default position of cut

[jjanes]

Hi I will tell you first I am new at CNC and still learning quite a bit every day. My latest question has to do with the positioning of the cut line. does Mach3 default to the center of the cutting tool diameter or 0 if none exist. For instance if I have a tool that has a 1/8" diameter endcutting bit setup and make a 1" x 1" square. If I measure it will the square be 1" x 1" when measuring from the outside edge, the inside edge or the center of the cutpath. I will assume it is the center. If this is indeed the case, is there a Gcode command or something that I can use to adjust for the actual width of the cutpath to make the 1" x 1" square measure that way from either the inside edge of the cut or the outside edge automatically based on Gcode know the tool cutting diameter. I know I can do it  manually using an offset for a line but what about a circle. How does an the offsetting of the cutpath get adjusted for curves I picture trying to cut a path similar to the letter 'S' on its side the offset would get screwed up.

Very confused at this point
Jeff

[Hood]

Mach will cut where the code tells it, have a read of the manual for cutter comp, it explains things a bit. CAM programmes usually do that for you by offsetting the toolpath by the radius of the cutter you have entered.
Hood

[jjanes]

I just need some clarity  how does MACH3 tell the machine to cut the outside or inside of a particular shape like in my previous post here assume the shape is the letter S on its side so what was its base is now the left side creating a cut path using what I think offset does by offsetting say
the x axis by the diameter of the cutting tool would I suspect leave you a mis-proportioned  s curve since it has both an inside and outside curve to it. I believe the system would have to make have of it in + offset direction and half in a - offset position with a gradual transition during movement along the y axis leading to the outside part of the curve in order to maintain the proportions.

I ask this because I was playing with GCODE itself and wrote a few lines to make concentric cuts and I could not find anything on forcing an outside or inside path directly through GCODE so the cam software must calculate the code ...Is this correct or is there something in GCODE I am missing.

[RICH]

If you do a search you will find an explaination about using G41 /  G43 that was posted by Graham.
You could also use one of the wizards and try an inside, outside , and on line cut of simple shape and compare the Gcode.
There are a few rules that apply to compensation as to how it is programmed.

You may also want to consider purchasing a book on programming written by Smid.

If you were to cut completely around the S and the offset used  left say .005" uncut for the letter , then the S would be .005" thick and true in shape about the center of the width.


RICH

[jjanes]

I was actually looking at the CNC book you mentioned amazon had it for about $40

[RICH]

There are two different books, Programming Handbook and Programming Techniques. I have both and like The Handbood as that gives you more background info and is an easier read. They are both good.
RICH