[jdebott1]

Okay, I've read over numerous posts on the forum, plus much more information about G02 and G03 arcs. And, after trying to run some tests with both, I'm now thoroughly confused.

I need a simple example of cutting a table leg pommel transition (very simple by hand on the lathe) that I can learn from. I'm attaching a simple drawing of this.

I am transitioning from 1 1/2 in x 1 1/2 in (38.10 x 38.10 mm) square stock to 1 1/4 in. (31.75 mm) round. From the Diagonal of the square stock, the transition will go from a radius of 26.9875 mm to 15.875 mm radius over a distance of just 12.70 mm. My CNC shopnotes works on the XZ plane, and here is the code I am trying:


N100 G00 X0.0 Z26.9875 (start point at beginning of square stock diagonal radius)
N120 G18 G03 X12.70 Z19.05 I12.70 K-7.9375
M30


I am getting a zero radius arc error. What I am missing?

Thanks for your kind assistance.

Joe D.

[jdebott1]

Okay, I've continued running tests and this code works for me:

N100 G00 X0.0 Z26.9875 (start point at beginning of square stock diagonal radius)
N120 G18 G02 X12.70 Z19.05 I12.70 K0 A50 F40
N130 G00 Z65
M30


I changed the G03 to a G02 move and changed K value to 0. I understand the K0 now, but isn't this a counterclockwise move and the G03 should work. The G03 makes the Z-axis rise out of the arc, while the G02 arc move cuts this perfectly. Can someone explain this to me?

JD

[ProToZyKo]

K is the incremental distance from start point to your center of radius in Z direction.
I is the incremental distance from start point to your center of radius in X direction.
I don't quite undestand how you turn :S but i think this is correct.
G0 X0.0 Z26.9875
G03 X12.70 Z19.05 K0. I6.35
Also you could use R instead of I and K, R being the radius you want.
Reason why G02 is working and not G03 could be becouse your center is wrong?

[sinha_nsit]

The rule is: CW or CCW is defined when you look at the arc from the positive side of the third axis.
Since the third axis (y-axis, in this case) points downward (using the right-hand rule for defining the coordinate system), you have to look from the bottom, not from the top which is our viewing direction.
So, what is CCW for us is CW for the machine.

[Benpen]

Arcs are simple in a lathe. Pick a direction (cw/ccw) and then what ever radius you want you move the same distance in z, add z to r and that's the distance to move in x. So if I want a .01 radius

Starting from
X0. Z0.

G2 X.02Z-.01R.01

Would achieve a .01 radius. Keep in mind that your tool radius will effect this. If you are using a .008 radius tool then programming a .01 radius will actually give you ~.003 radius when it cuts. You can use G40 to compensate but when you first start it's easier to remember to just add your tool radius to the desired radius for you R and Z values. Also remember this is a g2. It me be easier right now as you're working on the OD to to think of it as an exterior radius. Like if you wanted to round the corner of the stock over. For a g3 or interior radius like at the bottom of a shoulder you have to SUBTRACT your tool nose radius from your Desired R and Z. So in the above example if you changed it to a g3 what would actually cut is a .018 radius using the same .008 radius tool.


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