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  1. #11
    Oh one thing I forgot to mention...I measured the current into one driver (using both an ammeter and a shunt resistor) and when idle it's about 0.3 amps. It goes up a bit when the motors running, but either way that seems a bit low to me? I've got the driver set to 4.09A peak, I take it this is correct for these motors in bipolar parallel? The motor is only a little warm, nowhere near 80C.

    I'm currently using a 225VA toroid for just the one motor. There's no perceivable temperature rise on it so maybe I can run more than one motor from this transformer?

  2. you need 66% of the total motor peak current... so 3 steppers at 4A/phase = 3 * 4 *.66 = 7.9A. @ 60v thats 420VA

    remember that measuring phase current with an analogue device will show the RMS phase current. With a digital meter you are unlikely to get a useful reading because its highly spikey.

  3. #13
    Quote Originally Posted by irving2008 View Post
    you need 66% of the total motor peak current... so 3 steppers at 4A/phase = 3 * 4 *.66 = 7.9A. @ 60v thats 420VA

    remember that measuring phase current with an analogue device will show the RMS phase current. With a digital meter you are unlikely to get a useful reading because its highly spikey.
    I thought it was 8 amps per motor, since there's 2 phases?
    Anyway, I got lucky and won a 500VA toroidal transformer for 20 on eBay so I'll be using that.

    I changed the pulleys round (had to bore them out to the right diameter and stuff) to get 1:1. Now I'm getting 42mm/s on the X axis :)
    Bad news is the Y-axis for some reason refuses to even go at 25mm/s without stalling the motor. Not really sure why, maybe something to do with the belt tension and how tight the nut is...
    Not tested the Z yet.

  4. Quote Originally Posted by Jonathan View Post
    I thought it was 8 amps per motor, since there's 2 phases?
    Anyway, I got lucky and won a 500VA toroidal transformer for 20 on eBay so I'll be using that.

    I changed the pulleys round (had to bore them out to the right diameter and stuff) to get 1:1. Now I'm getting 42mm/s on the X axis :)
    Bad news is the Y-axis for some reason refuses to even go at 25mm/s without stalling the motor. Not really sure why, maybe something to do with the belt tension and how tight the nut is...
    Not tested the Z yet.
    No, thats peak current. In general the 2 phases are never both powered fully all the time so a sort averaging occurs and anecdotally (although Mariss of Gecko fame did show the maths once) its 66%!

    Its usual to quote feed speeds in mm/min for milling - so 2520mm/min is good, 1500mm/min isnt bad tho

    Strange... if you haven't already, try swapping driver channels to validate its not a driver issue, then motors (assuming they are the same) to validate its not a motor issue

  5. #15
    Quote Originally Posted by irving2008 View Post
    (although Mariss of Gecko fame did show the maths once) its 66%!
    Thanks for the clarification. Do you by any chance have a link to the 'maths' behind this? I'd be interested to see..

    Quote Originally Posted by irving2008 View Post
    Strange... if you haven't already, try swapping driver channels to validate its not a driver issue, then motors (assuming they are the same) to validate its not a motor issue
    (I quoted the feeds in mm/s since personally I think it's better to work with smaller numbers and easier to visualize, but I'll endeavor to stick with the convention from now on)

    I've only wired up one driver so far, so that can't be the issue. I'll try swapping the motors though. All the motors are the 3N-M ones.
    The handle for the Y axis (before I removed it) did seem a little harder to turn than the X-axis so I may try loosening the nut. I tightened it to reduce the backlash. Annoyingly to get to the nut you have to take the bed off the machine and all sorts...takes ages :(

  6. Surely its the gibs that determine how tight the slide is? although I'll accept endfloat is another contender

  7. #17
    Yes that's true, I'll check the gib strip. There's no end-float on the screw since there's thrust bearings, unless you're referring to something else?
    The nut is slotted with a bolt to tighten the two parts enabling you to adjust the backlash. Quite recently I tightened it to reduce the backlash, but maybe I tightened it too much and increased the friction excessively.

  8. AH, I was confused by the statement

    The handle for the Y axis (before I removed it) did seem a little harder to turn than the X-axis so I may try loosening the nut. I tightened it to reduce the backlash
    many people use the term backlash when they mean endfloat and i thought the nut you refered to was holding thr handle in place...

  9. #19
    I've had some luck with the Y axis now. I loosened the gib strip which helped a bit however it strikes me as being too loose now. I adjusted the backlash adjustment and now I've got 2300mm/min on the Y axis, but about 0.2mm of backlash instead of 0.065mm.

    Good news with the Z, 4600mm/min with 1:1 pulley!!!! It will do more if I change the motor to half stepping because the computer is limiting the pulse rate I can use at 1/4 microstep, however 4600 is plenty fast enough for an axis that's only got 92mm travel. I'll keep it at this ratio to preserve torque for drilling etc

    So to summarise:
    X, 2520
    Y, 2300
    Z, 4600

    Overall I'm very happy with this - can't wait to start machining things again! Thanks for all the help that's enabled me to do this...

    Also, could someone point me to a simple program to import a 2D .dxf and generate g code for '2.5D' milling from it?

  10. #20
    Try cambam, theres a free version and a pay version http://www.cambam.co.uk/

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