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Author Topic: Spindle RPM Readout Problem - S True not stable  (Read 5980 times)

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Spindle RPM Readout Problem - S True not stable
« on: March 17, 2010, 01:37:39 PM »
The problem I am having and can not seem to solve is the the Spindle True readout is not stable.  I am using CNC4PC's C3 Index Pulse card.  When I was using Mach3 VerR3.042.032 everything worked fine.  I could set the rpm with my VFD (using pot) say at 400 rpm, verify with rpm reader, and S True would read 400 rpm and vary only 1 or 2 rpm.  Since I downloaded later versions (currently have VerR3.042.037) the readout is not stable.  For example, at 400 rpm, it will hold 400 for a few seconds, then fluctuate down  (varies each time to different values 360, 375, etc) and then back to 400 rpm.  I've searched thru CNCZone and Mach Forum for threads and also read the document "Threading On The Lathe - Mach3 Turn".

Any suggestions?  Need to cut some threads, however with the readout not stable, don't want to attemp until solve problem.

Offline Hood

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Re: Spindle RPM Readout Problem - S True not stable
« Reply #1 on: March 17, 2010, 02:17:11 PM »
Does the spindle itself seem to vary? You should be able to tell by the sound of it if its as much as 30 or more revs. If it doesnt then I wouldnt worry too much, try your threading on a bit scrap and see.
You may get a more steady reading by enabling spindle averaging on Ports and Pins Spindle Setup page.

Hood
Re: Spindle RPM Readout Problem - S True not stable
« Reply #2 on: March 17, 2010, 05:31:42 PM »
Actual spindle rpm is steady.  Checked with tach.  Also no change in motor sound.  My concern was that before downloading latest Mach3 versions, the rpm readout was steady.  Wias not sure that the variations in S True readout and actual spindle rpm steady if it could impact Mach3's thread cutting.  Spindle averaging is enabled.

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Re: Spindle RPM Readout Problem - S True not stable
« Reply #3 on: March 17, 2010, 05:35:21 PM »
I think this may be due to the way the driver works in the latest versions. Art did a lot of work on it for threading as some fast computers were having problems. Afraid I dont use the parallel port so have not seen anything like that but if I were you I would try a thread and see. Maybe do an air cut first to see if all looks well then try with a piece of stock in.
Hood
Re: Spindle RPM Readout Problem - S True not stable
« Reply #4 on: March 17, 2010, 05:55:15 PM »
Will give it a try.  Maybe Art can address the problem with a fix for us that still have the "slow" computers.  I use the S True display to set spindle speed using VDF manually with pot.  With it not steady, makes it a little more difficult. 

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Re: Spindle RPM Readout Problem - S True not stable
« Reply #5 on: March 17, 2010, 05:58:16 PM »
Can you attach your xml, I will have a look just in case I can see a problem.
Hood

Offline RICH

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Re: Spindle RPM Readout Problem - S True not stable
« Reply #6 on: March 17, 2010, 06:17:50 PM »
I assume you have Threading on the Lathe Manual "REV 1".
I am not sure what the later versions of Mach do to the threading ( that's why i am still using .033 ).

Since you are manualy setting the rpm then it should come to that rpm and be rather steady, the less variance the better.
If you were controlling the VFD via PWM or  whatever and at the same time Mach is trying to control feedrate then they would
fight each other and you will have a mess. So manaul setting of rpm only.

Mach uses the RPM DRO  ( which is a true rpm reading based on an index pulse / it is accurate ) for the threading. Fluctuations of 25 rpm are going to cause you problems, yea, i know that the threading cycle will adjust for variations, but you may getting into the senerio stated above.

I am thinking that you may need to play with the debounce interval &  index setting in config some. Additionaly you may want to tweak the slot some.  

RICH

Re: Spindle RPM Readout Problem - S True not stable
« Reply #7 on: March 17, 2010, 07:34:06 PM »
When I start spindle the rpm comes up to rpm, say 400 and remains mostly constant then will drop to 377, back immediately to 400, stay there 20 sec or so, then maybe drop to 355, back to 400.  I've tried different debounce and index settings with the same result.  Right now they are set on 500 and 10.  My slot is 4.5" dia.  I calculated min. slot width at 0.143 at 3000 rpm (used as max) and originally set it there.  RPM was not stable and increase slot width to 0.8 and worked fine until updated Mach3.  Any suggestions on the debounce and index settings?  How about the slot width?  Would go back to earlier verison but did not save when updated.

Hood,  will send you the xml via pm.

Offline RICH

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Re: Spindle RPM Readout Problem - S True not stable
« Reply #8 on: March 17, 2010, 09:53:37 PM »
Just a thought......I have the same index pulse card as you, but have never put it to use as the Halls sensor i use just works fine for me here.
Others have used that board  and have had no gripes so i am not knocking the boad, but rather questioning the output.
There is no hysteresis adjustment i think.
I was thinking that you may be missing some pulses from the board sporadically and that is screwing up the number of pulses seen by the pc. Another thought could be noise as i was carefull to keep the shielded wire away from my motor etc. BUT you said it worked fine in the other version.
So kills those theories.....

I assume you did un-enable the Turn diagnostics in the plug ins?

RICH
 
Re: Spindle RPM Readout Problem - S True not stable
« Reply #9 on: March 18, 2010, 07:07:14 AM »
I too use the C3 index card, i am also using version 3.042.038 of Mach

I am using the SS but the spindle reads correctly and stable up to 3000rpm

The disk diameter is 100mm the slot width is 6mm

Maybe you could try changing the input pin as some BOB'S have faster pin inputs than others and you have to choose the pin assignments correctly.

Phil
The Good Thing About Mach3, Is It's very Configurable

The Bad Thing About Mach3, Is It's Too Configurable