From: George Anderson 
To: tkrajci{at}san.osd.mil
CC: Vladimir Galogaza , atm{at}shore.net
Reply-To: George Anderson 


The Stellafane site has a photo of just such a tester built with common parts..
http://www.stellafane.com/atm/atm_grind/atm_lap_stuff.htm
And I found Tom posted the same thing back on Nov 18 1998

       >>
>In Appendix J, page 392, of Texereau's book he wrote:
>"The Steel rod is tapered at a 14 degree angle and the tip is flattend
>(to about 0.004 inch)" ?????
>My Question:
>Do i have to remove the upper 0.004 inch of the tip, or shall i flatten
>it, till the
>diameter of the tip is about 0.004 inch?

Hmmmm, I seem to remember the tip was describes as .040" (forty thousandths).

I made mine .040" wide, not .040" removed.  I suppose it worked well that
way. . .the pitch I tested to the proper hardness worked quite well on the
20 mirrors I've made so far.

Tom Krajci

          >>


George Anderson
Montreal Canada

Clear skies and good health

tkrajci{at}san.osd.mil wrote:
>
> I made the post about the viscosity tester at work, and my book was not
> handy, so I did not try and describe it for fear of getting it wrong.
>
> Looking at the book now:
>
> Pointed steel rod weighted with 1Kg (2.2Lbs) is allowed to penetrate a
> pitch sample for 5 minutes.  Depth of penetration is measured, and
> compared to a chart/nomogram to see if the pitch is 'suitable.'  (The
> nomogram has temperature on one axis and penetration distance on the other
> axis...then you see if your results are within the preferred range of
> pitch viscosity.)
>
> The steel rod's point is tapered at a 14 degree angle and the tip is
> flattened to about 0.04 inch (about 1mm).
>
> You can use just about any framework of wood or metal with holes in it to
> support the steel rod upright while it's pressed down against the pitch by
> the 1Kg mass.  You do not need a dial indicator to measure penetration
> depth...any finely divided ruler will work.
>
> The desired range of pentration depth after 5 minutes is between 0.02 and
> 0.25 inches, with 0.07 inches considered the ideal.
>
> The nomogram shows a slightly complex relationship between temperature and
> viscosity.  With the nomogram you can make one test at a given
> temperature...and use the nomogram to find out at what temperature
> you 'should' be at for ideal results.  Without the nomogram you'll have to
> test at various temperatures until you find your ideal temp.
>
> I'll try and scan the nomogram and send it to interested users tomorrow.
>
> Tom Krajci
> Tashkent, Uzbekistan

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