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General Mach Discussion / Re: pulley ratio ,feedrate and motor tuning
« on: April 03, 2015, 06:23:43 PM »
Fred,
As the stepper rpm increases the torque decreases. What you want is power which is speed x torque.
So the power part of the curve is somewhat subjective / over a usefull or wanted range of rpm.
The current needs to be limited to the stepper as too much current will overheat the motor and can cause damage.
Increasing voltage can increase stepper rpm. All steppers are not the same in rating and preformance.
Usualy a curve is supplied with the stepper which shows a graph of torque available to rpm at some voltage. Very seldom do you see multiple graphs at different voltage ratings. The curve gives you a starting range for tuning, but, one still needs to adjust settings for max reliability. ( just a comment....if you spin the steppers shaft at various speeds it will generate a voltage
and interesting enough that voltage at some point will come to a max no matter how fast you turn it)
On my Sherline 400 approx in oz are used and on the small Atlas lathe 500 in oz are used. The 500 's have that rating at 3A & 36 volts. They can be on / idle all night and never get hot and never get hot when in use, warn in use , but not hot.
I have mine such that the gear raito is about 2.5:1 with the smaller pulley on the stepper. So the stepper speed is increased
at a loss of some torque but the torque delivered to the screw is increased by the pulley ratio. So the axis delivered power is somewhat max. Yet for the X axis it is directly driven, but, the screw a good pitch such that adequate resolution
is avialable. It's all a tradeoff in the end.........
I would suggest you go to the Gecko site as they some very good info on steppers. Also you may want to look at the
thread I did about the Atlas lathe conversion. If I recall correctly, info was posted about motor torque and anticipated preformance of the lathe.
A stepper can skip steps and you may never know it, but, usualy you can hear the skipped steps, if loss of stepping is significant the axis behavoir will be ........one of where it goes nobody knows...... control is lost or return to a position is no longer correct.
Thus for a stepper system RELIABLITY is important. Better to run the axis slower and accurately with repeatablity than
high speed / feedrate.
So, you the operator, learns what YOUR lathe is capable fo doing for different maching tasks, etc.
How much torque do you need.........well , enough to power the axis , some spare torque for reliabily, enough for
a resonable acceleration, and finaly enough to do the machining task. There are programs that can calculate all that,
but, stiil experince and judgement will be used by the manufacturer in the final sizing.
Done rambling.....hope this helped,
RICH
As the stepper rpm increases the torque decreases. What you want is power which is speed x torque.
So the power part of the curve is somewhat subjective / over a usefull or wanted range of rpm.
The current needs to be limited to the stepper as too much current will overheat the motor and can cause damage.
Increasing voltage can increase stepper rpm. All steppers are not the same in rating and preformance.
Usualy a curve is supplied with the stepper which shows a graph of torque available to rpm at some voltage. Very seldom do you see multiple graphs at different voltage ratings. The curve gives you a starting range for tuning, but, one still needs to adjust settings for max reliability. ( just a comment....if you spin the steppers shaft at various speeds it will generate a voltage
and interesting enough that voltage at some point will come to a max no matter how fast you turn it)
On my Sherline 400 approx in oz are used and on the small Atlas lathe 500 in oz are used. The 500 's have that rating at 3A & 36 volts. They can be on / idle all night and never get hot and never get hot when in use, warn in use , but not hot.
I have mine such that the gear raito is about 2.5:1 with the smaller pulley on the stepper. So the stepper speed is increased
at a loss of some torque but the torque delivered to the screw is increased by the pulley ratio. So the axis delivered power is somewhat max. Yet for the X axis it is directly driven, but, the screw a good pitch such that adequate resolution
is avialable. It's all a tradeoff in the end.........
I would suggest you go to the Gecko site as they some very good info on steppers. Also you may want to look at the
thread I did about the Atlas lathe conversion. If I recall correctly, info was posted about motor torque and anticipated preformance of the lathe.
A stepper can skip steps and you may never know it, but, usualy you can hear the skipped steps, if loss of stepping is significant the axis behavoir will be ........one of where it goes nobody knows...... control is lost or return to a position is no longer correct.
Thus for a stepper system RELIABLITY is important. Better to run the axis slower and accurately with repeatablity than
high speed / feedrate.
So, you the operator, learns what YOUR lathe is capable fo doing for different maching tasks, etc.
How much torque do you need.........well , enough to power the axis , some spare torque for reliabily, enough for
a resonable acceleration, and finaly enough to do the machining task. There are programs that can calculate all that,
but, stiil experince and judgement will be used by the manufacturer in the final sizing.
Done rambling.....hope this helped,
RICH
