Chamfering a cross hole with the tip of the bit using the C axis

Tip and Trick – 2011-09-05

TB-DECO

(e.g. form bore bit) and to save on a machining station it is possible to chamfer a cross hole with the tip of the bit using the C1 axis.

Example of a Ø 3 transverse hole:

Chamfering takes place in 4 stages:
FIG. 1	=	STARTING POSITION WITH THE BIT IN THE CENTRE OF THE HOLE
FIG. 2	=	APPROACH BY CIRCULAR INTERPOLATION
FIG. 3	=	INTERPOLATION 1/2 CIRCUMFERENCE AXES Z1/C1
FIG. 4	=	INTERPOLATION 1/2 CIRCUMFERENCE AXES Z1/C1
FIG. 5	=	WITHDRAWAL BY CIRCULAR INTERPOLATION, END OF CHAMFERING

Description of the movement seen from above:

Programming data:

1. Establishing the D argument for M198:
The D argument is used to define the part diameter so that work can be executed with the C1 "unwound " rotary axis. In our particular case, if the form is unwound, the result obtained is an ellipse. In order to obtain a satisfactory result, the default value to be introduced in argument D as the starting basis, must be equivalent to the diameter d. In order to optimise the result obtained for the part, it may prove useful to change this value by reducing it until a satisfactory outcome is achieved.

2. Offsetting the bit for chamfering:
Chamfering is executed using the tip of the bit. Consequently, an offset L is required. This offset value depends on the extent of chamfering. In the above example, L = 1 mm.

Programming features
Line 8 - 9: Circular interpolation G3 (Figs. 3 and 4) is programmed along a 1 mm radius (R1). This value corresponds with the offset L used in this example.

ISO code for milling operations:

1.	M198 D7
2.	G4 X0.5
3.	G1 Z1=-11.5 X2=10 G100 T22
4.	G1 C1=0 G100
5.	G1 X2=7.5 G100
6.	G1 X2=5.5 F300 G94
7.	G3 Z1=-10.5 C1=0 R0.5 G191
8.	G3 Z1=-12.5 C1=0 R1
9.	G3 Z1=-10.5 C1=0 R1
10.	G3 Z1=-11.5 C1=0 X2= 5.5 R0.5
11.	G1 X2=10 G100
12.	M199

Comments :
In order to proceed with chamfering, a new operation line containing axes C1 and Z1 must be created as the master and an X2 line as the slave.