Vickers Bl 8 inch Howitzer cannon of 1917

[SillyOldDufferModerator @sillyoldduffer]

Posted by Mick B1 on 19/05/2022 16:13:26:

Posted by SillyOldDuffer on 19/05/2022 09:31:04:

…

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

[Mick B1Participant @mickb1]

Posted by SillyOldDuffer on 19/05/2022 17:04:12:

….

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.

[mal webberParticipant @malwebber91786]

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.

[Clive HartlandParticipant @clivehartland94829]

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.

[Mick B1Participant @mickb1]

Posted by Clive Hartland on 19/05/2022 19:50:47:

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.

…

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

[Jon LawesParticipant @jonlawes51698]

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

Looks like the technique is still the same now!

[Clive HartlandParticipant @clivehartland94829]

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.

[mal webberParticipant @malwebber91786]

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.

[Robert Irving 4Participant @robertirving4]

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

[Jeff DaymanParticipant @jeffdayman43397]

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

[mal webberParticipant @malwebber91786]

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

[mal webberParticipant @malwebber91786]

Edited By mal webber on 27/05/2022 23:11:36

Edited By mal webber on 27/05/2022 23:13:56

[mal webberParticipant @malwebber91786]

pic is from previous page.

[Robert Atkinson 2Participant @robertatkinson2]

Not directly related but the pictures of obturators reminded me of this accident report:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727954/20180823-Challenger_SI_Castlemartin_Redacted_RT.pdf

In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.

Robert G8RPI

[Mick B1Participant @mickb1]

Posted by Robert Atkinson 2 on 28/05/2022 10:11:04:

Not directly related but the pictures of obturators reminded me of this accident report:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727954/20180823-Challenger_SI_Castlemartin_Redacted_RT.pdf

In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.

Robert G8RPI

Horrifying.

[mal webberParticipant @malwebber91786]

Hi all, managed to broach out the shape for the plug the last couple of nights, next will be the threads and to see if the breech and plug will fit together, a couple of pics on the plug before I start with the threads.

Thanks, Mal.

[mal webberParticipant @malwebber91786]

Hello all, managed to thread the breech plug last couple nights which all wen't well up up to the point of trying the breech ring on, the breech ring didn't want to go on first couple of attempts so bit of shaping here and there with some needle files and it screwed into place,the plug and breech are in scale with the Howitzer except the o/d of the breech ring which is about 25mm smaller,next is to get the plug to swing into the breech all good practice before I make a steel one which will take a lot longer, couple pics on how it turned out.

Thanks Mal

[DiogenesIIParticipant @diogenesii]

That's some work, Mal – think your post must have slipped by people in all the festivity..

..fascinating watching this take shape..

[DalboyParticipant @dalboy]

Even though I may not post replies but I for one have been following the progress on this build and am amazed at the craftmanship involved. I can only imagine how how the threading was done on this and the time involved in producing it.

Many thanks for the updates as the work progresses

[VicParticipant @vic]

I agree, some amazing work on the project.

[BufferParticipant @buffer]

Mal

Could you explain to us how you have cut the interrupted threads?

Thanks

[David George 1Participant @davidgeorge1]

Hi Mal are you considering displaying it at the October Midlands show. I know it is not finnished yet but it would be marvellous to see your workmanship.

David

[Pete RimmerParticipant @peterimmer30576]

Here is a link that was just offered up on another forum which has a lot of detail on breech block threads. I thought I would add it in here for interest:

https://d.lib.msu.edu/etd/8139/datastream/OBJ/download/Some_engineering_features_of_a_modern_breech_mechanism.pdf

**LINK**

[Robert ButlerParticipant @robertbutler92161]

Bump!

[JellyParticipant @jelly]

Posted by Robert Atkinson 2 on 28/05/2022 10:11:04:

Not directly related but the pictures of obturators reminded me of this accident report:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727954/20180823-Challenger_SI_Castlemartin_Redacted_RT.pdf

In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.

Robert G8RPI

From a safety lessons perspective that was a really worthwhile read, particularly the section addressing how the fail-safe design had failed to anticipate an operational practice developed four years later, and the safety reassessment having been predicated on the accident scenario being implausible, based on the correct drills being followed up to that point.

 

Initially it left me thinking that I'm fortunate to work in an industry which has at this point become extremely thorough in assessing the risk from equipment being operated in unintended states and the potential for a chain of events that lets it happen…

But it further rumination left me thinking "If I was the technical representative on that safety study would I really have spotted the potential for such an unusual operational scenario?".

 

Which got me thinking about the limitations of the somewhat theoretical approach to HAZOP (HAZard and OPerability) studies often taken, in the context of deciding that a specific equipment condition is or is not plausible enough to consider as part of the study.

For a complex piece of user maintained equipment (like the L30A1), there's a real need for the design authority or safety study leader to ensure a thorough review of ongoing operational practice, empirically and/or via observation of normal users to has validated existing assumptions that rule out consideration of a risk still hold, and that's a potential gap that could easily happen in my sector or elsewhere…

Thankyou.

Edited By Jelly on 12/05/2023 14:13:49

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