
High precision air bearing CNC lathe and grinder [video] - djoldman
https://www.youtube.com/watch?v=sFrVdoOhu1Q
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hwillis
Part 10 [1] of his prototypes series also features incredibly impressive
precision. He starts off with a $10 piece of aluminum that took maybe an hour
or two to make, and is completely accurate down to nanometers. I worked in a
nanotech lab with an electron microscope, and the idea that you could make a
mechanical device that could accurately move a few pixels on my screen blew my
mind. I thought I was hot shit with all my electrons and magnets... nope.

Dan's flexure is so sensitive that radiative heat from his hand moves the end
stage 100x more than mechanical input. You could move it by shining a laser
pointer at it. Insane.

The final part [2] is also very neat, and starts with a really remarkable
demonstration of stiffness.

[1]:
[https://www.youtube.com/watch?v=PaypcVFPs48](https://www.youtube.com/watch?v=PaypcVFPs48)

[2]:
[https://www.youtube.com/watch?v=MtxA20Q-Uss](https://www.youtube.com/watch?v=MtxA20Q-Uss)

~~~
omegant
He is a great educator, he also replies questions in his youtube account. What
a great guy!

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plumeria
Nice, thanks for sharing this.

His Youtube series about "Building Prototypes" looks interesting:
[https://www.youtube.com/watch?v=xMP_AfiNlX4](https://www.youtube.com/watch?v=xMP_AfiNlX4)

Here is a bio about Dr. Daniel Gelbart:
[http://graduation.ubc.ca/event/honorary-
degrees/2009-honorar...](http://graduation.ubc.ca/event/honorary-
degrees/2009-honorary-degree-recipients/daniel-gelbart/)

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ars
I don't understand how it's accurate to a micron - that grinding wheel wears
after use. Wouldn't that throw off the accuracy?

I was expecting some sort of laser calibration during cutting but he didn't
say anything like that. (i.e. don't make the machine accurate to a micron,
just measure accurate to a micron and adjust the cutting real time.)

~~~
jacquesm
That's why grinding wheels have such huge diameter (inner grinding is much
harder because of that), clamps are typically non-distorting (magnetic) and
the force involved is a very small fraction of what happens during normal
turning/milling.

In finish grinding after your setup the trick is to remove very little per
pass so the workpiece does not warm up which would cause it to expand removing
too much material. That's why you use _coolant_ and not so much a cutting
fluid (this also helps to flush out the residue from the stone and the
material being ground). A single pass will remove a fraction of a micrometer
(100 to 500 nm) and you count passes.

Another thing to keep in mind is that a lathe with an accuracy of motion of 1u
produces workpieces with a diameter accuracy of 2u.

Doing this repeatably is _really_ hard, and doing it in absolute terms is
witchcraft of a higher order.

Usually accuracy of a ground product is not only about the diameter or some
other dimension of the workpiece but about flatness of the surface or
roundness (runout).

~~~
WalterBright
Witchcraft is right. I tried really hard in college in the machine shop to
accurately make parts, and failed pretty badly. The machinist who ran the shop
would sometimes take pity on me, eyeball my setup, touch the tool bit to the
grinding wheel, turn a knob a hair, and turn out perfect parts.

It was maddening!

A 4 jaw lathe chuck was my enemy. No way in hell was I ever able to center a
part in it.

~~~
luckydude
I know your misery. I've got a Logan 820 lathe (quick change gear box, does
8-224 threads per inch; change one gear and you can do 4 threads per inch).
The ways are worn so to hold a 10 thousands over 5 inches I have to twist the
bed. I twist it with a level like this on the carriage:

[http://www.starrett.com/metrology/product-
detail/Precision-M...](http://www.starrett.com/metrology/product-
detail/Precision-Measuring-Tools/Precision-Hand-Tools/Machinsts-
Levels/Levels/199Z)

I didn't get that one, $863 is spendy. I got a Russian copy for $150.

Anyhoo, you put that level on the carriage and then crank the carriage back
and forth over the range you want straight, adjust the levelers on the legs.

I can turn mild (cold rolled) steel and hold a 10,000 of an inch for almost 5
inches and then it goes to hell. And the head stock bearing is crap, the
originals had some preload but the replacements do not so I have to use a live
center in the tailstock to put some load on them or it doesn't work.

Watching that video? I'm in awe.

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markbnj
Amazing. I don't know anything about the gentleman's background, but obviously
the term "master machinist" is insufficient to describe him!

~~~
ohazi
[http://spie.org/x42147.xml](http://spie.org/x42147.xml)

"Creo was sold to Kodak in 2005 for about $1 billion, and I retired from
optics a happy man."

~~~
markbnj
Well, that kind of win will let you build as much cool stuff as you like :).

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gruez
demonstration @
[https://www.youtube.com/watch?feature=player_detailpage&v=sF...](https://www.youtube.com/watch?feature=player_detailpage&v=sFrVdoOhu1Q#t=505)

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Animats
Now that's the deluxe model. Solid granite ways and air bearings.

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skeuomorf
Very cool. I've been wanting to get into machining for a while (haven't had
the time yet) and I was planning to do that by building my own machines
(foundry, precision lathe, milling machine, drill press,..etc) with the aid of
Dave Gingery's books [0] but I am still not sure about them (they use imperial
units, which I loathe and they might be outdated).

[0]
[http://gingerybookstore.com/index.html](http://gingerybookstore.com/index.html)

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tlarkworthy
That airbearing demo was surreal.

~~~
roflchoppa
Yeah man i want my motorcycle to have bearings like that, also want valves for
my motor with that clearance.....

~~~
hwillis
Unfortunately the key to this design is you have to force air through it
constantly. The weight of the inner part is pushing a miniscule amount of air
through the gap constantly, but you need a pump for extended operation. Still,
its possible, if you're willing to put down a few grand for it.

It still works without forced air, just not nearly as well. You really need to
force the fluid to get the high carrying capacity, or use a higher viscosity
fluid so it doesn't get displaced as easily, which is actually how standard
ball bearings work. A moving ball bearing has no contact between any metal
parts.

~~~
jacquesm
> A moving ball bearing has no contact between any metal parts.

In theory. In practice however balls do contact the races and eventually wear
them out even when properly lubricated.

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derekja
Been watching his videos for months. What beautiful work!

~~~
jacquesm
Yes, it's amazing. That whole machine is a work of art.

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ars
How does he mount the internal cutting material to the shaft while making sure
the two stay exactly concentric?

~~~
jacquesm
Usually there is some kind of 'runout correction' after the mounting. Reverse
the process and it's the wheel that's ground, so simply running the newly
minted wheel against a stationary one should do it.

~~~
kragen
I was wondering that, too. Thank you for explaining.

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kragen
Thank you, djoldman. This video is incredible. I'm now watching all of
Gelbart's YouTube videos on my phone. The depth of expertise shared in every
one of them is unequaled. I hope he gets a better camera setup soon.

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johnohara
The granite ways do a great job of absorbing vibration.

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bluthru
Yikes, that needs a safety shield.

