Speeds and feeds when spindle speed is limitted

[mac1911]

I have a 1990s smithy 1220 and the fastest belt set up will get to 1600 rpm at the chuck.
Working with smaller dia using the little machine calculator im getting much higher chuck speeds for dia and HSS tooling, carbide is even faster- seeing now why carbide is jot always working well on my lathe.

 

[benmychree]

You just have to work with what you have, use cutting tools appropriate to the speed available; most everything made in the past was made with HSS tooling. My go to lathe has a max speed of less than 500 RPM, somehow I manage to make it work.

 

[markba633csi]

You can use carbide tools at lower speeds- I do it all the time. Maybe not optimum, but it works
You want to be using carbide tooling that has high positive rake angles though- not neutral or negative, and razor sharp

 

[Jake M]

Working with smaller dia using the little machine calculator im getting much higher chuck speeds for dia and HSS tooling, carbide is even faster-

The best thing you can do is look at that chart as a "speed limit sign". You don't want to go over it, but anything less is fair game. (Even if people are honking, not your problem. In a production shop, on heavy machines, and where production rate can justify reduced tool life, that speed limit is where you want to be.

In practice, your best bet is going to be to put something in the machine, and see what speed works with YOUR tools, YOUR workpiece, and YOUR lathe. That will be the best speed to run at. Surface speed, depth of cut, feed per rev, the rigidity of the machine, the rigidity of the material are ALL going to play into what's going to work out best. They're all interrelated, and they all are going to take some "try it and see" to find out what really works.

seeing now why carbide is jot always working well on my lathe.

There's a dozen reasons why carbide tools don't always get along with lighter lathes. Don't forget that "carbide" isn't a type of tool, there's approximately twelve billion different types, geometries, grades, shapes, sizes, chip breakers, coatings.... But in general, I agree. Small lathes like (reasonably) well ground high speed steel bits better than they do insert tools. Yes, inserts can work, and sometimes work well. And some modern materials weren't even invented when some of our slow "hss" lathes were built... So there's compromises to be made no matter what approach you take. It need not be an exclusive decision to go with one or the other, but being able to hand grind a tool is a great skill to have on a small lathe. Or any lathe really. You never know when you're gonna want too make up something for some odd thing you thought would be a good idea until you were half done and realized you're stuck and you've to have some special thing for some situation you made that nobody's ever thought of before,,,,

 

[mac1911]

The best thing you can do is look at that chart as a "speed limit sign". You don't want to go over it, but anything less is fair game. (Even if people are honking, not your problem. In a production shop, on heavy machines, and where production rate can justify reduced tool life, that speed limit is where you want to be.

In practice, your best bet is going to be to put something in the machine, and see what speed works with YOUR tools, YOUR workpiece, and YOUR lathe. That will be the best speed to run at. Surface speed, depth of cut, feed per rev, the rigidity of the machine, the rigidity of the material are ALL going to play into what's going to work out best. They're all interrelated, and they all are going to take some "try it and see" to find out what really works.



There's a dozen reasons why carbide tools don't always get along with lighter lathes. Don't forget that "carbide" isn't a type of tool, there's approximately twelve billion different types, geometries, grades, shapes, sizes, chip breakers, coatings.... But in general, I agree. Small lathes like (reasonably) well ground high speed steel bits better than they do insert tools. Yes, inserts can work, and sometimes work well. And some modern materials weren't even invented when some of our slow "hss" lathes were built... So there's compromises to be made no matter what approach you take. It need not be an exclusive decision to go with one or the other, but being able to hand grind a tool is a great skill to have on a small lathe. Or any lathe really. You never know when you're gonna want too make up something for some odd thing you thought would be a good idea until you were half done and realized you're stuck and you've to have some special thing for some situation you made that nobody's ever thought of before,,,,

Half way through…. Never ending event here.

I have been trying to turn smaller pieces and its been a little struggle.

 

[rabler]

Speeds and feeds are an attempt to (over) simplify a bunch of factors into a pair of numbers:
1) Material removal rate: higher speeds and feeds is faster -> less cost in production
2) Tool life: regardless of material, faster means hotter which increases wear, and chance of breakage. But to shallow produces rubbing w/o cutting
3) Surface finish: different cutting speeds leave better finish, typically faster is better
4) chip control: too slow tends to produce strings rather than chips
5) chatter: certain speeds will build up chatter or ringing, generally slower and more feed helps
6) machine ability (RPM and HP) and rigidity
and probably a few others.

All of these factors are effected by the size/type of lathe, material you are cutting, cutter material and geometry.
Speeds and feeds are an attempt to optimize the first two or three items on that list. Generally with small hobby machines and work, #1 is much lower priority than in a production facility. Try to get a feel for how speeds and feeds effect all of these things, but primarily the finish and the chips you get.

 

[tq60]

Our SB 14.5 with VFD cn overspend a bit, but we usually stay slow, and use carbide for most things.

If turning smaller than say 1/2 inch higher speed may be fine, but not really needed.

This is a hobby and not production.

Carbide was designed for production, large bites and or speed.

Slowing down makes little difference.

Depth of cut depending on the shape.

HSS allows one to fine tune the cutter, and often is cheaper, have not used it in years other than parting

Sent from my SM-G781V using Tapatalk

 

[Shotgun]

Here's a hint:
Chuck a relatively large diameter piece of stock, then take a facing cut with whatever tool you're trying to "categorize". Take several cuts with varying depths, all at the same speed setting(r).
You will see the surface finish change from inside to outside. It's a familiar pattern to most of us. Pick the center of portion where you like the surface finish the most and measure the diameter(d).
Write in your notebook that pi*d*r is the sfm you'll use for that tool. Write several lines if the good finish spot changed at different depths of cut. You'll also want to do this for each type of material you care about.

 

[piper184]

I'm confused. Pi*d*r
Pi =3.1416
d=diameter (in what unit?)
r= RPM?

to get surface feet per minute don't you need d to be in feet not inches? Otherwise it would seem to me that the result is surface inches per minute.