Spot facing is a machining operation that creates a flat surface around a hole, usually to provide a seat for a fastener or a bearing. Spot facing can improve the accuracy and appearance of the hole, as well as reduce stress concentration and corrosion. Spot facing can be done on a CNC machine using the G82 code, which is a drilling cycle with dwell.
Usage format
The general format of the G82 code is:
G82 X Y Z R F P L
where:
- X and Y are the coordinates of the hole center
- Z is the depth of the hole
- R is the retract height
- F is the feed rate
- P is the dwell time
- L is the number of repetitions (optional)
Explanation
The G82 code performs the following steps:
- Rapid move to the XY position of the hole center
- Rapid move to the R plane (above the hole)
- Feed move to the Z depth
- Dwell for P seconds
- Retract to the R plane
- Return to the initial position or move to the next hole (if L is specified)
The G82 code can be used to spot face holes of different sizes and shapes, as long as the tool diameter is larger than the hole diameter. The tool can be a drill, an end mill, or a spot facing cutter.
Example
Here is an example of a G82 code to spot face four holes in a rectangular pattern:
G90 G17 G54 G00 G80
T1 M06 (Select tool 1)
S1200 M03 (Set spindle speed and direction)
G00 X10 Y10 (Move to first hole center)
G43 H01 Z2 M08 (Activate tool length compensation and coolant)
G82 X10 Y10 Z-2 R1 F100 P0.5 L4 (Spot face first hole with dwell)
X30 (Spot face second hole)
Y30 (Spot face third hole)
X10 (Spot face fourth hole)
G80 (Cancel drilling cycle)
G00 Z50 M09 (Retract and turn off coolant)
G28 G91 Z0 M05 (Return to home position and stop spindle)
M30 (End of program)
Here is a text diagram to illustrate the spot facing operation:
Y
^
|
| *----*----*
| | | |
| | | |
10 | *----*----*
| | | |
| | | |
0 | *----*----*
| | | |
| | | |
+------------------------> X
0 10 20 30
* : Hole center
---- : Spot face