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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 -----

From: Noell Wilson

To: bpennino.ce@charter.net

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 ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3..com ---------------------------------------------------------------- Attached File: (Bearing-on-mirror.JPG: Open and save) Attached File: (Level-after-bearing-moved.JPG: Open and save)

: http://fer3.com/arc/m2.aspx?i=126645

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