You’re right; I think we probably mentioned the lathe thing as a workable general principle, rather than a specific suggestion for this case.
While we’re here (I hope nobody minds me hijacking this thread, but the question is very similar to the OP), suppose I wanted to make a number of wooden cogs/gears in, let’s say three different sizes - ~2, ~4 and ~6 inch diameters - what’s the best method of cutting the teeth? (I suppose I also need to do a bit of calculation on the precise dimensions to make sure the teeth are compatible between the three sizes of gear.
[IANAWoodworking Expert] Just how accurate do you want the gear teeth to be? Evenly spaced, involute profile, the whole works? Or Flinstone-style square-tooth gears? If the former, I’d just buy 'em instead of trying to make 'em. Although I suppose you could physically construct the gear tooth curves and cut 'em out with a scroll saw. [/IANAWWE]
Probably the simplest way to do this is going to involve a router and some kind of jig wih a rotating axis (like the centers of a lathe with a lot of other rigging). You can then traverse the router parallel to the gear’s rotational axis once to cut each valley between the teeth. You will have to index and rotate the gear properly to assure the right spacing of teeth around the circumference, and you will have to get very accurate depth of cut as well. You may also need a special router bit to get the right tooth shape.
I warn you that this is more difficult than the OP by at least a couple orders of magnitude.
I forgot to mention material difficulties: it’s tough to get a thin 6" disc dimensionally stable enough to work as a gear for very long. Not impossible, but you’d find it difficult.
Definitely nothing more complex than square-toothed cogs; stability would be a problem, but the project I have in mind would be mounted on a backboard and faced with perspex; the whole assembly would be three cog-thicknesses deep, so all of the spindles could be packed out with spacers to keep everything in register.
Choice of material is a tricky one; plywood would offer stability and strength, but I think the exposed endgrain on the teeth would lead to serious problems with wear; some sort of dense, firm hardwood might resist wear, but have a tendency to warp; MDF would work, but it isn’t wood.
MDF would not handle the sideways force on the wheel for very long. Are the wheels supposed to look nice? I have not done something like this, but the first solution that pops to my mind would be to cut round plywood circles the diameter of the desired wheel excluding the cogs. Then using a router table with a modified finger joint jig cut out 1/4" deep slots “however” wide and the same “however” apart. Then cut small hardwood blocks as thick as the plywood, by “however” wide by 1/4" plus the length of cog desired. This gives you the stability of plywood and the durability of hardwood.
It won’t be too pretty, but you brought up the plywood first Just be sure to use Baltic Birch, but I am sure you already knew that.
Wood gears are tough. The solutions I’ve seen (usually in the context of wooden clocks) usually involve lathes with indexed heads (e.g. you can reliably rotate the chuck by precisely X degrees) and custom made router bits to cut the teeth where the router slides on a jig parallel to the axis of the gear. It was immediately after reading the article on how to do this that I decided I was never going to be making a wooden clock.
I do assume that if you needed multiple identical gears that you could get away with machining a geared cylinder and cutting off slices as needed.
A lathe wouldn’t have worked for the OP’s original purpose as he needed holes drilled off-center – something a lathe is noted for not doing well.
The wooden gears I’cve seen have all been huge ones in wind/water mills, but I’m looking to make something a little smaller (more on that in a moment).
Machining a cylinder and cutting slices would mean that all the gear teeth had short (radial) grain - this would make them weak.
What I want to do is to make a machine that is entirely contained in a perspex-fronted case; when a handle is turned, marbles or ball bearings will be conveyed to and fro by a number of different mechanisms, such as a lifting chain, a row of walking cams etc. I might actually try making it entirely out of clear acrylic instead.
Fine Wood working had an article on making gears for a wooden clock, and it was replublished in “Four easy projects and 17 ones that no human being can do”*. Briefly, and as much as I remember, the gears were glued up from 3 pieces of hardwood, to get the grain in the correct direction (each piece is a triangle, obviosly, with the 3rd side curved). The teeth could be cut with either a chisel sharpened normally, then honed with waterstone, followed spiderwebs then the first light of the dawning sun**. Alternately, a scroll saw with a round blade works pretty well, although it will require practice.
Oh, I found the article, but just because it took someone years to work out how it was done, they expect us to pay for it. The link seems to be cookie related; go to www.finewoodworking.com, search for “gears”, and check the “Making wooden clocks” article out, but note they are asking some indeterminate amount of money for it. A milling machine and lathe are mentioned in the article summary.
This may not actually be the real title.
** or use your own way; just make sure it’s sharp.
Just be sure to use Baltic Birch, but I am sure you already knew that.