Somewhere, over the years, it seems I picked up some sense of what
cutting speed is.
However, when asked 'what is cutting speed?', the best I could come
up with was it is related to tensile strength of the material, blah,
blah, blah. (almost literally I'm afraid)
Anyone have a good description of what cutting speed is?
It's the rate of movement at the point of contact of the tool, generally
measured in feet per minute. In some cases it's the rate the material
moves (lathes, for example) and others it's the rate the cutter runs, mills,
lurker wrote in news: email@example.com:
Cutting speed is the rate at which the tool tip passes the material (or
the material passes by the tool tip), in either feet per minute
(sometimes feet per second) or meters per minute (or meters per second).
It has nothing to do with strength of the material, material type,
feedrate, or anything else. It is simply a speed measurement.
RPM = (4 * CS)/D
As you can see from the formula, CS (cutting speed) is dependent only on
2 variables, RPM and Diameter (either workpiece or tool, depending on
lathe or mill)
Algebraic manupulation of this basic formula allows you to solve for CS,
D or RPM.
Not true. Depends on the operation at hand. In sawing (or milling,
shaping, etc.), it would be the tool tip passing the material. On a lathe,
it would be the material passing the tool tip. Both cases are proper.
Anyone that prefers to cut at the "sweet spot", where material behaves much
better than at other speeds, and those that prefer to cut at a speed that
doesn't destroy the cutting instrument. It also becomes quite critical
where grinding wheels are concerned, for they are rated at a given
"hardness" based on a given RPM, which quickly changes as you speed up or
slow down the grinding wheel. Surface feet, or cutting speed, is important
to successful machining.
(clip) However, when asked 'what is cutting speed?', the best I could come
up with was it is related to tensile strength of the material, blah, blah,
blah. (almost literally I'm afraid)
So, I ask myself, why would you think that cutting speed has something to do
with tensile strength? And, I answer myself, "Becasue it does, but not in
the way you think." The method of calculating cutting speed, based on
radius and RPM is absolutely correct. But, the question of what is a good
cutting speed to use comes from the other direction: what are the
properties of the material being cut, and how much punishment will the tool
stand. I am sure that tensile strength could be a factor, along with
toughness, hardness, etc.
A city wide blackout at Sun, 28 Dec 2003 05:06:31 GMT did not prevent "Leo
Lichtman" from posting to rec.crafts.metalworking
the follow>(clip) However, when asked 'what is cutting speed?', the best I could come
Cutting speed (I was told) is a value used to figure RPM, given the
diameter of the piece/tool.
It varies from material to material, and from tool composition to tool
composition. E.g., the cutting speed for aluminum (in surface feet per minute)
is different than the cutting speed of Aluminum, if the cutting _tool_ is
different. (HSS v Ceramite v Tungsten Carbide, v polycrystalin bonded
trainagles, v what ever.)
Also, CS is dependent on "other factors" - tool life being one of them.
Again, while the CS for NMS100 is 170, go slow on the roughing cuts, as the
scale from forging will eat cutters at that speed. So slow down a little.
"Machinability" is the term you are looking for. Cutting speed is not
property of a material since it depends on the type of tool being used.
For example, a HSS tool might cut 6061 aluminum at 300 SFM (surface
feet per minute)
while a carbide tool could cut the same material at 1000 SFM.
Cutting speed also depends on the length of tool life required from the
tool. In other words,
cutting faster means resharpening or replacing the tools more often.
Machinability is determined by several factors. One of the most
important factors is
hardness. A steel which cuts easily when annealed will have to be cut
the steel is hardened. Another factor is the alloying elements in the
additives to steel will make it more machinable, like lead, sulfur or
elements added will make steel less machinable, like nickel or chromium.
There are volumes written on the subject, I'm not going to put too much
In the real world, published cutting speeds for machining various
different kinds of tools are just starting points. Optimum speeds for
are found by experimentation.
Cutting speed in the proper perspective is best applied to planing, shaping,
and sawing operations.........
No diameter involved........as of yet...........
To apply to circular cutting operations, simple algebra is applied.
How fast can you pull the tape outa that Stanley tape measure ???
And what if the end inadvertantly gets caught inna lathe chuck ???
Or how many feet of string would get wound up per minute if a piece a string
were to get caught up on the drill ???
( Sorry if I come off sounding like some troll, I done trained quite a few
in my time, this is the exact parrallel I always used, it usually seemed to
All good and valid general info, as to "ideal" cutting speed............this
IS material and tool specific.
Published numbers should be looked at as guidelines only--recommended
The cutting sfpm numbers, for cutting a given
material with a given tool, are pretty well
established, and tabulated.
The feed rates however, as a function of things
like tooling, material, machine hp and rigidity,
are some of the toughest to determine, except
by experiment. The late Robert Bastow had an
excellent discussion about how this is done,
with the essence being: start feeding by hand
until the machine complains, then back off a bit.
Set the power feed to just about catch up
with the previously set hand feed rate.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
pyotr filipivich wrote in
CS or, more appropriately, Surface Speed, is simply cutting speed,
diameter and RPM dependent, it has no relation to material, tool, feed or
The Ideal CS for a certian machining operation on the other hand, does
vary depending on a large package of variables (tool, tool geometry,
cutting fluid, material, material condition, machine rigdity, part set-
Unfortunately, the rules don't necessarily apply across the board, something
that is likely very true for the home shop types. Those that use
antiquated machines are highly unlikely to have proper speeds at their
disposal, considering their general high usage of carbide tooling. The
older machines were geared to run HSS and lack rigidity, speed and horse
power to take advantage of the capabilities of cutting tool technology of
That isn't my approach, especially not on a lathe. Rarely do I start a cut
that isn't near a decent feed rate, but when you've run the same lathe for
over 35 years and it's capable of taking respectable cuts, that is likely no
surprise. Any of us that have worked in the shop, especially in
production, likely do the same thing.
At best, I'd have a small problem with the hand feed rate. Inconsistent
hand motion would be a poor indicator of feed, something that would be far
better by power, be it too slow or too fast. If one has a quick change, it
takes but an instant to change the levers while under cut, which is how I
fine tune a cut once under way. I can see, however, that if one prefers
to run a machine such that a heavy load can easily stall the machine, my
method of working would not be a good idea. I've never stalled my
machine because of the cut, although I've had it grunting many times, so I
don't risk breaking carbide tooling. An acquaintance chooses to run his
lathe with the belts loose enough that the spindle can be stalled, more or
less a safety factor for him. Needless to say, one could hardly ever
take advantage of the capabilities of a machine under those conditions, so
efficient feed rates and depths of cut would be a small consideration.
Harold & Susan Vordos wrote in message ...
If I recall correctly, Robert was referring specifically to the horizontal
mill in that instance.
The horizontal mill likes a manly feed rate, and when you're talking about a
6in dia cutter with a tooth gullet as big as your thumb, horsepower is
likely to be the limiting factor.
Paul K. Dickman
I guess what I am really trying to ask is "How is the rate derived?"
How is it determined that xxx sfpm is best for cutting 303 stainless
with a high speed steel cutter, for example?
Harold & Susan Vordos wrote:
That would make sense. The first time I ran a horizontal with a side
cutter (back in the 50's) was a real eye opening experience for me. It
was almost frightening, the feed rate a cutter like that can handle. On
light duty equipment the likes of which I have now (Bridgeport, but I have a
right angle attachment for it) I think I'd do exactly as Robert suggested.
Rigidity and horse power come into play with side cutters, so you'd likely
have to break the rules considerably when running larger cutters on smaller
machines. I know for sure I'd not run the cutter according to the formula,
highest allowable speed and proper chip load per tooth. Yep, he said a
That I'm not sure of. I have never given it any thought, but I have
certainly relied upon the accepted speeds as a basis for applying cutting
instrument throughout my years of machining. There are many variations to
the rules, so they should be considered strictly as guidelines, however.
Example: Sawing with a band saw. The thickness of the material effects the
acceptable speed. Thin material can be sawn much faster than thicker
material, because the interval of time the blade makes contact with the
material is much longer on thick material than thin (duh!), so the heat
generated by the cut does not elevate high enough to burn the edge before
it's off the part being cut. Pitch of the blade then becomes a serious
consideration, so the chip load doesn't overcome the length of cut so there
is no place for swarf to accumulate, but is not so coarse that there aren't
at least two teeth in contact with the work at all times. All the rules
change when you run the saw above about 1,500 fpm, however, where one can
then move into the realm of friction sawing. Don't even need teeth for
I think that the likely answer to the question is one whereby enough history
of machining has been recorded that it is well known that particular
materials behave in a predictable fashion. It is more than well known
that 300 series stainless, for example (excluding the free machining
grades), have what could best be described as a high friction coefficient,
and require much lower sfpm than mild steel, for example. Run the cutter
the least bit too fast and it burns the tip.
It becomes quite apparent that the moment one moves into the alloys, each
element added to the base metal changes the characteristics, and I would
assume the amount of each element would effect the cutting characteristics,
though not necessarily in a liner fashion. Again, I imagine it has
been recorded by history more so than a formula one can apply across the
board. There's just way too many minor factors that influence the final
outcome, including depth of cut, feed rate, whether cutting wet or dry, what
type of coolant, etc..
Perhaps someone with a degree in this area could enlighten us.
lurker wrote in news: firstname.lastname@example.org:
Starting points are given in Machinists Handbook, but these, as far as I
know, are derrived from experience or tooling manufacturers recommendations
based on their in-house experiments.