Subject: Re: Diamond laps & files

From: [email-masked] (Gavin Donahue)
Date: Thu, 12 Dec 1996 16:35:55 -0700

In article <[email-masked]>,
[email-masked] (Steve Rayner) wrote:

> The old time watchmakers made diamond laps & files as required.  This 
> often required them to smash a diamond with a hammer!  Today, most rock 
> hobby shops have vials of graded diamond dust.  The old timers hammered the
> diamond powder into pieces of sheet copper.
> -- 
> Steve. 
> 
> ******************Knowledge is wasted if it is not shared.*******************

What wonderful tidbit. It gave me an idea...
As a youngster I polished a telescope mirror blank using jewelers rouge on
a "tool" formed from hot pitch against the ground blank. The testing
procedure (focault (sic)) involved analyzing interference patterns created
by a primitive pin hole light source and knife edge rig to correct the
surface. The surface of the pitch (or was it beeswax?) Was scored
selectively to raise it and the polish/test cycle repeated until the
surface was accurate (within 1/4 wavelength of visible light was claimed
possible) or your arms gave out. All the stuff came from Edmond Scientific
Co. It may be possible to produce a useful lapping surface by adapting
some of those techniques. Start with a good optical flat (or the shape you
need) like a front surface mirror from an junk photocopier. Apply a
release agent like PVA or wax. Spray a coat of lacquer and dust with the
graded diamond while still wet. Shake off the extra. Put this in a plastic
bag and the bag around a shop vacuum inlet and draw a little vacuum to
produce intimate contact with the surface. The bag should press on both
sides of the mirror evenly. After it's dry, coat with epoxy and bond to a
suitably rigid base. After its cured the mirror should release and the
lacquer can be removed with thinner. The lapped surface being developed
can be coated with glycerin to make it reflective enough for the optical
testing as needed. Maybe this will put the high precision guys onto
something.

---

From: "Bill Harnell" <[email-masked]>
Date: 13 Dec 1996 06:25:45 GMT

A tool and diemaker I know purchased an old cast iron
surface plate, applied a light coat of oil and sprinkled
diamond dust on the surface plate which he then used (and
still does after 40 years) as a lap.

Seems that the cystalline structure of cast iron allows
fine diamond particles to embed themselves into the lattice
structure where they remain.
-- 
Bill Harnell <[email-masked]>

Steve Rayner <[email-masked]> wrote in
article <[email-masked]>...

---

From: Steve Austin <[email-masked]>
Date: Sat, 14 Dec 1996 23:14:42 -0500

> structure where they remain.
We use a lot of diamond lapping compound at work.  To charge a
round lap we smear it on two hardened HSS plates and then roll
the lap between the plates while tapping the top plate with a
light hammer.  The laps themselves are fairly soft mild steel. We
try to keep them tapered about a thou over 12 inches or so.  A
set of laps for working on a 2mm hole might remind you of a
handfull of raw spagetti.  
Steve A.