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Author Topic: Thermal Height Control (THC) bouncing problem. CNC Plasma  (Read 10531 times)

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Thermal Height Control (THC) bouncing problem. CNC Plasma
« on: June 01, 2012, 02:53:08 PM »
I have a Plasma Route CNC plasma cutting table with 3 axis stepper motor set up.  It is running mach and has a thermal height control (THC) that the company provided.  The THC has a "brain" that senses off the plasma cutter and sends information to Mach 3.

My Problem:
I can cut with no problem when The THC is turned off.  The cut is very smooth and almost straight up and down.  When I turn the THC on the Z axis jumps up and down continuously during cutting which produces a terrible cut (jagged and tapered). 

Question:
How can I adjust the THC so that it cuts smooth like it does without it on.  I have to Use the THC because all the plates I get are always bowed. 

I'm in a pinch and need this quick, Please help.

Offline BR549

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Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #1 on: June 01, 2012, 08:46:38 PM »
The osillations come from running  the vel of the z faster than  the THC can keep up with. The z overshuts and then the thc tries to correct and it overshoots again and again CUt the max velocity of the z in half. If that slows it down but does  not stop it cut it in half again. 

Plasma route SHOULD be able to give you the correct settings for the Z axis.

(;-) TP

Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #2 on: June 04, 2012, 12:19:05 PM »
Thanks for your reply BR549 but I have tried that.

My system is in inches.  My velocity was over 90 and I tried backing it down a couple times and even brough it down to 10.  The problem still occured.  I've adjusted the acceleration as well. watching the z, I can see the motor turning left and right constantly during the cut. 

I've been trying to get ahold of plasma route for a week straight and they will not answer or return my phone calls. 
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #3 on: June 05, 2012, 12:16:30 PM »
do you have a thc speed dro on your plasma screen?
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #4 on: June 05, 2012, 02:55:36 PM »
Please see attached images of my system.  I'm new to Mach plasma.  I'm more familiar with mach mill.  I hope these pics answer your questions.
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #5 on: June 05, 2012, 09:52:02 PM »
 change the thc rate dro to 6 from the 15 and see if that works. adjust that number up or down.  i use at 6-7 with a z jog speed of 90.
i set it at 15-20 when moving the z manually with a joystick when flame cutting.
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #6 on: June 07, 2012, 09:54:11 AM »
Tripleblack, Thank you so much.  That fixed my problem.  Well It will cut good using a 40 amp tip on plates 1/16" through 1/4" and using a 60 amp tip for sizes greater than 1/4".  If I cut 1/4" with a 60 amp tip it still cuts bad.  I'm fine using the different tips though.  I set my THC feed to 5.  Thanks for the help everyone.
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #7 on: June 07, 2012, 12:16:04 PM »
what plasma cutter is it? hypertherm?  make sure that the air pressure is set to the recommendations of the plasma cutter manual.and dry air.  higher pressure does not make it cut better or cut thicker material. i run at 70 psi with a powermax 1100, 80 amp nozzles.
Re: Thermal Height Control (THC) bouncing problem. CNC Plasma
« Reply #8 on: June 07, 2012, 12:24:05 PM »
The plasma is a miller spectrum 875 auto line.  The only thing I saw in the manual is not to use more then 120 or 130 psi.  I'm gonna look at it again.