From: vantonova@aol.com (VAntonova)
Subject: Re: V8 powered large NC mill in manual mode
Date: 2000/06/10
Message-ID: <20000610002454.01127.00000321@ng-fd1.aol.com>
Newsgroups: rec.crafts.metalworking

>> Might a V8 automotive engine be fitted to a large NC mill in use for
>> high speed milling experiments, and provide shaft power to the
>> spindle, with the alternator charging batteries connected to an
>> inverter for control, feed, and computation?
>
>Sure, but I wonder if you really need that kind of power?

Blanchard grinders run 50 to 200HP. Impressive to see a large grinder cutting.

>I read a book on high speed machining, where they were running a 1/2"
>end mill at 85,000 RPM, and removing something like 600 Cu. inches a
>minute of aluminum.  They ran out of spindle horsepower, with a 75 Hp
>direct-drive AC spindle.  They were running at several hundred IPM
>feedrates.

I did some experiments on this type of stuff. I played around with a mill
running 1000 inches a minute, spindles running up to 60,000RPM so on. The 1000
IPM mill was exciting to be around. A guy punched in the wrong number for a
servo loop gain and the Z axis vibrated so violently the machine literally was
jumping off the table (it was a 2000Lbs tabletop miniature gantry mill). I made
a mistake and had a servo runaway. The results were many bent parts (including
the leadscrew). An interesting thing was that the mechanical stop, a 1/2" rod
of aluminum about 4" long. It hit so squarely it didn't bend, but it shortened
and got about .075" thicker in the middle!

I ran a 5HP spindle at 24,000RPM with a 1/2" carbide end mill through aluminum
at 150IPM. 3/8" deep. Dry (no coolant). Hot chips shooting everywhare, got my
blood moving holding the e-stop button next to the machine.

We had a bunch of people from Boeing watching and they wanted some 7075
extrusion 1/8" thick cut to shreds. They had a special end mill for the job
that spirals down (forces chips and work down instead of up). It worked
beautiful on the extrusion when placed on wood blocks, forced it down and no
chatter. Ran 400IPM no problem. We routed some holes, and 3/4" slugs from the
middle of the holes shot out. Not many were recovered. One shot past a
spectator's ear and he thought it took his ear off.

They wanted to cut solid aluminum with the end mill. 1/2" diameter, 1/4" deep,
and forcing the chips down into solid aluminum. I told them they are nuts, I
won't be near the thing if they wanted to do that. We argued for ten minutes,
then I figured, customer's always right, let them have their way. The machine
hit the aluminum at 100IPM and 24,000RPM, 1/4" deep, fully enveloped (1/2" wide
slot with 1/2" end mill). The noise was a screaming explosion for about a
second. No chips flew, and the end mill didn't break. On closer examination,
the end mill was completely loaded with aluminum, and the slot was full of
molten Al. The end mill melted it's way through and the Al solidified on the
other side of the end mill.

>I can't imagine using this sort of stuff for any routine work.  Remember,
>this thing could also be turning about $600 a minute of aluminum (or
>$6000 a minute of Titanium) into scrap if anything went wrong with the
>fixturing, tooling or the program! I hear there is a part in some new
>aircraft - I think it is military, but not sure that starts out as an
>11,000 Lb billet of Aluminum, and weighs 11 Lbs when it is completed!
>That's a lot of scrap!

I spent a week at Boeing, looking at aluminum being shredded. Among many
interesting things, I saw them chemically etching 10 thou off 1/8" plates in
the effort to save weight, milling 1000Lbs Al forgings down to 200Lbs, and
Boeing using $8,000 hobby-type wood routers (can't remember the name) with a
porter-cable router for a spindle and exposed acme screws with nylon nuts for
cutting structural aluminum parts. By the way a 747 varied by one foot from
nose to tail due to allowed tolerances. Had interesting thoughts on the flight
home.

>Finally, there are probably some serious problems in sending torque
>long distances at such speeds.  So, your options are to have a >speed-up
>gearbox in the spindle, and then have the entire machine distorted by
>the tool torque times the speed-up ratio, or send the torque all the way
>down the spindle at high speed, with a string of bearings to keep the
>spindle from whipping.  I doubt it would work.  That's why the use
>direct-drive AC spindles in these machines.

Youre best off driving an alternator with the engine and go though an inverter
and an AC motor at the spindle. That's now all the big machines are done.

I had a chance to get a huge German mill from Wisconsin a while back. It was
made in the 60's as a tracer mill for making large molds and dies (type of
stuff for stamping truck frames and car bodies). Something like 6x12' travels.
It was sunk 6' in the ground and was about 14' above ground. Had a 50HP geared
spindle. Not high speed, it was made for plowing thought steel. It was
retrofitted for CNC. One hell of a nice looking mill. I talked to the guys in
the shop, who told stories of starting off 20 years ago in the shop and getting
stuck shoveling chips off the mill. They displayed scars all over their bodies
from hot chips. The poor fellow that got the job of shoveling chips wore a
thick leather suit, gloves, face shield, etc. Chips would still get buy and
touch skin. The mill would make chips as fast as one could shovel them away. I
almost took it, but it would have cost over $40,000 to dismantle it and ship to
to CA. A wall would have to come down, and the machine taken apart into 3
pieces. Total weight was over 140,000Lbs.

>(Yes, there are some machines that have coolant-driven or air-driven
>high speed spindles, but these are for finishing operations, and deliver
>maybe 1 Hp max to the spindle - not 75 HP +.)

Boeing has 25HP and up water-turbine (high speed) and hydrostatic (high torque)
mills. There was a Monarch-Cortland mill at Lawrence Livermore lab that had a
50HP hydrostatic/oil turbine spindle. The hydrostatic motor would be for low
speed, and the oil turbine goes up to 10,000RPM. It ran light (auto trans.
fluid type) oil and had a huge radiator for cooling the oil. It was very noisy
and leaked a lot. They had it scrapped. If I had the place to put it, I'd have
grabbed it.

Alex.