Circle Help Trouble getting the right code.

[ibuildstuff4u]

I'm trying to have the machine cut some custom spacer rings out of 1/4" micro plywood and getting the machine to cut the second circle is getting to be a challenge when writing it with the G code. I'm asking it to cut a .750 diameter circle out and then move to the outside of that circle and cut a 1.290 circle out. The part looks like a large washer in the end. I'm using a 1/8" diameter cutter and am using the cutter compensation to compensate for it, but for some reason I can't get the code to position and cut the second circle. They don't line up with each other and the two circles over lap each other. I could really use some help!!!

Here is a small sample of the code...

This is what I'm using right now, it works, but the second circle is a few thousands off from the first one and nothing adds up. To me " i " should be the same as the first circle, but that doesn't work at all so I messed with the numbers until it got close.

Thanks for the help! Dale P.

G20 G40 G49 G90 (Set up machine)
G0 X0 Y0 Z .100 (Zero out the axis)
M3 (Turn on the spindle)
G0 X .940 G42 D1 (Turn on cutter comp starting to the left along with the starting move for the cutter comp)
G1 Z -.100 (lower Z)
G1 X .750 Y0 i .375 j0 (Inner circle)
G0 Z .100 (Raise up Z)
G0 X .275 G41 D1 (Turn on cutter comp starting to the right along with the starting move for the cutter comp)
G1 Z -.100 (Lower Z)
G1 X .485 Y0 i .650 j0 (Outer circle) *** I know these numbers are wrong, but what I figured out to be correct don't work at all.
G0 Z .100 (Raise up Z)
M5 (Shut off Spindle)
G0 X0 Y0 (Re center each Axis)

[ger21]

What control are you using? The control can dictate how you need to lead in with comp. I'm not sure if your doing it correctly?

First, you have G1' when it should be G2 and G3.
Second, you need to turn off comp with a G40 between your circles.
Third, how are you cutting a circle when you start at X.940 and finish at X.75?

Do you have to use comp? It's a lot easier to do it this way.

G20 G40 G49 G90
M3
G0 Z0.1
G0 X0.375 Y0.3125 Z0.1
G1 X0.375 Y0.3125 Z-0.1
G2 X0.375 Y0.3125 Z-0.1 I0.0 J-0.3125
G0 X0.375 Y0.3125 Z0.1
G0 X0.375 Y0.7075 Z0.1
G1 X0.375 Y0.7075 Z-0.1
G3 X0.375 Y0.7075 Z-0.1 I0.0 J-0.7075
G0 X0.375 Y0.7075 Z0.1
G0 X0 Y0
M5
M30

[Get lucky]

This is how I would have programed it.

G20 G40 G49 G90
M3
G0 Z0.1
G0 X0.375 Y0.2025 Z0.1
G1 Z-0.1
G42D1Y.3025F?
G2 J-0.3025
G1X.3125
G2J-.3125
J-.3125 (Would add depending on finish requirements)
G1G40Y.2125
G0Z.1
G0 Y0.8175
G1Z-.1
G42D1Y.7175
G3J-.7175
G1Y.7075
G3J-.7075
J-.7075 (Would add depending on finish requirements)
G1G40Y.8075
G0Z.1
G0X0Y0
M5
M30


My .02

And it dose make a difference on the control

[kvom]

To add a few minor comments--

1) Cutter comp may be useful here if the part's precision is important and the tool diameter needs to be adjusted via the control. Otherwise it is just as easy to offset by the radius as suggested by ger21.

2) Finishing the cut without arcing away would leave a witness mark in metal. Not sure on plywood, or if this is important.

3) The choice of G2 vs G3 (and G41 vs G42) may depend on whether the finish on the wood is affected by climb vs. conventional milling.