PDA

View Full Version : Granite for Bearing Surfaces?



Herb Helbig
02-11-2005, 02:41 PM
Analytic balances and gravity pendulums traditionally used steel on agate or quartz for bearing surfaces. And watchmakers use corundum for jeweled bearing. Has anyone ever used granite for machine tool bearing surfaces?

------------------

topct
02-11-2005, 03:46 PM
Egyptians

brunneng
02-11-2005, 03:54 PM
bwaaaa haha ha

egpace
02-11-2005, 11:14 PM
Herb,
Maybe some of the early "ROCK"well lathes.

I have seen granite surface plates used as a bearing surface for shaker tables at 2 different test labs (Shock & Vibration testing). A steel plate slides back & forth on the granite surface with a thin film of oil between them. The lab tech claims they never have any wear problems.

Ed

Herb Helbig
02-11-2005, 11:25 PM
Good to see not everyone is a full time comedian! Thanks Ed!

------------------

Evan
02-11-2005, 11:50 PM
Here is a page about those shaker tables with granite bearings.

http://www.udco.com/stseries.htm

Here is a machine that uses air bearings that glide on granite.

http://www.rockwellautomation.com/anorad/products/airbearingsystems/n-type/n320.html



[This message has been edited by Evan (edited 02-12-2005).]

barts
02-12-2005, 01:30 AM
We used some of those Anorad products back in
1986 or so to build a inspection robot (custom
cmm)... good gear, but the electronics were pretty temp. sensitive....

- Bart

egpace
02-12-2005, 01:24 PM
<font face="Verdana, Arial" size="2">Originally posted by topct:
Egyptians</font>

Could very well be, according to the hieroglyphs, the image below is of spherical granite replacement bearings being brought into Snefru's Chariot Axle Repair Shop.


http://img.photobucket.com/albums/v233/egpace/machinist/granite.jpg

Yankee1
02-12-2005, 01:48 PM
Hi Herb,
My Ohaus reloading scales use knife edges against agate for precision readings to one
ten thousand. Clean dust free bearings are accurate.

Herb Helbig
02-12-2005, 04:09 PM
Thanks all! What I'm wondering is whether cheap granite surface plates could be used for some home brew machine tools.

------------------

spope14
02-12-2005, 05:15 PM
I think they have a granite way lathe in the American Precision Museum in Windsor, VT. Big one to boot. Darned nice looking tool!!!! I stop by there every year - kind of easy and mandatory living 10 miles away.....

I am not sure that there may be some iron or cast ways on the granite, but I do believe the granite is scraped and such for the tailstock. I remember Ed Battison, the former curator and friend of mine, mentioning and taking great pride in this machine - as he should. Can't see why this would not work with air or a good way lube.

sauer38h
02-12-2005, 05:26 PM
I've seen several applications for granite plates as the base for air bearings. The important property there wasn't the hardness of the granite, but its stiffness and stability with changes in atmospheric conditions (temperature, humidity, etc - although the equipment was used in air-conditioned clean rooms). I did some work on a machine which printed the patterns in photoresist to make circuitry directly on large glass panels for flat-screen displays. That machine used a large granite base with an Electroglas-type (patent ripoff, actually) air bearing on top, and an optical assembly held above it on a granite bridge assembly. In that application the granite was being used as a structural member. Granite isn't particularly strong or stiff, but its damping is good (ie, a bell made of granite wouldn't sound like much).

The hardness of granite can be disappointing. The quartz granules are hard, but the matrix they're in isn't particulary hard. So generally, if one wants hard bearings without the non-hard parts, one uses jewels, as in clock and watch bearings. That's the equivalent of using the quartz only and leaving out the rest of the rock.

The Starrett salesman around here used to travel around with little specimens of granite in his briefcase. That damn case must have been $%^&*# heavy. I still have one of the samples - it's my smallest surface plate, 3"x2"x7/8" thick.

One of the reasons Starrett used granite for surface plates must have been that it was handy, and cheap. (OK, two reasons). Starrett was sitting on a mountain of the stuff out there in the unfortunately-named town of Athol, MA. Blasting by some other firm on the other side of the mountain has ruined all the granite so far as surface plates are concerned, though.

Granite can be difficult to use as a machine element because it's hard to bolt things to it. Another air bearing application I was stuck working on had holes drilled into granite plates, with threaded inserts epoxied in. However, after the bolts were in and torqued, the epoxy would start to creep under the load, and in a few months the torque setting on the bolts had decreased to approximately zero. They had no idea it was happening until I asked the field guy to check for it specifically. The problem can be solved, but it's not easy, and the machine starts to get expensive if the designer does too many things that aren't easy.

egpace
02-13-2005, 08:00 PM
Herb,
Found some water lubricated granite bearings. Samuel Fitz used them in the 1800's for his water wheels.
Ed

From the website...

"At the Isaac Pierce Mill in Washington, Fitz's men built a wooden breast water wheel because there was plenty of water available, and they could make the wheel about 8 feet wide to hold plenty of water. An overshot wheel would have had to have been substantially smaller in diameter and would have developed much less power. The wheel had French Creek granite bearings lubricated with water. The granite came from Valley Forge, Pennsylvania".

http://www.angelfire.com/journal/millrestoration/excel.html

Herb Helbig
02-13-2005, 08:41 PM
Thanks once more to all -

sauer38h - thanks for your good information and comments. I wonder whether grave stone repairers have hit on an excellent adhesive for granite. I like your comment about a granite bell. Probably would ring like a lead zepelin!

egpace - Great link! Thank you. I recommend it to everyone!

------------------

Rustybolt
02-13-2005, 11:09 PM
I had an idea once of making a lathe bed out of reinforced concrete with steel ways imbeded in it.