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  1. #11
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 46 Minutes Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Quote Originally Posted by A_Camera View Post
    .....I don't know what the real torque is at 2280 rpm, which is what the rpm is now when the chuck runs at 380 rpm, but it is enough to drill in steel.
    Sorry, I hadn't twigged that you were planning on using this motor for the SPINDLE drive. That's probably not the best idea if I have understood what you are planning. I'd seriously recommend you use a proper VFD rather than a stepper or servo drive, which are intended for position control, rather than speed control.

    Forgive me if I've got the wrong end of the stick here. I have no desire to criticise so much as help you avoid disappointment. Perhaps Jazz or someone else will dive in here, in the interest of constructive advice.

  2. #12
    Quote Originally Posted by Muzzer View Post
    Sorry, I hadn't twigged that you were planning on using this motor for the SPINDLE drive. That's probably not the best idea if I have understood what you are planning.
    No Muzzer, it's for a 4th axis.
    -use common sense, if you lack it, there is no software to help that.

    Email: [email protected]

    Web site: www.jazzcnc.co.uk

  3. #13
    Quote Originally Posted by Muzzer View Post
    Sorry, I hadn't twigged that you were planning on using this motor for the SPINDLE drive. That's probably not the best idea if I have understood what you are planning. I'd seriously recommend you use a proper VFD rather than a stepper or servo drive, which are intended for position control, rather than speed control.

    Forgive me if I've got the wrong end of the stick here. I have no desire to criticise so much as help you avoid disappointment. Perhaps Jazz or someone else will dive in here, in the interest of constructive advice.
    You have misunderstood the thread. I have a very good VFD and have no intentions to replace that. This is a 4th axis which I experiment with as a lathe / 4th axis combo.

  4. #14
    Quote Originally Posted by JAZZCNC View Post
    That would be an expensive mistake, large motors like Nema 34's require lots of voltage to spin fast and by lots I mean 150V+ to get any reasonable speed with torque.
    I don't mean stepper, but servo.

    Quote Originally Posted by JAZZCNC View Post
    The price of AC servos has come down to such a level that they nearly match High voltage drives which are required to get speed and torque from large steppers. So I would look at those before large steppers.

    I have these 600w AC servos on my plasma machine and while only 1.9Nm they massively outperform the 4.5Nm closed-loop stepper motors. Which at just over $200 is a very good price, I would fit these and pay the extra over the JMC or any of those types of DC servo every time. (They also do them with a brake)

    https://www.aliexpress.com/item/3304...5be81468ni78om

    Like I said before if you are going to go this far then do it right the first time because while digging deep hurts I always find it works out cheaper than experimenting and far less hassle.
    Yes, but my problem is space, so I would like to avoid larger motors. All AC servos I have seen take up a lot of space, and even though the PSU is just a simple transformer, it does need a large one and that takes space, unless it is driven directly from the mains. At this stage, I'll avoid both for now. If need arise, I may change my view, or like I said before, buy a real lathe, which functionally will most probably be better than what I can build. To be honest, I think it would be more point in upgrading a real lathe with a large AC servo then doing it in my DIY "poor man's lathe" which will probably end up being pretty expensive in the end, I know that, but I want to try, learn and improve incrementally. I know that such approach costs money, but for me it is more fun this way. Starting a huge project to build a perfect and powerful lathe takes a long time and I don't think I have the patience to do that. Also, I am just an amateur "machinist", don't have any real need for this except as a hobby, so I am not at this stage interested in starting a huge project which will never be finished.

    I feel that this hobby is like a black hole, it can swallow everything, including ones family life, fortune, space and time, so I must set some sort of realistic limit to my ambitions. I am well aware that this, once ready, will be far away from perfect, but that's OK for me, even if some parts will in the end not be used, or replaced shortly after a test.

    Right now, I am aiming at some DC servos, but I think before that decision is made, I will build the X and Z out of real parts, which for me will be based on some HGR20 and HGR15 linear rails plus 1605 ball screws.

  5. #15
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 46 Minutes Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    I think there may be some confusion over terminology here. The Lichuan servos that Dean linked to are generally known as "AC servos" and don't need a separate psu - they take 220V mains directly. The term "DC servo" is not clearly defined but generally involve brushed motors ie an H bridge output and a 2 terminal motor. These aren't used much these days.

    You might also talk about "brushless DC servos" (BLDC) which are pretty much the same as an "AC servo" but they drive the motors with a trapezoidal 3 phase voltage rather than the sinusoidal one seen in an AC servo.

    The various open and closed loop steppers have 200 or more teeth per rev, whereas an AC servo is likely to have only a few poles per rev.

    An AC servo motor will be more power dense than an equivalent AC induction motor (VFD etc) and also more power dense than a stepper. AC servo and AC induction will both create a fairly flay torque speed characteristic, whereas the torque from a stepper falls off quickly with speed. Gearing down a stepper "to increase the torque" may not actually gain you much / any torque in some cases due to that torque fall off, unless you are focusing on stall torque.

    As Dean says, there's a lot to be said for going AC servo and those Lichuans are very keenly priced. There's no right or wrong here but that's just some input from my side. I develop motors and inverters in my day job and (sadly) use them from time to time in my workshop.

  6. #16
    OK, thanks. Anyway, there are AC servos which use less voltage than the mains, but in all cases they require a beefy transformer, a large driver and even the motors are larger. I have no space or need for that at this moment, even if it would be much better for the purpose. Remember that this is mostly just a test, a proof of a concept with a goal to build something to play and learn with.

    I think the only difference between AC and DC servo is that an AC servo driver has the rectifier built into the driver, while a DC servo must be fed using an external DC PSU with a rectifier circuit in the PSU. When I say DC servo, I mean just that the driver needs DC current, but it is still a servo, and NOT a closed loop stepper. Basically, I have written off the use of closed loop stepper, mainly based on what Dean said before, except that I will not at this stage buy a large one, but aiming at a 180W type from JMC, namly this one:

    https://www.aliexpress.com/item/3294...79092e0eprgamN

    I checked the manual and the software, and must say I am impressed considering readability, configurability and contents, and since this will be my first servo, I think that is important. It fits my size needs and I don't have to build a new PSU / control box. If in the end it turns out to be too weak, I can always move the motor to my CNC and replace a NEMA23 stepper of one axis, and buy a new and stronger servo with break as Dean suggested, but that will not be now. First I want to finish the project and see it working.

    I think you are wrong about gearing. Torque is multiplied by the gearing, so indeed I gain a lot. Of course, since the stepper is pretty weak, it will not be much at high RPM, but never the less, it will be six times (minus some losses, but we can ignore that here). Of course, gearing down is giving the most torque benefits in holding, but there is a benefit even when rotating. Of course, that would not be needed at all if I had a large enough motor, but that's for later times.

  7. #17
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 46 Minutes Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Quote Originally Posted by A_Camera View Post
    I think you are wrong about gearing. Torque is multiplied by the gearing, so indeed I gain a lot. Of course, since the stepper is pretty weak, it will not be much at high RPM, but never the less, it will be six times (minus some losses, but we can ignore that here). Of course, gearing down is giving the most torque benefits in holding, but there is a benefit even when rotating. Of course, that would not be needed at all if I had a large enough motor, but that's for later times.
    You seem happy to redefine terminology, which is fine but may cause confusion when you try to communicate with others.

    Have a look at the torque-speed curves for the stepper motor you are considering. If you fitted a 2:1 reduction gear you'd double the stall torque perhaps. But if the torque at a new, doubled operating speed had dropped to half of what it was, you'd have gained nothing - you'd now have the same final torque at the same speed but you would have halved your max speed (the all important "rapids"!). My conclusion is that you might as well go direct drive with steppers.

    For a servo it's different - you really need to step the speed down by a factor of 2 or 3 to boost the final torque to something more generally useful. Also, not many ballscrews will be happy to run at the max speed of a servo which is usually around 3000rpm, give or take. So to me, steppers are best used in direct drive and servos best used with a belt drive reduction ratio of between 2 or 3. But as I said, there's no right or wrong!

  8. #18
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 46 Minutes Ago Has been a member for 6-7 years. Has a total post count of 417. Received thanks 61 times, giving thanks to others 10 times.
    Here's a randomly chosen image from Oriental Motor, showing a typical torque speed characteristic for a stepper motor:
    Click image for larger version. 

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    https://www.orientalmotor.com/steppe...er-motors.html

    If you gear down the output by 2:1, you might move from eg 500rpm to 1000rpm and in the process you'd drop from a pullout torque (loss of position) of ~45oz-in to 27oz-in (forgive the Mercan units). After the supposed doubling up of torque through your expensive reduction stage, you'd actually end up with ~54oz-in. That's an increase of ~20%, not 100%. See what I mean? Some of the Chinesium steppers have even worse torque curves. Sure, you double the stall torque but unless you plan to use your machine as a press, that's not much use to anyone.

  9. #19
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 3 Days Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,908. Received thanks 360 times, giving thanks to others 8 times.
    Muzzer, did you look at the latest link A_Camera posted?

    It's for a low DC voltage supplied integrated AC servo motor...
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  10. #20
    Muzzer, try to understand something. I bought this 4th axis rotary chuck and it comes with a belt giving 1:6 reduction. It is NOT something which is a choice, the belt is a necessary thing in it, not an "expensive reduction gear" which I design. In fact, direct driving would be impossible because there is a hole through the rear, so unless you want to give that up, you MUST have a belt or some sort of arrangement to drive the chuck. Besides, if we take your own torque chart as example and my actual 1:6 gearing then you can see that at 2280rpm that motor should have approximately 10 oz-in (units make no difference in the calculation). Now because of the gearing, the torque is 6 x 10 = 60oz-in but the rpm is down to 380. So, yes, while the torque is not that much bigger, but still bigger, and is definitely 6 times the value read from the chart. Not much is gained compared to direct drive at low rpm, but never the less, there is a gain, even with your motor chart. I have also said that the gearing is mostly a help between zero and very low rpm, I am aware of that, but still, there is no way you can directly drive this chuck, except through putting in a 1:1 belt, but that would mean I lose even holding torque, which is the very reason these belt ratios are used the first place.

    Now, to make something clear, this is the motor I am considering: https://www.jmc-motor.com/product/980.html
    It says: "Nema 23 Integrated AC servo motor 180W" ...and it is not a printing error, because I am sure it is the same as any other AC servo, except that the driver is fed using maximum 50VDC, so the rectifier is outside the driver, as I said before. The motor has a 0.6Nm (85 oz-in) torque all the way to 3000rpm with a max torque of 1.5Nm. Now, by using the same 1:6 belt I'd get 3.6Nm holding torque AND all the way to my current maximum chuck speed, which is 380rpm. In other words, I gain at the speedy end, but lose on holding torque, since my current steppers have 1.8Nm x 6 = 10.8Nm, but my current stepper has 0.5Nm at 1500rpm, which is quite a bit from 2280rpm (my current speed). I have no torque table above 1500rpm. My guess is that the torque is very low at that high speed. With the servo I could go to 3000 rpm (or even more), so that would definitely be beneficial for the rotation, but not for holding torque.

    Yes, I know that combining a 4th axis and use it as a lathe is not a good idea according to a professional, but to me, this is just for fun, I don't aim at competing with anyone except myself. I aim at getting experience, knowledge, having fun, enjoying my time, exercise a hobby and so on.

    Correct me if I am wrong, but don't say that I "happy to redefine terminology", because I am not. I did not make any calculations before, but definitely not redefined anything and torque is definitely increasing when you add a reduction gear. I think you understand that very well, but if you don't understand what I am saying that's a different thing, and is perfectly possible that I am not that clear, but that does not justify such statement. I am not stupid, I can read charts, make calculations (in ANY sort of units) and so on. You are not the only one with engineering background and long and prosperous career.

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