Qtplasmac with proma thc 150 Z axis up and down too quick!

Hi all,
I have helped a friend to mount a plasma cnc using linuxcnc with qtplasmac gui, the working area is with 3000x2100mm, Z travel with 350mm for perhaps in the future install a rotary axis.

We install proma thc 150 and all works really well until we start to cut 20mm of steel.
The Z axis starts to go up and down very quick causing bad quality in the cut, for this height of 20mm we have setup the plasma with 87 amps and proma thc 150 with 152 volts at a feedrate of 400 mm/minute.

The plasma is a Roluk inverter cut 100 HF with Autocut A 101P torche.
Until 10/15mm of cuting all runs good but cutting 20mm the quality isn´t so good, this plasma is anounced to be bable to manual cutting until 45mm  so even discounting some for cnc cutting it should be "easy" to cut 20mm.

Any help will be apreciated, thank you in advance.

We have changed the P value to 8, minor changes in cut quality, then to 6 then to 7 and it seems 7 is the value, very thanks.
Maybe tomorow we will change the z axis speed.
How can we change z axis cut speed without change in stepconfig?

thank you very much for your attention i will give feed back.

Thank you Tommy.
We think z axis is really really with huge speed, we have exagerated on purpose and fine cut height with this setup is with value of P=3%.
So tomorow we will balance the speed of z axis, we have speed up the z axis to speed up probe speed because we have a floating switch.
In sheets with 2x1,5m cutting pieces with 200x100mm and so, probe speed is a issue if is slow, so perhaps we will fine tune this to balance the speed workflow.

thank you

Thank you for your help always...!
Here some examples of plasma cnc working. Don´t know how put videos, i show you some images.
Machine was made here in Portugal! by us, with support of you in this forum and linuxcnc.org and youtube...
I think this machine in last 3 months, have cutted almost 6 tons

Very thanks

There is a limit we can do to help you with the Proma 150 you are using. Tommy here is probably the most experienced with them.
eusurplus is also in Portugal. I suggest you contact them and upgrade to a Mesa card with a THCAD and replace the proma. (I don't think Tommy has used a Proma for years)

I'm glad someone else wants to make probing as fast as possible. It can be done!
Here is a super short video I did

Thank you Rod
We have seen Mesa cards and THCAD system.
In first place we were prepared to equip this machine using UCCNC AXBB-E board with proma thc 150.
Then after some research we discover linuxcnc and this forum after my first build and no longer left linuxcnc.
So we bought proma thc and conect to a lpt board but yes maybe you are right in a industrial environment and near future we will upgrade to mesa card with Thcad system.

Also try to upgrade to a non hf plasma to take advantage of omic probes like in your video since HF Plasma and omic probes are not friends i guess.