end mill speeds

[Eric CoxParticipant @ericcox50497]

.Have been trying to calculate end mill speeds. I've found two formulas on t'internet.

1) SFM*3.82 / Dia

2)SFM*12 + Dia * 3.142

which is correct

[Eric CoxParticipant @ericcox50497]

[kevin grieveParticipant @kevingrieve63008]

not sure which is correct but this guy has a real simple way to calculate speeds on his web site,as well as other tutorials.

http://www.tomstechniques.com

hope this helps.

[David JuppParticipant @davidjupp51506]

Looks like they started out the same, but have been copied incorrectly at some point

2) ought to be (SFM*12)/(Dia*3.142) which is equal to 1}

[Gary WoodingParticipant @garywooding25363]

You might find this useful. There is also an Android version.
**LINK**

[John HaineParticipant @johnhaine32865]

Gary, that looks brilliant. Just downloaded to my iPad, seems to work very well.

John.

[steveteeParticipant @stevetee]

12 S

———

Pi D"

Always worked for me. The cutting speed in feet per minute would be 40 for cast iron and 70 for steel

So for a 2 inch cutter on steel

12 x 70 =840

3.14 x 2= 6.28

=133 and a lot of decimal points

Back in the real world somewhere between

about 110 and 140 rpm would do nicely.

Multiply speed in feet by 12 ( to covert to inches) divide by the circumference of the cutter gives you the revs that give you the cutting speed in inches per minute

[websnailParticipant @websnail]

Never worked it out in my life, always worked by feel.

That's the beauty of manual machines

[Rik ShawParticipant @rikshaw]

Websnail – agreed – nothing quite like a little tactile feedback – if it doesn't like it then it will tell you – simples!

Rik

[jason udallParticipant @jasonudall57142]

Too lazy this morning..how far out would 10, 000 rpm /dia (mm) be?

[jason udallParticipant @jasonudall57142]

Lets try…say 70 feet/min
2″ cutter
Above we get 133 rpm.

10 ,000/(50.8)= 196 rpm

Working through from70 f p m would give 6790 /dia
In any case there is a constant that from taste/experience gives a finish you desire and once established a simple divide by cutter diameter will yield an rpm you probably don’t have anyway…
Don’t get hung up on number of flutes…that only effects depth of cut not spindle speed

[MadMikeParticipant @madmike]

"Don't get hung up on number of flutes"????

That's not strictly true when using end mills or other multi tooth cutters. The feed in feet/inches/metres etc per minute equals the feed per tooth per revolution multiplied by the number of teeth. So the speed of spindle needs to be such that you can achieve the feed rate which is both safe and efficient.

Steve 40 fpm for cast iron, and 70fpm for mild steel is very low even for HSS tooling. For example cast iron should be roughed at around 170fpm and finished at around 250fpm. Mild steel at 100 and 150fpm respectively.

Carbide tipped tooling substantially increases all of the above such as 200 to 350 surface feet per minute.

Of course all of the above assumes machinery in good condition, tools ground correctly, machinery with sufficient rigidity to allow the speeds refered to.

[jason udallParticipant @jasonudall57142]

Mike.. I was referring to the Surface speed..yes in feed rate and depth of cut are effected by tooth count.
And yes 70 fpm is probably very conservative. .
..

[colin hawesParticipant @colinhawes85982]

I reckon 500 RPM for a 1/2 " dia HSS cutter on mild steel and other sizes approx. proportional ; ie 1000 RPM for a 1/4" dia cutter.

[BazyleParticipant @bazyle]

For amateurs spinning too fast means feeding impossibly fast to avoid rubbing and hence overheating. Better to work out how fast you want to turn the handle and work back to a minimum 1 thou feed per tooth cut.

For industrial use with cooling the target speed is the speed of sound in the material – so around 250fpm.

[Anonymous]

Posted by Bazyle on 31/03/2014 17:33:28:

For industrial use with cooling the target speed is the speed of sound in the material – so around 250fpm.

Never heard that one before! The speed of sound in cast iron is more like 10000 feet per second, although it varies widely according to the precise mode.

Andrew

[Roy MParticipant @roym]

Eric,

It's easier in metric.

start from the recommended surface speed.

r.p.m (n) = Vc (given surface speed in metres/min) x 1000 then divide all that by the circumference of the cutter (Pi x D )

Grey cast iron 18-25 m/min. Fz (feed/tooth) ; dia 6mm .02mm. dia 20mm .071mm.

dia 50mm .13mm. These feeds are for a full width slot (Ae=1)depth equal to half the cutter dia,(Ap=0.5)

Feeds are adjusted depending on depth (Ap) and width (Ae) of cut.

Roy

[BazyleParticipant @bazyle]

Andrew, I just looked up on the web and a couple of sources gave the speed in 'iron' as 5100m/s so roughly 250fpm.

At the atomic level nothing cuts, a tool just forces cracks to open. Cracks propagate at the speed of sound. Hence the most efficient way to 'cut' is to follow along as the crack opens up.

[Les Jones 1Participant @lesjones1]

Hi Bazyle,
I don't understand your maths.

5100 m/s = 5100 * 60 meters per minute = 306000 meters per minute
306000 meters per minute = 306000 * 1000 (to mm) /25.4 = 12047244 inches per minute

= 12047244/12 feet per minute = 1003937 feet per minute

I can not see how you get 250 feet per minute.

Your value for the speed of sound in iron works out to 16983 feet per second to put it in the same units that Andrew used.

Les.

 

Edited By Les Jones 1 on 31/03/2014 23:09:11

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

A crack in metal can propagate at any speed from zero speed to creep speed to very fast indeed .

What happens in any particular case depends on a very large number of factors including probability .

Most real mechanical objects failing by rapid crack propagation do so in times of order milliseconds to seconds .

More common though is failure by creep speed crack propagation – sometimes takes years for components to fail .

Fascinating subject and much more to it .

Michael Williams .

[Author]

Posts