Microstepping choice

This topic contains 9 replies, has 5 voices, and was last updated by  Dui, ni shuo de dui 2 months ago.

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  • #10308

    Aze Aze
    Participant

    Hi, (I already searched in the forum and on internet, but I’m not so good in english). If I well understood, it seems than, for milling, 1/16 will be better than 1/32 microstepping, isn’t it? Even 1/8?
    I followed Vicious’ instructions to be in 1/32, but I can feel by hand, simulating a load, than I can easily move a bit the motor from one step to another when the motor is enable.

    What’s the best choice of microstepping for milling please? (Or at least your choice). I don’t care about the noise and speed when milling ;=) I just want to be more precise.

    #10312

    Jason
    Participant

    While I am not sure what the best choice is, I know that the higher your micro stepping is the lower your holding torque is. For precision you will want to go higher, but your trade off is power. With that you may have to increase the current to your stepper motors to increase the power. Cooling your drivers will be important and possibly cooling the motors themselves. I would say if you can use 1/32 with skipping steps stick with that, as that will give you the highest degree of accuracy.

    Please correct me if I am wrong… I am far from a pro with this stuff.

    #10315

    Jeffeb3
    Participant

    This is interesting. I didn’t know that. I found a very detailed page on the tubes about it:
    http://www.micromo.com/microstepping-myths-and-realities

    I think they are saying that if the error in position is 1/32 step, the motor will only have 4.92% of the motor’s max torque, with more torque coming with more steps.

    The consequence is that if the load torque plus the motor’s friction and detent torque is greater than the incremental torque of a microstep successive microsteps will have to be realized until the accumulated torque exceeds the load torque plus the motor’s friction and detent torque.

    Simply stated, taking a microstep does not mean the motor will actually move! And if reversing direction is desired a whopping number of microsteps may be needed before movement occurs. That’s because the motor shaft torque must be decremented from whatever positive value it has to a negative value that will have sufficient torque to cause motion in the negative direction.

    I’m don’t think that this means the CNC will move more with lower stepping, because it seems possible, and totally intuitive that if the motor was moved by 1/32nd of a full step, then it would be applying 4.92%, but if the deflection was greater, say 1/16th of a step, then the torque resisting it would go up to 9.8%, so in the end, you’re really not getting less deflection, but it means that 1/32nd stepping isn’t really giving you that much more accuracy. In fact, that’s in the equation for Tn. The term N/uPFS is going to either be 1/16 or 2/32 when you are trying to move by the same distance in either stepping mode. Do you read that the same way I do?

    I’d rather see some experimental testing. I’m not sure a good way to do that would be. Maybe it’s as simple as changing to 1/16th or 1/8th and using a force gauge/deflection measurement? Do you have to do the experiment at different offsets from the full step, I wonder?

    #10333

    Ryan
    Keymaster

    I played with this a lot for a few different reasons. So there are a bunch of papers out there about this, all kind of conflicting. Another one says something along the lines of holding torque depends on where you are on the sine wave, if your steps happen to hit a full step position you still get all the holding torque. Same with 1/2, 1/4, ect.. And then you get in to holding torque, isn’t as important as power while in motion. I gave up and just did some crude tests myself.

    I started with a large circle and plotted it with the cnc, I changed the step rate and at 1/8 stepping and a 20″ circle you could clearly see the stepping, so that was out. 16th stepping had no visible jaggies. I also tried to measure the power while in motion with a scale at 1/8 vs 1/32 and saw no noticeable difference. So I went with 32nd. I am seriously considering a force gauge to test the new parts and I would love to test this as well.

    I do want to switch back to 1/16 but for speed reasons. I don’t like maxing out the arduino processor for 32nd stepping so soon I will switch to 16th just to have some overhead, if that works that way.

    #10353

    Aze Aze
    Participant

    Thanks everybody. I will try 1/16 later, and I’ll see if the result is better or worst (or the same). Both my 3D printer are in 1/16 and it’s enough for precision (maybe I’ll switch in 1/32 for the noise, but just for that).

    #38639

    Hi guys,

    I’m digging up this thread in order to ask: is 32th step finally matters in terms of quality?

    First reason is: I’m using some TB6560 drivers on my second CNC, and they are limited to 1/16 steps. Should I invest in some 1/32 drivers at some point, and if yes, why?
    Second reason is: I plan to give the plasma an other try on the MPCNC, and achieving high speeds is necessary while cutting some thin steel sheets. With 1/16th steps, the CNC could move much faster since it wouldn’t get too limited by the arduino processing speed.

    I saw that there were some answers hereunder, but I’m not really sure about what to conclude, maybe due to my limited english.
    So, could some nice folk here summarize it in an easy to understand way so that the dummy I am could be sure of what he’s doing?

    By the way, wouldn’t going for 1/16 solve all the problems of rapids people had?

    Thanks in advance!

    #38643

    Ryan
    Keymaster

    1/16 hasn’t shown any noticeable quality differences.

    The power at lower microstepping is very debatable and there are a few papers out there “proving” both.

    At 32nd stepping we are limited to 190mm/s I think that is plenty. The max speed issue really comes down to the steppers themselves, torque drops off dramatically after 60rpm’s regardless of step rate.

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    #38661

    Jeffeb3
    Participant

    I think the Z axis is the only one that approaches the microprocessor speed limit (and that might have gotten better with the T8 leadscrew?).

    My understanding on torque is that if you choose 1/32 and you land on a step that isn’t a 1/16th, then you will have very little torque holding it at that 1/32 spot. If the rig deflects to the 1/16th spot, then the torque is increased to the same value as the 1/16th stepping. That says to me that if you are really getting a lot of resistance, then 1/16 and 1/32 are going to act the same, but if you are in something with very little resistance (including internal machine resistance), then 1/32 will give you a bit more precision.

    Keep in mind that 1/32 is 200 steps/mm and 1/16 is 100 steps/mm. I don’t think anyone would suggest that we are getting 0.01mm accuracy on any home made CNC machine…

    My advice (to anyone) is to do whatever’s most convenient between the two. Dui, if your hardware doesn’t support 1/32, then stick with 1/16. If you are a beginner here, and Ryan’s firmware is configured for 1/32, then stay with 1/32.

    1 user thanked author for this post.
    #38662

    Ryan
    Keymaster

    agreed

    #38665

    Ok, great, I’ll stick with 1/16 then.
    I also think about switching to 1/16 for the MPCNC, a bit more torque (though it is not really the thing I’m looking for), but more importantly higher speed for plasma cut, where torque is not at all an issue.

    Thanks for your clear answers

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