CNC THC Plasma Cutter - Mach4 settings and THC

If you want to use a CNC plasma cutter with Mach4 and would like to configure it, here is a quick guide on how to setup the THC (torch height controller).

Table of Contents

The Mach4 version 2 has support for THC plasma cutter. If you have been using Mach3, there are some differences in settings for THC in Mach4. First we would like to point out that it is necessary to download the latest version of the Mach4 software. You will find iton www.machsupport.com/software/mach4/. Also important is that you use the latest PoKeys setup package and PoKeys Mach4 plugin to support torch height controller.

The THC plasma cutter wiring – already done

In this article we will not talk about how to connect the THC – torch height controller PlasmaSens (or other) to the plasma cutter and CNC controller PoKeys57CNC. We assume you already have a working plasma system. You can find all the information about CNC plasma cutter setup in our previous blog post with information about wiring and electronics.

Mach4 plasma – settings for motor tuning and plugin

For plugin settings, the only thing that need to be enabled is probing input pin. It can be any of the native PoKeys pins. Please check out our blog post for Mach4 probing for more information about probing (it should also be set up in Mach4 config window). Next thing that should be enabled is “Read EasySensors” in “miscellaneous” options.

PoKeys plugin settings for plasma cutter with THC — Plugin settings for PoKeys controller and PlasmaSens with probing

The first major difference compared to Mach3 is the configuration of the motors. With Mach4 plasma THC is handled with so called out-of-band (OB) motor. For example, if your THC plasma cutter uses Motor2 for Z-axis you will need also to enable axis OB1(6) and select the Motor for that axis. In our case, we will choose Motor5. Very important thing are motor tuning settings. Settings of Z-axis motor, in our case Motor2 must match those of Motor5 (OB1-axis).

Motor tuning settings for Mach4 CNC plasma cutter — Mach4 motor tunning setting in control configuration

Other configuration in Mach4 settings include the output for the relay for turning the plasma cutter ON. One option is relay on PoKeys57CNC controller that has to be selected as “Spindle ON” which turns on with M3 command. As mentioned, probing input has to be selected and mapped in the same way. Selected pin should match the one selected in plugin settings.

settings for digital input and output for THC plasma cutter — Mach4 control settings with Input and Output signals selected

Mach4 THC plasma settings

On the “Configure” tab, the new Mach4 version offers the user a window to configure the plasma screen. For use with torch height controller PlasmaSens we must select “Analog” mode and for “THC Axis” we choose 6 (OB1- axis) which we previously configured. Under “THC1(Analog) Settings” we must write correct “Analog Voltage Input Register” name. The name depends on PoKeys serial number. In our example, we must type exactly: PoKeys_40570/PlasmaSens HV. Please insert your serial number from PoKeys57CNC controller for your settings (PoKeys_xxxxx/PlasmaSens HV). Do not forget to mark “Use Analog Voltage for Arc OK” and enter the minimum and maximum voltage for Arc OK signal. That voltage is the high and low limit for cutting and it is not the final voltage, at which you will be cutting.

Mach4 plasma- Plasma Screen Configuration — Mach4 plasma – Plasma Screen Configuration

Testing the wiring and input signals

For testing that the settings are right, there is Machine Diagnostics tab in Mach4 home screen. The probe can be triggered manually and if everything is right, light should be on for the probe signal. The ON/OFF for the plasma cutter can be (carefully) tested with M3/M5 command in MDI or with buttons for the spindle. The THC On signal is activated when PlasmaSens detects the voltage of the plasma with appropriate value in window for the Arc OK.

Before first cut – THC Cut Start Settings window and THC tab

We set Target Voltage, Adjust Rate and Ant-Dive Rate:

Target Voltage: the voltage Mach4 will maintain for optimal cut
Adjust rate: the speed at which torch will move to achieve Target Voltage
AntiDive Rate: the rate at which XY Blend Velocity will disable AntiDive function

If there is a problem with plasma cutter moving up and down too fast during cutting in a wave pattern, the Adjust rate should be reduced. Too fast of the adjust rate is not beneficial for regulation of the height of the plasma torch.

THC plasma cutter settings in Mach4 screen — Plasma cutter – start cutting parameters

Mach4 Plasma screen has “THC Cut Start Settings” that allow users to define the start of the plasma cutting process:

Include Touchoff /Omit Touch Off: enable/disable the probe input in case we want to omit the material touch off as part of the M3 sequence (no probe or testing)
Max Find Distance: distance the torch (Z-axis) will travel to find the material top, probe’s switch activates
Touch Speed: units per minute Z-axis will travel during the probing
Torch On Height: Z-Axis position at M3 command
Pierce Height: the Z axis position when a pierce begins
Arc OK Delay (ms): Time in milliseconds, the THC waits to start controlling height
Pierce Delay (ms): Time in milliseconds allowed to complete piercing material
Cut Height: optimal distance between the material and torch during cutting
Min: Minimum height THC, while trying to achieve target voltage moving the torch down
Max: Minimum height THC, while trying to achieve target voltage moving the torch up