Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: giannis121 on August 30, 2007, 04:07:59 AM

Title: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on August 30, 2007, 04:07:59 AM
As you know, when cutting with plasma, in proportion with the direction of cut, the kerf side changes. So, when cutting CW the kerf should be outside and when cutting CCW the kerf should be inside.
Now my question is:
Can mach3 calculate the kerf automatically by a given value in a DRO?
If no, can i use different tools from the "tool table" to do it? (how does this table work?)
Any ideas would be helpfull...
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on August 30, 2007, 01:15:46 PM
The Gcode G40,G41,G42 are the Gcode commands for kerf on/off. Best you take care off it in your nesting software as there is no reverse run possible in G41,42 blocks. If you loose the cut, you cant go back to restart.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on August 31, 2007, 01:51:56 AM
First of all thanks for replying.
OK, my nesting software gives G41 when CW and G42 when CCW and G40 at the end.
So, now, mach recognizes the kerf on/off and stop? And where can i set the kerf width?
Because (if i understand well) kerf is the gap that plasma leaves on material through cut.
So, if i have a rectangle shape of 100 x 100mm and the kerf width is 3mm, the path should be at 103 x 103mm,
and the final cutted rectagle will have the 100 x 100mm.
Can you help on this?
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on August 31, 2007, 05:27:15 AM
Yes I can help you, I use MAch3 for plasma. The g41 and 42 is your tool offsets and can be set in the Mach3 environment. I use Cadlink's profile lab for nesting and post processing, but I take care of the kerf in the parts I generate in Turbocad. This is really because of the limitation to do reversing in Mach3. Mach3 will not allow you to run reverse if you lost the cut whilst in g41,42 blocks. This is essential with plasma cutting, as you might have to change consumables whilst in a cut. When you pause the motion you will overshoot the cut because of the slowdown parameter.

But if you want to use the g41,42 just set the kerf in the tool offset facility.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on August 31, 2007, 05:38:07 AM
OK,
but where is that tool ofset facility?
I cant see it on the menus.
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 03, 2007, 03:31:19 PM
Hey man, I forgot about this topic! Shees, I'm getting old. I believe the offsets are the G54 and onwards settings in the "Config" drop down menu under "fixtures".

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on September 10, 2007, 01:48:56 AM
Whacho, i tryied that (the g54) and seems that it follows again the original path.
Where can i find some information about all these g54-59???
I know nothing about them...
Ciao!
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 10, 2007, 05:16:49 PM
No, the g54 is a tool select, with an offset parameter in the tables you save as I said earlier(the offsets are the G54 and onwards settings in the "Config" drop down menu under "fixtures). So you slect the tool at the start of your code, then you implement the g4X codes in the codefile as normal.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 10, 2007, 05:27:02 PM
I put some visuals up, it should help.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on September 11, 2007, 07:09:24 AM
Maybe i cannot understand exaclty what you say.
I put in the code before the G41 or G42, the G54 command:
.
.
.
G54
G41
.
.
.
I set at the fixtures (that very helpfully you uploaded) the kerf width that i want for axis X and Y.
Then i load the code.
The shape is a rectangular 200x200 mm.
So, i am expecting the cursor to go to 3mm around the shape (if the fixture is 3mm) which means 203x203mm.
Am i right?
Does it need anything else?
Because it does not work.
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 11, 2007, 02:06:05 PM
To be quite honest, I will have to go back and check how I did it, because I abandoned the kerf compensation because of the no-reverse in g41,g42 code. I will check it out and get back to you.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 11, 2007, 03:40:30 PM
Ok, this is it! Disregard all I said before in this thread. I got rusty cause I played with the offsets way back. I went through the whole excercise and then everything came back to me, including why I don't use the G40,G41,G42 codes, and it's not just because you cant do reverse or jog in the kerf enabled modes.

To get it to sort of work, you go to the "config" menu. Click on "tool table". A selection box apears. In slot one you can type plasma as the name. The kerf will be the diameter setting. Enter your kerf diameter and save.

Now the kerf is saved in slot 1 of a possible 255 settings. Don't use the G54 command. You use the G41D1 command. The D1 designates the tool number with it's diameter in slot 1 you entered before as I described. So, D1 is TOOL1. D does not mean diameter. I think you cannot use just G41/42, you have to select the tool. Someone who has more experience and watching this thread can correct me on this. But in my setup it won't work unless I specify the tool number. But this is where you will discover that Mach3 don't work kindly for plasma application.
So to cut a square your code could look something like this.

%
G21
G91
G00X10.00Y10.00
G41D1
M07
G01X0.00Y100.00
G01X100.00Y0.00
G01X0.00Y-100.00
G01X-100.00Y0.00
M08
G40
G00X-10.00Y-10.00
M30
%

You might get an error about concave cut in cutter radius compensation or something like that. Then you could do this:
%
G21
G91
G41D1
G00X10.00Y10.00
M07
G01X0.00Y100.00
G01X100.00Y0.00
G01X0.00Y-100.00
G01X-100.00Y0.00
M08
G40
G00X-10.00Y-10.00
M30
%

You won't get the error, but the kerf compensation ramps up to full diameter at second corner of the square. No good, cause you'll be cutting into the job.

That's one of the few reason's I gave up on it, and I did post something about the G41/42 some time ago, but Brian replied that the way Mach3 is written, its a big problem to change the code and I have to compensate for the kerf in the CAD software. I don't use Lazycam, but I did read something about this in an earlier thread.

Well, Sorry for leading you on a goosechase.

Whacko
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: giannis121 on September 14, 2007, 08:26:56 AM
I did exactly what you suggest above.
But now the program stops at the G41D1 command,
by showing white the next command on the screen,
and with no error generated. Just stops there waitting.
Should i make any configurations? (I tried a few things in the general config menu, but nothing...)
 ??? Please help!
Title: Re: How to calculate the kerf width for plasma cutting?
Post by: Whacko on September 14, 2007, 10:59:50 AM
If the program stops there it is most propably an error. That is one of the reasons I don't use the G41 etc codes. I had problems with it, and then worked around it. Maybe Brian or someone else can step in here and give you advice.

Whacko