FIX: IHS Triggering Before Torch Touches Plate

We have heard a few people having one or both of the following symptoms:

  1. Randomly, the torch will drive down for IHS, but never reach the plate before raising up to fire the torch.
  2. Randomly, the torch will drive down for IHS at an extremely slow rate. It touches down on the plate as normal but takes much more time to get there.

Both of these symptoms are caused by one thing: the IHS switch is being triggered before the torch reaches the plate. Recall that an IHS event involves the following sequence of events:

  1. The torch rapids down to the plate at a rapid rate, triggering the IHS switch
  2. The torch rapids up a small amount (~1/8") which untriggers the switch.
  3. The torch SLOWLY feeds down to the surface of the plate, triggering the IHS switch a second time. At this point, the Z position is recorded.
  4. The torch rapids up to pierce height, fires, and then rapids to cut height before motion begins.

Now lets discuss the ways that the IHS switch can be triggered even without touching the plate. The IHS switch is a normally closed switch and the weight of the torch and slide assembly are what keeps it closed (along with a 1/2 pound spring which offers further switch closing force). There are 3 primary ways that the switch can be opened and triggered:

  1. the torch touches the plate and unloads the switch (GOOD!!)
  2. There is insufficient slack on the torch cable. When the torch drives down the tension on the cable pulls up on the torch which unloads the switch.
  3. Excessive preload on the V groove ball bearings causes excessive friction with respect to the slide moving up an down.

If you are facing this problem, the first and easiest thing to do is to make sure you have sufficient slack in your torch cable. Try to provide the most slack possible.

If that doesn’t fix the issue then you will need to adjust the preload on the V groove bearings. In the image below, you can see that there are two eccentric axles with which preload adjustments are made. Using a 5mm wrench, turn each counterclockwise to slightly reduce the preload. Be careful not to reduce it so much as to introduce excessive freeplay. The goal is to make certain the slide can move up and down freely so that the switch stays closed at all times when the torch is not touching the plate.


The fix for IHS sticking and causing slow probing cycles or high (in the air) pierces is to add a software debounce to the IHS cycle. We have implemented this in a firmware update to the Motion Control Board and new versions of the two Post Processors. If you are not having this issue, you do not need to update either of these.

1. Download XLoader to flash the firmware onto the Motion Control Board.


2. Download the Updated Gen2 MCB Firmware (v1.2ls).

CrossFire Gen2 Motion Control Board Firmware v1.2ls:

3. Download the appropriate Post for your software workflow.

Fusion360 Post Processor v1.6:
SheetCAM Post Processor v1.6:

4. Flash for Motion Control Board with the updated Firmware.

Make sure that FireControl is not running while flashing updates.

In the Windows Device Manager we see both THC and CrossFire MCB devices. The CrossFire Gen2 MCB is listed as ‘USB Serial Device’ and the THC unit is listed as ‘USB-SERIAL CH340’. Note the COM port number of the Gen2 MCB (in our case COM4). The THC device is COM23.

Next on the XLoader app, select the hex file from above (the .hex file that you downloaded above), the ‘CROSSFIRE CNC’ Device and the matching COM port (in our case COM4) for the Gen2 MCB as determined above. Make sure the baud rate is also set to ‘115200’ and then hit Upload, wait for it to successfully upload and then close Xloader before opening up FireControl again.

When you open FireControl again, you should see the Machine connect with a Firmware version 1.2ls.

5. Install your post processor into your CAM software.

Follow the instructions in the Software Tutorials to install.

6. Re-post your program using the new post.

The new post uses an altered IHS sequence which measures the height of the material in two passes- one from above and one from below- to get a more accurate height measurement.

7. Run your Program.

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