25 Pounder info needed.

[David Dunlop]

Just a thought, Tony, but I wonder if the telescope body is brass and perhaps aluminum was chosen for the telescope carrier to lessen potential damage to the scope. I think good quality optics during the war got a lot of 'TLC' wherever possible.

Hope you have rehydrated for 2017!


David

[Private_collector]

I think that is most likely, David. Next weekend I will have a close look at the scope.

[Private_collector]

To add to last couple of posts, regarding use of aluminium in sight carrier parts. Once all the mechanical parts and the large brass part are all off the sight carrier frame, it became VERY light. You guessed it, it's aluminium also, and today all the paint was stripped off. That is a job I don't want to do again. It took hours to get almost every bit of paint off, followed by a thorough wash down and quick scrub with the wire cup on places I could get to.
20170108_175305-resized-1024.jpg
Have a close look at the above photo. Any exposed point where two dissimilar metals touch, has evidence of significant corrosion of the aluminium. This occurs, regardless of the 'other' metal type. IE: It occurs where Aluminium touches mild steel, brass, or bronze. This does NOT seem to be as significant an issue where Aluminium touches aluminium, but it has suffered to a lesser degree. I mention all this merely as a point of curiosity. It won't affect me, beyond need to apply some filler here & there. Also interesting, when running the wire cup over the surfaces, small flames could be struck between the two! Not sparks......flame, up to about 3/4" in length, and these did not fly off as sparks do. Must say I don't really think I've put an abrasive cup on aluminium before, but I have cut the stuff with a disk and shaped using a grinder disk, and I have not seen this phenomenon in the past.
20170108_175315-resized-1024.jpg 20170108_175345-resized-1024.jpg
Some parts got their final coat.
20170108_175509-resized-1024.jpg
Others got a thorough clean, and are now ready to be put in place, once the final little pieces have been acquired. For example, I still need a pair of small brackets for centre of the cross-levelling screw assembly.
20170108_175517-resized-1024.jpg
I'm also having difficulty in locating the correct size/TPI nut that holds the range indicator handwheel, in the above image. Local hardware retailer now stocks only metric nuts & bolts. Bunnings has a better range, and does have imperial sizes, BUT not all types of imperial threads. They certainly don't have the one I want. I've got some TPI and thread width gauges laying around somewhere.

[David Dunlop]

Is it possible that cast sight carrier frame is magnesium, Tony? Were the flames you noticed a bluish white and throwing white smoke?

Cast magnesium parts were not uncommon in the aviation industry during the 1930's and 1940's when the danger of using it was not fully understood. Douglas built a number of DC-3/C-47's with cast magnesium bits in the wing root areas and it was one of those aircraft that caught fire and crashed after the war killing either Buddy Holly or Ricky Nelson. The tip off to investigators were the eye witness reports of the plane giving off a whitish flame when it flew past in the night sky, and it being described as 'flare like'. If memory serves, the crash was the result of a gas leak in a Southwind Heater igniting next to a large cast magnesium component that in turn lit up. The investigators were surprised that magnesium had been used in some of the Douglas production run.

David

[Private_collector]

I considered that, and you may be right David , but I REALLY hope it isnt magnesium.
If it is, that will completely ruin my plan to have a new section welded onto the bottom.

I'm sure Rob Nixon will be able to tell us what these parts are composed of. I'll email him soon. I do know the assembly was made in Canada, as it carries their Defence Dept. markings on two parts. They were very thorough with applying part numbers to everything sufficiently big enough to take a stamp.

[David Dunlop]

A possible simple test for you, Tony.

If there is a surface, or edge, you can access which will be concealed following reassembly, take a sharp knife and cut away a small wafer. With a pair of tweezers, or small needle nose pliers, insert the wafer in an open candle flame. If it puffs into a bright white light, you have magnesium. If it just turns to white oxide, its aluminium.

David

[david moore]

David is right - it's almost certainly magnesium - aluminum would not flame - despite the misinformation put about by the steel industry after the Falklands war that Brit aluminum ships burned because of aluminum use!
Aircraft wheels were almost always magnesium in the war - a lot made in the Alcan plant in Kingston, Ontario. That could be exciting if a tire burst. Magnesium casts very nicely but is extremely difficult to make into sheet. There was a lot of magnesium capacity in the war and it was used wherever possible to replace valuable aluminum.
If it does set alight, do not use water on a magnesium fire - it makes it worse! Have to use sand as per the ARP instructions re (magnesium) incendiary bombs!