If you know a site, or if you have a list of the speed requirement for
turning metals on a lathe, I would appreciate it. On my quick change gearbox
on my lathe it shows the speeds, but I like to know how fast I should have
the spindle turn if I'm turning let's say aluminum and soft steel
maybe...The same maybe, if I could impose for a milling machine as well....I
used to have all this stuff, but whenever my grandson visits me, and he
needs small things, he borrows it, and then forgets to give it back to me.
Then if I need it, I can't put my hands on it....Peter
I don't know of a site with that info, must be somewhere.
But it's rather easy;
Metals have an optimum surface speed, based on tool wear, and
Surface speed is how fast the tool travels over the work, in feet per
FPM for common metals using High Speed Steel tools:
Hard Steel/Stainless 50
Soft Steel/Iron 100
(Many other speeds are quoted, this is generic, and nudged for memory
So, if you have a 6" diameter steel blank in the lathe. The
circumference is 6" x 3 (Pi) = 18 divided by 12 to get feet = 1.5'
Since steel is 100 fpm, 100 / 1.5 = 66 RPM for the best
All these numbers are approximate, too slow increases tool life, fine
for a home shop, that likes to watch the machine. Coolants and lubes
will make a big difference.
Faster wears the tool tip quicker.
Is there not some negative impact on the cutting tool if it is running too
slowly? I have recently gone through the same deliberations and have to say
that good tables were hard to find on the net.
I read a book which included correct speeds in a chapter. Their caveat was
not to let the tool "rub" - whatever that means. My take on it was that this
happens at slower speeds than recommended but could not understand it
They also suggested that the speeds you quoted should be adjusted according
to the operation: For instance for countersinking they suggested using
speeds 1/3rd of those normally recommended.
There were also notes about the feed speeds and the material of the cutting
tool affecting the correct cutting speeds, so in the end I was rather
confused. Nowadays I rather tend to err on the slow side...
Sounds like me and the kid working in the shop a few years ago. I was the
tortoise, he the hare. He went fast and broke shit, I finished first by
going slow and easy. But now, he's been a pro for six years. he just plain
works circles around me. He still asks me to do the manual lathe work. The
old guy has a better touch for that.
There are great tables for carbide inserts. Every manufacturer has a web
site for this, giving optimum speed and feed by material for each insert.
On Thu, 24 Apr 2008 04:40:19 -0500, "Karl Townsend"
As a sort of rule of thumb erring on the side of slower cutting speeds
with higher feed rates will generally remove more material in a day
then high cutting speeds with lower feed rates.
The lower cutting speeds usually let you get more cuts between
sharpening too :-))
(correct email address for reply)
On Wed, 23 Apr 2008 23:43:05 -0700, "Michael Koblic"
Nope, you can run it as slow as you want. It is the high speeds that
do you in.
"rubbing" would be insufficient clearance on the tool bit.
That is usually correct but it has less to do with cutting speed then
being a multi edge cutting tool. Reamers are also prone to this
problem which has to do with being a multi edge cutting tool. Reamers
are also prone to this problem which has to do with multiple cutting
edges not cutting evenly or "chattering" leaving a poor finish or out
of round hole.
Look at it this way. The cutting speed is the highest continuous speed
that the tool will sustain. Now, stock removal is a somewhat different
story and you may find that because of old age, a lack of machine
rigidity, more frequent tool dulling, or other factors a slower
cutting speed coupled with a higher feed rate MAY remove more material
per hour/day the a higher cutting speed with a lower feed rate.
(correct email address for reply)
On Thu, 24 Apr 2008 19:56:33 +0700, Bruce in Bangkok
Or insufficient feed rate!
Cutting speed is only half the equation-- you also need to consider
the feed rate (thou per tooth or whatever).
The cutting edges have to be moved into the work fast enough that they
bite in and don't just rub against the work (feeding too fast causes
The feed rate in thou per tooth is independent of the cutting rate, so
if you are turning very slowly the feed rate will be slower in terms
of inches per minute, but the same in terms of thou per tooth, if that
makes any sense.
The optimum feeds and speeds are dependent on the type of tooling,
coolant used, the material being cut, whether it's a roughing or
finish cut, and other factors. Google for some numbers. I've generally
used 80 sfm for HSS tooling into mild steel.
More in Wikipedia: http://en.wikipedia.org/wiki/Speeds_and_feeds
"it's the network..." "The Journey is the reward"
email@example.com Info for manufacturers: http://www.trexon.com
Make a spreadsheet with the speeds for your lathe or mill as rows,
common work diameters as columns, and the FPM formula in the cells. If
you don't have MS Excel you can download Calc from Openoffice.org.
I will probably be shot down in flames for this, being a mere tyro,
At school, we were told where to look in the textbook for the optimum
cutting speeds - they do vary with the material.
BUT - these were the max speeds in a production environment and were
designed to get maximum ECONOMIC life out of the tooling - faster
meant unacceptable tool wear and so increased downtime and cost,
slower meant...you didn't get as much work done. (The temptation is,
of course, to run it fast and take big hogging cuts - fine if you know
what your doing...)
Run it at a speed you feel comfortable with, slow is not a BAD THING
if you aint doing it for a living and being paid per job. Dont let it
rub on one spot, heats up the tool, stuffs it.
Feed rates are probably more important, IMHO. But agin, slow is better
than too fast.
So saying that, one of the instructors faced off a topslide mounting
plate I was making - insanely and dangerously fast to me, but he got
a BEAUTIFUL finish, in one pass - but then, as a toolmaker now a
teacher, he knew what he was doing....
From memory, (again, probably wrong - its in my locker at school..)
the Southbend 'How to run a Lathe" book, widely available as a free
download has the formulas - a great quick reference guide. Pity its
in imperial, I am being taught exclusively in Metric. Can think in
metric now for machining, still in feet/inches for everything else.
Makes life confusing, to say the least. Got a imperial micrometer here
I got at a junk sale - no idea how to read it...
Oh, yes - was told to run reamers at the slowest possible speed/feed -
lessens chance of damage to expensive tools...
(photocopying charts and nailing them to the wall behind the lathe/
mill is a GOOD IDEA -)- nomographs? - is that the right term?
On Thu, 24 Apr 2008 05:27:00 -0700 (PDT), firstname.lastname@example.org wrote:
eons ago there was a guy creating a table for 'model engineer'
magazine giving the cutting speed vs rate of removal. the table was a
rectangular grid of figures. typical sweet spot being in the middle of
the left hand end.
for the simple reason that he wanted to fill in a value in every
square in the table he ran the lathe and made the cuts at all the
down in the right hand lower corner was discovered a range of speeds
where the cutting rate increased substantially. the tools ran red hot
but the removal rate was far higher.
that bottom right corner is now where most of industry works.
we work at home in the left slower end where it feels right.
Find the correct surface speed range for each material here:
Then look at this chart to find the spindle speed for whatever surface speed
and diameter you need:
no math needed.
make a facing cut across the end of the billet. set the speed of the
job such that the smoothest finish area is out where you are cutting.
usually you will find one area that cuts just right for a lovely
finish. if you dont see one sharpen the tool again and try another
I made a simple spreadsheet and pdf file several years ago
using conservative figures for smaller equipment. You can
find it here:
The spread sheet should work in MS Excel, but I don't have
anyway to test it. The pdf is just a spread sheet printout
with suggested values. That values should work with either
drill bits or lathe stock.
It lists several materials and suggested rpm's for material
from 1/32 to 8 inches in diameter. If you use the spread
sheet you should be able to just change the value for the
"SFM to calculate" field and come up with your own custom
It was built using an old version of Quattro Pro, so I have
a Quattro version around too if some needs it. I know that
version works :)
SFM. The spindle speed is dependent on diameter, cutting tool material and
material you are machining. Surface Feet per Minute is the speed of the
material in the cut in feet per minute.
HSS 425 Aluminum 75 Steel
Carbide 1000 Aluminum 280 Steel
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller
Hmm ... what lathe is this? Most quick-change gearboxes on
lathes are for setting the thread pitch being cut, or the feed rate when
turning, not the spindle speed.
There may also be a set of levers in a gearhead lathe to select
Well ... there are multiple factors which are involved in
determining the optimum speed for a lathe. (And bear in mind that the
people defining "optimum" are those doing lots of work for money, so a
speed that wears out the tool a bit faster, but gets more work done in a
day is "better" for them.
And if you are threading up to a shoulder, you will want to run a
*lot* slower than the optimum speed, to keep from crashing your lathe.
But here are some factors which apply here.
1) The material being cut.
2) The material of the cutting tool -- usually HSS in a hand-ground
tool or some carbide in interchangeable insert tooling.
3) The *diameter* of the workpiece. The larger the diameter, the
faster the material is passing by the tool for a constant
So -- the figures given are SFM (Surface Feet per Minute),
calculated from the diameter and the spindle speed.
You look up the proper SFS for the combination of the tool
material and the material which you are cutting, then calculate the
spindle speed using the maximum diameter of the workpiece (you can speed
up as you reduce the diameter, if you want to re-calculate. To be
precise, multiply the diameter in inches by Pi (3.14159...), which gives
you the circumference in inches. Then divide by 12 to get the
circumference in feet. Divide this into the SFM for the tool and
material combination, and this will tell you how many RPM you want --
*maximum*. And this assumes a powerful enough machine to produce this
speed. Yours may or may not be that powerful. Don't be afraid to
divide the speed suggested by four if you are not in a *production*
To determine the SFM -- look it up on the web or with a program
(you've got some pointers for this), or buy a copy of _Machinery's
Handbook_, which has all of this you need. Pick up an old copy, it will
be as good as a new one for a hobby machinist.
Now -- there are speeds which will give a better finish, but
this is the sort of thing which you learn for your machine, tools, and
Remember -- not all steels are the same. Figure that a free
cutting steel can probably be run four times as fast as an unannealed
steel like 4140.
With carbide and aluminum, you can probably run as fast as your
machine will turn -- though this might produce a poor finish as the
aluminum melts and welds to the tool.
The same principles, except that you care about the diameter of
the milling tool instead of the workpiece -- and you also have another
factor -- chip load per tooth. Count the number of teeth on the cutter,
and multiply by the chip load per tooth to get how fast you can feed,
again if you are in a *production* hurry.
So -- visit *him*, and borrow it all back. :-)
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