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Author Topic: Newby with a question about Spindle Step/Dir setup  (Read 6346 times)

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Newby with a question about Spindle Step/Dir setup
« on: October 18, 2008, 12:31:06 PM »
Hi I have been using Mach 3 for about a year now and love it.  I have a Enco square column bench mill I have converted to CNC.  I am using some Allen Bradley Ultra 100 servo drives setup in stepper follower mode.   I just put a servo in for the spindle motor and set it up for the same step/direction setup.  The problem I have is that it ramps up nice but when the spindle stop is set it does not ramp down.  It just stops suddenly.  I have a geared head so it is really hard on the gears when running at high speeds.  Is this a setup problem on my part or am I missing something.

Offline Hood

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Re: Newby with a question about Spindle Step/Dir setup
« Reply #1 on: October 18, 2008, 05:28:16 PM »
Afraid I have not got the servos on the spindle of either the lathe or mill yet so cant talk from experience. I would have thought however that on the motor tuning page for the spindle motor you would set your aceleration (and thus decelleration) and Mach would heed that, is that not the case?

Offline jimpinder

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Re: Newby with a question about Spindle Step/Dir setup
« Reply #2 on: October 19, 2008, 12:55:05 AM »
A bit like Hood - no experience with these, but:

Ports and Pins/Spindle SetUp - check the delays for Spin Up and Spin down, and the Relay off setting. I assume you are using the Spindle drive step/direction, not an axis drive already.

As a matter of interest try this on an axis step/dir output, drive it as though you would an axis and see if you have the same effect - to see if this is an electronic problem or a mechanical one. If you use a fairly high steps per inch, and do a G0 A1000 or something similar and see if, at the end of the move it stops dead or decelerates down.

My spindle motor drive has a brake - which you can set or leave. On brake it stops very quickly (which I assume is for safety) - so is there something in the drive electronics, or even the motor, which stops it dead if the step pulses are missing. I must admit, although it is fitted, I prefer to let the spindle slow down itself - it is easier on the nerves.
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Re: Newby with a question about Spindle Step/Dir setup
« Reply #3 on: October 19, 2008, 01:35:52 AM »
I am using the Spindle drive step/direction and not the axis drive.  My axis drives do accel and decel nicely like they should.  The spindle motor will accel just like I have it set up in the motor tuning and I thought should decel just the same but that is not the case.  Another thing that happens when changing spindle speed from lets say 1000rpm to 500rpm is that is immediately changes and when going from 500rpm to 1000rpm it will accel nicely up to the new speed.
Re: Newby with a question about Spindle Step/Dir setup
« Reply #4 on: October 19, 2008, 11:27:52 PM »
Sounds like something that needs to be addressed in Mach. I've got a tormach that runs Mach3 - It's got the analog spindle. They run it as step/direction though, and I assume that the step signal must just go in to some charge pump or something and get fed in to the VFD as an analog signal.... but same deal. An increase in speed is nice and gentle. A decrease bumps, thumps, etc. I assume with a true servo, this would be a pretty violent thing.

I notice that on the VFD, I have to set the decel pot carefully. I needed a replacement VFD back a few months ago (under warranty YAY!) and I had to tune it. The Accel pot could be set almost anywhere, because Mach was ramping it up, but if I set the Decel pot wrong, when I reduced speed a lot or stopped, the VFD would error out with an overvolt. The motor was generating too much juice in the process of slowing down too quickly, and was literally acting like a generator. They all (motors) do this of course, so it needs to be addressed.