I posted this on the CNC zone but am starting to think I have a Mach3 configuration issue as I review the numbers.

I recently hooked up the A axis to my machine.  I've been running XYZ for some time with no issues.  The A axis has the same (Gecko) configuration (resistor setting) as the other steppers but runs very hot.  If I let it run it will get to the point that after turning it off the stepper feels like a gear that has sand in it if I try and turn it by the hand wheel.  I'm currently having to stop and turn off the CNC system power at tool changes and let it cool for about an hour.  This is limiting me to about 7 minutes of maximum run time before an hour cooldown.

I'm starting to think this is a Mach3 configuration issue as I had to modify the A axis settings to some pretty radical numbers to get decent speeds.  Below is what I posted on the CNC zone forum;

I have a 1:72 reduction in my rotary table

Steps for the XYZ are 40,000
Steps for the A is 400

Velocity (in/min) of the XYZ are 19.98
Velocity (in/min) of the A is 2032

Acceleration of the XYZ are 1.5
Acceleration of the A is 168.75

G's of the XYZ are .0038
G's of the A is .43

Now, I can assure you I'm not cutting 2032 in/min (I wish!) nor pulling an acceleration of 168.75. This is a small Sherline and although I am cutting delrin with a nice sharp bit the A handwheel is spinning at about 3 revs/second at most. It is faster than the others but not by that much. That in itself makes me wonder....the A axis doesn't know it going through a reducer. It's just spinning....why did I have to ramp it up to over 2000 in/min to get a stepper rotation speed slightly higher than the XYZ when they are at 20 in/min?

Thanks,

Mark

For a rotary axis the units are degrees so your steps per unit would be
200 x 10 x 72 /360 = 400 which you have correct.
The Velocity you have set is 2032 degrees per min and not IPM like you were thinking.

Why things are getting so hot I dont know.
Hood

ah....now I get it.  I didn't notice the degrees/min...that makes sense.

Pretty sure I have a stepper headed south. I had my ear down by it and noticed what I can only describe as a 'miniature sizzle'. I listened to the others and don't hear that. I swapped the cables with the Y axis cable and the sizzle is still heard in the A axis stepper (it didn't follow the cable). I would like to swap a stepper to confirm but that's a major evolution with my system.

I also 'turned the A stepper down' to the same as the others(A axis= X, Y, or Z axis times 72) so did that with the velocity and acceleration. That got me to about 1430 in/min and 108 acceleration. However, I don't think that's going to do anything but by me a little time if I'm lucky.

Looks like I'm off to order a stepper

Thanks,

Mark

is the a axis stepper the same type as the other axis, as it could be that you're putting too much current into the a axis stepper

It is the same.  I think I found the problem.  I had converted my non-CNC sherline rotary table to CNC by building brackets and such and using a flexible coupler.  I assumed this wouldn't be a problem but I tore it all apart and discovered the stepper is fine...It is apparently some binding in the stepper/rotary table.  I noticed on the Sherline site they don't sell a kit to convert the rotary table as they say it can't be done based on how the table is made.  I think the extra drag is just causing it to heat up as it's working too hard.

they say it can't be done based on how the table is made

I CNC'd my Sherline table and works fine for indexing. Just mounted it to a frame and the motor is directly connected with a coupling. Make sure that the motor /coupling is aligned with the shaft from the table.

Using a stepper for indexing is ok but if you are going to try to use the rotary in a linear mode then the stepper is a bad choice and you should use a servo. The rotary table is not made  to spin at high rpm.


RICH