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Jarrett - the titanium bulkheads for a F-15
started out as a 4'x8'x2' ingot. they had to keep flipping it over while
carving away so that it didn't curl. when completed I could pick up the
entire bulkhead with one hand. none of the cross-sections were over 1/4"
thick. I believe they had 7 axis capability. titanium would cut at
5"/minute, whereas AL could run at 70". we didn't use punch cards (that
was college for me!), but memory was measured in "K", like wow, 640K! I
remember hearing that the machining files for an entire F-15 took ONE
GIGABYTE! wow, imagine that. now I have a 50 gig hard
drive.
4 million a second?! that's like a measurement
every 8 degrees for every cutter head blade turning at 25,000rpm.
we used to joke about carving a one piece
titanium canoe on a weekend when no one was watching.
----- Original Message -----
Sent: Wednesday, January 31, 2007 8:08
PM
Subject: [FlyRotary] Re: gantry
mill
No Kevin I wasn't aware, I'll have to go do some
'googlein' and check it out. CNC has come a long way from the good ol'
days of punch cards and reel tapes :-) While its nothing in comparison to
McDonnell, the control I'm using on my machine runs at over 4Mhz per
axis, that doesn't sound like much when we have comp's running in the Ghz
but, thats 4 MILLION resolved position calculations and movement
commands per second.The tool will pass through 12 million resolved points
per second at full rate [when runing 3 axis at full rate and can drive up to 6
axis at this rate if desired] I don't ever plan to run it that fast or to
that high of a command rate as its not needed in my case. As you'd stated
machining a huge titanium bulkhead would need a higher performance system
which can hit these resolutions and stop if an error is found. I have no idea
what Titanium is worth, but I'm sure I don't want to have to foot the
bill for a buggered up part :-). The gantry on my mill isn't that heavy, its
only about 3/4 ton but that was enough :-) moving stuff like that around in
your own shop w/ little to no heavy lifting gear can be a challange for sure.
A twin gantry mill would sure be a site to see, I can't imagine writing the
code for that, even w/ a proper CAM. It's always exciting to hear of others
who have done the same thing and had success.
Thanks!
Jarrett
----- Original Message -----
Sent: Wednesday, January 31, 2007 8:50
PM
Subject: [FlyRotary] gantry mill
Jarret - when I worked at McDonnell-Douglas
they had a twin gantry mill. the bed was like 40', but the newer
fighters had no pieces over 15' so they added another mill. the
gantries were huge, weighing many tons. a secondary, independent
computer would run while parts were being milled, checking for any errors
(not good on say titanium bulkheads that take 2 months to mill). if it
detected an error it could shut the gantry down within less than thousandths
of an inch. they told me that it sounded like an explosion when all
that tonnage hit the wall. these machines had footings the volume of a
2 car garage.
I was in the home built soaring club for a
while. there was a man building a plug doing exactly what you
outlined. he was connected with a university and used their
equipment. maybe his plane is the "lighthawk" I believe? he was
proud of his ability to produce many parts that all fit to tight
tolerances. I didn't know if you were aware of this
project. kevin
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