by Dean Beeman
I'm going to build the smallest gears first. These won't be needed until much later in the build, but this is a good introduction to the difficulty you're facing in getting every spoke and gear exactly where Da Vinci's concept placed them.
We've been through the wonders of the human eye. Since drill bits will wander based on the grain of the wood, and even the most careful center-punch will be slightly off-center, my advice is to experiment with this set of gears until they are nearly-perfect.
I've used spray contact cement to create a sandwich of 1/32nd mahogany and aircraft plywood., To keep the dried mahogany from shedding I've soaked it with a heavy coat of spray lacquer. (Any thin shellac should work.)
Once the piece dried, I used the leather punch to punch out 8-wheel blanks. (One of those blanks is underneath the drilling template.) You only need 4 of these, but the tolerances are such that any drilling error will ruin a blank, and I'm going to choose the best set of 4 from the drilled collection.
If you cut out some outer portion of the tiny wheel from the schematic and school-glue it to an acrylic (or other clear) scrap, you have the pattern for the first drilling template. (In my opinion it's important to see through the template into the blank.)
Once you center-punch and drill (1/32nd bit) the template holes, place your template on a blank (as in the photo) and look at the pattern. If it isn't more-or-less perfect you aren't ready to move on.
Drill a set of wheels and insert short lengths of 1/32nd brass rod into the holes. Once the cage gear is populated, insert a longer (1/16th) rod into the center hole and slowly rotate the gear. Any non-uniform spacing will be obvious (and fatal). A finished set of gears is above the small template.
I trimmed the rods with the nail clipper, sanded them smooth to the wheel and applied CA glue dots to each spoke. The glue should wick into the joint.
Once that set of gears is ready it's time to move on to the larger, but no-less precise larger gears.
The template for the larger gears is not that complicated, but at this scale must be just as precise. I constructed mine by solvent-welding a 1/16 x ¾ x 2 ½" acrylic scrap to a 1 ½" x 2 ½" base. The scrap is on-edge at a more-or-less perfect right angle.
Placing an identical scrap to the first, I drilled 1/32nd register holes through both scraps. This results in a template with a movable face. After placing rods in those holes, I sanded the outside edges flat and square to each other. This results in an outer register edge that is fairly precise.
Using the (yellow) circle cutter in the photo I scored a couple of blanks. I then rough-cut the circles, drilled 1/32nd centers, bolted the wheels together using the machine bolt, and then turned both wheels. Either a rotary tool or a drill will work as a lathe.
The larger template is used for both larger wheels. In the photo, I have placed pins through the holes that I drilled to get uniform tooth spacing. The bottom (green) pin is inserted through a hole that corresponds to the spacing of the outer teeth, and the side (black) pin registers to the inner teeth.
In both cases you drill a hole using the template, rotate the wheel, place a rod through the hole you just drilled, rest that rod on the template face and drill another hole.
A blank wheel and a drilled wheel (with the inner teeth trimmed) are below the template.
For both large wheels, I have trimmed the teeth to 1/8".
After the drive wheel was finished I mounted it on the shorter pedestals using the pad eyes and a short length of 1/16th rod. To keep the outer teeth from catching the pedestal I cut and placed a tubing sleeve (spacer) over that rod.
I haven't provided dimensions for that gear because there are none. My overall length is 1".
The center holes for the intermediate gear axle (1/16th) should line up with the drive gear axle. Build those wheels, and use lengths of tubing to space them in the center and at the posts.
At this point the drive gear should freely drive both intermediate gears.
To create a little slop in the final (cage gear) assembly I used 1/32nd rod inserted through 1/16th holes. The slight-of-hand that I mentioned is one length of tubing that keeps these gears centered and another set that extends out to the paddles.
Once the cage gear axle and gears are placed through the pad eyes at the top of the posts all three gears should rotate freely.
The paddles can be solid, but I built mine using 1/16th mahogany for the shafts, 1/32nd mahogany for the blades, and 1/16th basswood for the hub. The holes through the hub are 1/32nd, to accept the axle.
The pedals can be constructed using any 1/16th wood. I constructed mine using the scrap of rosewood.
After everything worked I capped the drive wheel with chestnut and the intermediate wheels with mahogany.
A scrap of thin leather is fitted into the slots in the pedals. Da Vinci chose not to show hinges, so I haven't added them.
Note that the only items that are glued are the gear teeth and spokes. One of the important elements of a machine is the ability to take it apart, replace a part, reassemble it and put it back into service.
So, my version of Da Vinci's machine can be completely disassembled and rebuilt.
I plan to mount the model in a case alongside a photographic reproduction of the original sketch. (Next photo.)
Now may be the time to address the question of whether the machine works.
Da Vinci's machine, as drawn, would have worked perfectly. Mine does too.
The second and less-important question is whether either machine could power a boat. If you want to ride in a boat that spins in a perfect circle I have a machine that works perfectly.
Here is that model and that image:
If you want your boat to sail in a straight line, Da Vinci's dilemma is now yours and mine.