Odd Q on machine stability
Existential Angst
Several times mention has been made of dancing machines, and the importance
of firm anchoring, level-ness, etc.
Suppose a machine -- cnc or manual -- was placed on a very light but very
rigid base, which was then suspended in the air by 4 or so guy wires from
overhead beams.
So the machine would be level and un-twisted because of this light rigid
base, but it would be free to swing.
How would that affect its performance, accuracy, etc.?
I would hazard to say that there would be no ill effects at all, cuz of
well, Newton'n'shit.....
Heh, if there were springs in the guy wires, sure would help with building
vibration, wouldnit?
But, I was wrong once before, and it could happen again.....
Iny thoughts?
--
EA
John R. Carroll
> Awl --
> Iny thoughts?
Just two.
First, up your meds.
Second, if you try this on, be sure and film it.
LOL
--
John R. Carroll
Larry Fishel
wrote:
> Heh, if there were springs in the guy wires, sure would help with building
> vibration, wouldnit?
Would probably help with small vibrations, but without some sort of
damping there might be a chance of an escalating harmonic in the
system. Still probably wouldn't affect operation any more than being
bolted down...until the springs or cables finally failed.
Jim Wilkins
wrote:
> Suppose a machine -- cnc or manual -- was placed on a very light but very
> rigid base, which was then suspended in the air by 4 or so guy wires from
> How would that affect its performance, accuracy, etc.?
> EA
Air-supported tables like these are the standard in optics labs, and
we put our wafer probes and microscopes on them at Unitrode:
http://www.newport.com/Optical-Tables-and-Vibration-Control/137658/1033/catalog.aspx
The large leg in each corner contains a rolling diaphram air cylinder
controlled by a position regulator that does a pretty good job of
keeping the table level, much better than springs would. They work
very well until you need to torque larger fasteners, then they bob and
rock like a diving float.
jsw
Kirk Gordon
Dood!
Einstein was good at "thought experiments". You're not. And Newton
is gonna kick yer ass in five or six different dimensions if you ever
try this for real.
First, there's that stuff about how a body at rest tends to remain
at rest unless acted upon by drugs or alchohol or something. That does
NOT refer to the whole body, if said body is made of parts that can move
with respect to each other. What it refers to is the center of the
body's inertial mass. So when you hit the rapid button and make the
machine's table move to the left, everything else about the machine is
going to move a bit to the right, so the center of mass stays where it
was. And if you move the saddle away from you, the rest of the machine
will come toward you. Etc. And that's gonna be a problem.
If the guy wires were all taught and balanced and everything before
you moved the table, they're not going to be that way after you move it.
The platform and machine body are now in a different place, having
moved to compensate for the change in mass distribution when you jogged
X. So the tension on the wires is now unequal. And, gravity being what
it is, the whole machine and base will start another bit of movement,
swinging pendulum style toward a new location where the tension in the
wires is equalized again. And that swing won't go away till friction
eats it, which can take a very long time. And every new axis motion
will add to the swing. And add to it. And ADD to it. And so on.
If you attempt to move Z the wires will either loosen a bit (Z-
motion) or tighten a bit (Z+), for the same Newtonian reasons. And,
since wires (or anything else, if you stress it enough) are elastic,
they'll just naturally want to "rebound" a bit when the motion stops.
So in addition to swinging back and forth from XY motions, your poor
dizzy Fadal will now be bouncing up and down, platform and all. And
don't even THINK about adding springs!
Worse, none of the moving parts of your Fadal is likely to have its
own center of mass on a line that goes through the center of mass of the
whole machine. That means the forces described above will form
"couples", which will cause rotation. When the table moves left or
right, the machine won't just pendulum swing in the other direction.
It'll also try to twist itself around it's center of mass. Viewed from
the operator's position, it'll twist clockwise if you move left, and ccw
if you move right, or vise versa, depending on whether the X mass is
located above or below the main mass center. Same problem when you move
Y or Z (top of machine twists toward you or away from you). This causes
even more distress for the poor guy wires, which will now be out of
balance in god knows how many ways, and will need to hang on while the
whole machine does some MORE pendulum/gravity swinging to equalize
everything all over again.
And before you know it, you and your poor machine will be swinging
back and forth like a 10,000 pound tether ball, twisting in at least
three axes simultaneously, and screaming like a kid on one of those
insane multi-dimensional amusement park rides that's specifically
engineered to make people lose their lunches from both ends at once.
And then, since you asked, there's the small problem of vibration.
And here's the relevant question: If you were a machine tool, and if
you had a whole bunch of nasty little compression waves running all over
the inside of your body, and if you really REALLY wanted those waves to
go away, becaue they hurt, and itch, and make your eyes water, and more,
what would you most like to grab hold of for stability?
A. Some long, skinny, flexible, stretchy pieces of cable?
B. A big-ass chunk of concrete, conveniently attached to the entire
earth, with all its zillion trillion gazzillion tons of rock and iron
and stuff?
If you guessed A, you'd better own a good helmet and a generous
supply of barf bags.
Nuff said. Have fun!
KG
DoN. Nichols
> On Jan 9, 2:27�pm, "Existential Angst" <UNfit...@UNoptonline.net>
> wrote:
>> ...
>> Suppose a machine -- cnc or manual -- was placed on a very light but very
>> rigid base, which was then suspended in the air by 4 or so guy wires from
>> overhead beams....
>> How would that affect its performance, accuracy, etc.?
>> Iny thoughts?
>> EA
>
> Air-supported tables like these are the standard in optics labs, and
> we put our wafer probes and microscopes on them at Unitrode:
> http://www.newport.com/Optical-Tables-and-Vibration-Control/137658/1033/catalog.aspx
I remember those well. We had them in our laser labs.
> The large leg in each corner contains a rolling diaphram air cylinder
> controlled by a position regulator that does a pretty good job of
> keeping the table level, much better than springs would. They work
> very well until you need to torque larger fasteners, then they bob and
> rock like a diving float.
Also -- watching as you put something heavy on one corner, and
after it stabilizes, take it off and watch again.
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Existential Angst
news:4B490AFF...@gordon-eng2.com...
Did you read what HalfNutz said, in one of my recent rants? That I could
out-verbositize *you*!!
I think we are at least neck and neck, eh? :)
Well, I didn't doubt for a minute that pendulum-like motion and rotation
would accrue, but would it affect the machining *results* of a part?
And, regarding the motion, suppose the machine were constrained at the
coners by horizontal springs, and in the vertical by springs. Couldn't this
actually *relieve* internal stresses in a machine, with no sacrifice of part
accuracy?
--
EA
>
> KG
>
Jon Anderson
> Second, if you try this on, be sure and film it.
And post it to YouTube!
Jon
John R. Carroll
Sure but what you are describing is the floor you are suspending your
machine from.
Damn but you're funny!
Get yourself a Camaro and hang with the Homies Dude.
Grab your balls and say "YO! F'ing Moulie"
--
John R. Carroll
John R. Carroll
Absolutely. He might send it along to AFV first though<G>
--
John R. Carroll
Wes
>Well, I didn't doubt for a minute that pendulum-like motion and rotation
>would accrue, but would it affect the machining *results* of a part?
I wonder how this would affect the tuning of the servo system?
The more important question, is how much coolant are you going to dumping out of the
coolant tank due to wave action.
Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller
Existential Angst
news:4b48d8a1$0$4980$607e...@cv.net...
I think the real "utility" to this Q, beyond any impact on accuracy (which I
don't think there will be) is that a floating design might be more
"structure/building friendly" say, for machines mounted on a second floor.
Or, in garage-type ditties, more neighbor friendly ito of transmitted
vibration to the next house, etc.
Not a biggie, just never saw the big payoff to bolting shit down like an
earthquake was coming.
A proper floating design would have no tendency to walk, either.
--
EA
>
> --
> EA
>
>
Jim Wilkins
wrote:
> ...
> Well, I didn't doubt for a minute that pendulum-like motion and rotation
> would accrue, but would it affect the machining *results* of a part?
> And, regarding the motion, suppose the machine were constrained at the
> coners by horizontal springs, and in the vertical by springs. Couldn't this
> actually *relieve* internal stresses in a machine, with no sacrifice of part
> accuracy?
Why not float it on a raft in a pool of coolant?
The first time you walk up next to it and punch in a rapid traverse
it's going to run you down like a rhinoceros.
Does AFV have a category for that?
Nice one, KG
jsw
Bill
"Existential Angst" <UNfi...@UNoptonline.net> wrote in message
news:4b48d8a1$0$4980$607e...@cv.net...
Okay. Put your safety glasses on. Stand on the platform in front of your
machine. Adjust wires, springs, reductape. Go to MDI. Type in 10000 M3.
Press cycle start. Type in M5. Press cycle start. HANG OOOOOOONNNNN!!!!!!!
Peter DiVergilio
I once worked at a dealership under the main air compressor which was hung
from the (metal) roof trusses by steel rods and compression spring brackets.
We called it "Skylab", and just ignored it after the first few days of
working there. It was there for 10 years before I started with no problems
and might still be there now, 30 years later.
--
Peter DiVergilio
All the money I ever wasted was spent trying to impress somebody who was
never going to like me anyway!
John R. Carroll
Better yet.
S10000 M3
M4
M3
M4
An M8 might be a good idea at that point to hose down the released bodily
fluids and such.
--
John R. Carroll
Jim Wilkins
> ...
>
> Better yet.
> S10000 M3
> M4
> M3
> M4
WE HAVE IGNITION...AND...LIFTOFF
D Murphy
news:Sp6dndEKoNzt29TW...@giganews.com:
LOL.
OTOH, this is how new things get invented. A crazy idea, everyone laughs
and points out the flaws, he thinks, "OK, it's gonna move, how can I
constrain it" and the next thing you know you end up here -
http://www.parallemic.org/
Basically the same idea, with some of the more egregious bugs worked
out.
--
Dan
John R. Carroll
I've had to deal with this issue my entire working life Dan.
High speed robotics is right at the core of the injection molding industry
today. It is if you want to compete anyway, and you have the same issues to
deal with in what EA is mulling over. Tool changers causing part
imperfections has been a real issue in the milling industry right along.
In the mid 90's I bought a big beam robot out of the BK of a Texas molding
company to use on a 630 ton Toshiba hydraulic press.
All I wanted was the metalwork and we stripped it completely when it
arrived. I replaced the air/oil drive with a fast pitch ball screw set that
Beaver Precision built for me and hooked it up to a pair of Fanuc's high
speed alpha series (3600 RPM) servo's.
The thing was lightning fast and worked pretty good until the vacuum chuck
was holding the twelve pound part we wanted to remove from the machine. The
vacuum wouldn't hang on to the part when the robot retracted out of the
machine. I should have stopped and though about that for a minute but what I
did instead was install a spring activated mechanical clamping system we
cobbled together. The chuck would move in and when it grabbed the part, six
fingers engaged to clamp the part from behind. I figured the part wouldn't
fall of then, and it didn't.
When the robot accelerated the part upwards I ended up with the entire mess
sitting in what was left of the discharge shute at the bottom of the machine
and a big old pile in my britches. You see, I hadn't bothered to set up the
acceleration ramping time constants on the drives, only the decel so the
servo just came on at 2000 RPM. The screws were six pitch. OOPSIE!
Anyway, I'm just poking fun at PV/EA/whatever.
The M3/M4 thing at ten percent below max RPM is something I actually do when
commissioning a machine however. Busted the 35 Kw geared head on a Formosan
machine once. Took about twenty minutes. Smoke everywhere.
Sales guy had said you could reverse the spindle all day long at 3000 RPM
when I asked him about rigid tapping.
I guess they have really short days in Formosa......
That would also explain why all of these guys think they are well hung.
Imagine what ten inches is if an entire day is 35 minutes long.
LMAO
--
John R. Carroll
Existential Angst
news:29a43015-da34-4c7f...@u7g2000yqm.googlegroups.com...
===========================================
Well, mebbe like a slow rhinoceros -- or a fast turtle.
With, say, an 8,000 lb machine, and a cupla hundred pounds of table
force/acceleration,
the resulting machine acceleration would be on the order of 1/4 of a meter
per sec
per sec -- about 9"/sec^2 or 3/4 ft/sec^2 -- visavis the 32 ft/sec^2 of
falling objects.
And THEN, only for the duration of the table travel -- presumably it would
go back
again in the other direction.
But, I used the guy wires only for visual emphasis.
The real point, made in
my other replies, is whether having the machine mounted in a constrained
floating arrangement in x,y,z, on good die springs would affect accuracy.
Funny you mentioned floating -- I was once musing with someone on the
possibility of having a machine shop on a small barge -- heh..... hopefully
right offshore of a really high-quality ghetto -- Camden, Philly, etc.
Well, far enough off-shore so that I cain't hear the fukn rap music....
I figger the homeyz are not big on boating yet -- altho I do see them on the
Yonkers Hudson in their fukn skidoos.... goodgawd....
--
EA
cncmillgil
Chips just float away, pump in out side atmosphere for coolent?
On Jan 9, 10:11 pm, "John R. Carroll" <nu...@bidness.dev.nul> wrote:
> D Murphy wrote:
> > "John R. Carroll" <nu...@bidness.dev.nul> wrote in
> >news:Sp6dndEKoNzt29TW...@giganews.com:
>
> >> Bill wrote:
> >>> "Existential Angst" <UNfit...@UNoptonline.net> wrote in message
What ever happened to"sENOIR ManuaL" swinging the door every shot?<g>
We had Wittman robots on the Engels - Sweeet! If there was one bad
cavity they prgrammed it to drop that one in the scrap pile, while
others were placed individually in trays. Cool shit. I did alot of EOA
tooling for them whilst getting my wings on setup & processing. Those
side robots are really freakin cool. Ever see the Engel training
video, done here loacally at Winsler? Now thats a 1st class facility.
They'd have black tie events on the molding floor.
>
> Anyway, I'm just poking fun at PV/EA/whatever.
>
> The M3/M4 thing at ten percent below max RPM is something I actually do when
> commissioning a machine however. Busted the 35 Kw geared head on a Formosan
> machine once. Took about twenty minutes. Smoke everywhere.
> Sales guy had said you could reverse the spindle all day long at 3000 RPM
> when I asked him about rigid tapping.
> I guess they have really short days in Formosa......
> That would also explain why all of these guys think they are well hung.
> Imagine what ten inches is if an entire day is 35 minutes long.
> LMAO
>
> --
> John R. Carroll
--
~g~
Cliff
>OTOH, this is how new things get invented. A crazy idea, everyone laughs
>and points out the flaws, he thinks, "OK, it's gonna move, how can I
>constrain it" and the next thing you know you end up here -
>http://www.parallemic.org/
>
>Basically the same idea, with some of the more egregious bugs worked
>out.
Animaris Rhinoceros
http://www.youtube.com/watch?v=Y2KkGFuRLew
Strandbeest
http://www.youtube.com/watch?v=3_eY22R0TWE
http://www.youtube.com/watch?v=jo5mH9yx3So
Cliff
>OTOH, this is how new things get invented. A crazy idea, everyone laughs
>and points out the flaws, he thinks, "OK, it's gonna move, how can I
>constrain it" and the next thing you know you end up here -
>http://www.parallemic.org/
>
>Basically the same idea, with some of the more egregious bugs worked
>out.
Animaris Rhinoceros
BottleBob
> Awl --
>
<snip>
> Iny thoughts?
Dancing machines, eh? Thoughts? Well here's one.
How about putting a VMC within a cage so it can tilt back and work as
a Horizontal with all it's attendant advantages? Opps, there go the
tables and the tools in the carousel. :(
OK, let's put a HMC within a cage to rotate it forward so it would be
as easy as a Vertical to set up. Then tilt it back for machining. Eh?
LOL
--
BottleBob
http://home.earthlink.net/~bottlbob
cavelamb
> Existential Angst wrote:
>> Awl --
>>
>> Several times mention has been made of dancing machines...
>
> <snip>
>
>> Iny thoughts?
>
>
> Dancing machines, eh? Thoughts? Well here's one.
>
I can remember an ISS hard drive (600 megabyte monster - about
the size of a dish washer) way back when dancing across the floor.
One of the monthly programs would make it cha cha cha!
--
Richard Lamb
http://www.home.earthlink.net/~cavelamb/
"The clock of life is wound but once, and no man has the power
to tell just when the hands will stop, at late or early hour...
Now is the only time you own. Live, love, toil with a will.
Place no faith in time. For the clock may soon be still."
BottleBob
EA:
Some shops try to isolate machining centers by mounting them on
anti-vibration rubber mounting pads.
And conversely, some machining center's frames (either castings or
weldments), are so light duty (read flimsy), that they NEED the extra
torsional stability and rigidity that screwing them to the concrete
floor affords.
--
BottleBob
http://home.earthlink.net/~bottlbob
DoN. Nichols
> Talking about lift off: wonder if NASA needs any machinists in space?
> Chips just float away, pump in out side atmosphere for coolent?
O.K. Please explain what you would be pumping in from outside?
Not much out there. :-)
Cliff
>BottleBob wrote:
>> Existential Angst wrote:
>>> Awl --
>>>
>>> Several times mention has been made of dancing machines...
>>
>> <snip>
>>
>>> Iny thoughts?
>>
>>
>> Dancing machines, eh? Thoughts? Well here's one.
>>
>
>
>
>
>I can remember an ISS hard drive (600 megabyte monster - about
>the size of a dish washer) way back when dancing across the floor.
>
>One of the monthly programs would make it cha cha cha!
http://www.fourmilab.ch/documents/univac/fastrand.html
"one of the most impressive peripherals"
"The FASTRAND� II"
[
Fastrand (� Sperry Rand Corporation) is a nonfloppy rotating cylindrical device
used for storing angular momentum. The total angular momentum available is
slightly reduced if the data-storage option is fitted, owing to the braking
effect of the read-write heads on the magnetized surface. (Kelly-Bootle, S.
1995. The Computer Contradictionary, Second Edition. Cambridge: MIT Press.)
]
[
FASTRAND n. [copyright Sperry Rand Corporation.] A nonfloppy rotating
cylindrical device used for storing angular momentum.
In the event of a power failure, the FASTRAND can be coupled to a standby
generator for several days. Note that the total angular momentum available is
slightly reduced if the data-storage option is fitted, owing to the braking
effect of the read-write heads on the magnetized drum surface. Three or more
FASTRANDs should not be switched on simultaneously at the same site without
consulting Sperry's in-house geophysicist. The latter will also advise on the
correct lattitude-dependent orientation of the drum axis to avoid data loss due
to coriolis forces.
- reproduced from Stan Kelly-Bootle's book, The Devil's DP Dictionary, 1981
McGraw-Hill
]
--
Cliff