Plasma Table Z-Axis Issues

I've had this table up and running for a week now and the set up is Mach3, Gecko 540, CandCNC B.o.B interface card and a LCTHC. Initially, everything went fine I had all the axes adjusted and was learning how everything functioned together. When all of the sudden the Z-Axis would stop homing in the right location, so if home was +1" it would be +1.25", then I noticed the pierce height was drifting one time it'd be .75" then the next time say .1". One other thing I can't figure out is the THC quit working about the same time. If I set the tip voltage at 100v it'll just cut at whatever it wants, however, if I shut off the tip saver it'll obey the tip voltage commands. While I thought I could live without the tip saver function it still doesn't solve the pierce height issue or the loss of the Z-Axis height. I readjusted the Z-Axis and played with Mach 3, but I'm not sure if it's software or hardware at this point. I'm still fairly new to all of this unfortunately.

Thanks in advance for any help you might be able to offer!

Matt

It's probably losing steps in Z while you cut. That is dependent on the Z mechanics and the motor tuning. The parameter in MACH that determines the Z velocity WHILE THC IS ACTIVE is the THC Rate. It is a percentage of the max Z velocity. You can't use the full velocity for THC moves because the acceleration curve is not used during THC moves so too hign a speed will cause lost steps. You can see lost steps if at the end of a cut using the LCTHC it does not lift the correct amount you have programmed in. MACH keeps track of all Z moves even if the motor does not actually move so they get out of sync.

Run a simulation of the code with the THC off in MACH and the torch off. Put it in single block mode (diagnostic page as "SINGLE"0. That single steps you one line every time you puch the RUN button above it. The moves are all G-Code (not from the LCTHC) and have to be absolutely correct before you can get the automated part to work right.

I'm not sure I understand your Z home being some where up in the air ?? Z zero is the top of material (where ever that happens to be and will move on you) and with the LCTHC the Z Home is the touch-off switch with the flaoting torch holder. Tip saver comes on when you have a condition where the actual torch voltage is the preset percentage ABOVE the preset. The THC Delay should delay the THC from reacting prematurely tot he pierce cycle it you have it set to a time LONGER tahn the pierce delay + the plunge time + the beginning of the cut at the correct height. You can't tunr over control to the LCTHC if you are not already cutting at the approx the right height and it has settled down from the pierce and plunge.

Remember the LCTHC does not set the TORCH Volts. That is proportional to the gap so if you fire it up in the air and plunge down to the wrong initial height then the voltage will be all wookie and the LCTHC will see that as a voltage fault and turn on the TIP saver. See, the voltage spikes like that if the torch cuts into a void (more air than metal) like at the end of a closed cut and the TIP saver is a dynamic anti-dive to stop the dives you get when the torch hits the end or crosses and kerf or close to one)

TOMcaudle
www.CandCNC.com

Tom,

I'll try all of those things this weekend as soon as I can make it my shop! Thanks for the reply..

Matt

Tom,

So I did some testing and I found that even when cutting a straight line on a flat sheet the Z axis climbs while the tip gap remains constant. The Anti-Dive is set to off and indicates +60.0. The Z THC speed was set at 30% should it be set lower... something like 10%? I'm not sure that I should have that on.. Perhaps that's been the issue the whole time?

Matt

Yep, you're losing steps on your Z. Lower the THC rate. Try 10% first, then increase that if you feel it's too slow for what you need to do.

Quoting my first response.

Quote:

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Originally Posted by Torchhead

It's probably losing steps in Z while you cut. That is dependent on the Z mechanics and the motor tuning. The parameter in MACH that determines the Z velocity WHILE THC IS ACTIVE is the THC Rate. ,,,,,

TOMcaudle
www.CandCNC.com

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Any axis who's actual physical position does not agree with the DRO for that axis is either losing position (motor stalls from trying to accelerate too fast up to a given velocity) or the axis calibration (steps per unit is way off).