sheetcam.com

I have just done a first few cuts with my new DIY plasma CNC.
I made a simple file in sheetcam basically a square 50x50mm with a tab on one side that is 30x3mm and also a slot in the centre of the square 30x3mm to try the fit of the tab in the slot. I am using 3mm thick mild steel.
The piece came out exactly on size for the outside cut, but the inside cut although on size has a beveled side on the X- and the opposite on the X+ side.
The two sides are very beveled and also parallel to each other as if the torch was angled at about 45 degrees.
I checked the torch mounting and it looks OK to me and why would the outside cuts be vertical while the inside cuts are slanted but only on two sides?

There are a number of things that can cause beveled cuts. The torch not being perfectly plumb in both the X and Y directions being one of them. The torch being too high or too low will also cause bevel cuts. The consumables in the plasma torch can cause the bevel if they are getting worn, are incorrect parts, or have some contaminants in them.
There is nothing in the software side of things that can cause the bevel, other than the torch height. If your cut height is always correct (that's not always a given), then you are left with checking mechanical issues.

Not knowing all the particulars of your machine, that's the best I can do for now,
Steve

WyoGreen wrote: ↑Wed Jan 22, 2020 5:58 pm There are a number of things that can cause beveled cuts. The torch not being perfectly plumb in both the X and Y directions being one of them. The torch being too high or too low will also cause bevel cuts. The consumables in the plasma torch can cause the bevel if they are getting worn, are incorrect parts, or have some contaminants in them.
There is nothing in the software side of things that can cause the bevel, other than the torch height. If your cut height is always correct (that's not always a given), then you are left with checking mechanical issues.

Not knowing all the particulars of your machine, that's the best I can do for now,
Steve

Thanks Steve, it gives me something to work on.
The torch is brand new, so the consumables should be OK. Torch set at 3mm above work for start cut and at 1.5mm while cutting.
As this is my first cut I have not explored other settings yet. I checked the angle of the torch and it appears to be vertical to the work piece.
The air supply is highly filtered and also has a dryer so there should be no contaminants.
What confuses me is that the outside cut is perfect apart from a little dross, but the inside cut has this strange beveled edge only on two sides.
Maybe my acceleration is a bit too high as well as the inside corners are a bit rounded rather than being square.

cut direction.....

https://www.hypertherm.com/Download?fil ... &zip=False

clockwise for an outside cut part and counterclockwise for an inside cut hole

regpye wrote: ↑Wed Jan 22, 2020 6:29 pm The torch is brand new, so the consumables should be OK.

Don't be so sure. I've ruined a set of consumables with one bad pierce.

robertspark wrote: ↑Wed Jan 22, 2020 8:51 pm cut direction.....

https://www.hypertherm.com/Download?fil ... &zip=False

clockwise for an outside cut part and counterclockwise for an inside cut hole

Thanks Rob, I will check on that, should be able to see in sheetcam.
That is a very interesting article, has a lot of other info as well that is useful.

djreiswig wrote: ↑Wed Jan 22, 2020 9:33 pm

regpye wrote: ↑Wed Jan 22, 2020 6:29 pm The torch is brand new, so the consumables should be OK.

Don't be so sure. I've ruined a set of consumables with one bad pierce.

Thanks djreiswig,
Not sure what to look for in the consumables, so I guess I will do a visual check and see if there is something that doesn't look right.

Check the hole in the nozzle. If it is not round or scarred up on one side you will get bad cuts. We have some magnifier glasses that we use. You can see the rough texture on the edges of the bore with them.

djreiswig wrote: ↑Wed Jan 22, 2020 11:53 pm Check the hole in the nozzle. If it is not round or scarred up on one side you will get bad cuts. We have some magnifier glasses that we use. You can see the rough texture on the edges of the bore with them.

Checked the consumables, all OK.

robertspark wrote: ↑Wed Jan 22, 2020 8:51 pm cut direction.....

https://www.hypertherm.com/Download?fil ... &zip=False

clockwise for an outside cut part and counterclockwise for an inside cut hole

That fixed that problem, I was cutting both the wrong way.
Now another problem has arrived. The controller is freezing after the first cut or doing some very strange movements (going all over the place)
and yet yesterday there was no problem. Same settings for power and air pressure, same file, just reversed the directions.
I think maybe I am still having problems with EMI, and will have to put some pullups on the limit pins as they are floating at present.

regpye wrote: ↑Thu Jan 23, 2020 2:23 am That fixed that problem, I was cutting both the wrong way.

That'll do it.

What plasma cutter?
What motion controller?
Usb, ethernet or parallel port interface?
What gcode interpreter / motion control software (mach3, uccnc, linuxcnc??)
How did you wire everything up?

robertspark wrote: ↑Thu Jan 23, 2020 7:33 am What plasma cutter?
What motion controller?
Usb, ethernet or parallel port interface?
What gcode interpreter / motion control software (mach3, uccnc, linuxcnc??)
How did you wire everything up?

The plasma cutter is a Chinese CUT50P pilot arc machine. Suppose to be CNC compatible but it has a lot of EMI to deal with.
Motion controller hardware is my own design using a nano microprocessor and opto legislators on all inputs, uses a USB interface and firmware is GRBL 1.1h
Using Universal Gcode Sender to send the code to the processor.

All stepper motor cables are shielded and shield is only connected at the control box end. Ferrite beads on most cables. Ferrite beads (4 of them) on USB cable. A common earth is used for the control box, CNC frame and the plasma positive output. The electronic are all contained in a sealed metal box that is earthed to the common point on the machine. The mains power supply has an EMI filter and also ferrite cores before it reaches the UPS.

Limits have been disconnected until I sort out the EMI problems, will change the micro switches for a different system, maybe proximity sensors or micro switch modules with EMI ferrules added. I have disabled the homing and the hard limits in GRBL and also fitted 10K pullup resistors to the limit pins so they are not floating.
Waiting on some more shielded cable to come before re-wiring the limits. Limits were working perfectly until I started the plasma arc and then the system froze. Disconnecting the limits was not enough to make the system work while cutting, I had to disable hard limits in GRBL to get the system working better.
Can now make cuts but still have a few random problems of wandering and freezing up. I am sure it is due to EMI problems still.

From all the posts I've been reading lately, it appears these Cut50 type machines are Hi-freq start machines, which put out a lot of electrical noise when they fire the torch. People seem to be spending a lot of time and money trying to get their tables to work with the the Plasma cutter.

I hope you are able to get your table and torch to play nicely with each other, Steve

Is that one of those "Pay me now or pay me later" kind of deals?