Re: [ATM] Commercially available spherometer with MitutoyoDigimatic Indicator

[Mike Lockwood <melockwo@uiuc.edu>]

Terin,

Terin Lyr D'Amico wrote:
> Does anyone know of any commercially available spherometers utilizing the
> Mitutoyo Digimatic Indicator?
> I'm growing addicted to frequently measuring via spherometer while grinding,
> and am interested in acquiring a good, precision spherometer.

It really is a great thing to be able to see how the radius is 
changing after a wet or three.

> The 50 millionths of an inch accuracy of the Mitutoyo Digimatic Indicator is
> very enticing.

I use the same indicator, with 0.5" travel.  0.000050" = ~2.3 waves, 
so you can measure to that accuracy over whatever span your 
spherometer has.  This saves a lot of time, especially when making 
flats, or trying to accurately meausure the ROC of a convex mirror. 
It allows tuning of radii all through fine grinding.

> I personally don't have the resources to machine my own, otherwise I'd
> pursue that route.

You simply need a bar with contact points on either end and the 
indicator in the middle, or a disk with a hole in the center and three 
equally spaced holes with ball bearings glued in.  3/16"-1/4" aluminum 
plate is nearly ideal for a disk.

Maybe there's an ATM or machine shop nearby that can help you make a disk?

Alternatively, you can buy an inexpensive pulley of the approximate 
diameter you want.  You also need a centerpunch, hammer, and drill. 
You drill three holes as equally spaced as you can around the outer 
edge (using dividers), getting them as close to the same distance from 
the center hole as possible.  The holes are countersunk, and ball 
bearings are super-glued into them.  Then you use commercially 
available bushings (probably obtainable from the same place that you 
get the pulley from) to make the center hole 3/8" diameter, and 
install a nylon setscrew to hold the indicator in place.

I will try to add some photos of my various spherometer bases to my 
web page soon.  I have been meaning to do that for a while.

	Mike Lockwood

_______________________________________________
ATM mailing list http://www.atmlist.net/