Hotchkiss 6 pounder QF in Rhino3D

[DrPR]

I have been following this thread with interest. I have looked for drawings and photos for the 40mm saluting guns that were used on US Navy ships from WWII up into the 1980s - and perhaps longer. There are some similarities to the Hotchkiss gun, and a lot of differences.

I have never found a good photo or drawing of the saluting gun breech mechanism.

Phil

[mcg]

Phil, in Canada, some Hotchkiss 3 pounders were ultimately used as saluting guns. I came across their history here:

The text was a screen grab from this site:

http://wwiimodeller.co.nz/tag/photo-wal ... -mounting/

Drawings of the breech block mechanisms at a high level of detail are problematical. I have been using patent drawings for breech block details but the end product in 3D CAD is, necessarily, a composite taken from several Hotchkiss patents and from an old textbook that seems to feature redrawn patent illustrations. In any event, patent drawings are not dimensioned and rarely represent in full a manufactured product. It would probably take a trip to the national archives to get truly scale drawings to work from. There were several different quick firing guns that might have been repurposed, I suppose, as saluting guns. In the US these were chiefly manufactured by Driggs Schroeder. Driggs was the inventor, and the patents (and drawings) were in his name.

I have been sketching the Hotchkiss mechanisms mainly as an effort to figure out how they worked. Many of the details will not show in the finished 3D model.

However, I was pleased to see that even with the breech block up, closed and locked, some mechanical detail still "reads".

When the breech block is dropped, more detail appears.

In my early 6-pdr, which had no recoil system, the view of the breech block details and mechanism should remain fairly open. Michael

Edit. Ran an image search on US 40mm saluting guns. They are purpose built although some are mounted on crinoline mounts which antedate WWII and are apparently left over from the QF era. In these instances it seems plausible an old QF was directly replaced with a new 40 mm saluting gun.

There are also some YouTube videos of 40mm saluting guns performing a 21 gun salute. These show one sailor loading and a second operating a double lever/crank. The crank seems to accomplish the whole sequence -- I don't see a trigger. The image search turned up a close up of a breech, snapped in a public park, but the block and mechanisms are missing.

[mcg]

The 6 pdr is cocked by rotating the double lever counterclockwise. A cam on the lever's shaft operates against a (what? A follower or a finger, let's say) mounted on an extension of the cocking shaft, that is, the shaft bearing the hammer.

Bear in mind that the cocking shaft is mounted on the breech block, which elevators up and down. As the double lever is rotated counterclockwise, the crankshaft roller moves freely through an arc milled into the breech block. During this initial movement of the lever, the breech block remains stationary -- but the cam and finger engage, the finger is nudged downward decisively, and the hammer is cocked.

The encounter between the cam and the finger is brief. As soon as the crankshaft roller reaches the end of its arc, the breech block is free to fall. It weighed 51 lbs and dropped quite suddenly -- carrying with it the cocking shaft and finger. Here is the mechanism shown in the clear.

On photos of some the QF's in the Hotchkiss series, there appears a short hand lever extending downward from the finger at a right angle. This small lever would have made it easy to cock (or slowly release) the hammer by hand if necessary.

[mcg]

When the breech block is fully elevated the protruding tab end of the sear comes to a precise stop against a lever. This lever is to be rotated downward by pulling the trigger.

The grip is modeled in 3D with a 2 rail loft. The origin of the rails is a point at the base of the grip. The loft proceeds from an ellipse near the base of the grip to a slightly rounded rectangle at the top.

The grip was solidly mounted to the QF. The gun could be fired by hand or remotely, by means of a small, short lanyard looped through the guard.

A modeler in my area made a really impressive physical model of the USS Maine. It included a QF and its pistol grip. I was examining the model at a show, and was amazed to discover he had somehow made a tiny trigger. "An eyelash," he explained.

[mcg]

From this point, it is necessary to leave aside the highly detailed Hotchkiss patent drawings and work from a pastiche of other drawings and photographs. We do have good line art for the shoulder brace. The steel "tiller arm" on which the shoulder brace is mounted varies in style, size, and fixings from one QF to another and from the 3 pounder series to the 6-pounder series.

By good luck, there exists this (probably cc 1890's) photo of a Hotchkiss 6-pdr on the USS Oregon. It is almost a plan view, so I have overlaid the shoulder brace drawn from line art, and will proceed to draw an approximation of the steel arm on top of the photo.

The cylindrical rubber shoulder pad was probably natural polyisoprene. It was white. It is not black because it was not compounded with carbon black, like a modern black rubber tire.

[mcg]

Many of the Hotchkiss QF's are fitted with plates flanking and closely fitting the trunion. These serve as a very solid attach point for the traversing arm. If the barrel is temporarily erased it is possible to see how closely the plates are fitted on the model. This was accomplished with a Boolean subtraction. I think of these plates as wrenches, with the traversing arm as the handle. (In retrospect I can see this was an error. The side plates are parts of the gun�s cradle. They serve as mounts and guides for slides on which the gun tube recoils. 1-23-2020)

The arm itself is loosely adapted from the photo below of a Hotchkiss 3 pounder, and from the photo in the preceding post of the 6 pounder on the USS Oregon.

There was a variety of mounting points and shapes for the traversing arms, but documentation is thin. I am happy with what I have here so far, but it should be regarded as free lance, not scale. Michael

[mcg]

The design and curves for the shell deflector were pulled from photos of a surviving QF on
Kuivasaari Island, near Helsinki. The gun was manufactured by Driggs-Seabury
in Bridgeport, Connecticut.

The deflector was mounted to the traverse arm. A shell rapidly ejected backward out of the chamber would hit the deflector and fall to the deck.

[Alexey Loginov]

Pad on the butt was made of gutta-percha.

[mcg]

Thank you Alexey. Do you know what type of wood was used? Michael

[Alexey Loginov]

Walnut

[mcg]

Many thanks, Alexey -- this is very helpful. Michael

[mcg]

This version of the Hotchkiss 6-pounder is fitted with a recoil brake, noticeable underneath the gun tube. It is also fitted with two side plates. These support parts of the recoil mechanism, but it is difficult to guess how they work, exactly, from most photos.

In 2017 I found some fairly good 3-view drawings of the recoil mechanism for a Hotchkiss 3-pounder. Here is a side view:

The basic components include the brake cylinder, a U-shaped cradle with a front bridge arcing beneath the barrel, and the gun tube suspended on slides within the cradle. The slide and guide rails are more evident in a view from behind:

The 3-pdr drawings show what elements to look for but do not directly apply to the 6-pounder.

Finally I came across a photo snapped of a 6-pdr on the USS Olympia that is a great help. It was taken from behind and the traversing arm has been removed, so there is an unobstructed view.

The photo clearly shows the thickness of the plate, and since it has not been painted over, it is possible to see the merest outline of the slide it contains and guides. Here is a CAD sketch of the two plates with the slides extended to the rear, as they would be in operation.

The CAD image and file are labelled "Guides & Slides." Note that the slides are beveled top and bottom to lock them into the guides. The gun tube is attached to the slides, and the guide plates carry "new" outboard trunnions. These replace the trunnion that was solidly molded into the barrel in the earlier Hotchkiss 6-pounders, which had no recoil brake save the crinoline mount.

Not shown is a front bridge that arcs under the barrel and connects the two side plates to form a typical U-shaped gun cradle.

[mcg]

The slides are secured to barrel's jacket with a ring mount, probably shrunk into place. The ring and the slides are modeled as an integral casting.

In order to mount the ring and slides the original casting had to be modified. Here is the original Mark I version with trunions mounted directly to the barrel.

Below is the modernized version, with the trunion deleted. Note that the aft section of the jacket is now perfectly cylindrical.

Finally, here is tha jacket with the ring and its integral slides mounted.

This entire recoiling mass, maybe about 600 lbs, slides aft freely and suddenly against a spring when the QF is fired.

[wefalck]

Inside the recoil-spring there is no hydraulic shock absorber ? They became quite common on larger guns at least from the early 1870s on.

[mcg]

Hello wefalk,
Yes, the brake contains a piston and cylinder for the hydraulic shock absorber. This is a Hotchkiss drawing for the 3 pounder, but we can probably assume a similar brake was used on the 6 pounder.

It appears to me the central shaft is anchored at the forward end by a bolt to the cradle. The cylindrical housing recoils with the gun tube while the shaft remains fixed. I am looking for some means for the fluid in the shock absorber to circulate as the piston moves, but not seeing it.

edit: Actually in this design the piston is fixed, and the cylinder oscillates back and then forward. mcg

It would be very helpful if you could explain how this brake worked. Many thanks. Michael

[wefalck]

Normally, the piston has various small holes in it through which the fluid (e.g. glycerine) is pressed from one side to the other. The number and size of holes is adapted to the viscosity of the break-fluid used. The spring then moves the gun forward again into the firing position, squeezing the fluid through the holes in the opposite direction. The break-fluid has to have a fairly high boiling point, as a considerable amount of heat is generated by the movement. This limited also the number of shots that could be fired per hour in order to dissipate that heat.

[mcg]

Many thanks, wefalck. This makes it perfectly clear how the energy of the recoil is dissipated in two strokes, aft and foreword.

I notice the piston and cylinder dimensions set logical limits on how far the gun tube can move. Michael

[Grimsby]

Hi, New here. I'm very glad I found this site. I recently obtained a 6 pdr gun. Yes, the real deal. In brief, from the markings, it has a Mark X Mod slide on top of the gun. It is from the Root and VanDervort Eng company 1917. The gun is a 57mm and breech markings: 6 pdr Br. Mech Mk II Mod. Gun no: 293 A 26245-1 Stamp is from Bridgeport Conn and I cannot see the other part of it.
There are more markings on the slide.
Your diagram of the breech has helped immensely to understand it and it is slowly opening up.
I have attached a picture of it. I have found many sites and cannot find one just like it. That is, with the rather large slide on top. I'm cleaning the sight (a lot of brass and only use a brass brush of course). and hope to get it working soon.
I'm trying to find out where it came from and if it was a working gun on a ship or somewhere.
Is there such a site to put in the SN or other information to find this out?

Thanks for any help.

[mcg]

Welcome to the forum.

Some observations and possibilites:

No pintel.

The base and perhaps the trunnion bearings look as though they might have been improvised. Are these film can bearing housings waterproofiing?

The brake unit may be broken or opened or corroded away in such a way that the springs have expanded and, in effect, lengthened or telescoped the brake assembly.

About as close as I can get is this drawing of a Mark IV, which was specialized for anti-aircraft in WWI.

It has a rotating base instead of a pintel, a broomstick instead of a shoulder-fitted traversing arm, and two recoil brake components mounted above the tube. Might be a cousin of your antique Mark X cum Mark II.

Root and VavDervoort has an interesting history, here:

http://oldengine.org/members/plowe/rv-e ... dnance.htm

Root & VanDervoort may also be a key to researching this find. Bridgeport manufactured commonplace Hotchkiss 6 pounders under license. But all the unusual components in your example are R & V and date from the WWI epoch. We can speculate that these components upgraded and specialized the already archaic Mark II design, in 1917, for some specific purpose: AA, coastal defense, maybe the deck of a submarine.

Might try searching the National Archives for ordinance made by Root & VanDervoort.

[mcg]

Found a photo of a Hotchkiss 6 pdr recovered from the USS Maine. There are a few other photos that show the cradle assembly, but this is the most helpful I have come across. This Hotchkiss is in South Carolina, here:

https://www.historiccolumbia.org/online ... -uss-maine

The cradle consists of the two guide plates united by a bridge. The whole assembly appears to be a single casting, subsequently machined.

At the center of the bridge is the retaining nut for the brake. The large disk visible below the bridge in the CAD sketch is the piston of the shock absorber. The piston is fixed in position -- the cylinder slides back and forth with the gun tube.