I have been using a CAP 04 capacitance based THC for a couple years now and it works very well. The CAP 04 has both Pros and Cons over conventional voltage based THC systems.

Pros

  • Works with both plasma and flame cutters.

  • Does not dive when CNC slows down for corners or circles.

  • Can work as an initial height sensor (IHS) even over a painted or rusty surface.

  • Can run and test without the plasma cutter running. This is major plus for setup.

Cons

  • Because it is a physical sensor it is much more work to install.

  • The sensor ring is a consumable

  • Crashes require re-tuning the sensor and ring

  • The sensor ring can get in the way

  • When the cut gets 1/2” or so from the edge of the stock the torch will dive.

While the CAP 04 has its place, I decided to start testing some voltage based systems.

THC Selection Requirements

These were my initial requirements when choosing the voltage based systems:

  • Provide UP, Down, and ArcOK signals to the CNC control system

  • Have the ability to disable the THC for rule based plasma CNC operations

  • Ability to be used with Mach3 Software and Windows

  • Cost under $350 delivered

  • Provides both an interface module and sensor module.

The reason for the separate interface module and sensor module is that they are less sensitive to interference from the plasma cutter. This also means the interface module can be located where it is more convenient to view and control.

Based on my initial research I will be looking at the following three systems.

  • PriceCNC AVHC10

  • MiniTHC

  • Polabs PlasmaSensOut

Update 1/28/2020 - I decided to drop the Polabs PlasmaSensOut module as it is not compatible with the Geckodrive G540.


The Test Platform

I will be using this CNC Construction set with the plasma upgrade option installed.

The system has both a UC100 and UC300ETH motion controller installed, so I can switch back and forth for testing purposes.

The PC has both Mach3 and UCCNC software installed. I also have boot options for both Windows 7 and Windows 10.

The system sports a downdraft system, floating head, and a Hypertherm Powermax 65 plasma cutter with machine torch and CPC port.

Once all the THC systems have been tested on the above platform, they will be moved to this one.

It also has a downdraft system, floating head and an Everlast 50S plasma cutter with hand torch.

Note that the Everlast 50s does have a CNC port that features both divided and full arc voltage output. Show here it has a CAP04 THC installed. This will be removed, and a floating head attached. The floating head will be used as the IHS.


Bear with Me

Please bear with me, as I will be installing all these systems at the same time so things may look a little crowded.

In addition many of the parts will not be permanently mounted so that I can move things around as needed.

IHS

A torch height control system requires an initial height sensor (IHS). These are used to detect the surface of the metal as you start each cut. The IHS comes in three forms, Touch, proximity, and floating head.

I will be using the floating head that is based on this book:

Heavy Duty Floating Head