THC settings confusion

[fest]

Hi,
I'm new here and just few days ago me and my father assembled all the electronics for plasma sheet cutter for his workshop. Mach3 is running fine, all axis move without problems, and I can even do some basic cutting (when THC is disabled). We use THC301d hardware with their default screens for Mach3.

What is strange though- the THC on/off button in main screen does not respond. The only way to get THC to work is to check 'Enable THC UP/DOWN movements even if not in THC mode'.
This leads to next problem- a preset voltage of 130v is set on THC front panel. When machine starts cutting, actual voltage is lower- let's say 100v. I do see the UP LED flashing on the front panel, and THC Up input is active in Mach3 diagnostics screen- so no problems in Mach3 config, but Z-axis moves down- both on the machine (torch moves closer to material) and in Mach3 - it goes from Z2.5 to Z0.<something> which triggers the limit switch and machine halts. At that time THC DRO reads -2.4. The question is - why does the machine behave this way? Is there an error in my configuration or default screens/macros? Maybe if I just switch up and down inputs in ports&pins config, it would behave correctly, but I think it would be confusing to have THC down input flashing in mach and torch going up?

I have THC Max set to +1 and THC Min to +0.2 - so I assume if cutting height is 2.5 mm, THC could only adjust Z-axis from +2.7 to +3.5? (I just realised the positive-only settings could be causing this problem- I'll try to THC Min to -1 and see what happens.

Z-axis positive direction is up- when jogging machine and in G-code moving in Z+ direction moves torch up, and moving in Z- moves torch down.

Any help or directions would be appreciated

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[Torchhead]

Lets start with the THC Button. If it fails to respond then it's probably because you are running a DEMO version of MACH. It disables the THC Logic even though the signals are coming in. Get a licensed version installed

2. If the THC is not working then your voltage preset mean nothing. It's just cutting along at whatever voltage it happens to cut at.

3. if you set your THC Min to .2 that is almost 1/4" above the material so cutting down at .125 or .063 where most torches operate would not work. If the material warps down it makes it even worse. Set you THC Min to either 0 or slightly negative. You just want to keep it from plunging down forever if it sees a voltage spike. That setting is a lot less important if your THC has the anti-dive built it (I think the 301D does).

Make sure you understand where the top of material is (Z 0) and how the automated touch-off works to find the proper height to pierce at.

[fest]

Torchhead, I really appreciate your help.
1) I didn't see this limitation of demo version mentioned anywhere in Mach3 docs. My father still considers alternative options because of ease of use for operators but I'm pushing him to Mach3+Sheetcam- that's why I still run demo.
2) It's weird, but THC does work, kind of. Just works in the opposite direction (but this migh be related to the fact that I have turned THC on in spindle settings).
3) I use metric units everywhere, so 0.2 means 0.2 mm, but will try to set it below zero. THC301d has antidive indeed: http://www.texasmicrocircuits.com/TH...301Dv4back.jpg (carefully, heavy file).

The machine uses capacitative sensor for touchless initial-height sensing, and I use SheetCAM which generates the required g-codes for homing Z axis and setting the offset.

[fest]

Long time since my last post, but we the problem actually was in old Mach3 version. Purchased & upgraded to the latest one and THC works almost smoothly.

There is now only one problem with homing of Z axis- when the Z axis position is increased by THC (plate warped upwards) and the cut is finished, when the cutter moves to next piercing point, it triggers a limit switch when homing Z axis (I have modified the Sheetcam post processor to home the axis on each cut).
It seems to me that the problem lies in fact, that THC correction value is not added/subtracted from Z axis position in Mach 3. After cutting, the real position of Z axis might be 10mm (from initial plate position), but Mach thinks it's 4mm. Now, if the plate below the next cut has also warped a bit upwards, when homing through 3mm (G28.1 Z3.00) it might trigger the limit switch before the middle point is reached - and that triggers a limit switch instead of home switch (floating head with a single switch). Isn't there a command in Mach3 that will home the axis, regardless where it's located without going through a middle point?
This is the problematic part of generated G-code:

N0450 (Operation: No Offset, Layer1, T1: Plasma, 3 mm kerf)
N0460 M05
N0470 G00 Z30.0000
N0480 X294.4400 Y59.7263
N0490 Z6.0000
N0500G92 G28.1 Z3.00
N0510 G92 Z0.0
N0520 G00 Z0.0000
N0530 G92 Z0.0
N0540 G00 Z6.0000

This is full code we were running:
spriego207.txt

[asuratman]

Hello Torchhead,
Is your THC depend on the type of driver? Can I use DMM-Tech in companion with your THC. Thanks.

[Torchhead]

Long time since my last post, but we the problem actually was in old Mach3 version. Purchased & upgraded to the latest one and THC works almost smoothly.

There is now only one problem with homing of Z axis- when the Z axis position is increased by THC (plate warped upwards) and the cut is finished, when the cutter moves to next piercing point, it triggers a limit switch when homing Z axis (I have modified the Sheetcam post processor to home the axis on each cut).
It seems to me that the problem lies in fact, that THC correction value is not added/subtracted from Z axis position in Mach 3. After cutting, the real position of Z axis might be 10mm (from initial plate position), but Mach thinks it's 4mm. Now, if the plate below the next cut has also warped a bit upwards, when homing through 3mm (G28.1 Z3.00) it might trigger the limit switch before the middle point is reached - and that triggers a limit switch instead of home switch (floating head with a single switch). Isn't there a command in Mach3 that will home the axis, regardless where it's located without going through a middle point?
This is the problematic part of generated G-code:

N0450 (Operation: No Offset, Layer1, T1: Plasma, 3 mm kerf)
N0460 M05
N0470 G00 Z30.0000
N0480 X294.4400 Y59.7263
N0490 Z6.0000
N0500G92 G28.1 Z3.00
N0510 G92 Z0.0
N0520 G00 Z0.0000
N0530 G92 Z0.0
N0540 G00 Z6.0000

This is full code we were running:
spriego207.txt

You have no value set for a switch offset so when it goes down, touches you zero the Z (proper) but then it just stays there (should lift up the switchoffset distance (download the DTHC manual from Our website and look at page 28. It will explain how to determine the switchoffset value and then where to use it either in MACH or in the SheetCAM post (but NOT both)

During a touch off you are telling MACH where the top of the material is in relation to the end of the torch. Once you get the offset properly working your pierce height should be exactly what the code calls for (6mm) which seems high for most plasma units but you probably have it set that high to get a net distance of about 3 mm.

Once you have the touch-off working properly then the Z will track all of it's movements. but they are relative to the last touch-off. You may want to set a higher rapid height and possibly a higher value for the Homing start. It's currently at 3 mm (which if the material warps or you have the wrong setup mentioned above it will slam down to the material in rapid Z BEFORE it starts a homing move. IF you have the Z home switch setup as a LIMIT too then it will limit before it actually starts a home move.

The rapid height (how far it lifts between cuts is part of the CAM (g-code) and should be about 12mm or more.

TOM caudle
www.CandCNC.com

[Torchhead]

It seems to me that the problem lies in fact, that THC correction value is not added/subtracted from Z axis position in Mach 3. After cutting, the real position of Z axis might be 10mm (from initial plate position), but Mach thinks it's 4mm. Now, if the plate below the next cut has also warped a bit upwards,

THC Corrections are absolute values in MACH the the Z cannot exceed (for mm setups the values should be something like +25 and -2. They have nothing to do where the position of Z is or the DRO value. It's just a safety value that keeps the torch from diving down to the end of its stroke if it runs off the material or into a void. It's less important on a unit that has integrated anti-dive but it has to be set greater than what you would expect the excursion to posssibly be.

TOM caudle
www.CandCNC.com

[Torchhead]

Hello Torchhead,
Is your THC depend on the type of driver? Can I use DMM-Tech in companion with your THC. Thanks.

The subject of this thread is the THC301D and is not our product so the answer to your DMM-Tech compatibility should be derived from the THC301D vendor.

I can tell you the DMM-Tech products use their own BoB and custom interface cables to the drives so It won't work with any of our MP3000 and DTHC based products which have a special BoB with a Port Expander to increase the number of Inputs and outputs in MACH for a single Port.

TOM caudle
www.CandCNC.com