G-Code Lathe Project - The Seal Cap Part 1

Part One - Writing a Proper G-Code Program Header

Before a single cutting move runs, a well written CNC lathe program should tell the tool setter everything they need to know. That is what the program header is for. In this first lesson we open the Seal Cap project, a complex lathe component with a threaded end, serrated grooves and a full bore, and we start by writing its supporting information rather than any cutting code.

The header carries the program number and version so nobody grabs an old revision, the machine and control it was written for, and a documented tool list. Every tool is listed with its search number and offset along with the insert grade and holder used for each operation. That last detail is the one most shops skip. When a repeat run picks a different insert grade from the one the program was written against, expect either a surface finish problem or a size creep, and nobody will know why. Document both, every time, and the results stay repeatable.

The Seal Cap uses eleven tools across its operations, from rough and finish turning through to threading, grooving, drilling and boring, and the header spells every one of them out. Written well, the header replaces external paperwork and keeps every run of this part consistent, whether you wrote the program six weeks ago or someone else sets the job entirely.

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.

The part drawing and every example program from this series, exactly as shown in the videos, sit on the handouts page, ready to download and keep.