Not being able to find a lot in the archives at Bovington on tank construction of these models especially the A13 Cruiser, it seems that the plate assembly to form the hull and turret was most probably a riveted construction studying the photos and line drawings, I assume that some form of frame work was used to rivet the armour plates to, just like the WW1 MkIV or French Renault FT tank. I noticed on the bottom of the Covenanter that the floor plan is made up of 6 large plates, all riveted in place, i assume to a type of frame work, made from flat strips, angle or T section.
The general construction of these models is a layer of D1 Steel (IT 110) riveted to a frame, with another layer of armour (IT 70, 80 or 100) bolted on to the D1 Steel. When you look at a photo of e.g. a Crusader, the knobbly bits are bolt heads and not rivets. The one exception is that the under layer of D1 steel on the Crusader and Covenanter is put together by welding, but the outer armour is still bolted on.
It was found in WW1 that an AP round striking a rivet head could convert the rivet into a red hot missile.I presume that is why the outer armour was either welded or bolted in later designs
Sorry, I need to amend my above post thus: The general construction of these models is a layer of D1 Steel (IT 110) riveted to a frame, with another layer of armour (IT 70, 80 or 100) bolted on to the D1 Steel. When you look at a photo of e.g. a Crusader, the knobbly bits are bolt heads and not rivets. The one exception is that the under layer of D1 steel on the Crusader and Covenanter turrets, which is put together by welding, but the outer armour is still bolted on.
Were bolts used because, I gather there was a relative shortage of trained welders, so the choice was "rivets or bolts"? Also, are these two different sized knobs on the Archer at Bovington both likely to be bolts? I also note some holes near the bottom where apparently some bolts have been removed or lost over the years. If I'm interpreting it correctly, there is a bit of a recess for the head of the bolt. edited PS - would any rivets used have round heads?
The whole riveting/welding saga is a bit involved, in that a shortage of welders is one of the excuses that the tank manufacturing firms used to continue using riveting, but the advocates of welding argued that this shouldn't have been an issue because training welders was a fairly quick and easy process. A more substantial argument was that welding took up more floor space than riveting, so that any production time saved by switching to welding was negated by a reduction in though put. Then there were arguments about just how big an improvement welding constituted, with the view being expressed by some that there was only a weight saving of about 5%, so was there really any point in switching? So there were a lot of niggling arguments, most of the manufacturers didn't really want to switch, and nobody important at the Ministry of Supply was prepared to make the big call of ordering a universal switch over.
I've not seen any documentation to suggest the unions had any influence on this, but then I haven't been looking for it! Generally, the influence of the unions on tank production appears to have been minimal from what I have seen, but it's possible that if I looked into one of the Ministry of Labour files I might get quite a different viewpoint. That said, the few strikes that I have seen documented tended to be wildcat rather than union organised. There was also the general principle that Stalin wanted British war production to be as efficient as possible, so the CPGB were going round British factories aggressively suppressing any Trotskyist or anarchist trouble making.
Weren't there some work stoppages or slow downs by union stevedores at the docks? Did they create any raw material shortages for tank production?
Funny thing about 5% is that while 5% less weight might not have made a huge difference in tank performance, I'd have thought it a worthwhile savings in materials.
Possibly but there are many factors for example did it use more or less energy? If you are using oxy acetylene welding torches what does it cost, if arc welding how much coal is burnt to produce the electricity? Is this more or less than the energy a riveting process uses? Which is quicker? What are the implications for quality control? How easy is it to inspect welds? What is the likely rejection/reworking rate? - and so on.
The big thing is that this 5% weight saving could all go into an increase in the frontal armour by 10 to 25mm, so it could be very significant. There are other advantages to welding, such as better resistance to HE, easier to waterproof for wading etc., but these weren't necessarily visible to the tank manufacturers. What happened in real life is that the manufacturers themselves started to become enthusiastic about welding, starting with BRC&W. The first big manufacturer that embraced welding was Vauxhalls, who were quickly followed by Leylands.
