Speeds and feeds horizontal milling
Brian Evans
mill. I was, for the first time, trying some production milling of 1018
CRS on the weekend using my Harrison mill in horizontal mode. The
Harrison, for those who don't know it, is a British horizontal mill of
about 1500#, using a 30 taper and 1.5 Hp motor.
Anyway, I was gang milling using two 5" dia cutters, 1" width, cutting
two 1" wide steps on both ends of some 1" square mild steel stock. I
had three pieces of stock in the vise, which I suppose could have
contributed to some instability in the setup. I was running at about 90
rpm, power feed was about .75" per minute, coolant was brushed on but
the chips were cool enough to touch, as was the cutter and the stock
after each pass.
The maximum depth of cut that I could run this setup at was .040" per
pass, and I backed off to .030 for most of the passes. The total cut was
.300". The machine would start to vibrate to what I felt was excessive
if I tried more depth of cut. My power feed isn't adjustable, I tried
slower RPM's which didn't help, and faster (150) rpms seem to start to
over heat the material (blued chips) and as I was using new HSS cutters
I didn't feel like over heating them. I was very happy with the finish
quality, especially when I took a .005 or .010 finishing cut at 250 rpm.
Any advice from anyone who's had some horizontal milling experience?
Thanks, Brian
Robert Bastow
>
> Read with interest the discussion on feeds and speeds
>
>
> 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
John Hofstad-Parkhill
Robert's post was refreshing, and gave a bit of creedence to the method I've
always used, not quite to the extreme he mentions but the same basic plan.
Work on getting as much metal as I can remove and still feel comfortable.
Really wanted to note that heat and HSS are not the enemies you might
surmise. Hot swarf is to be expected, particularly in steel.
Tom Holt
from Robert Bastow <Tubal...@hotmail.com> contains these words:
> 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.
(Long post snipped)
Hey, Robert, that was poetry...
James P. Riser
Wonderful post! Thanks for the benefit of your experience. BTW - what kind
of oil were you using on that machine? 8-)
Jim
Robert Bastow
Back off Jim..Back off ;^)
Mark McDade
confirms my sense that all the reading
I've done didn't tell me s**t - that I
just have to feel the vibes!
Mark
Robert Bastow wrote:
>
> Brian Evans wrote:
> >
> > Read with interest the discussion on feeds and speeds
> >
.
.
.
Ted Edwards
> Milling speeds and feeds are a real can of worms..not because there aren't ...
Great! I enjoyed reading that. Now to apply it to my Smithy. Same
principle even if my machine would fit easily on the table of yours.
Ted
Jon Elson
Brian Evans wrote:
> Any advice from anyone who's had some horizontal milling experience?
I'm no expert on horizontal milling, but TWO 1" wide cutters cutting the
full
face width at the same time seems like a strain. I assume you had the far
end of the arbor supported. How long was the arbor, and what diameter?
If it was a long arbor, and 1" diameter, the arbor could have been
vibrating.
To make that wide a cut, you either need a custom arbor that is much
thicker, or to keep the arbor short. Too bad the power feed won't go any
slower. I think you will have to up the spindle speed a bit. 150 RPM
is a just a little on the fast side of the best surface speed for this sort
of work,
assuming the workpiece really is mild steel. It comes out to 196 SFPM.
90 RPM is on the slow side. It may work out better to rough with a
very small depth of cut and a fast feed (or is .75 IPM the only feedrate,
or is it just your slowest). Well, you might have to rough by manual feed,
then.
Also, you should make sure your vise is not vibrating. know my Chinese
knock-off of the Kurt is somewhat flexible, and when roughng steel I
definitely can feel the vise vibrating. You might experiment with the
axis the vise is mounted in, to see if there is a stiffer way to set it up.
I know that if I took a cut like that, it would pull the work sideways
out of the vise if the cutting forces were in that direction(I've had it
happen)!
Finally, I think your Harrison may not be stiff enough for this sort of
work.
This is the sort of stuff that is done in one pass on monster horizontal
mills, but they may weigh 10 times what your machine does, and have 25-
50 Hp motors. Possibly, with some attention to making things as rigid as
possible, you could improve the depth of cut a bit, but I doubt you
could double it on that machine.
Jon
Brian Evans
Your answer was EXACTLY the one I was looking for!
When I was in college learning electronics, I had a bunch of friends who spent hour
memorizing all the formulas for all the circuits. At exam time, they went in with a
double-sided legal sized page filled with diagrams of every permutation of every
design. I couldn't seem to memorize as well as they did, so I learnt the first
principles and how to derive all the permutations, and tended to go into exams with
things like Ohm's law on my formula sheet!
Thanks for teaching me the "first principles" of feeds and speeds1
Cheers, Brian.
Jim Kreter
<Tubal...@hotmail.com> wrote:
>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.
>
<Major snip of excellent prose and technical wisdom.>
>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
Kudos Robert!!!
Think I'll go for a "cuppa".
Jim (sitting in awe as the sound of a large 3 phase motor winds
down in his head, coolant smoke slowly wafts away above the monitor
and he realizes that he has to brush hot swarf off the keyboard)