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Topic review - Hotchkiss 6 pounder QF in Rhino3D
Author Message
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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
Post Posted: Thu Jan 30, 2020 8:04 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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.
Post Posted: Wed Jan 29, 2020 12:59 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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.
hydraulic brake.jpg
hydraulic brake.jpg [ 79.99 KiB | Viewed 111 times ]

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
Post Posted: Wed Jan 29, 2020 11:58 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Inside the recoil-spring there is no hydraulic shock absorber ? They became quite common on larger guns at least from the early 1870s on.
Post Posted: Wed Jan 29, 2020 11:12 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Slides integral w Ring.jpg
Slides integral w Ring.jpg [ 66.24 KiB | Viewed 117 times ]

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.
trunion.jpg [ 40.19 KiB | Viewed 117 times ]

Below is the modernized version, with the trunion deleted. Note that the aft section of the jacket is now perfectly cylindrical.
Jacket w trunions deleted.jpg
Jacket w trunions deleted.jpg [ 19.47 KiB | Viewed 117 times ]

Finally, here is tha jacket with the ring and its integral slides mounted.
Jacked w slides mounted.jpg
Jacked w slides mounted.jpg [ 20.42 KiB | Viewed 117 times ]

This entire recoiling mass, maybe about 600 lbs, slides aft freely and suddenly against a spring when the QF is fired.
Post Posted: Wed Jan 29, 2020 10:33 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
57_45Br.jpg [ 207.7 KiB | Viewed 164 times ]

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:
3 pdr side view.jpg
3 pdr side view.jpg [ 55.96 KiB | Viewed 142 times ]

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:
3 pdr guides & slides.jpg
3 pdr guides & slides.jpg [ 19.63 KiB | Viewed 142 times ]

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.
USSOlympia hotchkiss brake.jpg
USSOlympia hotchkiss brake.jpg [ 85.51 KiB | Viewed 164 times ]

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.
Guides & Slides.jpg
Guides & Slides.jpg [ 34.17 KiB | Viewed 164 times ]

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.
Post Posted: Thu Jan 23, 2020 12:55 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Many thanks, Alexey -- this is very helpful. Michael
Post Posted: Sun Mar 13, 2016 5:13 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote

Post Posted: Sat Mar 12, 2016 3:18 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Thank you Alexey. Do you know what type of wood was used? Michael
Post Posted: Sat Mar 12, 2016 11:49 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Pad on the butt was made of gutta-percha.
Post Posted: Fri Mar 11, 2016 4:17 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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.
Deflector fr Bridgeport.jpg
Deflector fr Bridgeport.jpg [ 135.82 KiB | Viewed 974 times ]
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.

Shell deflector & mount.jpg
Shell deflector & mount.jpg [ 51.27 KiB | Viewed 974 times ]
Post Posted: Tue Mar 08, 2016 12:26 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
trunion plates.jpg
trunion plates.jpg [ 49.88 KiB | Viewed 996 times ]
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)

trunion flanking plates.jpg
trunion flanking plates.jpg [ 46.46 KiB | Viewed 996 times ]
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.
traverse arm.jpg
traverse arm.jpg [ 88.89 KiB | Viewed 996 times ]
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
Post Posted: Sun Mar 06, 2016 5:18 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
USS Oregon smaller.jpg
USS Oregon smaller.jpg [ 87.01 KiB | Viewed 1025 times ]
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.
Post Posted: Wed Jan 20, 2016 9:57 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
trig mechanism.jpg
trig mechanism.jpg [ 34.82 KiB | Viewed 1044 times ]
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.
loft from a point.jpg
loft from a point.jpg [ 27.33 KiB | Viewed 1044 times ]
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.
solidly mounted.jpg
solidly mounted.jpg [ 33.06 KiB | Viewed 1044 times ]
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.
Post Posted: Sat Jan 16, 2016 7:15 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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.
Outside view.jpg
Outside view.jpg [ 42.57 KiB | Viewed 1088 times ]
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.
external cams & b-bloc.jpg
external cams & b-bloc.jpg [ 30.14 KiB | Viewed 1088 times ]
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.
coupling cams.jpg
coupling cams.jpg [ 29.04 KiB | Viewed 1088 times ]
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.
Post Posted: Sun Jan 03, 2016 6:49 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Phil, in Canada, some Hotchkiss 3 pounders were ultimately used as saluting guns. I came across their history here:
saluting history.jpg
saluting history.jpg [ 107.9 KiB | Viewed 1132 times ]
The text was a screen grab from this site: ... -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".
block locked in up.jpg
block locked in up.jpg [ 34.65 KiB | Viewed 1136 times ]
When the breech block is dropped, more detail appears.
full down b-block.jpg
full down b-block.jpg [ 72.69 KiB | Viewed 1136 times ]
b-block dropped.jpg
b-block dropped.jpg [ 35.45 KiB | Viewed 1113 times ]
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.
Post Posted: Thu Dec 31, 2015 10:56 am
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
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.

Post Posted: Wed Dec 30, 2015 10:37 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
The two main remaining cuts to the breech block are indicated here.
hammer slot cutter.jpg
hammer slot cutter.jpg [ 21.34 KiB | Viewed 908 times ]
An angled, U-shaped cutplane was used to make the 46-degree slanted cut. The Boolean cookie cutter in the middle of the block is designed to open up a slot for the hammer. The cutter, which is in effect a mould to the inside of the slot, is here:
hammer slot reverse mould.jpg
hammer slot reverse mould.jpg [ 21.36 KiB | Viewed 897 times ]
Shown below as a test fit is the hammer in its slot.
hammer in slot.jpg
hammer in slot.jpg [ 57.41 KiB | Viewed 908 times ]
After some additional detailing, the completed breech block looks like this. Notice the cutouts at the rear of the block. These secure the springs and provide an exit port for the sear.
breech block complete.jpg
breech block complete.jpg [ 24.98 KiB | Viewed 908 times ]

The assembled breech block is shown below. Notice the firing pin projecting through the front surface.
B-block assembled.jpg
B-block assembled.jpg [ 53.99 KiB | Viewed 908 times ]
When this assembly is turned around it is possible to notice the wide slot that secures the mainspring, and the sear projecting from a tiny window at the back of the block. When the sear is pressed down by the trigger arm, the cocked hammer is released. The mainspring was left free to move back and forth a few millimeters in its slot as the hammer was cocked and released.
B-block w sear.jpg
B-block w sear.jpg [ 36.69 KiB | Viewed 908 times ]
Post Posted: Wed Dec 30, 2015 1:25 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
Hotchkiss used a ribbon type mainspring. The hammer was mounted inside the breech block. This screen grab shows the mechanism in the context of his patent drawing:
ghosted & cocked.jpg
ghosted & cocked.jpg [ 159.97 KiB | Viewed 990 times ]
Below is the device in isolation, shown cocked:
Cocked spring.jpg
Cocked spring.jpg [ 52.59 KiB | Viewed 1003 times ]
And shown again with the spring expanded.
Expanded spring.jpg
Expanded spring.jpg [ 52.87 KiB | Viewed 1003 times ]
His patent argues that because the spring simultaneously pushes up and pulls down, it produces less or perhaps more symmetrical wear on the mechanism. Another possibiity might be that he was "improving" his way around some rival patent. In any event, the ribbon spring is typical of the Hotchkiss series of QF's. Here is a photo taken long ago of a dismounted spring.
mainspring.png [ 6.04 KiB | Viewed 1003 times ]
Here is another view in a photo shot from underneath the breech block.
breech block sear mechanism.jpg
breech block sear mechanism.jpg [ 51.62 KiB | Viewed 1003 times ]
Immediately to the right of the mainspring is a ratchet and pawl that operates on the cocking shaft and securely cocks the mainspring.
cocking mechanism.jpg
cocking mechanism.jpg [ 39.83 KiB | Viewed 931 times ]
Here is a view from below showing the centered hammer and mainspring and, offset to the right, the sear. A linear spring bears upward on the sear. The left end of the spring is solidly anchored in the wall of the breech block.

In this view the cocking shaft is rotated counter-clockwise until the pawl on the spring-loaded sear catches the ratchet. The mechanism is shown cocked.

Finally, shown below is an X-ray view of the hammer and sear mechanism positioned inside the breech block. At this point they are simply embedded in the block. Next step will be to machine away a cavity and mounts for this mechanism.
X-ray of hammer installation.jpg
X-ray of hammer installation.jpg [ 69.28 KiB | Viewed 918 times ]
Benjamin Hotchkiss's obituary noted that he owned the Empire Spring company in Saratoga, New York. Thinking this might be a spring manufacturing company -- that he had perhaps bought in one of his suppliers -- I googled it. It turns out the Empire Spring Company was in fact a hugely successful producer of spring water, like Evian or San Pellegrino. Full of surprises, his story.
Post Posted: Fri Dec 04, 2015 12:42 pm
  Post subject:  Re: Hotchkiss 6 pounder QF in Rhino3D  Reply with quote
U.S. Patents can be downloaded as .pdf files from Google's patent search service. I use the "snapshot" feature of the Adobe Reader to select and extract the drawings from the patents as .jpg files. The .jpg images are then loaded directly into Rhino using a Rhino command, PictureFrame.

The 6-pounder is destined for installation on a CAD model of an 1898 warship from the Spanish-American war. I need four 6-pounders. The beauty of CAD modeling is that having created one intricate assembly, such as a gun or a lifeboat, you can simply copy it multiple times.

The 37 mm Hotchkiss sounds like a fascinating project. 3D printing I have not tried. I have used FirstCut for CNC machining of (commercial) components designed in Rhino3D. I have also used Rhino to produce files for laser cutting wooden parts for models.

Rhino3D was originally conceived and marketed as a plug-in for AutoCAD. Later it became a standalone program. I was certified in AutoCAD before I tried Rhino for the first time, around 2008, and the transition was not difficult. I still use both programs but I have always been more comfortable working in 3D.

These days, I suspect the best way to try out 3D or to experiment with it is SketchUP. There is a free version available, and lots of online training support.

On the McNeel site I see there is classroom training available for Rhino3d in Paris (CADAtlantique). Once registered as a student I imagine you could get an interesting price on the Rhino software package. In the US the student price is a fraction of the commercial price.

Finally, you might wish to look into AutoDesk's Fusion 360. It offers CAM as well as 3D CAD. Some discussion here: ... &t=2512531
Post Posted: Mon Nov 23, 2015 10:41 am

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