# Thread: Cut radius given chord length

1. ## Cut radius given chord length

The little grey square is a (not proportionally drawn) mold ear that needs to get attached to a circular mold with a 42" diameter.

A half inch end mill needs to cut the 21" radius along the 3" chord from point A to point B.

Anybody know how to write a G3 block to do that. I'd love to see it done with both the R address and the IJ arc center vectors.

Thanks.

2. I think I might have got it....

So it looks like 1.5^2 + b^2 = 21^2.

So 441 - 2.25 = 438.75, the square root of which is 20.9464.

G41X0.Y-1.5F12.D10
G3X0.Y1.5I-20.9464J1.5

Seems to get it....

Arc CCW
Start X0 Y-1.5 Z0
End X0 Y1.5 Z0
Center X-20.9464 Y0 Z0
Arc Length 3.0026
Plane G17 - XY
Start Angle 355.904
End Angle 4.096
GCode G03 X0 Y1.5 I-20.9464 J1.5

3. Here are the lines of code including cutter comp on and off
I have assumed that the center of the rad is your datum

G41 X2.5 D1
G3 X2.75 Y19.1214 I0 J0.25
G1 Y20.567
G3 X0.25 Y20.7485 I-2.75 J-20.567
G1 Y19.2609
G3 X0.5 Y19.0109 I0.25 J0
G1 G40 X0.55

4. Here it is with the Rad.

G90 G54 X0. Y41.8927 S1252 M03
G43 H1 Z0.1 M08
G01 Z-0.5 F5.011
G17 G02 X3. Y41.8927 R21. F9.772