NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Astro Compass maintenance
From: Zvi Doron
Date: 2005 Mar 24, 19:57 -0000
From: Zvi Doron
Date: 2005 Mar 24, 19:57 -0000
Two additional points: 1. Utilising a sudden brain wave I have now tested the alignment of the latitude scales by placing a long straight edge on the LHA drum, setting the Latitude micrometer to 0 and measuring the height of the ends of the straight edge abve the dsk surface with the instrument level. It proved that the micrometer is accurate - when set to 0 the LHA drum is perfectly level. It is just that the circular latitude scale (indicating 0-9 in white and in red) is not perfectly aligned with the micrometer but as its only purpose is to indicate units of 10 degrees latitude this is not a problem. 2. In a few books I have including Air Ministry Mual of Air Navigation AP1234 it is stated that the knob turning the LHA plates above and below the LHA drum should be pushed in to operate it and then pulled out to disengage it so that LHA is not changed accidentaly. This is a March 1944 model and it seems that it does not have this feature - the knob turns the drum, allbeit with a bit of effort required, but it has no push / pull movement as described in the books. Is that because it is a later model and the feature was not implemented, or is it again a result of hardened grease? Thanks again for any ideas regarding both my messages. ----- Original Message ----- From: Zvi DoronTo: Sent: 24 March 2005 18:22 Subject: Astro Compass maintenance > I have just obtained an A.M. (Air Ministry?) Astro Compass Mk II Ref > 6A/1174 4.C. > > It is in great condition but had been stored for many years and the grease > had hardened inside the mecanisms. The bearing plate and the LHA knob are a > bit hard to turn although functional. The Latitude and declination > adjustments are fine, although there is a slight mismatch (about 0.7 degree) > between the main latitue scale and the micrometer drum. The difficulty in > turning resembles what happens to Aluminium sextants leke the Freiberger > sometimes. > > My questions - > Can the LHA drum be stripped, lubricated and re-assembled easily? It has > three screws on each face. > Can the bearing plate be dis-assembled and lubricated? > What lubricant should I use? > Is there a way, using the little screw on the latitude micrmeter drum, to > align it perfectly with the main scale? > > Thanks for any information and happy Easter.