Gallery, Projects and General > The Design Shop
Bevel Gear Mill
RussellT:
I think Lew has got the key point here.
The link that Matt posted in reply number 25 shows how to make an involute form by rotating the blank and the rack profile cutter generates the tooth form.
If the shaper tool moves along a line that intersects the point of the cone of your gears then it will generate an involute form - and because the cone is larger at one end than the other the teeth (and gaps) will be larger at one end than the other.
From what you have said about your use for the gears I am wondering whether you are seeking too much accuracy. I have only made one bevel gear (a replacement for a hand drill) and after lots of measuring and thinking I realised that the gears were not an ideal form and had just been cut with a single cutter and cut deeper at the wide end.
On the other hand I generally aim to make things as accurately as I can - it's good practice for when I need to.
Russell
vtsteam:
Hi Russell, not sure what your point is here. There have been no disagreements with any points discussed so far, and I've never said I wanted to produce a perfect bevel gear.
The shaper/rack form method produces faceted teeth, and the fineness of the facets depends on your patience and the degree of carriage movement you chose between strokes. Also, if you want a true tapered involute shape on a bevel gear, it can properly only cut on one edge at a time. The same result can be had with a milling cutter, more quickly with the same provisos.
This is just a general discussion about bevel gear cutting so far with no conclusions for a specific device.
With regard to cutting along the cone, that was in post #1: "The main topic of interest would be wedge shape of the teeth. These converge on some imaginary conical center. If the cutter was thinner than the inner space between the teeth it could cut each tooth with two passes along a radial of that cone."
vtsteam:
I did a quick search for high temp silicone rubber compounds usable for zinc casting, and only found mention of their use in spin casting. More commonly available high temp rubber compounds are used at lower temps with bismuth, lead, and pewter.
The spin casting types for zinc seem to be supplied mainly as prepared disks for proprietary spin casting machines, and require vulcanizing before use. I'm still looking into it, but may not be easily possible to do simple rubber mold casting of zinc in a home shop setup. Zamak 2 seems a preferred alloy because of slower solidification.
vtsteam:
If commercial bevel gears (like the ones I ordered) really are accurately conical without undercuts, it should actually be possible to mold them in a conventional plaster mold. Though getting them to release might be a little tricky. I already have some bevel gears of the right size on a coiple of steam engines. I might give that a try. :dremel:
mattinker:
Two piece plaster moulds would be quit easy to make! Grease as a release agent.
Cheers, Matthew
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