Z-axis motor

Discussion in 'CNC Machines and Conversions' started by Rudy, Jun 5, 2019.

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  1. Jun 5, 2019 #1

    Rudy

    Rudy

    Rudy

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    Hi,
    I want to improve the Z-axis on my ZX32 mill. Not a CNC conversion, but it will probably require the same considerations as if I did. I will of cause make it compatible with making it a CNC if I go to the next step.
    The reason I want to do a motor driven Z-axix is that I want a more rigid and stable Z-axix feed. The quill on this machine is not the best in the business. And the depth control is somewhat "strange". With a stepper motor on Z, I can tighten up the quill for good. At least that is my plan.

    I have read threads here on the subject. Thanks everyone for your contributions. So much to learn from you.
    I have figured out that I should probably use a 25mm ball screw wit 5mm pitch. That is called a 2505 screw I believe. Will I want a double nut on this?

    The motor some use on the ZX45 mill is NEMA42 size with some 20Nm torqe. I don't know if that is overkill for my ZX32. Maybe a NEMA34 with 12Nm torqe is suficient? I plan to put on some gas struts to lighten up the share weight of the head.

    Guess the electronics is easy. DM860N?
    I also need a hand controller for this.

    Appreciate some advise on this.

    Rudy

    2017-11-05 14.37.08.jpg
     
  2. Jun 12, 2019 at 1:45 PM #2

    RM-MN

    RM-MN

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    I found little information on how to size the stepper motors for any axis as I attempt to CNC my SC 2 mini mill. I finally just bought some NEMA 23 with 650 mNM holding power that require a maximum of 2 amps. Fastening one directly to the X axis I tried milling aluminum and found that it had sufficient torque for my purposes. I do intend to use timing pulleys and belt to get a 2 to one torque amplification for the Z axis. I'll be sacrificing speed for increased torque. Hope this helps.
     
  3. Jun 12, 2019 at 2:39 PM #3

    Rudy

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    Thanks. I guess I'm into a lot more torque. Pulling X and Y on a smaller machine doesn't have to lift heavy loads, just overcome friction and tool pressure. The head on my medium size mill weights maybe 30 kg. And the rails have to be relatively tight.
    Thats why I'm brought to believe I need 12-20 Nm. That's the gap between NEMA 34 and 42 I believe.
    Rudy
     
  4. Jun 12, 2019 at 6:07 PM #4

    blighty

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    For comparison.

    I have an RF45. on the Z there is a NEMA 34 1200oz stepper running on 61.5v. ball screw is C5 2205 . ball nut has over sized balls.
    when it had dove tails on the Z the head was counterbalanced with about 30Kg of weights, rapids of 3500mm/sec. I now have linear rails
    on the Z no counterbalance . Now set to 4500mm/sec.
     
  5. Jun 12, 2019 at 7:36 PM #5

    Rudy

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    blighty, so if your bigger machine handles the Z with a 1200 oz/in (8,5Nm) motor, mine will certainly do with the 12Nm NEMA 34 I suggested to my selves. I will also put on gas struts anyway to neutralize most of the head weight.
    Thanks for the info!
    Rudy
     
  6. Jun 12, 2019 at 8:12 PM #6

    ddmckee54

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    I was watching some of the stuff on YouTube that CLOUGH42 has been doing to his Grizzly CNC conversion, which I think is about the same size as your machine. He has upgraded his CNC conversion from the original NEMA 23 motor on the Z axis to a NEMA 34 and is quite happy with it. Apparently he was never really happy with the Z axis rapid travel moves. I forget what kind of Z axis speed he was getting out of it after the motor upgrade, but it was impressive.

    I think your choice of the NEMA 34 motor over the NEMA 23 will probably be a wise move, and one that you'd probably want to do in the future if you went with the NEMA 23 stepper.

    Don
     
  7. Jun 13, 2019 at 9:50 AM #7

    Rudy

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    Thanks Don. I watched those videos. He's machine is smaller than mine, but I'm more confident with NEMA 34 size so far. I will also get a closed loop type in case I will go for a full CNC conversio som time later.

    So far I have figured out that I need a controller, power and a manual hand controller for this manual Z axis motor system?
    I see some buy from fasttobuy2012. I sendt them a mail, but no reply. Not a good sign...

    Rudy
     
  8. Jun 14, 2019 at 12:19 PM #8

    RM-MN

    RM-MN

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    Unless you are in a hurry to get the machine set up you might wait to install the gas struts. I read someone's post that said his setup worked better without the gas struts. You could decide to add them later if you wanted.
     
  9. Jun 14, 2019 at 1:35 PM #9

    Rudy

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    RM-NM, I'm in no hurry. I assumed the struts could do nothing but good, making the head lighter. However, thanks for the tip. I can easily do afterwards it if needed.
    Rudy
     
  10. Jun 14, 2019 at 4:10 PM #10

    Nibby2226

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    Hi,
    I used a NEMA34 motor with 2505 ballscrew on my BF30. The head is counter balanced to retain 20 - 30kg of downward weight. I think the motor is 12Nm running at 42V with a Gecko driver. The Z speed is limited to 20in/min to give chance catching mistakes before they cost a tool or a part The ballscrew nut is loaded oversized balls to limit backlash.
    https://www.cnczone.com/forums/benchtop-machines/107594-cnc-cad.html
     
  11. Jun 14, 2019 at 4:55 PM #11

    ddmckee54

    ddmckee54

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    You don't NEED closed loop motors. If your control system can handle the encoder feedback they will allow for greater positioning accuracy, i.e. compensating for missed steps. It sounds like you aren't going to a CNC control software yet, and are just motorizing your Z axis using a stepper motor telling it to run at a fixed speed until you tell it to stop.

    If it were me, I wouldn't commit to a closed loop stepper immediately. I'd buy a cheap-ish NEMA 34 with about the same torque/holding power as the closed loop version you've got your eye on. That way if the NEMA 34 doesn't work out it won't hurt quite so bad.

    Don
     
  12. Jun 14, 2019 at 6:55 PM #12

    Rudy

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    Don, I'm trying to resist the urge going full CNC. I might breake down some day. And then, I would probably regret. Looks like the price difference isn't all that big.
    I sit by the computer all day with electronic "CAD" at work and I really enjoy the old school manual machines on my spare time. Going home an do even more CAD, Well.. I don't know yet. However, as a tech nerd I would really want to build that CNC machine..
    Motorize the Z axis is in first hand to get a more stable machine by locking the quill witch is the weakest link on mine.
    Rudy
     
  13. Jun 15, 2019 at 6:39 PM #13

    Muzzer

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    Encoder feedback isn't designed to compensate for missing steps, so much as achieving fast and accurate positioning. If you are missing steps you have a serious problem with your system. How many controllers actually have inputs for linear encoders to be used for positional feedback - can you suggest a few examples? I'm not aware of (m)any in this market sector. They are also not very happy trying to compensate for backlash which is very nonlinear.

    Closed loop steppers are not expensive and have many advantages over dumb, open loop setups. There is quite a choice out there these days - don't be put off.
     
  14. Jun 16, 2019 at 2:44 AM #14

    ahughes3214

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    Rudy,

    I’ve left some info before on my setup; sorry if some is repetitive. I switched to full motor control for the z-axis and do not use the quill at all for positioning on my PM30 mill. I did not setup for, nor do I intend to go to CNC. Manual milling is my interest.

    I am currently running a Compumotor 83-135 Nema 34 stepper rated at 400 in-oz (2.83Nm). I do have a gas strut (McMaster-Carr 4138T630 / 100lbs) for the head. The gas strut not only offsets the head weight, it also provides some dampening effect. The head with carriage weighs 127lbs. Power to the stepper is 80VDC.

    This combination moves the head easily up and down. For manual jogs (joystick) I am currently driving it at 35-40 inches per minute. For my automatic memory moves, I drive it a little faster. I use the memory points to raise the head quickly to change a tool, etc. and then lower back to a rough position (+/- 0.010) prior to final positioning for the cut. If I find some time, I can make a video and try to post.

    The ballscrew is imperative for this performance. I use the RM1605 ballscrew which is more than sufficient in this application as it is rated for about 1500 lbs. dynamic load. Direct drive to the leadscrew is preferred to keep it simple and limit potential slop in the mechanism. I did not change the standard ballscrew or use a double nut. As a result I have about 0.007 backlash which is not a problem for me and manual milling. I rely on my DRO for all accurate and final positioning.

    Depending upon your method of motor control, if you plan for program/memory type movements, I recommend a closed loop system. I have been using an open loop controller, and if steps are missed (for example gib accidentally left tight when a move is initiated), the motor will stall and position is lost without the stepper controller knowing. As a result, the next move will not be accurate and a potential crash hazard.

    After experiencing the above issue, I decided to go to closed loop controller so my control system will know when a step is missed and stop the motor drive signal, or perform some other logic. I just ordered a closed loop stepper and controller combo (HSS86 hybrid servo driver & nema34 Stepper Motor Closed loop 4.5N.m 82mm 6A) and will be experimenting with this setup over the next month or so.

    I’d be happy to provide an update once I get it setup and running.

    Drew
     
  15. Jun 16, 2019 at 10:21 AM #15

    Rudy

    Rudy

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    Drew, Thaks for the helpful information. I'm starting to get a picture in my mind of how to do this.
    I would appreciate to follow your updates on yous setup.
    What are you using for joging and memory?
    Rudy
     

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