[TonyWish]

On a cnc controlled plasma I notice on a dome or an angled pc. of steel my torch will move up and down just under a quarter of an inch when cutting. It does this through out the entire cut like it is chasing the right distance but keeps over correcting. I have THC and the arc voltage runs about a 50 volt span. Is this normal?? It leaves a lot of slag and sometimes a lot of sparks.

So is this normal? If it isn't where should I look.

Thanks for your help.

Tony Wish

[larryy1022]

On a cnc controlled plasma I notice on a dome or an angled pc. of steel my torch will move up and down just under a quarter of an inch when cutting. It does this through out the entire cut like it is chasing the right distance but keeps over correcting. I have THC and the arc voltage runs about a 50 volt span. Is this normal?? It leaves a lot of slag and sometimes a lot of sparks.

So is this normal? If it isn't where should I look.

Thanks for your help.

Tony Wish

First pls check if it is on auto mode when u cutting dome or come to a corner, a good THC should disable auto mode in such situation. If your THC doesnt freeze auto mode, it might be the reason.
For the corner signal u need to set in your cnc system, there should be follow setting,
1. disable auto mode according to the distance to corner,
2. disable auto mode according to the diameter/semidiameter of round shape,
3. diable auto mode according to the cutting speed,

U need to check with THC supplier if the THC has this function or not, and check your CNC setting.

If your cutting always shake up/down, as long as it is on auto mode, that means the THC is over-sensitive. it needs your supplier's guide to adjust the sensitive of THC.

larry

[jimcolt]

Since you do not mention what type of THC or plasma system you are using....I cannot accurately help. Most conventional air plasma systems need the arc voltage (which is proportional to physical height) to stay within about a 5 volt plus or minus range when cutting....for best cut edge quality in terms of dross and angularity. Better height control systems are designed to maintain arc voltage within 1 volt of setting. 1 arc volt change is roughly equivalent to .004"...so when you see your torch moving 1/4" (.25") then the calculation is close to correct.

Some height controls have a gain or deadband adjustment. Sometimes the z axis slide assembly does not have enough holding power to stop...and overshoots the voltage, causing a correction (sewing machine effect) in the opposite direction.

Accurate torch height control is absolutely critical to good cut quality and long consumable life. I would suggest working with your supplier to determine the issue and make adjustments to maintain the voltage as suggested above.


Jim Colt Hypertherm

On a cnc controlled plasma I notice on a dome or an angled pc. of steel my torch will move up and down just under a quarter of an inch when cutting. It does this through out the entire cut like it is chasing the right distance but keeps over correcting. I have THC and the arc voltage runs about a 50 volt span. Is this normal?? It leaves a lot of slag and sometimes a lot of sparks.

So is this normal? If it isn't where should I look.

Thanks for your help.

Tony Wish

[Dustin407]

On a cnc controlled plasma I notice on a dome or an angled pc. of steel my torch will move up and down just under a quarter of an inch when cutting. It does this through out the entire cut like it is chasing the right distance but keeps over correcting. I have THC and the arc voltage runs about a 50 volt span. Is this normal?? It leaves a lot of slag and sometimes a lot of sparks.

So is this normal? If it isn't where should I look.

Thanks for your help.

Tony Wish

Hi Tony,

What type of THC system do you have??? Can you be a little more informative on your description of what is exactly happening from start to finish. It sounds like you are venting more than being specific for us cnc friends willing to help.... Thanks... I am currently having some thc problems also and will get to it probably sometime in this thread...

[TonyWish]

Jim,

Our system is a Thermal Dynamics A60 running on WINCNC. We got some of the problem fixed when we changed the PCB cards, however our arc voltage varies by at least 30 volts. Should I expect better?

Tony

[jimcolt]

Tony,

If the arc voltage varies more than plus or minus 5 volts...then expect cut edge angularity issues , collisions with the plate, dross and warpage. The height control simply is not accurate enough if it varies more than a total of 10 volts....which is about plus or minus .020".

The best torch height controls used on industrial machines must maintain plus or minus 1 volt......which means they maintain the proper cut height to plus or minus about .002".

With the variation you are experiencing....I suspect that either the z axis drive is "coasting" and over shooting the setpoint....which means it likely is oscillating up and down......or the electronics are allowing too much of a deadband. Maybe there is an adjustment or setting that will tighten up the control feedback loop.

Jim Colt Hypertherm