Help - G-Code Circular Motion for CNC Milling

[Elgin Clock]

From what I remember in my CNC class a few years ago, G Codes make circles by defining a center point and a radius. I think...

I'll see if I can track down my book and give you a better answer.

I know we had to hand type a program to make our first name in block letters and then make a program that included the radii of the letters, which was fairly simple if I recall correctly.

[Katie Reynolds]

Let's see ...

G02 = circular interpolation (clockwise)
G03 = circular interpolation (counter-clockwise)

Ok ... let's see if I remember this. We'll start with an arc.

You first have to identify the point at which you want to start your arc. We'll use (1,4) as our starting point.

The next step is the trickiest - you need to determine what the center point of your circle will be. mapping the whole thing out on graph paper is the easier way to do it, because then you can calculate the radius and you'll know where the centerpoint is (without a whole lot of trial and error on the actual part)

the coordiantes for your center point are your (I,J) coordinates. The beginning and end points will always be (X,Y) coordinates

Then, you need to identify your end point. We'll go with a quarter of a circle, which will put us at (6,1)

**make sure that there is an equal distance from the center point to your beginning and end points! Otherwise, your mill will hate you and make your part look funny**

For example:

N08 G01 X1 Y4 ------ will move your cutter to (1,4)

N09 G02 X4 Y7 I4 J4 ------- (4,4) - your (I,J) coordinates - is your center point. the cutter will move in a clockwise position until it hits (4,7) - your (X,Y) coordinates.

If you want a larger arc, change your (X,Y) coordinates.

For example:

N09 G02 X7 Y4 I4 J4 --- will give you half a circle.
N09 G02 X4 Y1 I4 J4 --- will give you three quarters of a circle.
N09 G02 X1 Y4 I4 J4 --- will give you a full circle.


Of course, you'll have to tweak this a bit to get the exact size circle you want and such but ... I hope this helped! (If you want a drawing, PM me!)

[sanddrag]

That helps a lot. Now how do I do this while moving downward? I don't want to take a 1/4" cut all at once of course. I could put like a G01 Z-.03 before the G02 code and then a G01 Z-.06 after and so on and so forth. Or is there a better way to do this? I know with G01 if you put like X1 Y1 Z-.5 it will ramp down until the Z axis reaches final depth of -.5 at X1 Y1. Is there a way to put G01 and G02 in the same line so the circle will like spiral down?

Mainly, I could just move the Z axis down a bit after running in a circle and then repeat but I think doing that would not make for a very nice bearing bore.

Any ideas?