Questions about Fixed Cycle

CNC mill exercise 4C: this is a sample question to illustrate the use of G81 and G83 commands. It is purposely made to change tool to demonstrate the two commands. If you do not need to change tool, it is not necessary to go home (G28).

Using G98 is never wrong. In fact, by default, it is always G98. It goes to the initial plane, making it safe, but wasting time. If you use G99, the danger is there.

You typed polit hole, I think you misspelled the word. It should be pilot hole. It is a hole that is used to guide subsequent drilling. In your first year, you may have leant centre drill. A centre drill acts the same as a pilot hole.

Both G81 and G83 are used to drill through holes, the difference is that if you r drilling a deep hole, you use G83, it may be blind or through hole.

Mostly, holes are drilled using twist drills. In our course, if it is not specified, all holes are drilled using twist drill, tip angle 118 degrees.

Countersink hole can be drilled before or after. However, by drilling countersink hole first, one can use it to serve as a pilot hole, thus saving the effort of machining a pilot hole to guide the subsequent operations.

It is not wrong, if you forget to turn off the coolant and the spindle at the end of the program because G2 or G30 command will turn these off at the end of the program. However, some tools feed the coolant through the tool itself, especially drills. If you forget to turn off the coolant at the end of the machining operation, the tool will carry the coolant when it goes home. (G28) So, it is advisable to turn the coolant off immediately after all the machining operations are done.

G81 is modal, you do not need to repeat it if it is not changed. Same for G98 or G99. So both ways of writing will not be considered wrong. Only that it is not necessary to repeat what is being modal.