Hypertherm 85 Torch Bouncing

I have a Plasmacam dhc2 4x4 and am using both the Hypertherm 45xp and Hypertherm 85 on this table (one at a time - of course). Here is the scenario:

11 ga. mild steel, pierce height 0.100", cutting height 0.070", time to pierce 0.7 sec, fine cut consumables, cutting speed 80 ipm, 45 amps, kerf width 0.052", digital height control set to "Standard Settings", air pressure 100 psi at regulator just before HT plasma cutter power supply. I am using the torch that came with the HT 85 and plugging it into either the 45xp or 85.

When cutting with the 45xp everything seems to work as it should and I am happy with the cut quality of my parts. However when I switch over to the 85 the z-axis is oscillating (torch "bouncing" or "see-sawing") during the entire duration of each cut. The z-axis active light on the plasmacam controller stays on during the entire cut with the 85. It does not come on at all with the 45xp while cutting (except for the z-axis height changes from rapid height to pierce height to cut height).

I have tried slowing down the climb and dive rates and increasing the zones as suggested in the Plasmacam manual. This did not help the situation. Since this is only a problem when using the 85, I am assuming that either something is causing the arc voltage from the 85 to fluctuate or the 85 is creating a large amount of EMI switching noise that is being picked up by the Plasmacam controller. The noise on the voltage divided arc voltage wires connecting the 85 to the Plasmacam controller (as observed on an oscilloscope ) is about 3 times as large as the comparable noise coming from the 45 under the same cutting conditions ( 150 V ac at 150 khz for the 85 vs. 50 V ac at the same frequency for the 45). I have read over most all of the posts that I could find that dealt with this sort of issue. It has been suggested that fluctuations in air pressure will cause arc voltage fluctuations. My air pressure seems to be fine, and I assume that if it was not I would be experiencing the same problem when using the 45xp.

Per the Hypertherm techs suggestion I have used the HT85 front panel display to monitor the actual gas pressure vs. the set gas pressure while cutting. The pressure is set at 69 psi and is steady at either 69 or 68 psi actual gas pressure.

I have tried running the HT85 on both 3 phase and single phase power with the same problem still existing either way.

The specific consumables I am using are: HT220857 swirl ring, Ht220842 electrode, HT220930 nozzle (Fine Cut), 220953 ohmic retaining cap, and HT 220948 shield (Fine Cut).

I will certainly appreciate any help anyone can provide to help me resolve this problem.

Thanks,

David Buchhauser

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