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    Re: How not to level an AH
    From: Bruce J. Pennino
    Date: 2014 Jan 23, 20:35 -0500
    
    Hello Noell and All:
     
    I was all set to buy a Starret Machinist level at $ 124 - 175 U.S., depending on the model (even more for some of the models), but decided to first try an inexpensive Empire "torpedo" level.  My torpedo level is 9 inches long and cost $15 or so. Its claim for establishing levelness is 0.0005" per inch, which is equivalent to 1.7 minutes of arc.  I use a regular mirror attached to a steel plate with three leveling screws as the AH. It works great. I level left to right and redo right to left. Reverse level again, then go halve way back with the bubble. Then same procedure top to bottom,etc.  I get accuracy of 2-3 minutes or so, which is good enough for me.
     
    I'm curious about the Starret level. Is it unsatisfactory?
     
    Bruce
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    ----- Original Message -----
    Sent: Thursday, January 23, 2014 12:23 PM
    Subject: [NavList] How not to level an AH


    Someone suggested a ball bearing on the mirror as a way to level an AH. It didn’t work for me. I bought some new 5/16” grade 25 chrome ball bearings from eBay ( Sphericity 0.000025 ; Max Surface roughness 2.0 microinches). ( The highest bearing listed is class 3 with 0.000003 and 0.5 )

    I carefully leveled the mirror with a Starrett machinist level inside where it was warm and comfortable, everything on the table, and to within less than half a mark. It was difficult to touch the adjusting screws, much less turn them, without moving the bubble. I have a ½” thick plastic base with three rubber feet that is spot drilled on top for the three adjusting screws with ¼-20 threads. The screws are a loose fit and very easy to turn but the coarse threads make final adjustments exacting.

    Anyway, I adjusted as precisely as I could with the level and put the ball bearing on the mirror. It didn’t move. Good job! Photo – Bearing on mirror. Then I moved the single end screw a tiny amount – Mr. Bearing still didn’t move. More - nothing. I think I finally turned the screw about one full turn before the bearing rolled. Photo – Level after bearing moved.

    I cleaned the glass again – same result. I think that these ball bearings are in the very good class although there are some NASA class ones available.

    I had visions of the perfect AH with a tiny hole drilled in the plastic base for storing the ball bearing “level”. At this point I don’t think that will work.
    Regards, Noell

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