GeoLane at PTD dot NET wrote in message
...
On Sat, 31 Jan 2009 00:43:58 -0500, "Ed Huntress"
wrote:


The lubricating qualities of your cutting fluid are very important when
you're machining in a non-commercial setting and your machine is
low-powered
and/or flexible, and if you're using HSS or you're trying to extend the
life
of your carbides.

Few of
us hobbyists are pushing our tools that hard, because we value tool life
more than flat-out production rates.

And the key thing for
most of us is that we'll do better with straight oil for most cutting of
steel than we will with coolant applied from a bottle, a drip, or a brush.

I think the key misunderstanding many beginning hobbyists have is the
reasons *why* coolant is used in commercial machining. It isn't for
reasons
that apply to most hobby machining. For most of us, oil is better. And
there
is no reason, for most of us, to go to the trouble to apply flood coolant
just to cool the cutting tool. The simpler answer is to slow down a bit so
you don't need to cool.

There. g

Ed. How about expanding on that. Tool Life is the main consideration
for me when milling. On the lathe, I just sharpen the HSS tool -
without dipping.

Good. Dipping bad. HSS can handle heat but it doesn't do well with thermal
shock. That's also true with most harder tool materials, too.


To find the RPMs for milling cutters (or lathe work) I've been using
the rule of thumb
RPM=Cutting speed x 4 / diameter of cutter.

In general, I use a cutting speed of 60-80 fpm for mild steel although
I recall the books say 80-100 for mild steel.
What speeds do you recommend to prolong HSS milling cutters for steel
/ stainless/ aluminum/ brass
Any rules of thumb that you use?

I'm going more from data than experience, because I learned far more about
cutter behavior near the margins from interviewing material engineers and
manufacturing engineers than I ever learned in my home shop. Sometimes it's
hard to get them to talk much about HSS because it's hardly used in
commercial turning, and mostly for small job-shop-level milling, these days.

However, they've done extensive testing over the last century and my general
recollection is that HSS's edge life falls off distinctly when you get
within 20% or so of the tempering temperature (assume 1100 deg. F for that).
Again, from memory, the handbook recommendations for surface speeds tend to
produce temperatures right around that -20% point. So you'll get a small
improvement in edge life if you reduce speeds below that, but the dramatic
improvement occurs when dropping from higher speeds.

I stay below the recommendations unless I'm having a problem with surface
finish (which I often do -- that's a subtle thing for most of us hobbyists
to deal with). I haven't run many tools to destruction so that's as far as I
can go on my own experience.


How about chip load per tooth?
Feed it till it squeals or vibrates ;-) ? [sounds like what T Nut
implied in a post from long ago]

Higher feedrates produce more tool life per unit of metal removal, which is
a big deal for commercial shops. There is some relation between feedrates
and heating of the tool -- it's not completely independent as some would
have you believe -- and there is a stronger relation with depth of cut. The
latter is because there is more total heat going into the tool with deeper
cuts, but not as much of an increase in opportunity for the heat to be
conducted away down the tool shank.

All I can tell you is that feedrates in milling or turning, in a hobby shop,
shouldn't obviously burden the machine. Squeeling or vibration are threats
to your bearings as well as to your tools. I tend to push feedrates until
the machine tells me it's straining and then back off, when I'm roughing.


Which oil are you using and how do you apply it to a milling cutter?

I use Buttercut, which is straight lard oil. I will switch to a
mineral-based oil (Blaser's, if I can get it in small quantities) when I run
out, because it generates less smoke. I don't do much milling but I make
sure it covers the path the tool will take, and I squirt it from a can right
into the cut, in addition. I've used drip oilers and I think they're peachy
for a small shop and a small mill. I don't have one now.

How do you keep it from going everywhere?

I don't machine fast enough, or with enough quantity of cutting fluid, for
it to be much of a problem. I have rigged a vault-shaped hood of clear
plastic (very thin and flexible enough to spring it in place by hand) over
the carriage of my lathe when I needed to. I hold it in place with tape but
I'd make something permanent if I used it often. On my mill, which I don't
use anymore, I have used a similar setup. I used to get big sheets of thin
acrylic from an art supply store for my advertising business -- not the
really thin stuff, but maybe twice as thick as you'll find in craft stores.
I just saved a bunch of them and they wound up being my spray shields.


How are you clearing chips from a slot if you're not spraying the oil
with compressed air?

Badly. g That's one of the strong points of flood lubrication, and I think
coolant is better at that job than oil. Mostly I use a china-bristle paint
brush and try to flick them away, when milling. It works okay but not great.
I'm not an absolutist about not using compressed air but I try to avoid it.

Chips jammed in a slot shortens cutter life too.

Tell me about it. That's wrecked a lot of surface finishes for me in the
lathe, and a few cutters in a mill when I worked in a commercial job shop
for a short time, but I've gotten better at grinding a small chip groove in
lathe tools that, rather than breaking the chip up, directs it to the right
and away from the cut. Breaking up fine chips can be difficult or nearly
impossible.


Although I recently purchased a spray misting device for my mill, for
the past 20 years I've just been machining dry and living with
whatever end mill life I got. Always looking for ways to improve
things.

Lubricant will help. You don't need much just to reduce the tool load and to
improve edge life. It won't cool much if you don't use a flood, but you know
how to handle that by slowing down.

I'm wary of mists for manual machines. I know lots of people use them, some
love them, and I've heard very little about actual health problems from
users. But it can't be good to breath that stuff.

'Sorry I don't have much specific for you. You've got the idea for surface
speeds. If you lubricate the cut in steel, even poorly, you should notice
several improvements from doing so.

Regarding recommendations you may hear to use bacon fat: Good for
bandsawing, but I can't believe it's as good for turning or milling. Bacon
fad or lard is just lard oil plus the stearin that makes fat stiff. The
stearin will keep it from wicking right into the cut. With a saw, the
dynamics result in a smeared-on layer of lubricant *always* being in the
cut, anyway. On a lathe or mill, I suspect bacon fat will just cling and not
do nearly as much good.

And keep in mind that I was not denigrating coolant, only pointing out that
it's much less lubricating than straight oil. And I consider it to be more
messy than straight oil, except perhaps in a larger machine with a sump,
strainer, and pump. I've used it in my South Bend lathe and my old mill, and
I don't like it nearly as much as oil.

--
Ed Huntress