Really what you are looking for is range... If 20% works for everything you do, great, if you need to adjust the setting for thick and thin stuff then you really want some range to the adjustment, unfortunately the trade off is that you won't have phenomenal z axis rapid speed worthy of braging to your friends at the bar...  But it will work great, and the only time you use the rapid z axis speed is after touch off up to Pierce height, and a clearance move or safe z move after cutting.

Or cutting very thin sheet where a slow Z will not track in time as the sheet warps etc.

In use, i never adjust mine, just set and forget.

Dave, have you got a plunge rate for your zaxis.

I've now got a pmx45, 230v too.

After pierce where it moves down to cut height have you read anywhere or are aware of a recommended plunge from pierce to cut height, the reason why I ask is because of my fiddling with sheetcam post processors (no I ain't broken it yet), I noticed that some use the cut feedrate to drop from pierce to cut, whilst this may be OK for thin stuff with fast motion it may lead to an overcut a start (divot) where you have pierce delay and then a slower than it needs to be drop to cut height before motion.

(May be over thinking something here.....)

I'm currently plunging at 2400mm/min this is the max rate I have set in motor tuning for the Z axis.

I don't think I have ever read a recommended rate, the only recommendations I have seen are ' as fast as possible' as a very slow plunge will increase pierce time and cause divots.

I have my M03 macro set to ActivateSignal instead of DoSpinCW as it operates faster, also my THC ArcOk current is set to a low value so it triggers as soon as possible.

The way I look at it, once a hole is blown through (pierce delay), there's no need to hang about. Just get down to cut height ASAP and move into the leadin / cut.

I would hazard a guess that on thicker steel there could be some advantage to piercing with a mixture of pierce delay and slow plunge rate (the move from pierce height to cut height). For instance, on thick steel, as the pierce progresses the distance from torch to metal "surface" is increasing. On a 30mm plate let's say you start a pierce at say 5 or 6 mm then by the time the pierce has blown out metal half way through, the torch to metal distance is now about 20mm. Perhaps a slow plunge rate starting at that point is an attempt to get the torch a bit lower/closer to the metal "surface". Of course it can only go as low as the cut height.

Like I say though that's just a calculated guess as to how a slow plunge rate could have some use. Personally all I've ever done is blown a hole then moved to cut height at max Z speed (Sheetcam plunge rate).

Keith.

My preference is to blow the hole then get down ASAP, every time, I would rather control pierce with pierce delay as its controllable.

In an ideal world the change from pierce to cut would be instant i think.

Rob,
 I was not wanting to change the motor tuning (speed) setting.  My "height detection" software slows down to a crawl if I do it that way.  It will hold my 1% setting set in the XML file if I never try to change it on-screen. 

If I understand your reply... the fundamental Mach code has this valve screened at 5% or higher.   Too bad... it is what it is, I guess.

What height detection software?

Is it just a g31 or g28.1 macro for touch off?

What z axis screw pitch are you running with what stepper ampage and voltage?

Rob

Rob,

The "height software" I found and edited to suit my  needs.  I have a very fast and robust Z drive. I like it that way.  The motor is running on 60V, a couple of amps with a 1605 ball screw.

The "height software" detects the metal, moves to transfer height, turn on torch, pierces , them move to cut height.  This works fine.  If I slow down Z full speed,  it increases my run time a lot.  On short cuts (artwork), I spend more time in that software than running the cutting Gcode.