View Full Version : Proper Chip Loading article

Your Old Dog
01-01-2009, 09:10 AM
I have a current post running where I ask how to determine the proper chip load. Pfilburn offered up this post from Robert Bastow on another website. I thought it might warrant it's own post to make it easier to find in the search engine. It is very well written and informative to boot.

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.

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

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

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

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

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
.................................................. ..

01-01-2009, 10:44 AM
From the thread whence it came:

That's exactly my point Philbur -- that's Teenut (Robert Bastow)'s famous post to rec.crafts.metalworking. It was a lengthy (and polite) discussion about calculating speeds and feeds, and most of the pro machinists were advocating calculating (or looking up) the correct speeds and feeds, when Teenut went into his poetic missive.

Unless you've got 50 years in the business like Teenut or Lane, you're not going to be able to "feel" the correct feeds and speeds like a master Tool and Die maker can...

But more to the point, with all that experience and art, a Master Tool and Die Maker is empirically finding the same values that have been calculated for you in the Machinery's Handbook. Yes, you need to tweak those values according to the power and rigidity of your machine, but mild steel will always cut best at 100 SFPM, regardless of what machine, and what cutter, and aluminum will always cut best at 200 SFPM...

So you can spend a lifetime trying to learn the correct speeds and feeds by feel, or you can just look it up in a table, and get most of the benefits of their extensive experience in 3 minutes :)

That's not saying that after looking up the correct cutter speed you're going to start making parts like Lane, but at least you have taken care of one source of errors...

J Tiers
01-01-2009, 11:23 AM
And the most interesting point about it is that it says basically the same thing a number of us have said.......

There is another point also, which may also be relevant....*

There is a basic SFM limit when you look at material and cutter, within which the speed/feed can be adjusted to get the results you want.

it is going to be a different speed and particularly feed, for a 375W machine as opposed to a 7.5 kW machine. It HAS to be, since the two machines cannot remove the same amounts of material, due to the 20x difference in power.

For any given speed, the feed will determine the power needed with a given cutter. If the resulting feed for your power is too small and will just rub, or is too large, then you might have to change the speed in order to get a chipload per tooth that makes sense. The usual table won't tell you that.

Then also, the tables, as mentioned in the quoted post, are for maximum material removed.... meaning fastest possible work/least time per part. Is THAT your goal in the home shop? Probably not.

At that point, you can throw out the tables.

All you really need to know is the very basic information...... 1) what the limiting SFM for the material and cutter is. 2) what the reasonable chip thickness per tooth is for the cutter and material.

With that, and the number of teeth on your cutter, you have everything you would ever need. You can decide if you are "pushing for max" or if you are doing normal home shop work and just want to get the job done without wearing out the cutter too fast.

odds are that you don't regard cutters in quite the same way as industry. They regard them as disposable tools. For you they are relatively expensive items... a $250 slab mill (only a cheapie) is not something you want to replace too often.

* That other point...... Teenut seems to have been very opinionated.... and made a lot of assumptions which are "included in" his posts and answers....

Just look at his post recently quoted here, which said that way oil was the worst thing a home shop person could use on their machine... that it would wear out the machine.

Obviously there were a number of assumptions made in that answer, which are likely to be dead wrong in many, or even most cases... So that other post can and probably SHOULD be totally ignored as BS.

You must "filter" all of Teenut's posts, and indeed all of OUR posts also. Everyone is making an assumption, and it may be wrong for you.

Some posts are just wrong anyway. This is the internet..........

01-01-2009, 11:46 AM
You must "filter" all of Teenut's posts, and indeed all of OUR posts also. Everyone is making an assumption, and it may be wrong for you.

Some posts are just wrong anyway. This is the internet..........

"Teenut" (Robert Bastow) is the same guy who posted that a Home Shop Machinist should absolutely, positively not use way oil on his machines. :D

J Tiers
01-01-2009, 11:49 AM
* That other point...... Teenut seems to have been very opinionated.... and made a lot of assumptions which are "included in" his posts and answers....

Just look at his post recently quoted here, which said that way oil was the worst thing a home shop person could use on their machine... that it would wear out the machine.


01-01-2009, 11:52 AM
Sorry Jerry! I'm running around my office trying to keep my 15 month old from putting coolant fixtures in his mouth :)

01-01-2009, 02:16 PM
* That other point...... Teenut seems to have been very opinionated.... and made a lot of assumptions which are "included in" his posts and answers....

That is a bit of an understatement! Teenut WAS very opinionated, and was quite aware of and almost proud of that fact. He did have something to say about most topics, but was a good guy that loved a debate.

For any that do not know, he was a very prolific poster on the rec.crafts.metalworking usenet group, before it got overrun by morons. He died from a bout with cancer a few years back. There are still a group of guys there that hoist a glass of the beverage of their choice on the anniversary of his death each January 11, at 9:15PM(EST), in remembrance.