different bits, different speeds

[Doozer]

aaaa

[Mcgyver]

That chart is about as attractive as looking at pictures of naked dudes.

-D

agreed, zero interest in either.

Guys, this is not a three decimal exercise. RPM = FPM * 4 / Diameter. that's it. Memorize a few common FPM numbers for the materials (work and tool) you use and you can do the whole speed calc thing in your head while you setting up the machine.

The other thing for beginners to note, is that the resultant rpm is the theoretical maximum. Its the point where going faster disproportionately increases tool wear, i.e. removal rate vs wear is no longer linear. For hss anyway there is no issue (except it takes longer) in going slower. Without knowing that, the beginner is sometimes perplexed; e.g. "how can I drill this little hole, my lathe won't go to 20,000 rpm", etc

[Doozer]

Just me talking here,
but the only material I have trouble finding a good
speed and feed for is cast iron. Too slow and it seems
to not leave a good finish. Too fast and the tool chatters.
I think this tricky dance is because, although Iron is not
very strong (20 to 30,000 psi), it is very tough and hence
the expression, it wears like iron. So for cast iron, I might
look up the numbers.

--Doozer

[polaraligned]

For hss anyway there is no issue (except it takes longer) in going slower. Without knowing that, the beginner is sometimes perplexed; e.g. "how can I drill this little hole, my lathe won't go to 20,000 rpm", etc

Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge. You really want to be making chips. After a bit of experience, you get the feel for how fast you should be cutting and what good chips look like. I learned the hard way years ago about stainless steel work hardening. Lost a few brand new 1/2" drill bits because I did not keep on the down feed hard enough. (304 is brutal) But even if the material doesn't work harden, rubbing is bad for the cutting edge. So yes, I agree that slower is fine as long as you are making chips that you can pick up and measure the thickness.

[Mcgyver]

Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge.

To clarify, I assume you mean feeding too slowly, in which case I agree. No point in spinning a million miles per hour and making dust.

[Doozer]

Just to expand on this for the beginner, going too slow is just as bad as going too fast. If you go too slow the cutter rubs and prematurely wears the cutting edge. You really want to be making chips. After a bit of experience, you get the feel for how fast you should be cutting and what good chips look like. I learned the hard way years ago about stainless steel work hardening. Lost a few brand new 1/2" drill bits because I did not keep on the down feed hard enough. (304 is brutal) But even if the material doesn't work harden, rubbing is bad for the cutting edge. So yes, I agree that slower is fine as long as you are making chips that you can pick up and measure the thickness.

You are very correct.
Stainless steel is actually a good learning tool for doing it right.
You need to get in there, play hard, and get out quick.
Like the Navy Seals.
Good practice really and a good feedback exercise,
if you are observant and adaptive.

-Doozer

[polaraligned]

You need to get in there, play hard, and get out quick.

Last time I tried that I ended up married...

[Doozer]

Bah dumb bum ching ! ! !

-D