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Author Topic: Lathe - set max RPM for CSS?  (Read 12154 times)

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Re: Lathe - set max RPM for CSS?
« Reply #10 on: January 23, 2012, 06:15:59 PM »
Hi Hood,

Very informative.  Thanks for the test results.

I am thinking through your observations.  Too much for my tiny brain this early in the morning.

Question "did the G48 S1000 command limit work as intended?"

If so, I may look at using the G48 Limit in the future if the opportunity presents itself.  Right now most of the parts I make are very small.

Regards

Chrisjh

Offline Hood

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Re: Lathe - set max RPM for CSS?
« Reply #11 on: January 23, 2012, 06:24:05 PM »
Yes G48 works fine
I may try tomorrow without the G48 just in case it is that that is screwing things up, actually come to think about it I have tried in the past I am sure without the G48 so likely its not the issue. Will test anyway just in case my memory is playing tricks ;D
Hood
« Last Edit: January 23, 2012, 06:27:42 PM by Hood »

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Re: Lathe - set max RPM for CSS?
« Reply #12 on: January 24, 2012, 08:07:56 AM »
With this resurrected, perhaps Andrew will shot it to Brian and they will fix it!! Wouldn't that be something? CSS is one of CNC lathe's nicest things. Threading and CSS are what make a CNC lathe a wonderful thing!!
Re: Lathe - set max RPM for CSS?
« Reply #13 on: January 24, 2012, 03:18:54 PM »
Hi Hood:

I did a test of your code on my machine. I had to create a profile for Mach to make it metric (it has inch lead screws).  I needed an excuse to have a metric profile as it could make the programing of metric threads a bit simpler.

It took the same time both directions and the actual speed of the screw is constant (at least as far and I could tell).

Here is the code"

%
(01/23/12 - Pin_mm.tap)
 
 N1 ( od turn )
 G0 G40 G18 G21 G80 G50 G90 G95
 G0 G53 Z-50.0
 T101 M6
 G0X150
 G48S1800
 G96S200M3
 G1X50F.1
 G1X150
 G97 S400
 M9
 M5
 M30
%

See video of operation.   http://youtu.be/5n8QdBuvfbw

Let me know if this helps.

Jim

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Re: Lathe - set max RPM for CSS?
« Reply #14 on: January 24, 2012, 03:30:25 PM »
Ok thanks for that, not seen the vid yet as its taking a long time to load properly for some reason.
So from what you say it seems to be working better for you but still not correctly as the X axis should increase in velocity with RPM increase or decrease with RPM decrease to keep the FPR as programmed.
I wonder why there is a difference, I had asked previously in other threads whether things worked right with the parallel port and it seemed it didnt but maybe its just different. I am using the SmoothStepper (ESS now) are you using the parallel port?
Hood
Re: Lathe - set max RPM for CSS?
« Reply #15 on: January 24, 2012, 03:53:26 PM »
Hi Hood:

Yes, I tested this way back and got diffferent speeds as I recalled.  I was using inch per rev. feedrates at that time.

This machine is using parallel port.

I will mess with the G98 Feed/Min and the G99 Feed/Revolution and see what I find. 

Jim

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Re: Lathe - set max RPM for CSS?
« Reply #16 on: January 24, 2012, 03:55:45 PM »
Ok Thanks, BTW its G94 F/MIN and G95 F/Rev

Hood
Re: Lathe - set max RPM for CSS?
« Reply #17 on: January 24, 2012, 09:20:45 PM »
Hood: 

Right.  G95 is the feed per rev.  That was actually set in the modal set line.   I was looking at the Smid book where he uses G98 / G99.

You can actually see the screen showing feed per rev change as the X axis moves toward the spindle center. When the rpm is doubled, the feedrate shown is exactly half. 

More testing.

Jim

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Re: Lathe - set max RPM for CSS?
« Reply #18 on: January 25, 2012, 04:49:11 AM »
Ok just done some more tests and now I get the axis travel time the same in both directions, things are still wrong however.
Ok first how I get the axis times the same was a clue I got from Jims code, I had noticed he only called the feed rate once, I had called it on each move. So what is happening is X moves to min and feed/rev has halved, previously I was calling  F0.1 and then moving out again so CSS then reset the FPR as 0.1 and as the axis moved out then it doubled it as spindle slowed. With not calling the F0.1 again then the move was starting at F0.05 so by the time it got to X max it had ended back at the F0.1.

Now this is still totally wrong as what Mach is doing is keeping the velocity constant(FPM), when in FPR mode that should not be happening as it kind of defeats the purpose of using G95.
What should happen is the FPR stays constant and the velocity (FPM) increase with spindle increase or decrease with spindle decrease.

Hood
Re: Lathe - set max RPM for CSS?
« Reply #19 on: January 25, 2012, 02:30:44 PM »
I think I'm confused again (happens easily) -

Playing with MDI and the gcode mode status line...

G94 give me a G94 (F/min ) mode - OK
G95 gives me a G95 (F/rev) mode indication - OK
G96 S********* give me G96 - in addition to the G94 or G95.... huh?
So it seems I can get these combinations:
G94
G95
G94 + G96   - a constant F/Min with CSS ??
G95 + G96   - ??

Once you've turned on CSS via G96, how do you turn it off?
I found G97 - that seems to be accepted on the MDI line, but no matter what I do, I still have the G96 in the mode status line...
I can't seem to get back to a non-G96 state.

Dave



Author of the MachStdMill Extensions for Mach3
www.CalypsoVentures.com