screws would be from Linearmotinbearings on eBay.
    items in linearmotionbearings store on eBay!
    RM1605 (16mm) on X and Y
    RM2005 (20mm) on the Z
    Lead = 5... I assume that is 5mm or .20" per revolution?

    Please correct my math if it is wrong.

    I am thinking of using:

    400W AC brushless servo motor (60EM-DHT-36)
    Max 3000rpm
    Rated torque: 1.27Nm(179 oz-in)
    Peak torque: 3.6 Nm(507.6 oz-in)
    Motor

    At a 2:1 belt reduction that = 358 oz-in Rated and 1015 oz-in Peak at 1500 RPM. 1500 RPM x .20" = 300ipm

    OR

    Direct drive
    900 Watt brushless AC Servo motor, NEMA34
    Max:1080 rpm
    Rated torque: 2.9 Nm(409 Oz-in)
    Peak torque: 7.2Nm(1015 Oz-in)

    1000 rpm x .20" = 200ipm

    What do you think?

    Edit:
    My current machine uses the 300 watt motors at a 2:1 reduction. I can get up to 188ipm in rapids and that is plenty for me and I think it would be fine for the larger table of the MD001.
    Kelly
    www.finescale360.com

  2. #2
    Join Date
    Mar 2011
    Posts
    525
    From the IH web site:

    Our Turnkey 3 axis CNC Mill uses 410 in/oz peak motors on the X and Y axis.
    The drive ratio is 4:1. So the ballscrew sees 1640 in/oz of torque.
    Our math: 410 in/oz x 4 = 1640 in/oz

    The Z-Axis uses a 648 in/oz x 4 = 2592 in/oz


    So the 507 in-oz motors from DMM at a 3:1 ratio would give me 1521 in-oz.
    With a 5mm (.20") lead screw that equals 3000 rpm / 3 = 1000 rpm.

    1000 rpm x .20 = 200ipm rapids.
    Kelly
    www.finescale360.com

  3. #3
    Join Date
    Mar 2009
    Posts
    1114
    It's been discussed and argued about a million times on this forum, but me personally, I'd prefer a slower machine that is reliable, rather than a really fast machine that faults all the time.

    I'd take torque over speed any day.

    Your math seems right though.

  4. #4
    Join Date
    May 2005
    Posts
    1662
    Lead = 5... I assume that is 5mm or .20" per revolution?
    5mm or roughly 5.08 rev/inch if setting up in standard measure. Always willing to tackle the easy questions LOL.

    I have the same machine and may take it cnc someday. Best of luck.
    Anyone who says "It only goes together one way" has no imagination.

  5. #5
    Join Date
    Mar 2011
    Posts
    525
    To clarify the motor I listed from DMM is the most powerfull they list. So while I am not looking for 200ipm rapids it looks like with the math I did I have some overhead in case I need to go to 3.5:1 or 4:1 to get the torque I need.

    If they had 800 in-oz I would just get those and not sweat it!
    Kelly
    www.finescale360.com

  6. #6
    Join Date
    Jun 2005
    Posts
    53
    Ive got the 300w dmms and my friend has the bigger ones with internal gearing. He is really happy with them. So powerful he said he bent his router a bit with them haha.

    I was at hui's house last weekend picking up some extra lmit switches and called him with questions a few times and he has always helped.

    I used to have an md001 and I would just run the nema 34 1000w motors direct drive. That would be a nice simple setup.

  7. #7
    Join Date
    Sep 2006
    Posts
    509
    To give you an idea of the minimum required to make the MD001 move, I used (and still am using) the 50oz-in continuous rated Nema 23 servos (350oz-in peak) on the X and Y axis with 4:1 reduction (ie 200 oz-in at the screw neglecting friction loss) and 5mm lead ballscrews form linearmotionbearing2000 on ebay. For the Z axis I started out with the same nema 23 servo and a 5:1 reduction (ie 250 oz-in at the screw). I was able to run it this way for a while but I had to have the acceleration dialed back on the Z, mostly due to tight spots at the top and bottom of the travel. I've since changed to a 119 oz-in (600oz-in peak) and I gained a little bit of acceleration.

    Personally the 400w servos are what I'd choose, unless going with direct drive and larger servos can save enough money to pay for themselves (1 belt and 2 pulleys per axis plus additional brackets versus a coupler for direct drive). Looks like the encoder is suitable for direct drive (12 bit accuracy ~ 4000 counts/rev @ .2" rev = 0.00005" )
    Checking out the pricing it looks like it can - the high torque servo & drives are only $48 more than the 400w servos & drives.

    Mike

  8. #8
    Join Date
    Mar 2011
    Posts
    525
    Mike,
    I have been following your conversion. Great job!!!

    I have been talking with Mr. Li at DMM and he also agrees that the 400 watt system will work on all 3 axis.

    I like the versatility of the belt drive and would rather spend the extra time building it then being locked into the direct drive. The numbers shake out the same anyway.

    I plan on ordering them soon.



    Quote Originally Posted by ninefinger View Post
    To give you an idea of the minimum required to make the MD001 move, I used (and still am using) the 50oz-in continuous rated Nema 23 servos (350oz-in peak) on the X and Y axis with 4:1 reduction (ie 200 oz-in at the screw neglecting friction loss) and 5mm lead ballscrews form linearmotionbearing2000 on ebay. For the Z axis I started out with the same nema 23 servo and a 5:1 reduction (ie 250 oz-in at the screw). I was able to run it this way for a while but I had to have the acceleration dialed back on the Z, mostly due to tight spots at the top and bottom of the travel. I've since changed to a 119 oz-in (600oz-in peak) and I gained a little bit of acceleration.

    Personally the 400w servos are what I'd choose, unless going with direct drive and larger servos can save enough money to pay for themselves (1 belt and 2 pulleys per axis plus additional brackets versus a coupler for direct drive). Looks like the encoder is suitable for direct drive (12 bit accuracy ~ 4000 counts/rev @ .2" rev = 0.00005" )
    Checking out the pricing it looks like it can - the high torque servo & drives are only $48 more than the 400w servos & drives.

    Mike
    Kelly
    www.finescale360.com

  9. #9
    Join Date
    Sep 2006
    Posts
    509

    Kit or just the drives?

    I never noticed on your last build if you used his complete kit or just the servos and drives. Are you planning on the complete kit this time or just the drives and servos? I'm just curious about the rest of the parts. I recently ordered some proximity switches from them but have yet to hook them up. They seem quite nice for the price though - hard to beat $10 each for a prox switch.

    Looking forward to your build - should be a whole lot easier with your cnc already.

    BTW - if your planning on ordering from Linearmotionbearing on ebay - my experience (and a few others) has been that the ballscrews are great (and get the ends machined or at least the drive end) but make your own end supports / bearing blocks - theirs have too many issues to be worth the price.

    Mike

  10. #10
    Join Date
    Mar 2011
    Posts
    525
    I used the full kit on my first build and will do so again on this one. I was so new to CNC I thought it would make life easier since it comes with power supplies, and tune up software. The software is used to tune the individual drives and test the motors etc. via comm port. Very handy to have.

    I also used the Liniarmotionbearing ball screws on my first build but I made my own bearing mounts and brackets.


    Quote Originally Posted by ninefinger View Post
    I never noticed on your last build if you used his complete kit or just the servos and drives. Are you planning on the complete kit this time or just the drives and servos? I'm just curious about the rest of the parts. I recently ordered some proximity switches from them but have yet to hook them up. They seem quite nice for the price though - hard to beat $10 each for a prox switch.

    Looking forward to your build - should be a whole lot easier with your cnc already.

    BTW - if your planning on ordering from Linearmotionbearing on ebay - my experience (and a few others) has been that the ballscrews are great (and get the ends machined or at least the drive end) but make your own end supports / bearing blocks - theirs have too many issues to be worth the price.

    Mike
    Kelly
    www.finescale360.com

  11. #11
    Join Date
    Oct 2010
    Posts
    448
    Quote Originally Posted by kregan View Post
    From the IH web site:

    Our Turnkey 3 axis CNC Mill uses 410 in/oz peak motors on the X and Y axis.
    The drive ratio is 4:1. So the ballscrew sees 1640 in/oz of torque.
    Our math: 410 in/oz x 4 = 1640 in/oz

    The Z-Axis uses a 648 in/oz x 4 = 2592 in/oz


    So the 507 in-oz motors from DMM at a 3:1 ratio would give me 1521 in-oz.
    With a 5mm (.20") lead screw that equals 3000 rpm / 3 = 1000 rpm.

    1000 rpm x .20 = 200ipm rapids.
    Using the theoretical values is not considered good engineering practice, practical values are 0.92 of the theoretical value and is the preferred value that should be used when calculating power.

    Also, the 5mm metric screws only have 0.196in lead, not 0.200in lead, a common mistake made by many it seems.


    If you want a 0.200in lead screw then I recommend you buy an appropriate screw.

  12. #12
    Join Date
    Mar 2011
    Posts
    525
    Very interesting... My current machine uses the 300 watt motors rated at 3000RPM and the same 5mm ball screw lead.

    Max rapids are 187

    200 IPM x.92 = 184


    Quote Originally Posted by dwalsh62 View Post
    Using the theoretical values is not considered good engineering practice, practical values are 0.92 of the theoretical value and is the preferred value that should be used when calculating power.

    Also, the 5mm metric screws only have 0.196in lead, not 0.200in lead, a common mistake made by many it seems.


    If you want a 0.200in lead screw then I recommend you buy an appropriate screw.
    Kelly
    www.finescale360.com

  13. #13
    Join Date
    Oct 2010
    Posts
    448
    Quote Originally Posted by kregan View Post
    Very interesting... My current machine uses the 300 watt motors rated at 3000RPM and the same 5mm ball screw lead.

    Max rapids are 187

    200 IPM x.92 = 184
    That is all wrong if you calculated 200IPM for a 5mm lead screw and used 0.200in as the lead value.

    If you calculated anything based on 0.200in lead when using a 5mm lead screw your values will be incorrect, a metric screw with a 5mm lead is 0.196in.

    You might wonder "Why is a Theoretical Factor (TF) used"?

    If you build 5 machines using the same identical parts and then measured IPM and Torque you would find they are all different but should never fall below the advertised values which is calculated based on the Theoretical Factor (TF).

    The standard design TF is 0.92% however some manufacturers use a lower value like 0.75% to de-rate the specifications to increase MTBF if the end user never pushes the product beyond the advertised specifications.

    If you want to know what your motor torque requirement is you estimate your required torque then calculate it with the following (assuming a reduction of 3:1).
    Design Torque Calculation: (Estimated Required Torque / TF) / Ratio
    1100 / 0.92 / 3 = 398.5507oz/in

    Some more calculations, let's start with a 400oz/in motor and a 3:1 reduction ratio.

    Advertised Torque Calculation: (Torque x Ratio) x TF
    (400 x 3) x 0.92 = 1104oz/in.
    If you get a higher (measured) torque value them your $hit is better quality but worst case scenario will be this value which would be the manufacturers advertised torque specification.

    Advertised IPM Calculation: ((RPM / Ratio) x Distance) x TF
    ((3000 / 3) x 0.196) x 0.92 = 180.23.
    If you get a higher (measured) IPM them your $hit is better quality but worst case scenario will be this value which would be the manufacturers advertised IPM specification.

    If you only get a max feed rate of 187 using a 3000RPM motor and a 3:1 reduction ration, you are above the theoretical feed rate 180 (always round values down) then I would say your machine is working optimally.

    If you want to guarantee a 200IPM feed rate then design for (200 / 0.92 =) 217.3913 (or higher)

  14. #14
    Join Date
    Mar 2011
    Posts
    525
    The machine was delayed and should arrive in a few days.

    DMM has quoted $1100.00 for 3 axis drives, motors, power supplies, cables, estop, limit switches shipped. I will order that soon.

    I will use LMB ball screws and order those after I draw up the mounting system.

    I am going to use a Fabco 4 stage ait cylinder for a power draw bar but need to figure out the right one. I also need to choose a VFD for the 3 phase motor.
    Kelly
    www.finescale360.com

  15. #15
    Join Date
    Aug 2008
    Posts
    962
    Kelly,

    Don't know if you've seen this but should be the info you need to determine which Fabco cylinder you want ..
    http://www.fabco-air.com/pdf/Sec_5.pdf

    On the VFD. I started with a Teco 7300CV (which several others seem to also be using) .. mine died on me while under warranty so I got a refund & bought a Hitachi SJ200 which is serving me well ..
    Teco has a computer program for setting up the drive (interface is extra) but it makes it real easy to do .. The Hitachi is set up manually with buttons on the drive so takes a little longer but once it's set you won't touch it much anyway.

    You ought to have a fine machine when done .. I am impressed with the outcome of your round column conversion.

    Gary

  16. #16
    Join Date
    Mar 2011
    Posts
    525
    Thank you Gary,
    I will check out that Fabco link.

    The machine arrived today and I was able to get it un-boxed and moved into the shop. This is one beefy machine!

    Notice the picture with my small round column machines in the background! The MD001 is about twice the size of the Jet JMD15's.

    Also take note of the yard stick I placed on the table for a scale!
    Attached Thumbnails Attached Thumbnails photo 1.jpg   photo 2.jpg   photo 3.jpg  
    Kelly
    www.finescale360.com

  17. #17
    Join Date
    Mar 2011
    Posts
    525
    I couldn't let it sit so I drained the oil, removed the motor, gears, head, and gear shift levelers.
    Attached Thumbnails Attached Thumbnails photo4.jpg  
    Kelly
    www.finescale360.com

  18. #18
    Join Date
    Nov 2006
    Posts
    40
    Congratulations on your new toy. I'm looking forward to your build. I have one like it and always looking for new ideas. Have fun and I sure admire your RC work.
    Ron E.

  19. #19
    Join Date
    Mar 2011
    Posts
    525
    Thinking about the belt drive tonight and I have read a lot of threads on the subject. Some are placing belts inside the head, others above the head.

    Most threads I have been reading the builders are attaching the pulley to the final gear shaft that the spindle shaft rides in.

    To me it seems simpler to eliminate all of that and mount a double pulley directly to the spindle shaft. I could secure it with 4 set screws that would key into the splines, 2 on each side. I would make a new top plate from 6061 aluminum.

    I would think that since the spindle shaft bearings are placed far enough apart they could support the side load of the belt without much problem? I would use V belts to start and maybe change over to a toothed belt later to reduce the side load on the bearings

    I would think the pulley could also be used as a flange for a the power draw bar mechanism to pull up against when in compression mode.

    The first picture shows the pulley I made for my other machine. The second picture shows an aluminum blank on the spindle shaft of the new mill.
    Attached Thumbnails Attached Thumbnails Pulley 1.jpg   pulley 2.jpg  
    Kelly
    www.finescale360.com

  20. #20
    Join Date
    Feb 2011
    Posts
    605
    I've had similar thoughts about belt drive, inside or outside, where to connect the pulley etc. When I get around to it on my machine I plan on modeling the head and then playing around with a couple concepts in CAD to see which one to go with. Simple is typically the best, and also the most difficult to figure out how to execute well.
    PM-45 CNC conversion built/run/sold.

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