1. Preparing for the build, design process, first parts
Introduction:
In early April, I joined Landships, announcing my plan to scratch build a scale model of the French 75 mm Canon de 1897. I selected this because of my grandfather's participation in a historic event of WW I. His unit, Battery C, 6th Field Artillery, fired the very first American shots of WW I on 24 Oct 1917 from their 75's.
Over the past months, I've periodically reported my progress on Facebook and Hobby-Machinist.com, now I'm finally catching up and starting a project journal here here on Landships. With text and images I will detail my progress, perhaps with somewhat less focus on the machining details than on Hobby-Machinist.com.
Source information:
To build this model, first I need detailed, dimensioned engineering drawings. I would have to make these drawings, based on the French military drawings and US Army Tech Manual drawings found online, and visits to actual cannons. The French drawings have no dimensions and the US Army drawings only have a fuzzy scale bar. The first challenge would be to figure out the scale of each drawing. Did this by starting with the few known dimensions such as bore, wheel size, wheel width, and barrel length, then figuring out the drawing scale and actual dimensions of full size part. Then use this size where that part appears on other pages. This method is working, but generates some fuzzy, conflicting results. Actually measuring visible parts on the guns is a key. The "first shot" gun is at the US Military Academy Museum, (West Point, NY). While it would be great to visit it, there are other 75s closer to my Southern California home.
So, in April, I visited the Camp Roberts Museum, San Miguel California to take pictures and measurements of their 75mm. Per the Tech Manuals, the cannon has two major sections,"gun" and "carriage", and there are several different combinations and versions. Unfortunately for me, their gun is the American M1897A3 version, so only the gun portion was relevant. Its carriage is significantly different (e.g. split trail, steel wheels, rubber tires) so it would not help my research.
Image: M1897A3 at the Camp Roberts Museum
Camp Roberts Museum, placard for the M1897A3
More recently, I found the proper French gun at the Orange County's Old Courthouse, just 70 miles away. Again, I got pictures, sketches, and measurements. On this trip I concentrated on the carriage, specifically the wheels, axle, and related parts, since this is what I have been making the past few months.
Image: French 75 at Orange County Courthouse. Note that the shield is missing.
Image: Wheel details at Orange County Courthouse
Design Process and Concepts
April and May were used climbing the learning curve on my CADD (Computer-Aided Design and Drawing) software (I use TurboCAD.) and studying the French and US documents. Earlier, I said the scale would be somewhere between 1:10 and 1:5 scale. Based on the size of my lathe, I decided that my build will be at 1:8 scale. This model will not be an actual firing gun, but will be as detailed and functional as my tools, skill, materials, and information allow. It will primarily be made from steel, with some brass, bronze, and aluminium. Where possible, I hope to use commercially-available, off-the-shelf (COTS) hardware (nuts, bolts, rivets, etc.) Hopefully I can find COTS gears at a reasonable price. No doubt I will have to make some small fasteners and gears. The design will be in inches although some metric fasteners might be used.
First Part: Axle
With enough knowledge and design concepts in place, I started by drafting the axle drawings, then began machining it from steel rod. The axle is not just a simple shaft. Traversing the gun is accomplished by moving the carriage to left or right along the axle using a central threaded section driven by a gear train. The axle has cambered, tapered ends for the wheel hubs, and three different diameters along its central section.
Image: Axle, sitting on its page in the Army Tech Manual
Wheel Hubs
The next parts to be made would be the wheel hubs. Each of these hubs are two-piece. There is the inner hub, which rides on the tapered axle end and which has a tapered outer diameter. Then the outer hub, which rides on the inner hub's outer taper. The 14 wooden wheel spokes then get bolted between the inner and outer hubs.
Image: the two-piece hubs, sitting on their page in the French drawings
Making the short external tapers on these hubs is easy enough on the lathe, just set the compound slide to 1° using an angle gauge. But cutting matching internal tapers required special tools. I machined two tapered "D-bit" reamers from drill rod, then hardened and tempered them. Not having done this before, I was unsure how well they would cut, or how long they might survive cutting steel. Therefore I decided to make the hubs from aluminum. The reamers worked perfectly on aluminum. Then, to hold the tapered axle ends while bending the camber, I drilled then reamed the matching taper into a steel rod, my reamer still held its edge. So, maybe later I will redo the hubs in steel?
Image: outer hub tapered reamer and outer hub flanges
Image: reaming the taper into an outer hub flange. Flange is temporarily screwed to a piece of wood for holding it in the rotary table's vise.
Coming up: I start the woodworking on the wheel fellows and cut steel for the tires.
Greg
-- Edited by gjmontll on Tuesday 25th of August 2015 03:23:55 PM
Almost every little piece on this 1:8 scale model has been a challenge. For the past three months I've been working on the wooden wheels. They are about 6" diameter and 3/8" wide, made of oak and steel. I'm still working on them, but today reached a point where I could place a pair of spokes into a fellow, as shown in the below picture. (Note: the wheel's wooden rim is made of 7 separate segments, each is called a "fellow.")
To get to this point required making the 14 oak fellows. First I cut, milled, and sanded them to shape. Today I started routing rabbets into the fellows to hold the spoke shoes. Once I finish that task, they still need additional rabbets for the metal plates that tie them together, and I need to drill holes for the fasteners that secure the shoes and plates.
As tricky as the fellows were, the spokes have been even tougher. For the gun, I need 28 good spokes. I started by cutting out over 40 oak pieces, 2.75" x 0.5" x 0.360". A 3/16" diameter boss was turned on the fellow end. This is to engage into the spoke shoe. Then, each of the sides gets tapered, a total of six different angles gets cut on the long sides. As I prototyped the spokes and developed my process, I used up all my spare blanks and had to cut out another 24 blanks. I think this is going to leave me with a surplus. The spokes are now roughly shaped. Each one now need final tapering on the sides, then chamfering the diagonals.
Each spoke fastens to the fellow using a steel shoe. (I suppose the original gun used cast iron.) These were cut from 3/8"square key stock material, then milled and drilled. The shoe final dimensions are 0.377 wide, 0.365 high, and 0.360 deep. Each one required over 16 machining operations. They have a 0.250 slot to fit into the fellow rabbets and are drilled for #0 bolts. I'm waiting on the fasteners to arrive.
And I still need to make the steel tire, welding or brazing a hoop of 14 gauge steel to exactly the proper size is going to be another challenge, but I did talk with a wheelwright last week who gave me good ideas.
The image below shows one wheel's set of fellows held in place with a hose clamp. One fellow has been rabbeted for the spoke shoes and two spokes put in place. Across the top is my fellow rabbetting jig and some loose fellows. Along the left are a few spokes and shoes oriented to show their various aspects.
Now that I've almost got my technique ready for mass production, I wonder about making more wheels for a limber and caisson.
Question on painting? Your feedback welcome!
I am uncertain how I am going to finish the cannon. I hope to display it in the nearby Miniature Engineering Craftsmanship Museum where obviously the focus is on the "miniature engineering craftsmanship. So I don't want the paint to obscure the details, but on the other hand, this is intended to be as realistic a replica as I can achieve of my grandfather's First AEF Shot of WWI gun. That actual gun is in the museum at West Point, and is camouflage painted in multiple colors. The wheels look to be varnished or painted brown.(The pictures don't show that too well.) But the gun I visited at the Orange County Courthouse is just painted gray and black - the wooden wheel parts are all gray. Other photos seem to show the wheels included in the camouflage pattern or painted yellow-green. See links below.
See a discussion about the proper coloration: http://gmic.co.uk/topic/64702-the-first-american-shots-of-wwi-french-75mm-west-point-museum/
And for the other camo scheme: http://www.firstdivisionmuseum.org/museum/online/toward_the_front/argonne/artifacts/entry1.aspx
Seems my choices are roughly this:
1. leave it bare wood and bare metal (not good from a preservation standpoint)
2. camo paint and/or varnish, like the First Shot gun at West Point (my likely choice)
3. some other varnish paint combo. (?)
I'm curious. Was there some official fixed camo pattern and color scheme or was it left to the soldiers to tailor the camo to whatever their current environment dictated? Did they repaint them for the season?
Many of you here on Landships seem to be experts on finishing models, what can you recommend for paints as far as references, brands, and techniques? Before I start actual assembly of the wheels, I should put some sort of sealant on the wood, right? (Note: I should be able to disassemble and reassemble the wheels as needed.)
Well done, Greg! Am sure the museum will appreciate the finished product. As far as finish, you could always use a clear finish to show your outstanding work while protecting the material. Look forward to seiing it at the museum.
I had hoped to finish the wheel assemblies by New Year's Day. Didn't quite make that date, but now the woodworking is done. I'm not sure how much interest this forum has in the model engineering details (this is a 1:8 scale project), but here are a few photos of my efforts.
Assembly in progress. The metal and wood have been primer painted as I await photos of the actual gun from the West Point Museum to see the actual shades and shapes of camouflage. (I spoke to their Arms Curator before Christmas and another hobby-machinist.com member will act as my proxy photographer.) The hose clamp acts as a temporary tire. Fasteners are #0 for the spoke shoes and #2 on the hub. I ended up making my own nutdrivers for the #0 nut and bolts.
Milling the rim of the fellows for a final truing.
Wheels on axle, with 1/2" slices of 6" pipe that will become the tires. You see the positive camber since the axle ends bend downward. The rabbets, slots and holes at the fellow joints will be filled with splice plates and #0 flat head bolts, once the tires are on.
I had first planned to make the tires from strips of 14 gauge steel, but not being a blacksmith, I knew it would be very difficult to do an adequate job of bending and brazing/welding. As it turns out, 6" Schedule 40 steel pipe is almost perfect, just a shave on the OD and bore the inside radius by 0.148"
Terrific! Are you going to do the caisson next? As an aside, I've a model French 75mm, but don't know the scale. What is the diameter of the wheels in real life?
I thought about making the caisson and limber and have a few spare pieces of spoke and fellow left. But after five months on the wheels, I'm going to concentrate on the cannon. My primary hobby is metal machining, not woodworking and it will be a pleasure to get back to it. (Although every piece, metal or wood, has been a challenge in one or more aspects of design and/or creation!) It's hard enough making the cannon's engineering drawings from photos, old drawings, and a gun 90 miles away. Information and access to a real caisson and limber are less available. Detailed photos and drawings of these auxiliary units seem less adequate and I have no full-sized specimen for reference.
Yesterday I started on the steel tires; and a correction to yesterday's post, my "slices" of pipe are 0.625", not 1/2". The tires will only be about 0.310", this extra width in the raw material is to machine a bevel on the inside. This will act as a guide ramp to press fit the tires onto the wheels and then will be cut off. This technique was recommended by another member on the hobby-machinist.com forum, he said he'd spent 6 months figuring out how to make miniature steel tires.
When done with the wheels and tires, next I make the wheel "hub caps" and lynch pins. I only have vague ideas on what these actually look like and operate. Can anybody provide me with details or close-up photos on this? In particular, I'm unclear on whether the cap pushes onto the axle or threads onto it, how the lynch pin locks in place, and how the end play is adjusted as the hub bushings wear.
After that, with wheels securely connected to the axle, I will start on the carriage (specifically the trail) and then the pieces that connect the axle to the carriage.
It always makes a model very special if there is a family connection.
In so far as finishes are concerned, it might be a good idea to see where the artillery artificers were trained - the Congreve Rotunda in Woolwich had many examples of apprentices' work. They were all quite exquisite and were not painted, but left bare, with the metal parts made from steel and the rest wood or leather, where appropriate.
The problem with aluminium is that it will oxidise over time, giving a powdery whiteish appearance unless sealed.
Two things I have noticed are:
1 the ring parts are called "felloes" (singular "felloe"); and
2 your felloes do not (as yet?) appear to have dowels to join them together.
Your method of using a known measurement as a scale determinant is good but, unless the drawings are very large, small things like the bore can be a bit too small to use - always use the largest known sized piece for your scaling, especially wheels and overall barrel lengths.
If you want to make one for showing off in its camouflage scheme, why not make resin castings of the metal pieces? If you do, make sure that the moulding and casting materials don't interact with the metal - you might have to varnish them beforehand.
On the aluminium oxidation issue: I have already primed them and will topcoat them after I get the proper coloration information from the actual gun at the US Military Academy (West Point, NY) museum. I really should have used steel for this. The inside hub piece has a taper to fit the axle taper, and outside hub piece has a different taper to fit over the inside hub. Cutting an external taper on the lathe is easy. Cutting an internal one of these small diameters is not. To do it, I had to make my own custom tapered reamers from drill rod (aka silver steel) then heat treat them. I was unsure whether my home heat treating would be adequate to cut the steel, thus I choice aluminum.
I had never seen the term "felloe" until I started on this project. And I did see it spelled as "fellow". But after your comment, I checked several books and dictionaries. You are correct, I found no use of "fellow", the only alternative term was "felly."
My felloes will be joined to each other with steel "splice plates" (my term for them), with bolts running through the tires and felloes.
I agree, one should use the largest reference dimension available. I'm switching to some new CAD software (Autodesk Fusion 360) that should help in the process.
As I near the point to begin painting on some of the pieces (the wheels), I have been awaiting details on the proper colors and pattern of the "First Shot" gun. One of my fellow hobby-machinists connection, Tino, lives near the US Military Academy (West Point, NY), whose museum holds the actual gun. Last week, teamed with the museum's Arms Curator, he executed his photo reconnaissance mission on my behalf. (Tino and I frequent the hobby-machinist.com forum, where I am providing more details on the actual construction details of my model engineering effort.)
Here is a link to his Flickr archive, a "French 75" folder with 172 excellent photos. Almost all are of the actual gun. They do a great job on documenting the camouflage and will be very useful in my CAD design work for my 1:10 scale version. A scale has been magnetically clipped to the gun in several shops to provide a dimensional reference. They were prepared to remove the leather covers from the muzzle and breech, but they were secured with safety wires. In addition to the French 75 itself, some photos show a 1:7 scale model 75, and of a few other armament items. Image IMG_4654 shows the soldiers posed around the gun. Is that officer standing alongside the barrel my grandfather? I don't think so, but it is possible.
Note: to set up this visit, I spoke with the Arms Curator, Les Jensen. He said the French guns came out of the factory with the camouflage. I'd assumed it applied by the troops in the field, appropriate to the environment. Apparently not. I wonder how much repainting the gun has had over the past century, both in the field and in the museum.
I did already have my own muzzle and breech photos from the gun at the Camp Roberts Museum and from the Old Orange County Courthouse. However neither of these guns were 100%, both missing at least a few parts from the breech area.
