Hi all , it seems with out 2 year old Micut cnc plasma the eratic thc is caused by our drawins and not the controller (so they say ) Les has re wrote a new post for us and made some difference but our torch still has the tendecy to go up at different time through the same drawing but wont come back down , only 3- 5 mm but thats enough height to melt our art to geter , we only use 1.6mm plate , if its our drawings that arnt as clean as they would like for the machine to run smooth , is there a programe that i can put in our drawings and clean them up , would appreciate any comments
Regards Ross 
I put some of this in my email reply but I’ll put it here as well as it may help others. If you zoom in closely on your artwork the edges are jagged. They look like they have been scanned from a bitmap image. Plasma cutters like smooth edges and jagged edges will cause problems. The machine has to slow down as it tries to faithfully follow those edges. As the machine is now cutting at the wrong speed the THC voltage will rise. At a guess your machine has anti dive which locks out the THC in this situation, leaving the torch at the wrong height if the work is not dead flat. Without anti dive the torch would probably drop until it hit the work. Arc voltage based THC is simple and robust but it needs the machine to run at close to the optimum cutting rate to work properly.
If you are converting scanned images, try using a different conversion package. For best results, trace the outlines manually in CAD. Manual tracing is slower but it generally produces much cleaner results.
I have attached section of a picture you sent me. If you look at the vertical cuts, they look almost like a sawtooth. This looks like vibration in the gantry to me. Try cutting a 100mm (4") square in the middle of the machine’s working area. Look closely at the corners. You will probably see that in one direction the cut looks ragged close to the corner, with it smoothing out as the cut progresses. This is the gantry vibrating from the sudden change of direction. Unfortunately this is a design issue. The gantry is just not stiff enough. Plasma machines have two conflicting design criteria - the gantry needs to be light to give good acceleration on corners but it also needs to be stiff to avoid vibration. Getting the right balance is difficult. Your combination of fine detail and high cutting speed exaggerates the problem.
One workaround for gantry flex is to cut close to the edge of the machine. Obviously this doesn’t help if you are cutting large pieces. Reducing the plasma power and cut speed may also help.