Tapping is a very common operation on cnc machining centers.
What is Tapping?
Tapping is performed by rotating the spindle clockwise. When the bottom of the hole has been reached, the spindle is rotated in the reverse direction for retraction. This operation creates threads.
But tapping is very easy to program on a cnc milling machine.
G84 tapping cycle is used for the this purpose. G84 tapping cycle just few parameters to program and easy to remember and understand.
G84 tapping cycle is a modal G-code, so is cancelled with G80 otherwise it will execute tapping operation on every X and/or Y move.
G84 Tapping Cycle Format
G84 X_ Y_ Z_ R_ F_
X Y – Hole position data
Z – Z-depth (feed to Z-depth starting from R plane)
R – Position of the R plane
F – Cutting feedrate
With Rigid Tapping, the ratio between feedrate and spindle speed must be calculated for thread pitch being cut. The calculation is 1 Threads Per Inch x rpm = tapping feedrate.
F (Feed) = RPM x Pitch.
G84 Tapping Cycle Fanuc Specific Parameters
Fanuc cnc controls has some extra G84 tapping cycle parameters, which you might use if you wish otherwise nothing changed.
G84 X_ Y_ Z_ R_ P_ F_ K_
X Y Z R F – same as stated above.
P – Dwell time at the bottom of the hole.
K – Number of repeats (if required)
G98 G99 with G84 Tapping Cycle
G98 and G99 are modal G-code that change the way canned cycles (G81,G83, G84 etc.) operate.
When G98 is active, the Z-axis will return to the start position (initial plane) when it completes an single operation.
When G99 is active, the Z-axis will be returned to the R point (plane) when the canned cycle completes a single hole. Then the machine will go to the next hole.
Feedrate overrides are ignored during tapping. A feed hold does not stop the machine until the return operation is completed.