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.

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.

Some parts got their final coat.

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.

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!

[Private_collector]

That's really beginning to worry me, guys. Magnesium would mean I could do a far lesser quality repair to the corroded bit. I will snap off a small piece of corrosion and take it across the road to my welders place for testing. I tried a small chunk myself, using my propane torch, and it didn't react in any way, but I know from experience that it would probably need more heat than i could subject it to, before 'flame on'. Anyone ever throw an old VW gearbox case into a bonfire? Wear sunglasses if you ever plan to, and be prepared to wait a while for the reaction to start.

When there was still decent hope it MIGHT have been aluminium, I was doing some mental planning on exactly HOW the repair could be fashioned best, and decided I would require purchase of some plain sheet aluminium to craft the new sections. The only place I know of in town that could easily supply me a small piece, has now closed down, and i was lamenting their passing and cursing my lack of luck with regards to the effort now needed to scunge just a small bit of aluminium plate. While puzzling over where to start looking, I suddenly realised that while I was sitting there cleaning parts, I was in fact directly facing a far larger piece of plain 6mm aluminium plate than I could ever expect to need. It was leftover from making my shield, and I had resisted throwing it out some time ago. With any luck, my metalworker/welder neighbour can bend 6mm on his enormous metal folder, and I will use that to fill the area left vacant by the corrosion. If the original item IS magnesium, I have a plan that should see a nice piece of aluminium grafted into place without requiring any welding.

[David Dunlop]

Tony. It is hard to tell from your photos, but is the corrosion damage on your potentially magnesium part on a load bearing surface for the part or other fittings?

If the piece in question just 'sits there', could you perhaps build up the missing bit with body filler, epoxy paste, or similar, and then carve/sand to the correct profile for painting?

David

[Private_collector]

No David, not load bearing, but whatever I graft on will need to be 100% fixed permanently in place, or cracks will eventually show around the edges. I did consider doing that, but using fibreglass. This morning I made all the sections to repair the hole once and for all.......hopefully!

I'm almost sure this thing isn't aluminium now. Seems lighter than aluminium, and it files differently. My welder friend isn't home today, so I never got the definitive diagnosis. Will watch for him tomorrow.


I didn't set anything on fire while cutting the rot away, and was VERY careful I did not put too much heat in one place. When all corrosion was cut away, I was left with quite a hole.


There are 6 separate pieces making the repair patch.
I taped them all together to see what the profile will look like. While it's not exactly original, it will do.

More details in the next posting....

[Private_collector]

Once all the aluminium repair sections are welded together, I will attach the entire thing as one piece. I'm not sure of method to keep this in place, but am considering construction glue and having a plate welded against inside of the repair patch, overlapping the inside edge of the original by at least 1". The metal of both items is thick enough for me to drill and tap the few holes for better fixing. I will need to be careful not to go too high with anything on the inside, because there is a gear toothed sector that adjusts up & down in there. If done carefully, I should be OK.


The new pieces sit better than they look in my photos. They're only held in reasonable proximity, with a few bits of masking tape.

The below photo shows the only piece that won't be seen, but it's important. This piece needs to help secure the large cover panel you can see sitting above it, and one hole will be required for a fixing bolt to keep the cover in place. That bolt will also help keep my repair in place. I should have no problem keeping the new bit in place, once all methods of fixing are used.

All these bits go together to fix one rust out!

[David Dunlop]

Nice work with shaping up the patch pieces, Tony.

Not sure if you looked into it on the web, but I poked about a bit and discovered one can tig weld magnesium, and even weld aluminum and magnesium bits together. Lots of sites about it and lots of videos.

Didn't know it could be done.

David

[Mrs Vampire]

Not mag alloy .. when this baby was made we had just mastered smelting al al over at silver water . There is a table of reactive elements and aluminum . Brass is not the culprit but steel is . In this case long term exposure to salt laden mist.

Moisture gathering on edges and low points . Use of al al to reduce weight . Made to British spec but weldable . A basic All

[Richard Farrant]

It sounds like this casting is of magnesium content. The guy in the workshop next to me was salvaging parts from a Ferguson TE20 gearbox and said that when he used a disc cutter to split the box (don't ask), it was like fireworks. I told him the casting were Elektron, which is a magnesium alloy. It was first used in the 1930's in the UK, a German development but a company in UK was producing it. The gun mantlet on the late 30's Vickers Light Tank Mk6a was Elektron and when one was being restored over here, I was doing some work on it and the welder fabricator had to build up corroded areas of it. This he done with TIG and used an Elektron rocker cover from a racing car to cut up and weld in, finished job was very good, but he said he had to do it in small bits in order not to have it catch alight. An old neighbour of mine worked for Dunlop during the war, machining aircraft wheels, he said you learnt quickly on not to take large cuts on the lathe otherwise the swarf would catch alight and cleaning up a lathe after it has been covered with sand is something you did not want to repeat.
Electron is lighter than aluminium but also stronger.

regards, Richard

[Private_collector]

I say, this is getting REALLY interesting for me! Metallurgy and welding are two subjects i know very little about, so i do appreciate all your input, folks. Today is my day off, and it's when i take Mother shopping, but I will be banging on my friends door as soon as i return home again, presenting him with all the pieces and a nice chunk waste material for him to toast with his oxy.

The information about TIG welding the two metals sounds very encouraging! God forbid there should be a simple solution to all this. It sure goes against everything my Father taught me, to glue something like this together. Once all the repair sections are welded together (away/off the ? Mg stuff), it doesnt really require a lot of welding to properly the two metals/pieces together. If TIG welding is the way to do it, my guy can do that easily! His work is fantastic.

I'll let you know what we have discovered, later on today.

[Richard Farrant]

Originally Posted by Gina Vampire

Not mag alloy .. when this baby was made we had just mastered smelting al al over at silver water . There is a table of reactive elements and aluminum . Brass is not the culprit but steel is . In this case long term exposure to salt laden mist.

Moisture gathering on edges and low points . Use of al al to reduce weight . Made to British spec but weldable . A basic All

Hi Gina,
I understand BHP had a plant in Newcastle producing magnesium by 1941 and Elektron was then produced in Australia for war work.

regards, Richard

[david moore]

Tony
You might want to insulate the al repair from the Mg - or else you will have the old problem over again! Even a good paint layer will do - at least for quite a few years!
Galvanic corrosion affects all dissimilar metals in contact - and magnesium is about the most reactive (and therefore protective - used as sacrificial anodes on metal boat hulls, props etc. ) Mg will dissolve in contact with Al ( or steel or copper) ; Al will dissolve in contact with steel etc. - there is a galvanic table.
Stop the electrical ("galvanic") contact and no problem even when moisture (or worse - salt) is present.
Though Mg has been around for more than 80 years in transportation, and we all know the Beetle engine block, it is still widely used - the instrument panel support in your car is almost certainly a Mg casting!

[Private_collector]

It took me a week, but I've just had the opportunity to discuss my welding requirements with the pro welder neighbour. He has been away in western Queensland for the past 8 days. I figured he was away. Hadn't seen his vehicle all week, and have been chomping at the bit to get his thoughts on my sight carrier repair patches. The outcome is encouraging. It would appear that the original section is indeed magnesium alloy. Potentially problematic to weld, but he is confident, and fully appreciates the peculiarities & unique properties of working with such an unusual metal. The welding should get done through the coming week, and I expect to have the finished product back with me by next weekend. There's nothing like having professional assistance with a tricky job like this!

All going well, I hope to be applying the minimal amount of filler needed to entirely disguise the grafted in repair section. Should have filing, filling, sanding, and priming done during, or ideally by next Sunday. If still enough daylight left after all that, I may even get color on. If so, reassembly may commence by Monday evening. That will be exciting, and will give me the first opportunity to see the parts working together again as one unit.

David, i understand your point. that has been worrying me as well. I'm afraid having the two metals in contact with each other is unavoidable, but I can assure you the finished product will have a far more sheltered life that it has enjoyed in past 70 to 80 years. I've been visiting my 'local' 25Pr for past 3-4 years, slowly taking measurements and photographs. In that time I've literally watched and (unwittingly) documented the guns slow, but inevitable, deterioration. Because I am only now rebuilding a sight carrier assembly of my own, my attention to the extent of same damage on their assembly was only drawn in past few months or so. I had to look back through some much older photos I had taken, to fully realise how badly (and quickly) the exposure to weather is breaking their weapon apart! It is both sad, and largely avoidable. My piece won't be seeing anywhere near such destructive elements. Once the entire sight carrier assembly is complete, including the horizontal adjustment parts I am yet to acquire (or make), the very next thing will be to create a suitable canvas cover for it. It's mostly needed to keep dust and airborne contaminants from settling on the surfaces. Water is an obvious peril, but i acknowledge humidity combined with surface debris is more subtle and just as dangerous, long term. With that in mind, my gun will live indoors, and ideally shouldn't see any rain. it's bound to at some stage though, and that's why the canvas cover will have a lining or waterproof vinyl on inside of the canvas cover itself. I know I can sew canvas reasonably successfully, although I am now banned from using my Wifes domestic sewing machine......(..apparently!) Sewing vinyl or similar waterproof material, and sewing it inside of canvas, is something of an unknown quantity. Or should that be unknown quality? Either way, we'll find out soon. It is also my plan to coat all bare internal surfaces with a lanolin compound, attempting to further reduce time related deterioration. I need to be careful there, because some internal parts will require grease and ablilty to move freely. Typical rust proofing products thicken over time and may gum up the internal workings/gears.

[David Dunlop]

Good news, indeed, on the welding project, Tony.

Not sure how humid, and for how long, that condition can last in your neck of the woods, but if you decide on the fully waterproof type of cover for your 25-PDR, give some thought to keeping some desiccant bags tucked under it to help keep things dry. Out this way when it is humid, when the air temp drops overnight, you can get condensation forming under plastic tarps.

Larger versions of the ones you often find inside NOS Military part packages is what I am thinking about.

Enjoy your weekend!

David

[Private_collector]

Now that's a good idea, David! Didn't think of that. Our humidity gets extreme here at times. I hate it. I swear, every summer is getting worse. I can forsee a geographical change in my future.

We use a product called Closet Camel in our walk through wardrobe, which does that exact job of removing moisture, but on a larger scale. It would be maybe 10-12cm long, 10cm wide, and about same depth. Wouldn't take much to adapt those to suit, and they even come 8n their own plastic case. I'll buy an extra one next shopping trip, and play around with how to suspend beneath the planned cover.

Now, i haven't checked this myself, but I have ben told that the blue (the ones I've seen) gel kitty litter/odour remover works in same way as the dearer moisture removers. That might be worth looking into as well. I could make my own container for it, and tailor it to my exact needs. I'll look into that type too, for curiosity if nothing else.

[Private_collector]

Look what I've got!


It's not finished yet. My welder mate had extreme difficulty with the welding, and as a result of the porous original magnesium and new repair of aluminium being different metals with different cooling rates, he wants me to add additional strength holding both together. He suggested I fill the inside of the repair with fibreglass, and overlap beyond the line of weld. We think about an inch and half would be plenty. He also suggested I buy Liquid Aluminium to fill welding imperfections. I'm having a look for that online now. If I can locate something suitable locally, I'll get into that job tomorrow afternoon.

My fellow had a hard time working this piece, and he's a professional welder who owned a large engineering works. If it gave him grey hairs, imagine what it would have done to me! I'm ever so grateful for what he has achieved. The next step is up to me now.

[rnixartillery]

Sweet Victory !! Well done.

Rob................rnixartillery.

[Russ Gregg]

Nice progress! Because both of these metals oxidize very quickly at first I would recommend bead blasting the area and coating it right away with some kind of epoxy (JB Weld, Araldite, Devcon etc., not sure what's available down there) to make sure there is no oxidation in the porous areas.

[Private_collector]

Yeah, I think that's a good idea, Russ. I'll find something suitable today, with any luck.
Today is when I take Mother grocery shopping, so I only have whatever time is left after that to go looking for my stuff. I'm hoping to seal the inside of the repair by applying whatever I use to fill that space. I had an idea in my sleep last night. I want to squish a kneedable epoxy down into the very lower portion of the repair. Ideally, that will start to come through the several holes that couldn't take a weld. Then I can really lather a fibreglass resin and Chopped Strand mat into the upper 3/4 of the space. Wouldn't expect to get both jobs done today, but you never know!

Thanks Rob, it is satisfying to bring something back from knackered, so to speak. I'm trying to find the two little bolts that join the pieces seen below. Do you by any chance have any of these available, or know what size they are?


Yesterday I bought the correct size bolt for the main shaft, that holds everything together at pointy end of the cone. Fortunately we have a real good bolt shop in town, and after 10 minutes of his searching around, without result, the bolt was discovered. I expected it would be an imperial size, but it is a metric 9mm size. Don't remember what he said the thread pitch was, but it was either 1" or 1.25". It is a beautiful fit, so he found the right one, but I thought it interesting that thread pitch was given in imperial measurement, though bolt size was metric! I bought a handful, even though I only need one right now. History has taught me that if a size is used in one location, there's probably some used somewhere else too.

As much as i loathe some modern technology, i must admit there are some very useful applications available for tablet computers. For example, there are a range of applications (Sorry, can't bring myself to call them "Apps" in discussion) for sourcing bearings and seals. Timken have a good one, NTN one is OK also. Could be useful when trying to replace dodgy ones. I speak generally here, the bearings on my sight carrier are fine and will not need replacement.

[hrpearce]

Tony JB Weld might be easier than putty it is more fluid and will fill all the gap. Tape up the outside and pour the JB in and sand off the tape when dry.

[Private_collector]

Rob, do I just ask for J B Weld, or is there another specific name? I see J B Weld brand has a lot of products.

[rnixartillery]

Originally Posted by Private_collector

Yeah, I think that's a good idea, Russ. I'll find something suitable today, with any luck.
Today is when I take Mother grocery shopping, so I only have whatever time is left after that to go looking for my stuff. I'm hoping to seal the inside of the repair by applying whatever I use to fill that space. I had an idea in my sleep last night. I want to squish a kneedable epoxy down into the very lower portion of the repair. Ideally, that will start to come through the several holes that couldn't take a weld. Then I can really lather a fibreglass resin and Chopped Strand mat into the upper 3/4 of the space. Wouldn't expect to get both jobs done today, but you never know!

Thanks Rob, it is satisfying to bring something back from knackered, so to speak. I'm trying to find the two little bolts that join the pieces seen below. Do you by any chance have any of these available, or know what size they are?
Attachment 88338
Attachment 88339
Yesterday I bought the correct size bolt for the main shaft, that holds everything together at pointy end of the cone. Fortunately we have a real good bolt shop in town, and after 10 minutes of his searching around, without result, the bolt was discovered. I expected it would be an imperial size, but it is a metric 9mm size. Don't remember what he said the thread pitch was, but it was either 1" or 1.25". It is a beautiful fit, so he found the right one, but I thought it interesting that thread pitch was given in imperial measurement, though bolt size was metric! I bought a handful, even though I only need one right now. History has taught me that if a size is used in one location, there's probably some used somewhere else too.

As much as i loathe some modern technology, i must admit there are some very useful applications available for tablet computers. For example, there are a range of applications (Sorry, can't bring myself to call them "Apps" in discussion) for sourcing bearings and seals. Timken have a good one, NTN one is OK also. Could be useful when trying to replace dodgy ones. I speak generally here, the bearings on my sight carrier are fine and will not need replacement.

Tony.

I'm pretty sure I sent the two screws over with the bracket ! I remember sorting them out.

Rob............rnixartillery

[Private_collector]

Oh, oh! You know what that means, don't you?

I must have put them away 'safely'.

Will start looking this afternoon.

Sorry to bother you.

[hrpearce]

Originally Posted by Private_collector

Rob, do I just ask for J B Weld, or is there another specific name? I see J B Weld brand has a lot of products.

Just looked at the pack, JB Weld epoxy steel.

[Private_collector]