A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2016 Jul 31, 08:35 -0700
It has taken a while but I have finally completed a working model of the MHR1 sliderule. It was constructed using custom phenolic tubes from Wolfgang Hasper http://fer3.com/arc/m2.aspx/Borrowed-Bygrave-Hasper-jan-2016-g34233 and scales generated using postscript code available here http://fer3.com/arc/m2.aspx/Postscript-code-for-making-Bygrave-Scales-Stuart-jan-2015-g29918 . The scales incorporate all the painstakingly documented idiosyncratic markings present in the original MHR1 as documented here http://fer3.com/arc/m2.aspx/Ruminatons-Bygrave-Hohenrechenschieber-scale-markings-Morris-feb-2013-g22419
Tube fittings were made by constructing them in OpenSCAD and then 3D printing in black plastic from Shapeways.com which allowed me to partially circumvent my lack of manual dexterity.
The locking mechanism behaves in a way that is consistent with the information I have been able to glean from various sources and is loosely based on a suggestion given here http://fer3.com/arc/m2.aspx/wrapped-Bygrave-DouglasDenny-jan-2010-g11537 . As observed by others who have built working models http://fer3.com/arc/m2.aspx/MHR1-reproduction-Morris-apr-2011-g16115 the locking mechanism seems unnecessary as there seems to be enough friction produced by the felt padding between the tubes so that they stay put.
I am happy to share details and experiences with anyone embarking on a similar project.
While I can’t claim that it is an exact replica of the MHR1 it’s a pretty close working model. I have done a limited number of sight reductions at this stage but it seems to produce results with accuracy below a minute of arc without much difficulty.