Re: [ATM] Polishing to a sphere

[Bob Liesenfeld <wb0poq@visi.com>]

Guy Brandenburg wrote:

 (1) Get some netting (like the type that onions, garlic, citrus fruit,  or potatoes are often sold in); slit the bag into a single sheet. Dunk  the lap into some uncomfortably warm water for about 10 minutes (say,  130 to 140 dgrees, the hottest that normally comes out of a tap); then  lay the netting on the lap, and press the still-room-temperature mirror  (which has some cerium oxide slurry just applied) onto the lap hard  enough to make the impression of the netting into the lap facets. BTW,  with this method, you can tell easily whether the lap is really making  good contact or not.Then cold press with your pressure for about 5 to  10 minutes, and then polish normally for about 15 minutes. I suspect  you will find the drag (friction) from your lap will be dramatically  increased, and your figure will improve.

  This process works wonders.  I highly recommend it.

>
>
>   (2) If this still doesn't make enough of a difference, then you might  need to soften the lap itelf a little bit by either raising the ambient  air temperature or by chipping off all of the old pitch, putting it  into a large coffee can (or whatever), melting it back down, adding  about 1 teaspoon of turpentine, and casting it again and doing what you  ahve been doing in the past.

  I would add that you want to be >very< carefull with the turpentine.  Be sure the container of pitch is off and away from the source of heat before even opening the can of turpentine.  Also, a teaspoon sounds like a lot to start with.  I would add half of that to start.  It is easy to soften pitch, but takes a long time to boil off excessive volatiles (and it is stinky).  ;)


Bob L.

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