1. Get some tooling.
2. Buy some scraps—maybe 3/4 to 3” diameter, free-machining 12L14 and cheap 1018.
3. Make chips.
4. Write down observations.
I’ve had zero luck reading speeds and feeds from carbide insert charts—they are made for production environments. And I have not found that my lathe, which is supposedly too slow and weak for carbide (particularly the negative-rake tooling I like), subject to the claimed limitations. My lathe has a top speed of about 1100 RPM but I almost never go that fast, even when the book says I should.
Smaller stuff goes faster. 1018 is tough and stringy—if you get strings, stop and try something else rather than creating a dangerous bird’s nest. Carbide prefers deeper cuts, particularly with cheap steel.
Experiment with HSS tooling and learn how to grind it. What you learn will transfer to carbide better than you think.
The worst that can happen is you take too deep a cut and stall the lathe. If your lathe has plastic gears, experiment with increasingly heavy cuts until the lathe is straining, and write that down. With old flat-belt lathes, you’ll probably just slide the belt off if you stall it—no big deal.
Blue chips are fine and maybe optimal for carbide, but avoid sparks and strings.
Start with 2” stock, 250RPM, 0.005”/revolution feed rate, and a range of cut depths from 0.010 to 0.100 (radius, not diameter), though you’ll need a bigger lathe for the deeper cuts. Adjust until you like the results. This becomes your home setting. When the diameter cuts in half, double the spindle speed from your home setting. When the diameter doubles, cut the speed in half.
Practice, practice. But keep notes.
Rick “never landing on recommended values” Denney
