[How-To] Central Machinery 9x20 Lathe

[Nesse1]

The backplate is iron, and it will cut easily without lubrication. The chips will be crumbs, not chips like steel. I'd go medium-slow.

 

[Vin81]

10/4, So like 400 rpm’s?

 

[Nesse1]

Sounds like a good starting point...

Because the cast iron sort of crumbles when cutting, the pieces are small and fling off. You may need to fashion a shield of some sort. And wear a smock...

 

[Vin81]

Seems the case. I have been warned by many. I was thinking of having someone hold a shop vac near the cutter. See what happens.

 

[PNW_Guy]

For a super easy, and easy to remember RPM calculation for HSS tooling I use the following:

SFM - Surface feet per minute, or the distance the circumference of the cutter (drill bits & end mills) should move in one minute - or the distance the OD of the part should move in a minute on a lathe.
Aluminum & plastic 250 SFM
Mild steel 125 SFM
Hard steel 65 SFM

RPM = (SFM * 12) / Pi*D (convert the SFM to inches and divide by the circumference of the bit/workpiece)
But to simplify, pretend Pi = 3. Cancel the 3 and 12 to change the formula to:

RPM = (SFM * 4) / D

So, a 1 inch cutter (or workpiece in a lathe) cutting aluminum = 250*4/1 or 1,000 RPM

0.25" cutter in steel = 125*4 / .25 = 500/.25 = 2,000 RPM

It's not perfect, but it'll get you in the ballpark. But for cast iron I'm not sure what SFM to use. Probably 125, but I never use the stuff.

 

[Vin81]

Wow, thanks for all that info. Still trying to digest it all and grow some courage to cut the plate. Might tackle it Saturday.