Newsgroups: rec.crafts.metalworking
Subject: Re: Speeds and feeds horizontal milling
From: Robert Bastow <Tubal_cain@hotmail.com>
Date: Tue, 02 Feb 1999 23:33:41 GMT

Brian Evans wrote:
 
> Read with interest the discussion on feeds and speeds 
> 
> Any advice from anyone who's had some horizontal milling experience?
> 
> Thanks, Brian


Milling speeds and feeds are a real can of worms..not because there aren't
readily available GUIDELINES..but simply because different people have different
(honest) opinions based upon a whole range of different experiences.

THE ONE CONSTANT FACTOR IS CUTTING SPEED IN FEET PER MINUTE..It doesn't matter
whether I am using a 1" diameter slitting saw on my lathe cross slide, or you
are running a 10" diameter x 12" long slab mill on a 60 HP Cincinnati mill..if
we are both using HSS cutters on hot rolled steel, we are both limited to the 80
to 100 surface feet per minute.

You may find it hard to believe that, during a six year apprenticeship, during
which I ran SCORES of different mills..from the teensiest Instrument Mill to 48
foot Planer Mills...I never was taught, nor did I find it necessary to apply any
"magic formulae"

But the reason for that is simple..THERE AREN'T ANY!!

The objective is to remove metal as quickly (therefore economically) as
possible.  In the early days of (particularly horizontal) Mills it was common
practice for manufacturers to rate and compare them in terms of "CUBIC INCHES OF
METAL REMOVED PER MINUTE"  And, believe me, some of those old slabmillers could
shift IMPRESSIVE amounts of metal.

But there are so many other variables..some you have control over..width and
depth of cut, feed per tooth, coolant, tool geometry, SHARPNESS!! etc.

And there are a whole HOST more, that you , generally, do NOT have control
over..Age and CONDITION of the machine. Size of the machine, rigidity of its
design, its dynamic behaviour under load. the part itself, its rigidity and
clamping etc etc.  

Heck a Kray Mainfrain couldn't calculate all the "BEST" parameters for all the
jobs and all the machines in a large shop.

So how DID we do it? As do it we did..most Jobs were "on ticket" ...piecework! 
Commensurate with meeting specs. on fit and finish..we were paid to shift metal
as fast as possible.

In reality it was nowhere as complicated as one might imagine!  

Get a job ticket, go to machine..never seen it before! 

Clamp down job, install cutters.  Quick reference to Starrett Chart pinned in
lid of tool box (No-body figured it out in their head..the chart was quicker,
especially on a Monday morning!!)  X" dia at 90 ft/min = Y rev/min. Crank the
speed change dial (on most CINCI's, Kearney & Trecker, Herbert's etc the speed
and feed changes were through crank handles on large dials.

Now set the depth and width of cut.   HMMmm!  In MOST cases the fastest way to
shift metal was to engage as much of the cutter as possible get as many teeth
cutting as wide and deep as possible at the same time.."Bury the Bugger"  the
saying went.  That way you removed more metal per tooth, per rev and were less
likely to wear the cutter out before the job was done

Limiting factors..HP..got MORE than enough.  Machine rigidity..slide conditions
etc...NO IDEA..never seen the bugger before..only one way to find out though!! 
What's next..the work piece..this one is sturdy enough to take some
"elbow"...Set Up..NO PROBLEM..we soon learned to fasten things down so Dynamite
wouldn't shift 'em..before tickling them with fifty plus Horsepower.

Whats left?..the FEED rate..you know, how many thou per tooth per rev..I have
absolutely NO IDEA until all the other factors start inter-acting and the whole
stage play gets into the dress rehersal.

Curtain up time, light a fresh fag and take a last swig of cold tea.

Lights, curtain.. One last check around...spindle clear, feed disengaged, SAFETY
CHECK..these machines are NOT fitted with an "OUCH" switch. No "oily rags" about
(apprentices rubbernecking) No laborer shoveling chips out of the back of the
machine.  Bootlaces tied, floor clean and dry..two or three clear escape
routes..nothing to trip or fall over. Did I mention safety glasses?  Safety
WHAT??

Deep breath. Concentrate. Start spindle. Coolant, GENTLY feed cutter into job BY
HAND. Feel the cut, feel the whole set up shuddering and settling into
equilibrium as the cutter digs deeper and the motor starts to push some serious
horspower into its job slowly build up the hand feed rate until the cutter is
"Buried"..In full depth and width.  

Continue to gradually increase the feed rate, as every sense and instict strains
for any sign of trouble. So far so good..you figured the right starting
points..now you and the machine begin to understand each other and trust starts
to grow..We are NOT going to hurt each other or let each other down are
we!!!..Still gradually increasing the hand feed pressure..the machine, now all
the slack is taken up, all the castings have bent and bedded into unity..is
READY!! Quick check of the chips, cutter seems happy coolant flow good...You're
READY.

NOW!!  Lets show them what we REALLY CAN DO!!  start to crank the feed faster
and faster until you feel that first shuuder of discomfort..back off a
bit...engage power feed and crank the selector handle fast until you start to
feel the power feed catch up with and overtake your hand feed.  Ease off on the
crank handle..let the machine take over..But don't let go yet..Every sense organ
is tuned in as the machine settles down to a steady pace after its quick
acceleration..everything feels, sounds, smells, good....turn up the feed another
notch..settles down..happy..turn it another...settles happy...turn it
another,,machine grunts..unhappy..turn it back...happy. You just arrived at the
CORRECT FEED PER TOOTH !!!!

Slowly you relax, letting  your hands creep away from the knobs and handles..the
machine munches on..in equilibrium..chips and coolant sound like frying
bacon..machine is bunched into and happy with its job.  You turn to find the
cigarette..after that first puff..has burned away. Light another. wipe your
hands..gradually your senses retreat from the machine. as it does what it does
best..shifting metal. 

You have a bond of trust now.  You and that Machine.  It will let you know in
good time..in your secret language..if something start to go amiss.  It trusts
you, to hear and respond, before any harm befalls it. You are a team now..both
doing the job you do best.

Now you realise your throat is dry!! no cold tea left, check the clock check the
job...ten minutes left "in cut", before you need to stop and replace the
workpiece.

You turn, and without a backward glance, you stride confidently toward the
canteen for a welcome "cuppa"   On the way we happen to meet.."Hey Robert" you
ask "what feed rate are you using on that job?"   "Haven't a clue" say I  "go
check the dials..I'm off for a cuppa!!"

It may not be the answer you want Brian..But I'm afraid it's the only one I can
give you!

Happy milling.

Robert Bastow