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Edit/Note: This is NOT "the X/Y problem". The question I have asked here is exactly the question I need an answer to.

I'm not asking how to selected the correct RPM for a given situation (that's irrelevant to the current problem, and besides I already know how to do that), but rather asking about what RPM settings are available on machine and how standardized those settings are from model to model.

I have a project I'm working on where one of the parameters is spindle speeds on manual machine tools that that only run at discreet speeds. For example gear head lathes or Bridgeport clones with step pulleys. Part of the project would work much better if the numbers I pick, happen to exactly match what's offered by the machine tools other people are using. Is this even remotely possible? Are there a few standard sets of speeds offered or does each machine more or less end up with a different selection?

As a starting point; I have a Bridgeport clone that lists it speeds of: 80, 135, 210, 325, 660 1115, 1750 and 2720rpm. I'm also finding a number of images online that list the same numbers, so that seems to be at least one standard.

Are there other common sets of speeds for other kinds of mills? What about for geared head lathes? Etc?

BCS
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  • I asked a coworker of mine who has been a toolmaker for 50 years specifically about the manual lathe we just got and his answer was basically "not much you can do about getting your exact calculated speed". I then asked him what about how the speed changes on a lathe as you get closer to the center and, again, he said not much you can do about that without a vario speed machine. It's especially hopeless with a lathe where your distance from the center affects the FPM. – DKNguyen Oct 08 '21 at 03:00
  • @DKNguyen interesting. I think I've seen CNC machines that can handle things for facing cuts. On manual machines, at least with turning a diameters down the diameter changes slower so switching gears every few passes would be less unreasonable. – BCS Oct 09 '21 at 03:46
  • Yeah, on a CNC lathe it's not an issue since you (or it) can dial in any speed it wants at any time. On a manual machine it's kind of hopeless. – DKNguyen Oct 09 '21 at 04:13

2 Answers2

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You should derive your speeds from the cutting speeds needed for the sizes of drill bits or cutting tool bit lengths to be used and the material being cut.

Some materials need slower speeds, others cut well at higher speeds so you should design for a suitable range not just copy another machine - they made their own decisions.

Solar Mike
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    I'm needing to deal with thing in almost exactly the opposite direction. Very roughly speaking the situation is something closer to packaging sets of end mills to all given the same desired SFPM at the "standard speeds" offered by mills (it's not actually that, but I can't go into more detail). -- Are speeds standardized enough to make that even remote practical? Or would you end up with almost as many packages as there are models of machines? – BCS May 09 '21 at 22:58
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You can search for "end mill cutting speed material". I typed this into duckduckgo.com and found this page, for example, http://www.etantdonnes.com/MACHINE/TABLES/cuttingSpeeds.html

Small radius cutters turn faster than large radius cutters to generate equivalent SFPM. A special package of different cutters that all turn at the same speed will likely be equivalent diameters and of little demand. You can see that at the botom of the above webpage.

There are many webpages that list standard cutting speeds versus materials. This one also includes different end mill types: high speed tools, reamers, and carbide.

If you have a truly special end mill, I am sure that the end mill manufacturer will recommend the preferred cutting speeds for different materials versus end mill diameter.

Jim Clark
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    As with Solar Mike's answer, this don't actually answer *the question I asked*. The question this answers is "how to select cutting speeds" which is irrelevant to what I'm working on (and which I already know how to do). Also, the proxy example I gave is not "turn at the same RPM" but rather "diameters chosen to give the same SFPM for each RPM setting available on the mill". – BCS May 10 '21 at 19:59