Hi all

after doing some nice work on my little CNC plasma table, I have now got a job which uses all of its travel capacity.

The steel is a bit bowed, probably max 4mm variation so not too bad across 625mm.

What happened on the first cut was that it started out perfectly then the cut started losing penetration intermittantly, my guess was that the THC was not tracking properly the bow in the sheet and i ended up with too high a cut.

I am stuck between it being the cheapo Proma THC i bought, or a setting issue.

In Mach i have the THC anti-dive at 90% and THC Z rate at 7%.

The rate was low because before it seemed to be overshooting, i.e. the THC loop could not keep up with torch travel and was adjusting too much, too late.

I think the Z axis screw is 2mm pitch and direct drive from a small Nema23 motor.

Maybe the rate is too low, the THC is crap, or something else is not right.

As this is my first table, I have no idea how much travel a THC is supposed to compensate for so I'm not sure where to pin the blame.

Any tips would be much appreciated.

Hmm, just found this on a site called cncarena....

"
Once you have it working you will be disappointed in the ability to cut the thin stuff. It's just not capable of responding or moving fast enough to keep up with warps while you cut at over 200 IPM .

The pure speed of MACH THC keeps practical response down to about 60 IPM in Z speeds on a fast Z. Factor in the added delay of the Proma that uses relays on the Up and DOWN and you will be luck to get stable operation at 30 IPM or less. Think about flying a drone at 6 ft above the ground over hilly county and your feedback is delayed by 1 sec!

The system will work on very gentle rises like on thicker material and at much lower feedrates."



Now, 30ipm is only about 762mm/min and I'm cutting way above that, could this really be the issue?

Well it looks like the THC is just no good, if i tune it for slow cuts it works well, but could never manage a cut at 3300mm/min, pretty certain if up the tuning to go faster it will bunny-hop on slow cuts due to overcompensating.

Anyone recommend a THC ?

I have tried contacting CandCNC but had no response yet.

I had this reply from Proma....

 "THC 150 has about 150ms (0,1 - 0,15s ) processing time, o don't sure what many time need mach for reaction.
total time isn't very well for it. I think that better is use model SD (step dir) or full system MD+DV. both systems works alone (without software) and total delay time is about 70-80ms - for high speed still it's not very fast but better that compact THC."

Sounds like speed is not their thing?

I have a Proma THC and it keeps up to my machine when it works. I don't cut faster than 120 IPM, but if I can get Mach3 to move the Z the THC keeps up great! My problem is getting Mach to move the Z every time THC commands it. It work intermittently. What exactly did you setup in Mach? Where is the THC anti dive & THC Z rate settings? I've played with this for months already but maybe I'm missing something?!! I hope you find something that works reliably and keep us updated! Thanks, Brian

Hi

I have rate set at 9 and anti dive at 90%

I tried lowering anti dive but makes no difference, might try turning it off.

i have never regretted the lcthc from  candcnc. basic height controller that just works and not very expensive.

But does it work at speed too?

I have tried contacting them for two days now but no response at all.

No objection to buying one if it works but can't do anything without a reply

Still no reply from CandCNC, are they still going?

I did get one from a guy going by the name of randyray but he said he could not help interface it to my torch as it's not for automation.

i cut up to 240 ipm on 12 ga  .100 thick  . sheets are 170x60. your speed of the height controller is set in mach3 as a percentage of the z jog speed. my z jog is set at 200ipm
and is set at 7%. oxy flame cutting is set at 30% as height control is being controlled with a joystick. while you are at it get the feathertouch ohmic contact sensor.

candcnc probably is on vacation.

Thanks, just got back from a break away, will be picking this up again soon..