Another person trying to understand THC

Ok So I have been cutting for awhile and have had pretty good results.
I have a XR and always have THC turned on when cutting.
I have been reading where people check the cut height with a feeler gage, and find it way off from what it should be.
So went in the THC manual and started reading as I wanted to check mine.
So they tell you to do the following

“The best way to determine your Nominal Voltage is to perform a line test and monitor the Live cutting voltage in FireControl. We recommend cutting an 8-10” line at the desired cut speed and amperage for a given material and then entering this voltage value as the Nominal Voltage before cutting your part”

“To do this, jog your torch down to the material until you are at the ideal cut height. Next, turn off your electronics box and unplug the Z-axis motor from the electronics enclosure and run the line test while monitoring the Live voltage”

If I turn of my electronics enclosure fire control quits working, and sometimes crashes.
So what am I missing?

turn it off, unplug the z axis motor, turn box back on and run test.

sometime you gotta think outside the box.

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I read the documentation for a reason and when I find something that does not make sense, I like to double check. Thanks

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there is a few people on here that have programs thq5 cycles the z axis to a cut height so you can measure what your machine thinks the cut height is. and it doesn’t involve the torch so no cutting. I have one fixed also if you want it.


If you think that is the way to I would like to give that a try. Thank you

Forgive me if you know or understand already. The THC doesn’t know or care what height you use if using smart voltage is takes a sample and assumes it is the correct height and keeps that voltage.

You want to make sure you are cutting at the correct height the only way to know is to confirm it yourself.
This program will throw a alarm about the THC when you start it. It is ok just procede any way . the program will need to move about 4 inches in the x and about 1 in the Y if i remember correctly. i would use a thicker piece of metal that will not have a lot of flex to it to try this. it will not try to fire the torch so no need to have your plasma on. It will move a few inches then touch off the metal raise to pierce height the move to what is understood to be .060 cut height and end the program. You can measure your actual cut height there.

I started programming my cuts at .049 because of the difference in the backlash to get a actual cut height. I have also started writing in my voltage instead of using smart voltage.

Look over the file name you may want to rename it so it isnt confusing.
test line.tap (245 Bytes)

Lets see if I understand the basics

So when using smart voltage the torch touches off, goes to pierce height, when done piercing drops to cut height and then measures voltage for the first part of the cut to see what arc voltage is?

Do I have that correct?

If so, this program checks to see if the torch is dropping to the correct cut height to come up with the correct arc voltage?

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You have that correct. Once the torch is at cut height, the THC takes voltage readings for the first .25" and uses that as the target voltage to maintain torch height. If the initial cut height is not correct, the THC will attempt to maintain that voltage and keep the torch at that incorrect height.

If you enter a nominal voltage, the THC will try to maintain that voltage, regardless of the cut height that you entered in CAM. So, if the IHS system results in an incorrect initial cut height, the THC will move the torch to the height necessary to achieve the nominal voltage.


The program is just to confirm what it thinks is .06 is what it is.

It will go to what it understands to be .06 then you can measure to confirm.

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Ok so if I find the Cut height is off I can correct this in fusion correct?
If this is correct and I make the change in fusion this should make Smart Voltage work correctly.

If the above is correct what is the advantage of using Nominal Voltage over Smart Voltage?

yes you can correct it in fusion. What difference it will make I am not sure. say you are off by .015 you may or may not ever notice a difference in cut quality or consumable life. Then you do find you cut height to be off and correct it in fusion then yes smart voltage will work better. The advantage to using nominal over smart voltage i would say is a can of worms. I started out with the rw 45 of course there is not a list for the voltages and what not. When i upgraded to a Hypertherm the cut chart had the voltage in it so i just started using it.


@knick the advantage i see to using nominal voltage is

  1. it is recommended not to use smart voltage on anything thinner than 14 gauge if i am not mistaken.
  2. i adjust my nominal voltage setting to achieve my optimal kerf. i have not measured what my actual cut height is and reading this thread i am now curious so i just ordered a set of feeler gauges but what i have done for the last year is once i get my general cut speed and amperage where i want it then i continue with test cut lines adjusting the nominal voltage until i get the optimally narrowest kerf i can achieve.
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I came up with Pierce of .166 and a cut height of .084 that makes me high on both.
So Fusion shows Pierce at .150 so I would subtract .016 from that figure correct?
Same for cut, shows .063 subtract .021?

So if I get the cut height correct can I take the voltage I see when cutting with THC on and use it for Nominal?

I would assume you could. I can’t remember any of the voltages from when I was using my rw45. I would definitely make a program with the altered cut height to see if there is any difference in cut quality. Then run it like that for a while to see if you get any better consumable life.

Ok So I made the adjustments in fusion and cut some 1/8".
I have never cut 1/8" so I cant say if its a improvement or not but it cut great.
Cut THC on 45A 100 IPM

I will have to wait till I cut some 14ga to see if it made a improvement.

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