NavList:

From: Brad Morris <bmorris@tactronics.com>
Subject: [NavList 9423] RE: Manufacture of Bygraves
To: "NavList@fer3.com" <NavList@fer3.com>
Date: Saturday, August 8, 2009, 8:19 PM

http://cgi.ebay.com/U-Boat-MHR-1-Dennert-Pape-Sextant-Calculator-Slide-Rule_W0QQitemZ140338425807

currently on eBay.  Looks like a very nice one.

For all the talk of the Flat Bygrave (hat's off Gary), there is nothing, absolutely nothing like the feel of this solidly made, top rank instrument.  I recommend it highly!

Best Regards
Brad


________________________________________
From: NavList@fer3.com [NavList@fer3.com] On Behalf Of glapook@PACBELL.NET [glapook@PACBELL.NET]
Sent: Wednesday, August 05, 2009 11:19 PM
To: NavList@fer3.com
Subject: [NavList 9378] Manufacture of Bygraves

I was in London last month and made arrangements (with the assistance of Geoffrey Kolbe, thanks again) to see the examples of Bygraves and the HR series held by the Science Museum and by The National Maritime Museum. I attach two photos showing my hot little hand holding examples of each.

The Bygrave I saw was a Mk II serial number 105, the same one shown in Van Riet's paper. I measured the diameters of the scales, actually their circumfrances using a tape measure, and my numbers are very slightly different than his. I believe my measurements are accurate to one-half of a millimeter.

The circumfrances were:

Cotan   174mm
Cos     187mm
Cursor tube 203mm
Knob at bottom of cosine scale  207mm

Dividing by Pi gives diameters of:

Cotan 55.4mm
Cos   59.5mm
cursor 64.6mm
Knob 65.9mm

I am attaching two photos showing two details of the construction. One is a photo of the cotan scale showing that it was printed on paper and then wrapped around the tube. You can see the gap that has developed over time. The second shows a detail of the long pointer, it is bent downward to be near the cotan scale to eliminate parallax.

The National maritime Museum has three examples of the HR1 and one example of the larger HR2. The three HR1s were in cans and the HR2 had a cover and was obviously meant to be mounted on a desk. The first two HR1s I examined were in perfect shape but the third one (the one I am holding in the picture) was in poor shape. I am attaching two photos of the HR2 one showing the scale revealing the same construction method used in  the Bygrave, a paper scale glued around a tube.

It was a thrill for me to actually see these instruments. My first impression was that they are very big compared to the one I constructed which is only one and a half inches in diameter.

gl


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