NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Dolkas
Date: 2020 Nov 25, 17:38 +0000
Dave-
You can buy small screws with little O-rings attached, which makes it much easier to fill than chasing that little set screw and ball bearing as they roll around
your workbench. But first you have to spotface the area around the fill hole so the O-ring can seal against something smooth. At least that’s what I did, because I have to top mine off more than I’d like to. I think the thread is 2-56.
-Paul Dolkas
From: NavList@fer3.com [mailto:NavList@fer3.com]
On Behalf Of David Pike
Sent: Wednesday, November 25, 2020 8:30 AM
To: Paul Dolkas <paul@dolkas.net>
Subject: [NavList] Re: I'm forever blowing (sextant) bubbles
Paul Dolkas you wrote: Dave-So how exactly do you use a needle to insert bubbles into an A-12?
Paul
I only used the A12 as an example. In truth, it’s been a few months since my A12 was at the centre of my attention, and I can’t remember. I just kept ordering finer and finer needles on eBay until I got one to fit. I notice my finest is 26 Gauge (0.4mm);
maybe it was that one alough I've still got a strip of 10 so maybe it was 22 Gauge. The trouble is the fewest needles of any one gauge you can buy from China on eBay is ten, so I ended up with quite a collection of syringes and needles.
Maybe I never got chance to try the narrower needles, because I got myself into other fine messes around the same time. At an earlier stage, I had the great idea of sealing the little filler screw and the edges of the viewing windows with varnish. Bad idea;
the vanish found its way down to the little ball, and now it’s immovable. Worse still, the idea didn’t work; my bubble still grew. I suppose I could try acetone to loosen the little ball, but I’d need to be careful to keep acetone off the windows.
Then, having paid through the nose for a set of Bristol Keys from the USA so I could work on the bubble chamber, I thought I might as well use a larger key from the set to give the index mirror a little tweak. What do they say about ‘good intentions’?
As a final insult to Mr Link, my attempt to glue a fiduciary black spot at the centre of the window to help me hold the sextant level was also a failure.
I’m sure I read somewhere about that time of the best way to hold a bubble chamber whilst filling it, but once again, I can’t remember where. DaveP
