Hypertherm pierce height question

Maybe this question is most oriented for hypertherm plasma cutters users, as I do not know if the torches from hypertherm are different from the others.

I am in the decision phase of buying a hypertherm power max 105 with a mechanical torch to make a plasma cutter table. I am quite confused how the initial pierce height is done, because I do not understand how the plate is "touched off" with the plasma nozzle.

Taking in consideration most of the videos that I see from larger machines, the nozzle touches every time that it will pierce the plate very slowly. Is the plate height obtained because a electrical signal, that the nozzle closes when it touches the plate? it is a mechanical method (if so what happens in very thin plates?).
Hypertherm sells a complete Z axis, and the information that I got from Hypertherm is that the plate is know due to the larger torque that the motor must do when it hits the plate, that can be a problem in thin plates.

What do you people do?

This video is clearly mechanical as it can be seen part of the torch support to move:
This i do not know but seams working quite nice:https://www.youtube.com/watch?v=-cGSlkjMGlE

Thank you

Typically these torches use a "floating head" mounted to the z axis with a switch. When z is lowered the nozzle contacts the material but the z axis continues to descend until a limit switch on the floating head is triggered.
This should give you an idea...
wiki.linuxcnc.org/cgi-bin/wiki.pl?Plasma
forum.longevity-inc.com/showthread.php?4...tion-on-reliable-arc

John may have some pictures of his set up also.

On mine I use a proximity sensor.

Rick G

The floating head idea is not so good on very thin plates.
How do you use your proximity sensor? It is placed where? I also have now a machine with a proximity sensor that I call it on tool with a different offset so that the probe is done where the plate is going to be pierced, then I call the "plasma tool" and the nozzle goes to the same spot as the sensor, but I find this approach slow because there are two unnecessary movements (but it works fine).

The proximity sensor is mounted next to the torch tip on a pneumatic cylinder (about 2" away).
To find the height the machine moves to locate the sensor over the pierce location.
Then the pneumatic cylinder lowers the sensor to it's reading location to use as probe.
Z then lowers to to find the height of the material, stops, then slowly rises to set height.
The pneumatic cylinder then retracts to get the sensor out of harms way, and a relay disconnects the sensors output to avoid false signals.
The machine then moves the torch to cut location and pierce height.
May not be the fastest way to do it but works well for me .

Rick G

After research a bit, hypertherm sales a cap that is called ohmic cap (I think is the standard cap with a place to connect a wire to). This is intended for the touch off on the plate, at least is how it seams. I will probably give it a try as I want to use a magnetic base for the torch (so that when it gets hit it triggers a error state) and this way is not so practical to have a floating torch.

@Rick: Your method is equal to the one that I have now (but without the pneumatic). I really do not like the movement between the sensor and the torch, although I have it working for 10 years without problems.