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Old Git

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Old Git last won the day on April 22

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About Old Git

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    Staff Sergeant

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    Research, WWII, Normandy, NWE, Royal Engineers, Bailey Bridges, Modelling, Research
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  1. Old Git

    Q. Re QF 75mm on Cromwell

    For a couple of weeks now I've been suspecting that some of my dims for the tube on the 75mm are wrong, not all of them but certainly one or two and it's been a bit of a struggle to ascertain where I was out, although I was beginning to suspect it was around section E. The principal reason for suspecting an error was an old chart I found on my NAS which one of my contacts had sent me years ago. It purportedly came from a WWII Soviet evaluation of the Cromwell Tank and when the various labels were translated into English it gave some interesting info, especially on 'Length of Barrel (mm)' and 'Total Length'. As the sum of my dims did not come near enough to these figures I was beginning to doubt myself. The translated table is shown below... So I did a bit of digging and in the CHURCHILL VII AND VIII INSTRUCTION BOOK. ARMAMENT SECTION Covering ORDNANCE, Q.F. 75MM. MARK V and VA... Fitted to CHURCHILL VII. I found the following information... ORDNANCE, Q.F., 75 mm., MARKS V AND VA The 75mm. Marks V and VA guns fire fixed ammunition and are designed for use in tanks as replacement guns for the Ordnance Q.F. 6-pr. 7-cwt., Marks III and V. The barrel is externally similiar to that of the Ordnance Q.F., 6-pr. 7-cwt., Mk. V. Firing is by percussion, and obturation s effected in the usual Q.F. manner by the radial expansion of the cartridge case in the tapered chamber of the barrel when the gun is fired. It may be noted that, with the exception of the the extractor levers and the firing pin of the striker, the majority of the parts comprising the breech mechanism are identical and, therefore, interchangeable, with similarly named and numbered components of the Ordnance, Q.F. 6-pr., 7-cwt., Marks III and V Alternative designs of varous parts are introduced from time to time and incoporated in the equipment, usually to simplify manufacture and thus hasten production. Parts of guns in service may therefore be found to differ in some particulars from those about to be described, but these differences do not usually affect the functioning of the weapon, although they may occasionally concern the user when dismantling or reassembling the weapon. Whenever possible, particulars of alternativr designs have been given. Except where stated to be otherwise, terms such as left, right, front rear, upper and lower describe the position on the assembled gun of the various parts when viewed from the breech end with the gun in the firing position. PARTICULARS Diameter, bore ... ... ... ... ... ... ... ... ... ... 2.953 ins. Distance to centre of gravity from breech end - Barrel ... ... ... ... ... ... ... ... ... ... ... 32.15 ins. Barrel with breech mechanism and muzzle brake ... .32.6 ins. Gauge, Striker protrusion ... ... ... ... ... ..No. 40 (0.148 ins. to 0.158 ins.) Length - Barrel, without muzzle brake ... ... ... ... ... ..107.8 ins. Rear face of breech to muzzle brake extremities ...118.576 ins. Weights (estimated) - Barrel ... ... ... ... ... ... ... ... ... ... ... 3 cwts, 3 qrs. 2 lbs. Breech Ring ... ... ... ... ... ... ... ... ... .. 1 cwt, 1 qr. 21 lbs. Barrel with breech ring and muzzle brake - with breech mechanism ... ... ... ... ... ... 6 cwts, 0 qrs. 20 lbs. without breech mechanism ... ... ... ... ... ..5 cwts, 1 qr. 16 lbs. The data from Churchill book seemed to confirm the Soviet Gun table so I now knew that I'd made a mistake somewhere. I put it to one side until I could find time to dig deeper into it but, by happy coincidence, I had a PM today from Mike with revised dims which he'd taken from the 75mm tube on display at Bovi. Mike, thanks for that very timely piece of info, it saved me a trip to Bovi. For your own information you may wish to know that the threaded section of the tube is 103mm and requires 11 turns to be firmly threaded into the Breech Ring. The Soviet total length (2859.3 mm) would appear to be from the rear of Breech Ring to the end of the Tube, whilst the British/Churchill total length (118.576 /3012 mm) is from rear of Breech ring to end of Muzzle Brake. Doing a quick mental calculation I'd say the portion of the tube, therefore, held within the muzzle brake is, roughly, 85.6 mm 😉 Pete
  2. SWMBO says they must go, and so they must go!
  3. I suppose I could but I get enough grief from the wife about the stuff I've got without adding more to it, so these will go out with the bins tomorrow morning!
  4. The thing is when these were recovered they were in the middle of a big pile of rusted down vehicle. So rusted and corroded that nothing was recognisable in it and any part that we picked up just crumbled in our hands. There was a big headlamp type affair, of the type that one would nomally see mounted on Rollers from the 1920's but it crumbled to nothhing as soon as it was picked up. There were absolutely no etchings whatsoever anywhere on the glass and the state of decay on the metal and the fact that they didn't look at all laminated made me think that whatever it was it must be pre-war. Staring at them again this morning and having another futile search for etchings had me scratching my head again. Then it hit me, they're not windscreens at all.... they're glass shelves for a big -ass drinks cabinet . Where they were found, the pile of scrap around them and the curvature on top and bottom edges all suggested part of a vehicle but, in the end, the more prosaic explanation must be that they are just big glass shelves for a curved drinks cabinet. Now I feel like a bit of an arse! In my defence though I've had these in the shed for a year or so and everyone who has seen them has said the thing to me, "what vehicle are those off?"
  5. No body recognises these? Wow! First time you guys have let me down ;-) Seriously though, they are a bit of a mystery. Given their nature I'd hazard a guess that they're either pre-war or wartime. Their size would sort of pre-clude them from being a rear window so they are either the side windows of some form of estate, or a the front windshield off a one of those old Austins with the square window in front, the curves on the bottom and top edge suggest to me a a front windscreen but I can't for the life of me guess from what.
  6. Anyone know what these ancient windshields are off? I Found these buried in the copse at the end of my paddock. Have no clue what they're off or how long they've been there, but quite a while I'd guess. I think there was an AA emplacement in this paddock during the war, as it's at the approach run onto a WWII Airfield, not that the two are in anyway connnected but one never knows. They're most likely civilian, possibly wartime, and when I first saw these my initial thought was Austin Tilly or something like that, although to be honest I really don't have a clue but I'm sure one of you will know. Given that this is Oxfordshire they might be of a Morris or something? Anyone know?
  7. Old Git

    Q. Re QF 75mm on Cromwell

    Hi David, thans for the reply, do you mean that floor of the tank or the bottom of the turret (not the turret basket).? Am I right in assuming that there was water egress between the mantlet and the armour plate of the turret? I'm curious because on a recent trip to TNA I came across a scientific analysis on how cold tanks get in Winter and what the effects are on the crew (all part of designing effective CWW clothing for the crews). They analysed various parts of the tank and how Cold weather affected the heating in tanks, especially in tank with their engines off! Interesting stuff and it got me thinking about the severe winter of 44/45 and what it was like for the crews and when I realised that there could be water egress between the Mantlet and the turret I wondered if there was any problems with freezing water inside the turrets, and if so did it have any negative impact on their ability to get the tanks in action in a hurry.
  8. Old Git

    Q. Re QF 75mm on Cromwell

    Adrian, you're an absolute star mate. Those are views that we just never see and it helps a lot in understanding how these things actually look. It was only recently that I began to realise that the Mantlet was all cast in one piece with the Aroured MG cradle at the front. I had always assumed that the Armoured Cradle was cast separately and bolted onto the Mantlet. This caused me to view the Armoured cradle as part of the external detail, rather than internal, and because of that I designed them separately. As I said earlier, the only photos I could find of the Mantlet were either in situ or laying in a pile of parts from a resto, and all of them tended to show the back view. I'm gratified to see how close I got in my guesstimations, I had some drawings from the Tank Museum whch I had to scale up and I have found that it can be hit and miss with official drawings!. I have found drawings where items are exactly drawn to scale but then other parts on the same drawing are not, it can be frustrating to say the least! Which is why this thread got started. I had a couple of different drawings of the tube which purported to be in scale but the length, and look, of the B measument seemed to be all wrong and it took some poring over photographs to realise that it wasn't my calcs that were off but the actually drawings. Everything else in those drawings would appear to be in scale, except that one area. It makes no sense to me but I'm sure it made some sense to someone in the DTD Drawing office! So I was a bit leery of what I had deduced for the mantlet. I had the width at approximately 22" and from your photographs I can see that it's actually 22 3/4". My height measurement was taken from the bottom of the 'tab' and I'd thought I'd got that wrong too until I realised that your tape measure is passing through the middle of the MG aperture which must mean that your height measurement doesn't include the 'tab', and checking my dims I find that I'm almost a perfect match for height in that area. So, overall not too bad for scaling from a set of suspect 1/35 drawings from Bovi. Thanks again Adrian, the photos and measurments are fantastic, of course my OCD will now make me go back and mod my CAD drawings! Another question, if I may, from what I can see the Mantlet sits about an inch back from the front Armour plate on the Turret. This allows it room to pivot up and down and, using the bevels on the mantlet, give elevation and depression on the main gun. I know the Mantlet is contained within a 'box' in the Turret but what happens if you're gun forward into driving rain which is hitting the front of the Mantlet and, presumably, running down to collect just inside the turret. Was there a weather seal of some sorts to prevent this, or did they just have some form of weep holes in the turret to flush it out out on to the decks?
  9. Old Git

    Q. Re QF 75mm on Cromwell

    Hi David, yeah I have noticed that, I'm focusing on the 75mm and trying to ascertain what the mantlet looks like on the, unobstructed, Front face. All the photos and drawings I have show only the rear face. Still, I think I' getting there. I'vemocked up a scale mantlet in carboard and I can't see how the a full elevation of the gun wouldn't leave a bit of a gap between the bottom of the mantlet and the aperture. I ust check the manuals again to see what it says about Max / min elevation heights etc. Just as a matter of interest, and by way of a sanity check, does anyone have the Height x width x depth dims for the Mantlet? I think it's about 485mm x 558 mm x 90 mm (or 270 mm including trundle mounts). Is that about right? Pete
  10. Old Git

    Q. Re QF 75mm on Cromwell

    David, thanks for that, it all makes perfect sense, especially in terms of preventing splash and adding extra strength to the mantlet where it's been bored through for the tube. It seemed to me that the tab was a perfect match for the same area in aperture and I didn't understand why they actually had a tab in the first place, why not just continue the 'tab' for the full width of the mantlet, especially as I can't see where it could foul on anything inside the turret and below the MG cradle. The tab seems to be a pefect match for the corresponding area on the aperture, see below, and I just wondered if, when the tube is at full elevation, the leading edge of the tab passed over the rear edge of the aperture in the corresponding area. It looks like it wants to but as you say it would, possibly, leave a gap of several mm through which splash could occur. Pete
  11. Old Git

    Q. Re QF 75mm on Cromwell

    Quick-ish question for the Cromwell expert's. On the 75mm Mantlet there is a bit at the bottom, just below the tube, that sits lower than the rest of the mantlet. I've circled it below. When the mantlet tips backward to elevate the tube is the bottom, forward edge of this little 'tab' supposed to clear the aperture, by a few mm (just coming out over the groove which is there to allow the tube to depress a bit more) or does it just rely on the bevel, on the lower matnlet face, to give it clearance as per the rest of the bottom area of the mantlet?
  12. Old Git

    Q. Re QF 75mm on Cromwell

    Adrian, thanks mate I may well have a question or two on the Breech ring and Block, but what you gave me on the Mantlet allowed me to do finish up the following. It's not 100% complete just yet, there are a few details that need adding, including the counter-bore that you mentioned earlier, and the position of the aperture for the MG cradle needs to be adjusted, but if you spot any glaring errors do say so ;-)
  13. Old Git

    Q. Re QF 75mm on Cromwell

    Thanks Rick, to be honest I've learned a lot on this forum and the chaps, and chapesses, here have been absolutely brilliant and very generous with their time and knowledge! So I'm kinda standing on the shoulders of giants. I'm now working on the 75mm Breech Ring and Block, I've got most of the Breech ring figured out and some of the Breech Block. Sitting here trying to work out how the Breech ring looks from underneath where the innards are exposed at the bottom of the slot for the breech block. I think I might actually be able to work this out with a couple of paper cut outs, but we'll see. I could just as easily go mad counting the hairs on the palm of my hand!
  14. Old Git

    Q. Re QF 75mm on Cromwell

    So, I've pretty much worked out the dims for the tube now and as far as I can tell, if anyone else is interested, these are as follows... A = 570mm long and dia about 165.5mm (length is measured from Bevel B to the start of the thread, I think the threaded portion about 102mm long) B = 100 mm long C = 350mm long x 137.5mm dia D = 165mm long E = 1265mm long (to end of muzzle) x 111mm dia all dis + or - 1mm I'm now working up a CAD file for the mantlet. Hopefully, it'll turn out nice again (best George Formby voice there).