Gallery, Projects and General > The Design Shop
Bevel Gear Mill
timby:
--- Quote from: vtsteam on August 27, 2020, 01:50:44 PM ---A single tooth cutter can not be designed to cut a good involute bevel tooth on both edges, no matter how it and/or the work is rotated and translated. And no matter whether the tooth is involute profiled or rack profiled.
--- End quote ---
I have seen a bevel gear cutter that had 2 single tooth cutters on 2 shaper type heads set on opposing angles and each cutting on 1 side.
I did not note how the indexing was achieved.
vtsteam:
--- Quote from: Lew_Merrick_PE on August 27, 2020, 11:30:53 PM ---I guess what has been bothering me about this thread is that, in the terminology I learned as an apprentice, a Bevel Geat is a "cone shaped gear" designed to transmit torque around a "corner." Thus, the "focal point of the cone is the pivot about which the involute tapers to allow the "corner" to be "turned." If my gear set "tapers" by (say) .75° from the "base" of the cone to the "point" of the cone, then the unit must "pivot" .375° to either side of the cone's point to successfully generate such a "gear." I was taught to locate said cone's point concentric with a "pivot bushing" about which the "mount" could pivot and use "precision tapers" to control said "pivot." Does this make sense? -- Lew
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Yes, that's what I was thinking about. Most of the methods mentioned so far only approximate the shape you describe, because they cut as a series of passes, and therefore produce facets rather than smooth shapes. And those that use profiled involute cutters also only approximate the true cone tapered involute shape in form. The rack style if given an infinite number of passes would give a true cone tapered involute profile. This is analogous to how the two profiling methods work on a spur gear.
Since I want to make something that is simple in design and works relatively quickly, but only cuts one gear size and type -- that adds an oddball wrinkle to the question of which method to use and how to make a device that does it. I'm not shooting for how to make the perfect bevel gear, necessarily, though I'll take it if simple and speedy enough!
Way back in the beginning of this (to me) enjoyable bunch of imaginings about bevel gear shaping, Andrew suggested doing a 3D printed plastic CNC bevel gear, then lost wax (or PLA) investment casting it. Besides the fact that I don't do 3D printing, the time factor for producing bevel gears by that method would be very long. I also don't imagine the finish quality would be very good -- though things have probably advanced, I'm sure in the home shop level 3D world, so I can't say for sure. Anyway, I don't want to do that.
If casting was considered, I suppose I could however take existing well-cut bevel gears as patterns, and use a high temperature rubber mold to duplicate them in zinc alloy -- which I believe has a low enough melting temp, and good enough toughness for my purposes. After all my Craftsman lathe has zinc alloy change wheels and it's over 50 years old. I'm not sure how casting in a rubber compound with zinc would go, or what the finish quality would be, I've never tried it, but it's intriguing.
However this would also belie the title of this thread, which specifically says "mill" meaning cut. And I also boldly mentioned "steel" not zinc. What do you guys think? Should I hem and haw and try to wiggle my way out of what I said I wanted to do, and send for some hitherto untried rubber gunk, or should I continue to try to do what I said and make something weird and of little use to anyone else, with sharp teeth?
awemawson:
I suppose for best accuracy and finish you want a process that generates the true involute form like a hob does, and although I'm clear in my mind how that works for a spur gear, for the life of me I can't see how you would do it for a bevel gear.
All sorts of odd shapes can be hobbed but I'm not aware of a hobbed item the isn't parallel sided :scratch:
vtsteam:
That's pretty cool timby. :beer:
vtsteam:
--- Quote from: awemawson on August 28, 2020, 10:18:54 AM ---I suppose for best accuracy and finish you want a process that generates the true involute form like a hob does, and although I'm clear in my mind how that works for a spur gear, for the life of me I can't see how you would do it for a bevel gear.
All sorts of odd shapes can be hobbed but I'm not aware of a hobbed item the isn't parallel sided :scratch:
--- End quote ---
Andrew, I rashly stated earlier that a hob couldn't work because the teeth of a bevel gear converge.
But that's maybe not true if the hob only cut on one side of a tooth. Have to think about that for a bit.
(btw. all this stuff I'm thinking about has no doubt already been worked through long before, and resolved. I just like visualizing my way through things myself. This is what madmodding means to me -- well at least the mad part! :hammer: )
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