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Messages - Davek0974

2391
General Mach Discussion / Re: THC Setting Issue?
« on: July 30, 2014, 10:20:24 AM »
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?

2392
General Mach Discussion / Re: THC Setting Issue?
« on: July 29, 2014, 03:45:45 PM »
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?

2393
General Mach Discussion / THC Setting Issue?
« on: July 29, 2014, 10:51:10 AM »
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.

2395
The breakout board is generally the one with the parallel cable connected.

Any chance of a picture or link?


2396
In that case, if you shut the PC off and pull the parallel cable, does the relay drop out?

If no then my money is on a fried breakout board, it does happen.

2397
Probably not connected but I get this error if I try to start a cut without doing a re-origin first.

If i jog to start position, re-origin the display, then press start it works every time without warning.

This is on a plasma table.

2398
Is it controlled from a smaller relay on a breakout board?

Is this a parallel connected machine?

It is possible the driver for the relay has gone bad and is permanently on, if so a new board could be needed.

2399
I find 70% speed reduction works for me on awkward small holes! but that's relative to my machine I guess.

I am still having difficulty grasping why you would want to induce corner rounding, I spent considerable time and effort to get rid of it :) getting it was easy - just poorly design a machine and try to use it ;)

When you say slowing accel helped a bit, did you go way low?

I find that by using a reasonable speed (my machine is not very fast) and fine-cut consumables on my little torch, I can get good results on 1mm sheet

2400
I've just set a small table up and after many dozens of questions, the best results by far have been found by turning off all the cv dialogue in mach, just leave the Use CV mode on or put it in the g-code. Then tune the machine to have as high an acceleration setting as possible without losing steps and that's it.

I'm getting great corners, THC is working ok, I do use loops on some outside corners if I want really sharp corners.