Vickers Bl 8 inch Howitzer cannon of 1917

Nonetheless impressive! How did you go about it? There are two stepped threads and a blank sector:

My guess.

1. Bore the breech to suit the inner thread diameter and cut the thread conventionally.
2. Broach the second and third sectors,
3. Cut the second thread group laboriously, one at a time, over 60°.

Doable, but tedious skilled work; I'd get bored and mess-up. Is there an easier way, or am I left slack-jawed in amazement again? Plenty of good work shown on the forum, but your Howitzer is ticking all my boxes!

Dave

I have often wondered what the machining solution for these things was but have never seen anything

...The obvious solution was to make a sliding breech block...

Apologies I missed this.

Pak 40, not to scale or even 100% accurate. All made from stainless from the scrap tub apart from the nylatron tyres!

17" total length from tip of the muzzle brake to the towing hitch.

Hello all.

Richard that is a fantastic looking model of the PAK 40 very impressive and detailed nicely, good size as well at 17" thanks for sharing.

Peter couple of pictures on here when you start the build would be very interesting.

Mick thanks for the offer but will keep it as a model.

Dave that is pretty much how I went about it, although the cut outs in the breech would never work with a swing-away plug. So I have been trolling the internet for a good few days now and am about to start my second attempt, Ady1 it sure would make it easier to have a sliding plug.

Thanks, Mal.

Mal

How do you cut the threads though?

Thanks

I think you're right that there's an issue with a hinged breechblock carrier and the arc of insertion of the block creating interferences. I'm sure I've seen drawings somewhere of the the reliefs that were used to prevent them.

There an amazing and impressive animation of the breech workings of the 15" naval gun here:-

**LINK**

... but it skates over the problem and I wonder if it cheats...

You can see the relief arcs for the swinging breechblock on P7 of this document:-

**LINK**

The problem would be solved if the breech mechanism moved back slightly before and whilst swinging out.

The animation is amazing, but I can't see any sign of it - though the horizontal movement might be too small. Two possibilities: the turning arm on the right cams as it rotates, and the carrier pintle unscrews as well:

Not convinced by my own suggestion, though the comment 'Axial Vent Bolt is keyed to Carrier Pintle so doesn't rotate with Breech Screw' may be supportive.

By the by can't see the relief angles in Mick's other interesting document: page 7? Sorry if I'm seeing and not seeing again.

Dave

Edited By SillyOldDuffer on 19/05/2022 09:31:46

It only shows as 7 of 61 on the pdf page count at the top of the view - on the document image itself it's in the drawings facing page 10 as printed. There are arcs cut away to allow the swing-passage of the breech block. This will obviously have reduced the pressure limits for the closure, but equally obviously this will have to have been calculated for - though I've little idea offhand how to approach that...

Here's a screengrab:-

Looks as if there might be a corresponding bite out of the block itself too.

Edited By Mick B1 on 19/05/2022 16:27:47

Thanks Mick - obvious when the drawing is in landscape.

More geometry to making these than I realised. It's obvious that my theory about the Naval Breech coming out horizontally is wrong on the Vickers 1917, which your image shows has arcs cut to avoid fouling.

Interesting that the Naval breech is considerably more complicated than the land version. In addition to hydraulic power assist, it allows electrical firing with a safety interlock to prevent the gun going off before the breech is closed.

I wonder how reliable the obturator pads were? I'd expect a lot of flame to escape through the breech if a pad leaked.

Dave

With the mass of components varying roughly with cube of calibre, mechanical assistance became essential in calibres over 6 - 8 inch. The 8" round weighed about 250 lb, the 15" 1938 lb. Even if the 15" breech plug had been of proportionate length to the 8" howitzer's it'd still have weighed over 7 times as much.

Plus the naval guns were working close to technical limits of pressure and velocity, whereas howitzers worked at more modest levels, and required longer barrel lives for extended barrages.

Of course, Jolly Jack Tar was more the apple of the public and political eye than Tommy Atkins, too, and his development and construction budgets might have been more generous.

Catastrophes relating to shipboard cordite handling and storage - in and out of battle - are well known, but I've not heard of turret incidents triggered specifically by leaking obturator pads. Something happened to one of the County Class 8" cruisers that killed a turret in gunnery practice, but I don't know details. Certainly if a pad leaked, you'd expect it torch out the turret fatally and risk producing a flash in stored charges that could threaten the magazine. The only one I can think of was relatively modern on, one of the last US battleships in about '89 or '90, and I think the breech hadn't been correctly closed. There must've been a failure of some safety interlock for that to happen, not AFAIK obturator failure.

Hello

Not a very good picture here but you can see some of the undercuts or relief cuts to allow for the plug to swing in.

Re the accidents in turrets. Sometimes as the barrel is elevated the shell having been rammed into the leed can slip back, then, as the charge is ignited it explodes in the chamber with dire results.

I know of 2 cases, one was an M107 8" howitzer and the other happened in the invasion of Iraq on an M109 Howitzer.

The last one was shown on the tv reporting at the time, causing severe burns to close personell. The M109 was burnt out.

The RN Queen Elizabeth class fast battleships of WW1 were fitted out for 'any elevation' loading to improve rate of fire by omitting to depress the 15" guns between firing, but its use was restricted because of this risk - which could occur in action when there were severe demands on hydraulic distribution. Ramming was still carried out around 5 degrees elevation to wring the driving band hard into the leed.

I better stop digressin' now, and leave this thread to Mal and his outstanding work.

Edited By Mick B1 on 19/05/2022 20:10:56

https://en.wikipedia.org/wiki/File:M109BREECH.JPG

Looks like the technique is still the same now!

I think that the wiki ref. is a German breech, they modified their M109's.

The metal work was chemically blacked as was the US style breech.

Hello all, well the second attempt at the breech block is underway, all this is practice and to see if I can do it so decided to have a go at the breech in aluminium before cutting metal to save cutting time if things go wrong, this attempt will be in scale with the Howitzer that I am trying to build, managed to broach out the blank in the lathe now for some threads couple pics to see how it looks.

Thanks, Mal.

Mal, I have been continually impressed by your attention to detail on this project. Well done.

Looking great so far Mal! It's a tricky part. I suspect the gun works may have had a few rotary shapers to make those. (And conventional shapers too.) These rotary shaping machines could do arc shaped cuts starting and stopping at any angle needed. Setups must have taken ages. I've only ever seen one rotary shaper in a museum, I was born too late to see them in any shops I worked in.

Edited By Jeff Dayman on 25/05/2022 01:24:27

HI, well cut the threads as Dave describes a couple of posts ago and all was going well in till I forgot the depth then things started to go wrong, so too many spring cuts were taken to clean it up so I think the threads are out of pitch, will carry on with the plug to see what comes of it.

thanks Mal .

Edited By mal webber on 27/05/2022 23:08:40