Wizard turns/deg limited to 7 characters?

[Greg]

I have a rotary indexer with a 3.1 ratio, 3.1/360= 0.0086111111 . The wizard is limited to 0.008611 turns/deg. 0.0000001111 does not sound like much but a movement of 0.008611 turns on the rotary indexer corresponds to an angle of approximately
0.0266 degrees or 0.008762 inches on a control surface with a width of 3 inches.

8 thou of error is too great. Any way around this?

[Gary Campbell]

Double post

[Gary Campbell]

A couple questions before I answer, if I may.... 3.1:1 is not a common reduction ratio, how did you arrive at that number? Your numbers are accurate, but only at full steps, are you running a stepper at full steps? If so, why?

And the reason behind my questions is shown in the chart below. Using 1/8 or 1/16 microstepping reduces the step resolution to the 0.001 range for rotary blanks in the 2" and 4" diameter. That said, if true resolution is an issue you should consider a minimum of 10:1 reduction on a router 4th axis and 50:1 on a mill.

[suntravel]

Do not use Odd Numbers as a result for reduction rates, this will end up in rounding errors.

Rotary Axes are working in degrees, so take care that the step resolution can drive to 0.01 or 0.001 degree whatever precision you want to achieve.

Uwe

[Greg]

Gary Its belted with a 62/20 gears for 3.1 with 4000 steps per rev microstepping. I built it out of a lathe headstock a few years ago and have been running small parts successfully but recently have had some larger parts with with tighter tolerances and the error was glaringly obvious. I might have to redesign with a additional set of pulleys to get the gear ratio reduced.


Here is a pic with the back cover off to give you a visual.
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[Greg]

Do not use Odd Numbers as a result for reduction rates, this will end up in rounding errors.

Rotary Axes are working in degrees, so take care that the step resolution can drive to 0.01 or 0.001 degree whatever precision you want to achieve.

Uwe

Makes sense, Thanks. Looks like I have some work to do.

[suntravel]

I have 90:1 on my mill with 4000 Steps, works very well.

You can fit a harmonic drive on the stepper for high reduction without backlash.

Uwe

[Greg]

I have 90:1 on my mill with 4000 Steps, works very well.

You can fit a harmonic drive on the stepper for high reduction without backlash.

Thanks Uwe, I have been looking for something with 45:1 or 90:1 and I cant find much. Are you using a planetary gearbox? Do you have a link? How much backlash and are you compensating?

[suntravel]

I am using a Vertex HV6 with a stepper. That can be adjusted to almost zero backlash.

You could use a harmonic drive 50:1 or 100:1 and 40/36 pulleys.

Uwe