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  1. #41
    thanks JazzCNC

    It's been a while again as I had other things rear their head again, then this lockdown caper kicked off, and it's only now that I have rediscovered where i was at before. About to go and experiment with homing/limits
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  2. #42
    Quote Originally Posted by Crazy L View Post
    I think I might have an idea concerning the jog movements. I set frequency at 35000khz in ports n pins page, again, just following the set up, but I woke up this morning and thought I should change it back to 25000khz.

    So I'll try that when I get in from work.
    The higher you set the driver rev per number is when you need to mess with frequency because your max velocity available changes. That's when you need to change it to gain more available velocity. But.... with a parallel port board you should leave it as 25000 and set the driver number most suited.
    For example at 25000khz if you have a 5mm pitch screw then with settings driver=2000 rev and motor=400 rev per then this gives around say 5000mm/min allowance (rough guess)
    Then say settings of driver= 4000 and motor=800 the max drops to 2500mm/min available.
    The allowable max available is prob slightly less than these but that's basically how it works.

    I don't know what your screw pitch is but you'll notice that in my numbers based on a 5mm screw pitch the motors are set at 1/5th of the driver.
    So a 4mm the motor will be set at 1/4 of the driver setting. A 2mm will be set at 1/2 what the driver is and so on. Then it's a case of fine tuning once it's close.

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  4. #43
    Thanks for all your help guys, I'm learning all the time.

    I tweaked the axis stepping the other day to improve it a bit, making dimensions a bit more accurate. Upon machining a circle though, I have noticed it suffers at 3, 6, 9 and 12 o'clock, giving flat spots. Can I assume this could be a typical fault of the stepper motors or the board quality? Just a question really, trying to learn about this thing.
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  5. #44
    Have you measured backlash?

  6. #45
    Clive S's Avatar
    Lives in Marple Stockport, United Kingdom. Last Activity: 14 Hours 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 3,333. Received thanks 618 times, giving thanks to others 78 times. Made a monetary donation to the upkeep of the community. Is a beta tester for Machinists Network features.
    Quote Originally Posted by Crazy L View Post
    Thanks for all your help guys, I'm learning all the time.

    I tweaked the axis stepping the other day to improve it a bit, making dimensions a bit more accurate. Upon machining a circle though, I have noticed it suffers at 3, 6, 9 and 12 o'clock, giving flat spots. Can I assume this could be a typical fault of the stepper motors or the board quality? Just a question really, trying to learn about this thing.
    Have you checked for back lash?
    ..Clive
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  7. #46
    I have not.
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  8. #47
    As way of explanation - it's not normal (never say never) to lose steps etc in the motor as it decelerates towards zero (before accelerating in the other direction) - which is what is happening at your 3/6/9/12 o'clock positions in the X/Y planes. But what is happening is that any slack / backlash between the screw and the nut (or in the motor coupling or mechanical interface to the spindle), at the point of reversing direction the screw has a limited travel (defined by backlash) before it engages on the contra-face of the thread of the nut to allow it to start accelerating in the opposite direction. Whilst the screw face is moving to interface with the thread of the nut, the spindle isn't moving and that would present a flat-spot at the point of change of direction (3/9 o'clock on X, 6/12 o'clock on Y). That's why we've quickly jumped on to that as a first port of call.

    You can also lose steps on change of direction, but this would be limited to one per change of direction and unlikely to be substantially visible just scribing a circle.

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  10. #48
    Quote Originally Posted by Doddy View Post
    As way of explanation - it's not normal (never say never) to lose steps etc in the motor as it decelerates towards zero (before accelerating in the other direction) - which is what is happening at your 3/6/9/12 o'clock positions in the X/Y planes. But what is happening is that any slack / backlash between the screw and the nut (or in the motor coupling or mechanical interface to the spindle), at the point of reversing direction the screw has a limited travel (defined by backlash) before it engages on the contra-face of the thread of the nut to allow it to start accelerating in the opposite direction. Whilst the screw face is moving to interface with the thread of the nut, the spindle isn't moving and that would present a flat-spot at the point of change of direction (3/9 o'clock on X, 6/12 o'clock on Y). That's why we've quickly jumped on to that as a first port of call.

    You can also lose steps on change of direction, but this would be limited to one per change of direction and unlikely to be substantially visible just scribing a circle.
    Thank you very much for that Doddy. Though I do know what backlash is, hahaha, I have worked on some knackered machines in my time as a machinist (leadwell, Huron, Beaver) I'll be honest though, it didn't even cross my mind it could be that. I don't know if my machine has a gib strip, probably not as that is quite an old school thing now. I will have a look this weekend hopefully and let you all know.
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  11. #49
    I have, what feels like about .1 of movement in the Y. I've not taken anything apart, that was just holding the table and giviing it a push and a pull.

    I think that could be enough, as on a 10 mil rad, the flat is about 4 to 5 mil wide, sounds feasible that that could be what it is, thanks chaps.

    Next mission is to find out how it comes apart, haha.
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  12. #50
    Sounds a lot.
    I'd expect a 0.1mm difference at worst if it was backlash. It could be a factor that is certainly not helping though.
    How are your bearings? Have they come loose a little?
    I'd also try dropping the acceleration rate just to see if it is losing any steps on a direction change.

    Bit of checking and maintenence is on the cards.

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