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Cobbler
02-24-2011, 12:29 PM
I am not a trained or experienced machinist by any stretch so excuse me if this is a silly question... Does this tool exist?
http://i187.photobucket.com/albums/x308/kennyrolling/micrometer.jpg
It would be calibrated and used for accurately measuring an outside (and/or inside) radius. The two "legs" would be a set chord length and the micrometer part would measure the segment height then the scale would read out the radius of the circle.

Deja Vu
02-24-2011, 12:44 PM
I don't know if one(or a set of) exists, but they should! :)
If you went electronic you could also easily convert the readout for diameter with optional button for metric or imperial.

Black_Moons
02-24-2011, 12:54 PM
Can't say I have ever seen anything like that, However I did buy a set of these for around $20
http://www.lukesmachinery.com/Pictures/Gauge-Radius.jpg

Theres verious other types of them too, but I liked these the best out of the types I have seen, as they have inside and outside radius, with 90, 180 outside radius, and 45(?), 90, 180 inside radius (on the tool, Outside radius on the tool is used to measure an inside radius..)

SVS
02-24-2011, 12:57 PM
I've never heard of such a thing but I really really want one now.

Not sure it would actually be more accurate or useful than a radius gage set, but far cooler.

Optics Curmudgeon
02-24-2011, 01:11 PM
A similar device does exist, for measuring the radius of optical components. It's called a spherometer. A spherometer uses a knife edged ring or three contact points, since it's measuring a sphere, yours appears to use either two points or line contacts, and would work on cylinders. Google spherometer for a more details.

Paul Alciatore
02-24-2011, 01:18 PM
Back in my college days I used a micrometer that was intended for measuring the curvature of a lens or other spherical surface. It was called a sphereometer. It had three feet instead of two and I believe the feet and anvil were points with a small radius. Here is a look:

http://www.a3bs.com/measurement-of-length/precision-sphereometer-u15030,p_83_110_560_1144.html

Just Google "sphereometer". Many more examples.

Toolguy
02-24-2011, 01:19 PM
You could make your own pretty easily with a spare mike head.

Paul Alciatore
02-24-2011, 01:19 PM
I've never heard of such a thing but I really really want one now.

Not sure it would actually be more accurate or useful than a radius gage set, but far cooler.


Yes, if used properly it would be far more accurate than a radius gauge.

john11668
02-24-2011, 02:15 PM
You could try one of the patent search engines to see if the technology exists .
Choosing your keywords is paramount though!

ikdor
02-24-2011, 02:38 PM
It does, Mitutoyo makes them.
011394 for one of the spreaders, 543-285 B digital dial gauge with programmable formula's.
http://www.inspection.ie/shopping_admin/images/prod_img/Project7_Layout%20l1.jpg
Igor

Mcgyver
02-24-2011, 03:15 PM
Yes, if used properly it would be far more accurate than a radius gauge.

no kidding, to 1/1000 of a mm according to your link:eek:

TGTool
02-24-2011, 03:37 PM
For occasional use there are some ways to use 2 gauge blocks and 3 pins to calculate a diameter or radius from a less than half section. I think maybe Machinery's has the layouts and calculations. Very useful if you had to replace a disk or ring that needed to be a precise size but fractured into 3 or more pieces so you could no longer measure a diameter.

DICKEYBIRD
02-24-2011, 05:38 PM
I think Marv Klotz has a program for doing the calcs on his page somewhere:
http://www.myvirtualnetwork.com/mklotz/

Don Young
02-24-2011, 09:40 PM
My dad had a similar micrometer for measuring the diameter of crankshaft main journals with the crankshaft and engine still in the car. I do not remember the make but I do remember it used a V shaped frame to contact the crankshaft.

Cobbler
02-25-2011, 12:20 AM
After studying this a bit more, it seems that an "A" frame that holds a dial indicator could be made fairly easy to accomplish the task at hand. That tool with the website/calculator linked below and you are good to go!

http://www.1728.com/circsect.htm

The "A" frame would have an established chord length. The indicator would be zeroed to a flat surface, and the measurement on an arc would give an accurate segment height. Just for fun, I plugged in a 1" chord and .001" segment height and it kicks back a radius of 125"

Paul Alciatore
02-25-2011, 02:30 AM
no kidding, to 1/1000 of a mm according to your link:eek:

That sounds a bit optimistic. But I went back and read it and they do say 500 divisions on the circular scale. So if it has a 0.5mm thread, which is somewhat standard for metric mikes, then it would read to 1/1000 mm. But it will take a really steady hand to make use of such a fine capability.

And if it is really that sensitive, it should have insulating grips to prevent thermal effects.

I doubt that that is really a usable level of accuracy.

Jpfalt
02-25-2011, 07:00 PM
I recently used a weld throat gage to make some radius measurements. It looks similar to the Biocci gage pictured in one of the prior replys, but the spacing between the outside contact shoes is shorter, about 1-1/4". I zeroed it on a flat surface and then measured curve deviation from flat. Then you can trig it out, but I just put it directly into a Solidworks sketch and let the CAD software figure out the math.