Re: Cutter Radius Comp

[Ray Henry <rehenry-at-up.net>]

Frank

I did a little more looking at the cutter comp pages.  The provision for an
arc move to pick up diameter compensation will work from the inside rather
than the outside.  This should be better since I presume that you are going
to scrap the slug.

>From my tests it looks like you have to be really close with your guesses
in order to use the arc approach from the inside.  The following code
worked for me for tools larger than 0.492 in diameter.  (I snipped the
extra passes after the first circle in the code below.)  

(Assume that tool 2 is loaded in the spindle)
(that a .5" dia is loaded in the tool table)
(Center of hole is at X0Y0)

N0010 G53 G0 Z0
N0020 X-1 Y1 (load position)
N0030 G43 H2 (activate tool length comp)
N0040 G1 X0.5 Y-0.25 F25 S1000 M4 (tool location for arc computation)
N0050 g17 g41 d2 G3 r.5 X1 Y0 z0 F25 (start comp and arc approach)
N0080 X-1 R1 Z-.05 F3
N0090 X1 R1 Z-.1 F3
N0200 G40
N0210 G0 Z3
(Frank Hess)

I think what EMC does with this kind of approach is follow an arc from the
center of the hole you program to cut, to the starting point on the circle
you will cut.  It then stetches that arc so that it is tangent to the edge
of the tool where it is when you start the cutter comp and the arc move.
The code on line n0050 causes EMC to compute a half circle arc from the
center of your 2" circle to the start point at x1 y0 because the cutting
surface of the tool is at x.5 y-0.50.  This means that at the start of your
first programmed arc on line n0080 the tool is moving in the same direction
and is about the right distance out so that it doesn't gouge the surface.

I also asked it to ramp z down to the start of the cut during that same
move and it seemed to work fine.

To run smaller tools than 0.492 you would have to change the location of
the approach arc.  Probably moving the y value minus on line n0040 by about
half the diameter difference of the cutting tool would do the trick.

Larger tool diameters will not give an error because they approach the
starting arc like the outside move I posted earlier.  But larger tool
definitions might gouge the circle where it comes around to meet the
starting point.  I don't know that for sure.

If you want to mill out the circle in a single pass you could drill a hole
at X0.5 Y-0.25, poke the end mill through it and then start the cutter comp
and move in the arc described in n0050 above. 

Thanks for the challenge.  I think I know a lot more about cutter comp now.

Ray

-----om-----
At 08:04 AM 12/16/1999 -0500, you wrote:
>  In the future I will need to take an
>existing hole and  begin within the hole at the full Z depth and then circ.
>  This may present a challenge due to restricted