THC Sawing action (Too fast)

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TrinityFabworks
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THC Sawing action (Too fast)

Post by TrinityFabworks » Mon May 13, 2019 12:06 pm

I have a proma THC and when it moves up and down, it does so too quickly and causes a back and forth sawing motion. Is there a way to slow down the z axis on movements caused by the thc?

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Re: THC Sawing action (Too fast)

Post by acourtjester » Mon May 13, 2019 5:33 pm

Look at the other post you have
DIY 4X4 Plasma/Router Table
CandCNC DTHC-IV & Feather Touch
Hypertherm PM65 Machine Torch
Drag Knife and Scribe
Miller Mig welder
13" metal lathe
Small Mill
Everlast PM 256 tig

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Re: THC Sawing action (Too fast)

Post by tcaudle » Mon May 13, 2019 8:20 pm

In MACH3 there is a settng called THC Rate. That is the speed used when moving the Z from the external UP and DOWN. That will not change if its an ESS or some USB card interface but there should be a setting in those plugins to control the Z speed under THC . The number is a % of the full Z speed . The Promo has a lot of delay built in on its UP and down so trying to move too fast causes overshoot and rapid oscillation. Typical THC rates are in the 20 to 30 % range. Hysteresis controls the width of the "dead zone" (were there is no motion) every volt is about .005 distance so 4 volts changes the height by .020 (out of .060) To put it another way the material willhave to vary .040 (.020 up or .020 down) before the THC starts to move .

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Re: THC Sawing action (Too fast)

Post by TrinityFabworks » Tue May 14, 2019 7:58 am

tcaudle wrote:
Mon May 13, 2019 8:20 pm
In MACH3 there is a settng called THC Rate. That is the speed used when moving the Z from the external UP and DOWN. That will not change if its an ESS or some USB card interface but there should be a setting in those plugins to control the Z speed under THC . The number is a % of the full Z speed . The Promo has a lot of delay built in on its UP and down so trying to move too fast causes overshoot and rapid oscillation. Typical THC rates are in the 20 to 30 % range. Hysteresis controls the width of the "dead zone" (were there is no motion) every volt is about .005 distance so 4 volts changes the height by .020 (out of .060) To put it another way the material willhave to vary .040 (.020 up or .020 down) before the THC starts to move .
Thank you! This is what I was looking for. I will give it a shot in the next day or so, and see what I can't come up with. What would you say is a good normal plunge rate? I think my Z is set at 80 ipm on the plunge, with no idea what the percentage is on the THC movements. How many inches a minute do you think that the calculated THC movement should be set at?

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Re: THC Sawing action (Too fast)

Post by weldguy » Tue May 14, 2019 9:28 am

TrinityFabworks wrote:
Tue May 14, 2019 7:58 am
tcaudle wrote:
Mon May 13, 2019 8:20 pm
In MACH3 there is a settng called THC Rate. That is the speed used when moving the Z from the external UP and DOWN. That will not change if its an ESS or some USB card interface but there should be a setting in those plugins to control the Z speed under THC . The number is a % of the full Z speed . The Promo has a lot of delay built in on its UP and down so trying to move too fast causes overshoot and rapid oscillation. Typical THC rates are in the 20 to 30 % range. Hysteresis controls the width of the "dead zone" (were there is no motion) every volt is about .005 distance so 4 volts changes the height by .020 (out of .060) To put it another way the material willhave to vary .040 (.020 up or .020 down) before the THC starts to move .
Thank you! This is what I was looking for. I will give it a shot in the next day or so, and see what I can't come up with. What would you say is a good normal plunge rate? I think my Z is set at 80 ipm on the plunge, with no idea what the percentage is on the THC movements. How many inches a minute do you think that the calculated THC movement should be set at?
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Re: THC Sawing action (Too fast)

Post by tcaudle » Tue May 14, 2019 2:07 pm

Plunge Rate has nothing to do with the THC response . It sets how fast the Z moves from pierce height to cut height. The actual Z motor tuning sets the Z upper speeds (using a G00 Z## command) the THC rate is a % of that number. The THC in MACH has no acceleration setting so you have to run it at lower feedrates to prevent motor stall . Then you have the loop dalay between the Z motion and the THC signals. Like a bad echo.

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Re: THC Sawing action (Too fast)

Post by TrinityFabworks » Tue May 14, 2019 3:30 pm

tcaudle wrote:
Tue May 14, 2019 2:07 pm
Plunge Rate has nothing to do with the THC response . It sets how fast the Z moves from pierce height to cut height. The actual Z motor tuning sets the Z upper speeds (using a G00 Z## command) the THC rate is a % of that number. The THC in MACH has no acceleration setting so you have to run it at lower feedrates to prevent motor stall . Then you have the loop dalay between the Z motion and the THC signals. Like a bad echo.
Ok, so plunge rate in sheetcam is just the rate at which the torch goes down from pierce to cut height? Nothing else? Where do I set my z velocity then? Is it just in my motor tuning in mach3? Or do I set up the Z-speed in sheetcam?

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Re: THC Sawing action (Too fast)

Post by tcaudle » Thu May 16, 2019 5:02 pm

Z speed is the motor tuning value in MACH. THC RATE is the speed it runs at DURING a cut with the THC active. Its a % of the Z max velocity in motor tuning. Changing either setting effects the Z response during a cut.

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Re: THC Sawing action (Too fast)

Post by TrinityFabworks » Tue May 21, 2019 7:53 am

tcaudle wrote:
Thu May 16, 2019 5:02 pm
Z speed is the motor tuning value in MACH. THC RATE is the speed it runs at DURING a cut with the THC active. Its a % of the Z max velocity in motor tuning. Changing either setting effects the Z response during a cut.
I checked my z-speed last night at the bottom of the main screen in mach, and it is set to 20. My z speed is at 80 ipm, so 20% should be 16 ipm. I can tell you that it is traveling a lot faster than 16 ipm! It also won't let me change the 20 to anything else. Any ideas?

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Re: THC Sawing action (Too fast)

Post by tcaudle » Tue May 21, 2019 6:43 pm

So is there a input box for THC RATE on your screen. Not sure what Z speed you are referring to because screens in MACH are custom to the vendor. Is that a screen from Promo?

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Re: THC Sawing action (Too fast)

Post by TrinityFabworks » Wed May 22, 2019 12:14 am

tcaudle wrote:
Tue May 21, 2019 6:43 pm
So is there a input box for THC RATE on your screen. Not sure what Z speed you are referring to because screens in MACH are custom to the vendor. Is that a screen from Promo?
Yeah, thc rate is on the screen. It is just the basic mach plasma screen. It's just a normal version of mach 3

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Re: THC Sawing action (Too fast)

Post by TrinityFabworks » Thu May 23, 2019 8:42 am

Nevermind, I got it figured out. My Z-speed was at 80 ipm, and the thc rate at 20 so it was about 16 inches per minute. I finally got it to change, so I dropped THC rate to 10 and it no longer overshoots at 8 ipm.

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