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Author Topic: THC moves on the Z axis...  (Read 6569 times)

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Offline Davek0974

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THC moves on the Z axis...
« on: January 30, 2016, 10:23:19 AM »
Been doing some tuning on the table and got to the Z axis, trying to decrease plunge time etc.

I had it set originally at 1200mm/min and 900mm/s/s acceleration, this seemed a tad low so I pushed it up until it screeched which was at 2000mm/min so i backed off to 1500mm/min. The acceleration went way up to 5000mm/s/s before a screech so backed that down to 4000mm/s/s which gives an estimated 0.3g and 744rpm measured with a tacho on the motor shaft. I think thats ok for a 3.1Nm Nema23 motor. Steps per mm is 1000, 3mm pitch screw direct drive.

This has given a much snappier Z action and normal repeated G0 Z50 / G0 Z0 moves showed no loss of position.

My question is, is there a way to simulate a THC move - these use no acceleration and is usually where the trouble starts??
« Last Edit: January 30, 2016, 10:25:03 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: THC moves on the Z axis...
« Reply #1 on: January 30, 2016, 11:03:55 AM »
Yes there is a way (thanks TP),

ports and pins - toggle emulation on and my system was already assigned hotkeys U & D

Is it best to set THC rate as high as it will reliably run or can that be too high??
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: THC moves on the Z axis...
« Reply #2 on: January 30, 2016, 11:50:44 AM »
As fast as it stays reliable and avoids occilations.   ALSO check your setting in Scam for pluge rate for Z After the pierce. THAT helps with avoiding that dimple you may see on pierce.  It does not help to have a fast Zdrive unless you actually use it (;-)

(;-) TP

Offline Davek0974

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Re: THC moves on the Z axis...
« Reply #3 on: January 31, 2016, 08:35:23 AM »
Well, using the keyboard to bang the Z up and down I was surprised how lazy it really was!

I had 10% rate set and a max Z of 1300mm/min, Now I have 1500mm/min and upped the THC rate to 20%, It could handle 30% easily but 40% screeched and did nothing so I know I have a bit of slack still from 20 to 30%.

Now, this brings me on to a serious point that is baffling me - I have been bashing the crap out of my Z all morning, hammering it up and down with the keyboard, messing with tuning etc and it has behaved flawlessly all day apart from when being pushed too hard by my setting.

BUT, I put some code on and cut some tests and bugger me if the first time it hit a G00 Z3.8 for the pierce, it just sat and screeched, then next time it did IHS the rapid part of the G28.1 move screeched and was missed then it dropped at the slow rate all the way and carried on as normal.

This appears to be Mach3 not using the acceleration on the G00 move or the G28.1 move - is this a known bug/flaw/defect ??

I really do NOT think it is motor tuning as it has done it before and did not do it once using the keyboard to rapid the hell out of my Z axis.

Any ideas???
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline BR549

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Re: THC moves on the Z axis...
« Reply #4 on: January 31, 2016, 02:31:59 PM »
Well actually JOG uses a different process in Mach3 to move as compared to feed. Always TUNE/Test  the axis with G00 or G01.

(;-) TP

Offline Davek0974

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Re: THC moves on the Z axis...
« Reply #5 on: January 31, 2016, 04:11:33 PM »
I did, I made quite a few up/downs with G00 Z5 / G00 Z30 commands from the MDI line and it always worked well, no sign of a screech.

I also used my IHS calibration routine to run repeated sequences and it always worked.

When running code it screeched maybe once every 10 or so runs, now I come to think of it, I'm fairly certain it only did it when doing a G28.1 move.

I always presumed the jog with keyboard and shift simply moved the motors towards max velocity at the stored acceleration curve??
« Last Edit: January 31, 2016, 04:13:11 PM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives

Offline Davek0974

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Re: THC moves on the Z axis...
« Reply #6 on: February 13, 2016, 07:01:38 AM »
Spent the morning ripping my Z axis apart to replace the 10x2 screw & nut with a 10x4 combo.

This seems to have helped but my question is this - it now has the ability to be tuned from the previous 1500mm/min to 3000mm/min easily so should i take advantage of that or will make the problem return?

I currently have it set at 3000mm/min speed and 3000mm/s/s acceleration and it works fine during tests but have not done any cutting yet.

Steps per was a simple change from 1000 to 500.

It is a heck of a lot more snappy though :) I reduced the Z probing rate to 20% for the last portion of the G28.1 routine.

Another fantastic revelation was that because I have a probing subroutine now, I only had to alter the switch offset in Mach and it was back to it's accurate IHS in seconds - no messing with code changing etc :)
« Last Edit: February 13, 2016, 07:03:11 AM by Davek0974 »
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives
Re: THC moves on the Z axis...
« Reply #7 on: February 13, 2016, 07:32:07 AM »
As fast as it stays reliable and avoids occilations.   ALSO check your setting in Scam for pluge rate for Z After the pierce. THAT helps with avoiding that dimple you may see on pierce.  It does not help to have a fast Zdrive unless you actually use it (;-)

(;-) TP

.... any suggestions on plunge rate for sheetcam to avoid dimple on pierce?

Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”
Re: THC moves on the Z axis...
« Reply #8 on: February 13, 2016, 07:36:07 AM »
Spent the morning ripping my Z axis apart to replace the 10x2 screw & nut with a 10x4 combo.

This seems to have helped but my question is this - it now has the ability to be tuned from the previous 1500mm/min to 3000mm/min easily so should i take advantage of that or will make the problem return?


... this one is an interesting point that I'd be interested to know the answer to.

Your mechanical advantage has halved  (TR10x2D to TR10x4D).... hence if the motor stalled at 1500mm/min..... are you sure that your machine will make 3000mm/min, simply because your leadscrew pitch has doubled .... but your mechanical advantage halved?
Rob

Albert Einstein ― “If you can't explain it to a six year old, you don't understand it yourself.”

Offline Davek0974

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Re: THC moves on the Z axis...
« Reply #9 on: February 13, 2016, 07:45:24 AM »
Sanity says i should cut the rate back down and take advantage of lower motor speed / higher torque etc, but I can ONLY make the fault appear when running code, not when manually jogging or using the MDI, I am fairly certain it has only ever done it when running G28.1.

I am guessing that it set at twice the rate and twice the pitch I am actually worse off - it was doing 1500mm/min on 2mm pitch now doing 3000mm/min on 4mm pitch.

I could split the difference and go to 2000mm/min maybe?

But why only stall when doing G28.1 and why only when running code?
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives