Subject: Re: lapping

From: [email-masked] (Erik Halberstadt)
Date: 9 Feb 1995 09:56:13 -0800

Steve Rayner ([email-masked]) wrote:
: When making clock parts I did quite a lot of lapping in the lathes. 
: Lapping is done with POLISHING COMPOUNDS, not grinding grit.  I have laps
: for this purpose made from old files, and a bell metal ( Silicon bronze ?
: ) bar.  The polishing compounds come in sticks. Crush a little and mix to
: a paste with oil.  The old files used as laps have the teeth ground off,
: and the bell metal one is filed flat.  Put a little of the paste on a lap,
: and hold it under the workpiece, with the lathe running fast, and move the
: lap back and forth.  Internal expanding laps can be made of brass or
: bronze, they are worked back and forth in the hole, the same way.
: Lapping and polishing compounds are sold as:

: carborundum     
: diamantine (white diamond)  [ has no actual diamonds ]
: brown tripoli
: rouge

: You might also try cerium oxide  ( available from rock hobby stores ) as
: it cuts faster than rouge.  These two are used in optical glass polishing
: as well.

: -- 
:                                 Steve Rayner.

Bell metal is 66% copper and 33% tin... if anyone's interested.
Carborundum (IMHO) doesn't quite qualify as lapping compound, but what 
the heck.

Another inside lap method from my black powder days: center a brass or 
steel rod in the bore, and cast a plug of lead so as to self solder to 
the rod. Lubricate well and allow it to follow the rifling. Wash the bore 
well between grits/compounds and cast a new plug for each finer grade.

Erik