Im getting diviots from my Pierce point.

[MIFab]

Ok so I have a plasmacam with 3.11 and running a Hypertherm 380. Im having an issue when cutting inside shapes the lead keeps cutting into the project no matter what thickness of metal or how long I make it.I also have an issue of it not finishing the cut.

[aweston]

I also run Plasma Cam and notice the same issue, also round "dots" at lead in for cut lines. I wish I had the answer for you. I have tried adjusting pierce height and also cut speed but can not seem to correct it. I have had luck with correcting parts not fully cutting by selecting "overcut to reduce undercutting", or changing "gap at end" in the settings menu. If anyone out there knows how to correct the other issues I look forward to the post.

[MIFab]

Thanks Ill give them a try. Yea it makes projects look like crap if you cant fix it with a grinder .

[jimcolt]

Divots are usually caused by a change in cut speed. Think of the plasma arc burning away at the metal.....if your machine is moving at a constand speed you can expect a constant cut width and a relatively smooth edge. If you reduced your speed dramatically while cutting, the plasma continues to burn at the preset power level....so at slower speed the arc reaches out for more metal.....and will leave a wider cut path.

On lead ins that have a sharp turn into the programmmed part....the cutting machine decelelerates, stops, turns into the part. The plasma was on, and with this slower speed and stop it created a wider path then a divot from sitting still.

On lead outs at the end of the cut the motion stops and the plasma is electrically extinguished by the cutting machine.....plasma does not instantly extinguish, rather it takes a few miliseconds to lose its ionization, and a few for the air flow to stop, so it keeps burning a bit after the machine stops its motion.

High end industrial cnc plasma machines use some advanced technology to anticipate the shutdown of the arc at the end of each cut.....they shut the arc off in advance of the end of the part program and allow it to ramp down while the machine is still moving. This can be complex as the effect and the timing is different on each material type, material thickness and plasma power level. These industrial machines also use some advance software to automatically generate a lead in that works best for the particular material and power level.....which almost completel eliminates the divot from the beginning of the cut.

With the low cost, less sophisticated plasma cnc machines you can do similar things to minimize divots at the beginning and end of each cut cycle, but it is a more manual operation that may involve a bit of experimenting with your part drawing....especially the shape of the lead in at the beginning of the cut as well as the place at the end of the cut where the plasma shuts off. Further, experiment with the acceleration setting on your cnc machine.....increasing the acceleration and or cornering speed sometimes will minimize the divot assciated with the machine having to slow and stop to transition from lead in to cut path.

Here is a drawing of a radial lead in on the beginning of an inside cut (on the inside slot), as well as a slight gap at the end of the cut. The radial lead in makes it easier for the machine to transition from lead in to cut path, definitely minimizing the divot on the transition. The gap at the end of the cut (experiment with the size of the gap) often minimizes the end of cut divot. On the outside cut......try to do a straight lead in if the part has a good starting point...such as the outside rectangle in the picture.

Jim Colt Hypertherm

Ok so I have a plasmacam with 3.11 and running a Hypertherm 380. Im having an issue when cutting inside shapes the lead keeps cutting into the project no matter what thickness of metal or how long I make it.I also have an issue of it not finishing the cut.

[MIFab]

I would be happy with your explation but it comes and goes. I can do a hand full of pieces on the same thickness of metal and 4 out of 8 will come out perfectly and at ramdom .

[jimcolt]

It is not random, there will be an explanation for it if you are willing to troubleshoot. I suggest looking carefully at the parts with the divots and determine if they were all cut with the part in the same direction, or if you had nested some of them 90 degrees from others. Some binding that could be caused by the motion of your machine (such as a dirty rack gear, some rust on a way, some backlash in your drive mechanics, etc.) could easily be the cuprit. You will have to carefully look at where the issue is occuring and find a correlation.


Jim Colt Hypertherm

[MIFab]

Thanks