On 12/10/2017 12:19 PM, wrote:
On Fri, 8 Dec 2017 17:30:50 -0700, Bob La Londe
wrote:

On 12/8/2017 2:28 PM, wrote:

On Fri, 8 Dec 2017 13:02:15 -0700, Bob La Londe
wrote:

I never thought I'd be doing this sort of work ever. I am quite content
to high speed micro mill aluminum. When I was first learning I asked a
lot of questions here and elsewhere. Eventually I put together enough
information to where I can produce satisfactory results most of the time.

When I say micro milling I mean optimizing cut rates with modestly high
speed spindles (24K RPM) and pretty small cutters. Almost no milling
job that I do gets by without a finish pass without atleast a .0625 ball
mill. Quite often I have to use .03125 ball mills to finish some
details. I even have to break out the .0156 stuff once in a while.
That's the range I am talking about when I say micro milling.

For all of that work I use uncoated square end and ball end mills with
6-8% SC520 and water with a constant flood. Cutters last a very long
time and the results are good. Jobs often last for hours. Sometimes a
single tiny little cutter has to work for hours.

Well somebody offered me enough money to tempt me to do some similar
work in 4140HT. I've milled some hardened steels and hard tool steels
before. The numbers say 4140HT should be easier. Its a sort of
compromise. My past experience shows me that a low speed and feed with
an AlTin or TiAlN coated cutter works pretty good. That's fine when you
are pushing a 1/2" 5 flute end mill, but I have to do some of that small
detail work to finish this job. I need to push the envelope with ball
mills as small as .0156 for some of the finish work. I can break it out
so I don't have to finish everything with it, but its still going to
more time than just a few hours. HSM Adviser gives some numbers that
show days instead of weeks, but I wonder if there is anything I can do
to actually get those numbers. With aluminum heat and thermal shock is
not really an issue. With Altin in steal I don't run coolant, but I
admit I do throw a little cutting oil on the part. I've just never done
small or micro milling in harder steel. Well, I have engraved some
knife blades, but that's it.

I'm hoping I can cut down the learning curve, but I am prepared to break
some cutters and ruin some work pieces if I have to. Chip clearance is
probably also going to be an issue. Maybe an air blast to blow chips
clear and see what happens. The thing is we are talking about steel.
Steel chips don't blow clear as easily as aluminum chips.

I am open to any suggestions.

Worst comes to worse I am prepared to tie up my machines for a few
weeks. I certainly figure days even in the best case.
Greetings Bob,
You really need to make sure to get all the chips removed so that
there is no re-cutting of the chips going on. Especially with those
tiny cutters. And the chip load needs to be the same for each flute as
well as enough of a chip load to insure that the flute cuts instead of
pushing away. So your tiny cutters need to run very true. I suggest
you contact the cutter manufacturer for chip load requirements. I
think you should also run coolant or cutting oil. If I was doing this
job I would be using about a 10% water soluble coolant concentration.
And I would try to make sure the coolant flushes away the chips. So
aiming the coolant nozzle correctly can really help.
Eric


I've been doing some simulations and with the smallest cutters I am
still looking only 2-7 IPM depending on the cut at full 24K RPM. 7 is
only for light step over with chip thinning turned on in the calculator.
Maybe its time to invest in some 60K spindles just for this type of work.

I swear every day this gets scarier. I just got a request to cut some
graphite molds. I know less about cutting graphite than I do about
cutting steel. LOL. I may pass on that one. I have way to many jobs
on the board right now already that are outside of my comfort zone.
Yeah, more jobs can get scarier. Especially when new materials are
considered. Graphite is one material I myself would avoid because it
is so abrasive and dirty. I know this because I have machined it
before.
Because you are machining with small cutters at high speeds you
might be interested in this web site: http://www.precisebits.com/ .
Then again you may already know about it. If you don't then if you
visit the site you will discover a good source of knowledge regarding
high rpm cutting with tiny tools. I called them once with a question
and had a quite informative discussion and so learned some good stuff.
Cheers,
Eric


Yeah, Ron is a really good guy and pretyt knowledgable about small
cutters. Ages ago was using his collets in a Bosch Colt trim router
for milling aluminum. I burned a few of those routers. Still have one
mounted on my little CNC router.

As far as graphite, as I mentioned in another post, my plan if I had
gotten that job was to use my little (almost throw away) Chinese noodle
(limp like a noddle) router. If I ate the whole thing up a decent size
job would pay for another one. On my short list of plans is to make a
little better frame and move what's good on that router over to the new
frame. I'd lay the machine out on my surface plate and I'd be able to
replace any of the cheap parts even faster and easier than it is now. I
already have it in a box. I could slap some doors on it, and put some
vacuum in there with a shop vac to keep the graphite out of the shop. I
had doors on the box before, and they are laying around somewhere.

Only part that would not be super cheap to replace quickly and easily is
the YZ motors. The X can actually be outside of the box when I rebuild
it.