THCAD-10 + hypertherm 45 (nonXP)

depending upon your setup + which hypertherm you have the book should provide the target voltage.

a hypertherm PMX 45 (nonXP) with sheilded consumables on 1/4" Mild Steel has a feedrate of 60ipm (quality cut), and a target voltage of 120V, upping the feedrate to 75 ipm (production) will reduce the target voltage to 116V

unsheilded consumpables in both cases feedrate remains the same, but voltage is 118V

Also are you SURE that your cut height was 0.08in?

I don't believe that the 100K input impediance of the THCAD-10 will affect the sensed voltage that much

The combined resistance of the voltage divider will be 101961 Ohm (against 102 000Ohm) [0.3% variance], also allow for the tollerance of the resistors (expect 1% to 5% [I've not checked them]) The voltage you read could be slightly out.

Suggestion,..... do a touchoff at the start of the cut, zero the torch, then modify your gcode to stop at the end of the cut and then do a probe at the end of the cut and check the cut height (you may need to move slightly of your workpiece has any top dross). the numbers should be similar (i.e. both end at zero under the probing [not got into Linuxcnc yet, presume G31?]
All you do is apply an offset within Linux CNC.

I've not tried it, but there is also an option to try to use an autoleveler to correct z-axis motion for any variance between your material and your torch....

www.autoleveller.co.uk/

If you're not aware of the software it's worth a look on youtube just to be aware of it

You could use this to setup a number of calibration cuts where you log the voltage between points A-B where your machine corrects for any changes in material height by adding z axis corrections from point A - B via a set of probes between points A-B you then cut your material knowing that from points A-B with a material thickness that is unlikey to bevel / change with heat [much] you have a fairly consistent cut height...

Like I said I've not tried it (but may give it a go some time.... projects permitting....)

Looking at the test piece cut again (on a bigger screen than a phone...)

It appears you may have a slight bevel (inwards at the top), which may indicate that the torch is a little too high

image.thefabricator.com/a/articles/photos/1445/fig7.jpg

I am certainly going to try to get torch height control working... (it is all there now)

sam

skunkworks wrote: I am certainly going to try to get torch height control working... (it is all there now)

sam

Sam, are you using the external offset branch?

Rod

The autoleveler was not to avoid THC, but provide a means to calibrate the THC if required given the Z axis will then track between points A-B and level according to the advanced probing routine (it won't work for long cuts and it won't work for thin metal or near the end of the cut where the metal may twist and bend upwards with expansion).

Plasma beds & slats always have slag on them and the plate is never level hence this is just one thing I thought may allow someone to set the z to track from A-B whilst monitoring the voltage so you know a constant 0.08" cut height IS XXX voltage.