920 spindle speeds & "machining a backplate for concentricity."
Posted: Tue Feb 02, 2021 6:16 pm
So I suddenly needed a three-jaw chuck, which I have, but without a back plate. Got one off Amazon of the right size, but one that “must be machined for concentricity” to fit into the back of my chuck.
I have only ever turned briar or cherry. According to the machinist's table on this, the cutting speed for steel is 100 SFPM. And the formula is SFM [100] x 4 = 400, divided by the diameter of what you’re going to cut. In this case that is 2.875” = 139.13 rpm. Right? The lowest speed config. for my 920 is 130 rpm, so I guess that's the spindle speed I should use. I have a cutting tool with a carbide insert, so I guess I'll use that.
Have I messed up yet?
And here is my question to check my understanding: how come a metal lathe starts with such a “high” rpm? Is the explanation that most of the steel stock the 920 is “actually” intended for is of a smaller diameter?
Whenever I’m confused like this I tend to think I’m missing something, which tends to make me nervous as to whether I’m thinking straight or maybe there’s a gap in my am understanding. I’ve learned to be cautious about that where lathes are concerned. Can somebody check me out?
I have only ever turned briar or cherry. According to the machinist's table on this, the cutting speed for steel is 100 SFPM. And the formula is SFM [100] x 4 = 400, divided by the diameter of what you’re going to cut. In this case that is 2.875” = 139.13 rpm. Right? The lowest speed config. for my 920 is 130 rpm, so I guess that's the spindle speed I should use. I have a cutting tool with a carbide insert, so I guess I'll use that.
Have I messed up yet?
And here is my question to check my understanding: how come a metal lathe starts with such a “high” rpm? Is the explanation that most of the steel stock the 920 is “actually” intended for is of a smaller diameter?
Whenever I’m confused like this I tend to think I’m missing something, which tends to make me nervous as to whether I’m thinking straight or maybe there’s a gap in my am understanding. I’ve learned to be cautious about that where lathes are concerned. Can somebody check me out?