Tapping with one pulse spindle encoder?

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31 Dec 2012 07:53 - 31 Dec 2012 07:56 #28212 by machete
Hello!

I have very simple sensor on my spindle, it gives me only two pulses per rotation. (so it's not quadrature)

This is my .hal file part for encoder:

Warning: Spoiler!


This is very similar to this example: wiki.linuxcnc.org/cgi-bin/wiki.pl?Rigid_Tapping
Except my encoder is not quadrature.

I can see, that "spindle-rev-count" correctly counting rotations, but do it always "+1", no mater M3 or M4 is executing.

And G33.1 is not working (spindle is rotating, axis not moving).

This is my test-program:
Warning: Spoiler!


What am I doing wrong?
Last edit: 31 Dec 2012 07:56 by machete.

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31 Dec 2012 11:08 - 31 Dec 2012 11:11 #28215 by PCW
Pretty sure rigid tapping will require quadrature
and probably pretty decent resolution (say >25 slots)
at that.

Threading can get away with lower resolution as it
doesn't reverse and is done at a fairly constant speed
(so you can interpolate spindle angle between encoder edges
if need be for low res encoders)

Without decent resolution quadrature you would be
basically guessing what the spindle was doing for long
periods/angles during reversals.

Guessing wrong will break taps.
Last edit: 31 Dec 2012 11:11 by PCW.

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01 Jan 2013 08:03 #28245 by jmelson

Hello!

I have very simple sensor on my spindle, it gives me only two pulses per rotation. (so it's not quadrature)

And G33.1 is not working (spindle is rotating, axis not moving).

What am I doing wrong?

This can't work! For rigid tapping, you need fairly high resolution of
spindle position, plus accurate detection when the spindle reverses.
With only one signal from the spindle, you have no way at all to
detect the spindle reversing. Even if you did, the spindle could
go a whole revolution in reverse before that was detected,
certainly breaking smaller taps and overloading the spindle
with a big one.

I can't imagine rigid tapping with anything less than 25 pulses/rev
which would give 100 quadrature counts per rev. You also
need an index so it makes it happy for multiple-pass threading,
although this is not strictly necessary for rigid tapping.

Jon

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01 Jan 2013 20:52 #28250 by machete
OK, i understand.

I have read this:
wiki.linuxcnc.org/cgi-bin/wiki.pl?Closed...pindle_Speed_Control

And somehow decide that 1 pulse sensor is also enough for rigid tapping...

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02 Jan 2013 01:10 #28267 by jmelson

OK, i understand.

I have read this:
wiki.linuxcnc.org/cgi-bin/wiki.pl?Closed...pindle_Speed_Control

And somehow decide that 1 pulse sensor is also enough for rigid tapping...

No, this applies ONLY to constant speed spindles for milling, for instance,
and does not apply to anything where a tool is to be synched to the spindle
for a threading operation. There are ways to do lathe single-point threading
with a single pulse/rev, but those are not very good, either.

Jon

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