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Interesting reading Kevin! I've seen Boeing do a similar thing for their bid on the JSF [ I think it was] the machining of the bulkhead took two months or something.. Two guys picked it up and set it into the jig, it certainly didn't look to heavy after it was machined :-) I've seen some higher level milling machines on the net, seeing a 9 axis mill going at over 200ipm.. t'is a site to behold!
I suspected that McDonnell wouldn't use quite that old of equipment, but I'm still suprised when I go into a machine shop and see them operating equipment that is soooo old.. [ not punch cards but some still looked like they used 5.25" disks!] Three axis DRO's and almost zero control outside of manually entering the G-code. Sinoidal resolvers and tacometer's [ no high count glass scales or encoders back then :-)] No modern wizards etc.. very simple but very old stuff.. I hear ya on the size of computers, in h-school we had a Tany 32, and if you were lucky you got to run the Tany 64! The good ol' days.. :-) Now my pocket calculator has more juice than some of those old suckers..
4Mhz is moving, but if you want decent control of Feedrates and great finishes it all helps. :-)
That canoe would be great but I wouldn't want to guess what it'd be worth at the end of the day .. on the up side you could go canoeing in a volcano! Well.. that might be a teeny bit much... the portage up there wouldn't be too tough though!
All the best
Jarrett
----- Original Message -----
From: kevin lane <n3773@comcast.net>
Date: Wednesday, January 31, 2007 11:20 pm
Subject: [FlyRotary] Re: gantry mill
> 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.
> http://www.sailplanehomebuilders.com/whatmembersaredoing.htm
> http://www.glidersport.net/about3.html
> http://www.pure-flight.com/ and on and on.....
> ----- Original Message -----
> From: Jarrett & Heidi Johnson
> To: Rotary motors in aircraft
> 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 -----
> From: kevin lane
> To: Rotary motors in aircraft
> 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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