G-Code Lathe Project - The Seal Cap Part 3

Part Three - The G70 Finishing Pass

The finishing pass is where size and surface finish are actually made, so this lesson slows things down and walks the sequence block by block. The trick that keeps the program short is already sitting in it: the profile subroutine written back in the roughing lesson gets called a second time by the G70 finishing cycle. One profile, two purposes, no duplicate code to maintain.

Before any cutting starts, the spindle speed gets clamped with G50. When constant surface speed is running and the tool faces toward centre on a lathe, the control tries to hold surface speed as the diameter shrinks, and an unlimited spindle will keep accelerating until it hits a mechanical or programed limit. Clamping the top RPM first stops that runaway.

The finishing tool approaches with a fed move rather than a rapid, cuts the profile at a lighter depth and faster feed than the roughing pass, and is returned home with a machine reference move at the end so the tool never sits parked inside a dried coolant drip or near the part. Once again, the safety line at the top of the sequence resets the machine to a known state whenever this code starts, which makes testing routines like this far easier to trust.

Download the full G-Code handout for this lesson, along with the complete Seal Cap program, here

This free lesson series follows the Seal Cap build from first sketch to finished part and is a taster of what you will learn in the 4-Course G-Code Bundle.