Author Topic: Bevel Gear Mill  (Read 9930 times)

Offline vtsteam

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Bevel Gear Mill
« on: August 22, 2020, 09:22:33 AM »
I have always admired (and wanted to build) a complex dedicated gear cutter I had found in an old Model Engineer. I don't remember the exact name, without researching through my boxed issues, but it was a series of articles.

But thinking about that, now, the real reason I wanted to build a gear cutter in the first place was that the cost of bevel gears was high, and I wanted to build Westinghouse style steam engines, which generally require them for driving the steam valve. Good quality bevel gears are very expensive thee days. It was one of those times when you get seduced by the idea of building a major tool to do a different project you are actually interested in.

I was thinking this morning about how we tend to generalize and build multi-purpose tools, and ignore the possibility of building a much simpler single purpose machine tool. If I were pursuing it In the case above, it would be a simple bevel gear cutter for gears of at most 2" (50mm) in diameter.

It's true I could probably make a fixture for my mill drill that would do the job with lots of fiddling, but the idea of a single purpose powered tool that just cuts bevel gears somehow appeals more. I also don't have a rotary table. Need a bevel gear? Pull out the bevel gear tool and cut one -- not lots of reconfiguring the mill drill table with fixtures, locating cutters, setting up heights, depths positions, etc. And then when it's over taking it apart,

I dunno, maybe it doesn't make sense to anyone else, but I just like the idea of having something that, out of the box, does a straightforward job. Because it doesn't have to do anything else, it can be simple and compact, with a minimum of settings.

Small bevel gears generally don't have wildly different tooth numbers, so an indexing plate with a few sets of holes will do for that. They generally have a very limited set of bevel and pressure angles. You could get away with one each.

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.

Ideally a controllable speed small motor with direct drive to the cutter would be simplest. Cutter axis would probably be horizontal, and gear axis vertical. But it could be the other way around if that worked out better.

This is just noodling an idea. I'm not ready to build one yet because my shop needs major work to become useful again. But I like the idea of single purpose machine tools because they can be built simply, cheaply and be compact. They don't have to accommodate large objects, or perform flexible and complex tasks like a lathe or conventional mill does.

How would you build a mechanical standalone bevel gear cutter of the size and range I'm talking about here? Ideas and sketches are welcome.

Yup, I know I could cut gears on my lathe or mill with fixtures, or program a CNC mill to do the job. But that's not the project I'm interested in. I'd like to know what's the simplest most compact single purpose machine we could come up with, and especially if it could use scrap material or existing small motors.

Any takers for this design challenge?  :dremel:  :smart: :beer:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Bevel Gear Mill
« Reply #1 on: August 22, 2020, 09:46:25 AM »
Steve,

- you've done casting

- I suspect you've done 3D printing

Print your bevel gears in PLA and do 'lost PLA' casting - the PLA burns out very much like wax - bronze cast your bevel gears and any other small parts for the engines

BTW good to have you back generating ideas !
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #2 on: August 22, 2020, 02:39:16 PM »
Thanks Andrew. Sorry, nope never done 3D printing and likely never will. It has no appeal for me.

Afraid I'm also not talking about casting gears here, but soliciting design ideas for a highly simplified small dedicated bevel gear cutting machine. Any suggestions along those lines?  :scratch:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Joules

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Re: Bevel Gear Mill
« Reply #3 on: August 22, 2020, 03:22:38 PM »
Have you seen the Keith Rucker video.




Generally you need three passes.
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Offline awemawson

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Re: Bevel Gear Mill
« Reply #4 on: August 22, 2020, 03:25:35 PM »
Thanks Andrew. Sorry, nope never done 3D printing and likely never will. It has no appeal for me.



I thought the same when people were making Star Wars characters and not much else !

But I must say it's been an amazing contributor to the workshop making all sorts of little jigs and fixtures - most recent thing being a replacement table insert for my Band Saw. It would have been a pain to machine from solid but quickly drawn up (Fusion 360) and printed while I was doing something else!

I expect that the simplest bevel gear maker is probably based on a very small shaper mechanism - even hand operated. Relatively easy to tilt the axis of the tool as required. I seem to remember a design in Model Engineer based on a stretched taut steel tape that rotated the blank as the tool traversed.
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #5 on: August 22, 2020, 04:08:47 PM »
Thanks Joules, that's a great video. I do have several books on gear cutting, and also Machinery's Handbook, but good to see a bevel gear cut on video.  :thumbup:

I do have a horizontal mill, and could probably follow suit, but again this project would be a simplified standalone cutter. For my purposes of small Westinghouse type engines 2" gear diameter is actually excessive, and I think I'll modify that one capacity spec to 1" dia. max. That will make it easier.  :coffee:

Andrew, I'm not down on 3D printers or what people use them for, just not interested, personally. Mini hand operated gear shaper is possible, and a good call, with some definite appeal, but I had started thinking about a mill style with a small gear motor. I'm not sure what the power requirements are, or prices and availability. Could be prohibitive.  :coffee:

But anyway, as a start I'm rough guessing 400 RPM working speed for say a 1" dia cutter would handle mild steel or cast iron gears, or softer. There are a bunch of new 12-24VDC gear motors in the $20 range on Ebay, roughly 7 to 8 watts. I don't know if such low power could cut, and then there's the question of bearings. probably can't just put a cutter on the geared output shaft. So we'd need a supported spindle.  :loco:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #6 on: August 22, 2020, 04:14:56 PM »
Also part of the spec is I'd just be cutting 1:1 ratio gears for the engines. This probably means some of the machine setup angles can be built in rather than needing to be adjustable.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Bevel Gear Mill
« Reply #7 on: August 22, 2020, 04:22:12 PM »
If the material being cut is brass or cast iron I expect that the power requirements are minimal.

The shaper has the advantage of much simpler tooling. I've only once cut a bevel gear 'for real' rather than playing about - (it was the table feed for a Richmond universal mill) - the thing I got tangled up with was the offsetting of the cut to create the varied clearance at different diameters - (I was using a standard involute cutter and a table of offsets).

It worked OK but I'd not like to make a regular habit of making bevel gears that way  :bugeye:
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #8 on: August 22, 2020, 04:28:54 PM »
It might make sense to think carefully about the most LIKELY gear diameter and tooth number I'd need, and really focus on just doing that one job. That would allow a single indexing row of holes, a single cutter, some stops to do the change of angle and the set-over for doing the second and third cuts.

Or, maybe have separate modules for individual gear sizes that are comprised of a cutter and a set of stops that could interchange into the basic machine. I think being able to make 4 different standard bevel gears would fit my needs for a LOT of different size engines. I really don't need to make an infinite variety of bevel gears.

Really, starting with just one size would be fine.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #9 on: August 22, 2020, 04:29:56 PM »
Yes Andrew, your shaper idea is wearing away at my mill determinations. I may give in, after thinking rotary for a bit more.

But wouldn't we still have to offset and rotate for 3 cuts?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #10 on: August 22, 2020, 04:38:30 PM »
Okay, getting down to brass tacks, let's say we just want to cut  1" dia 16 tooth bevel gears.

(I have a good size model engine that has a set of Boston bevel gears that size. Seems like a good one to settle on.)
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Bevel Gear Mill
« Reply #11 on: August 22, 2020, 04:42:28 PM »
IIRC Machinery's Handbook has the table of offsets
Andrew Mawson
East Sussex

Offline Joules

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Re: Bevel Gear Mill
« Reply #12 on: August 22, 2020, 05:01:18 PM »
i would start by looking at the range of gears you want, are they all 45 degree bevel.  You can use a swivel bed plate for offsetting the cutters, right and left hand cutter profiles needed, assuming they are shaper cut.  Different sizes will need different focal points, will this be on an adjustable shaft with spacers, or dowel pins in the swivel plate.  The swivel plate can accommodate a range of gears with numbered peg holes for setup, that should speed things.  Using an index plate for the teeth one circle for each cut, so three circles per plate, left, centre and right.

LOL  I would 3D print this as a mock up to test the ideas before committing to metal.
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #13 on: August 22, 2020, 05:38:08 PM »
Yup all 45 degree bevel.

re. indexing. Simpler would be one circle per tooth number on the index plate and then have offset peg holes for the three cuts, like a vernier collet spinner.

LOL, much rather work in metal directly by brain and eye for something this simple. Different folks, different strokes. :beer:

Andrew, you are right. Hand shaper appeals mightily vs motors, spindles, electric cords. Let's get really basic! Thanks for that suggestion, it's perfect.  :beer:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Joules

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Re: Bevel Gear Mill
« Reply #14 on: August 22, 2020, 05:45:03 PM »
Your offset peg holes might not take into account the different angles per tooth count, but an offset peg bar per gear might do the job.   I was just thinking one disc per gear, and hole circle per cutter making it simple for anyone to operate, not just yourself.

i should have added, having offsetting holes might also lead to selecting the wrong one if they carry a few gears offsets.
Honour your mentors, and pay it forward.

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #15 on: August 22, 2020, 05:58:43 PM »
Okay, getting down to brass tacks, let's say we just want to cut  1" dia 16 tooth bevel gears.

Jules, 3 offset peg holes will work fine for the above.

If I actually wanted to cut 4 total tooth types for 4 specific gears I'd just have 12 peg holes, yes? They don't have to be in the same area of the base. Simple.  :thumbup:

But let's stick, for now to the design for just one gear type, above.  :whip:  :beer:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Joules

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Re: Bevel Gear Mill
« Reply #16 on: August 22, 2020, 06:07:17 PM »
Ok, got you are basing it on one gear.   You have me thinking about my thread milling setup being used on the lathe for bevel gear cutting now.
Honour your mentors, and pay it forward.

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #17 on: August 22, 2020, 06:10:07 PM »
Yes, that kind of thing happens to me,too!

Also your bar idea is nice for a more versatile gear cutter. I'm just limiting myself on purpose.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #18 on: August 22, 2020, 06:22:56 PM »
Anybody got links to dwgs of simple small hand shapers for ideas?

I do have Gingery's shaper book (power) -- practically memorized, and well, actually I have a partially assembled Atlas shaper in the shed. But I'd like to see what's out there that is simple.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Joules

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Re: Bevel Gear Mill
« Reply #19 on: August 22, 2020, 06:28:31 PM »
Do you have an old tailstock you can convert to lever operation.
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #20 on: August 22, 2020, 06:36:26 PM »
No, but I have patterns for casting one.

Found this on the Lathes.co.uk site:





Good to see at its most basic stationary and adjustable form.

I'll probably fabricate something of steel, though. and use clamps to attach to bench, instead of cast mass.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Joules

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Re: Bevel Gear Mill
« Reply #21 on: August 22, 2020, 06:41:57 PM »
Another thought is to design and build this to fit an arbour press.  If anyone else is playing along...

There was a set of Cowells castings on ME, I was tempted at the price, but having the Elliot 10M I doubt I would build a hand operated machine, let alone find space for it.

 :lol:
Honour your mentors, and pay it forward.

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #22 on: August 22, 2020, 06:56:52 PM »
The slides would have to be precise fitting -- they are basically ways in a shaper.

Thinking about this carefully, we only need about 3/4" of movement for the clapper slide. so the ways will be short. That means it's easier to achieve stiffness lengthwise. Could be double round bar stock ways.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #23 on: August 23, 2020, 01:23:10 PM »
New day, woke up with some thoughts:

Hand shaper based: Will require vertical travel because a tooth space can't be cut in a single pass. Therefore we need both vertical and horizontal slides, complicating things.

Horizontal mill based: Could get away without a vertical slide with a multi-tooth cutter, cutting a tooth in a single pass. ..... and even possibly with a single tooth fly cutter with low feed rate. Does require complications of a motor and a spindle. Does require horizontal adjustment and rotary indexing.

Attachment for lathe: This defeats the original intention of a standalone machine, but is probably the simplest and most compact. I see it as just a simple angled indexing fixture, and a fly cutter or boring bar between centers. I have those. The only thing I'd have to make is the indexing fixture, and then grind a cutter.

And an update of specs on a standard gear of approximately the one I proposed:

1.5 modulus 15 tooth miter (90 degree, equal size) - I guess 20 degree pressure angle vs 14.5?

btw. this size is available on Ebay from China at pretty reasonable cost, but that defeats the pleasure of solving the problems of making them, and making a tool to do it. I did order a pair of gears for only ~$9 incl. shipping, just to see what they look like -- but they might take a month or so to get here.

Also, good reference for bevel gear calcs, in Section 4.4 :

https://khkgears.net/new/gear_knowledge/gear_technical_reference/calculation_gear_dimensions.html

« Last Edit: August 23, 2020, 01:48:56 PM by vtsteam »
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Bevel Gear Mill
« Reply #24 on: August 23, 2020, 01:28:55 PM »
Boil them when they arrive  :bugeye:
Andrew Mawson
East Sussex

Offline mattinker

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Re: Bevel Gear Mill
« Reply #25 on: August 23, 2020, 01:38:11 PM »

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #26 on: August 23, 2020, 02:01:34 PM »
Nope Matt, I haven't. Very interesting, and that must be the Model Engineer/metal tape reference made earlier. I wonder if the same idea could be applied to a fly cutter on a horizontal mill (or on a lathe with boring table)?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline mattinker

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Re: Bevel Gear Mill
« Reply #27 on: August 23, 2020, 02:15:46 PM »
 The shaper is easier than a mill because of the cut direction in relation to the table travel! Have a look at this video!


Offline vtsteam

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Re: Bevel Gear Mill
« Reply #28 on: August 23, 2020, 02:20:54 PM »
Yes, but we'd have to make the shaper, and do that with a vertical slide.

A horizontal mill without vertical feed is easier to make.

And a boring bar between centers on a lathe (with a boring table) is simpler even than that.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline djc

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Re: Bevel Gear Mill
« Reply #29 on: August 23, 2020, 03:03:48 PM »
...I wonder if the same idea could be applied to a fly cutter on a horizontal mill (or on a lathe with boring table)?

Yes it can. It is just a means of getting co-ordinated linear and rotational motion. It is no different in concept to using gears from the mill leadscrew to drive a dividing head for helical milling. Does the same thing without the gears.

As to the machine, have a good sniff around the internet archive for gear-cutting books. There are many old ones now online and being in US, you have better access to Google books than we do.

The classic bevel gear people are Gleason and Bilgram. You can find all their patents online and you can probably find operation manuals for some actual machines at vintagemachinery.org .

You can get some good leads if you put 'bevel gear planer' and 'bevel gear shaper' into Google and look at images. E.g.

https://www.homemodelenginemachinist.com/threads/bilgram-bevel-gear-generator.9042/
https://www.practicalmachinist.com/vb/antique-machinery-and-history/bilgram-bevel-gear-attachment-342628/

See also:

http://vintagemachinery.org/mfgindex/detail.aspx?id=2969&tab=7 (mentions Woodbury's  book - well worth reading)

http://blacksmithandmachineshop.com/a-My-Foot-Hand-treadle-powered-Machines-in-My-Shop-Collection.html (Brown & Sharpe #13H extract from American Machinist)

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #30 on: August 23, 2020, 03:55:59 PM »
Thanks djc, I have lots of gear cutting reference books, but appreciate the suggestions. Thanks definitely for confirming that a horizontal mill can be rigged the same way.  :beer:

The main disadvantage I see to that method is it takes probably a minimum of five passes to cut a decent shaped tooth, and probably seven would be better. If 7, that's 210 passes for a pair of 15 tooth bevel gears.

In addition, on a lathe, each pass would take an adjustment of the carriage, so, 210 adjustments as well. (A shaper with racheting automatic feed would be less tedious.)

With the profiled cutter method on the lathe you would take 90 passes for the same pair. and you would only make 6 carriage adjustments and 6 index adjustments.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #31 on: August 23, 2020, 04:01:08 PM »
hmmm, since I would normally want to make pairs, anyway, would there be a way of cutting two gears at one pass? Might be tricky with two indexing wheels, and getting the gear blanks both exactly positioned in height. But maybe one indexing wheel geared 1:1 to a second arbor.....  :loco:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline mattinker

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Re: Bevel Gear Mill
« Reply #32 on: August 23, 2020, 05:21:10 PM »
Steve,

I think that it is interesting to see the action of the shaper gear set up as it reproduces a rack cutting tool. I understand that your looking for a "simple" way around this, replacing the shaper ram with a flycutter and a reciprocating carriage which traverses to allow the the blank to rotate is possible. It's the involute gear that results from a "rack" profile cutter is the "magic" bit!

Cheers, Matthew

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #33 on: August 23, 2020, 06:36:47 PM »
Yes I agree Matt, I really like that part a lot.  :med:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vintageandclassicrepairs

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Re: Bevel Gear Mill
« Reply #34 on: August 24, 2020, 03:18:31 PM »
Hi All,
I saw this book on ebay and thought someone here could be interested in Bevel gear theory ?
https://www.ebay.co.uk/itm/GLEASON-12-INCH-STRAIGHT-BEVEL-GEAR-GENERATOR-MANUAL-1941/264813653248

John

Offline awemawson

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Re: Bevel Gear Mill
« Reply #35 on: August 24, 2020, 03:46:18 PM »
I always fancied a 'Sunderland Gear Planer' but I'd have to reinforce the foundations and widen the farm gate  :clap:

Andrew Mawson
East Sussex

Offline engjas

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Re: Bevel Gear Mill
« Reply #36 on: August 26, 2020, 02:31:55 PM »
Hello
Have a look for articles by J. S. Eley on "Constructing a Gear cutting Machine" in Volume 100 of Model Engineer 1949. Long time ago yes but the machine he described was simple, bench top and had a bevel gear cutting facilities. The articles might stir your thoughts. I don't have access to my copies at present but you may find some closer to you.

Good luck on your journey.
John

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #37 on: August 26, 2020, 02:58:23 PM »
For me Andrew it was always building a Tom Jacobs gear hobbing machine which appeared in ME, and in modified form is still available as a set of castings from College Engineering. But that is a BIG project, and I still haven't even finished my lathe project (this year, for sure!)

Wow engias, I missed that one in ME. That's great, I will have to read the whole series -- as mentioned the Jacobs hobber was always a project I had in mind.

I keep waking up at about 4:30 AM by my mind already trying to solve bevel gear cutting problems and geometry. I'm thinking along the lines of Matt's suggestion of an acme/rack shaped cutter, but this time a mill type pivoting around a blank, and cutting a very close-to-true bevel gear involute. And then complicating that by cutting a pair of gears at once. I think it can be done, and I'm close to visualizing what that would look like. But I need a rest between noodling sessions to get it.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #38 on: August 27, 2020, 01:50:44 PM »
My understanding, now:

A rack or single tooth acme shaped cutter on a shaper can cut an ordinary spur gear to an involute profile by rotating the work on its shaft axis and faceting the tooth. It will always be a faceted tooth -- the more strokes per tooth, the more facets, and the finer it can approximate a smooth involute tooth form. This is illustrated by the rig that Matt linked.

A horizontal mill cutter of the rack form can do the same thing faster for the same number of facets, assuming it has more than one cutting tooth. Or cut more facets in the same amount of time, for a finer approximation of an involute tooth form.

In general, the rack shape is easier to form if making a cutter from scratch than a involute profiled cutter. And one rack style cutter serves for all gear tooth numbers, while an involute profiled cutter is suitable for only a range of gear teeth numbers and the actual tooth form cut is approximate.

A hob suitably geared to the work arbor and placed oblique to the work can be arranged to produce an un-faceted (smooth) involute profile because it acts like a continuously variable cutter. J Radford once did a lathe attachment that performed this way. As I visualize it, the tooth won't be completely uniform across the gear, but the profile will be involute at any particular cross section.

Moving on to bevel gears, a hob is not possible because the gear teeth converge.

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.

It can be designed to be narrower than a bevel gear's tooth, so that it cuts on only one edge, until rotated and translated to cut on the other edge after the prior pass. This is the principle of specialized involute profiled bevel gear cutters. As illustrated by the video Joules linked to earlier.

These work by first clearing the center space of a tooth cut, then they are rotated and translated to widen and shape that same space on first one side, then the other side, yielding 3 passes per tooth cut. Being involute profied cutters, they also only work with a small range of gear teeth numbers so must be available in sets.

The final possibility, and an interesting one for a home workshop bevel gear cutter, is using a rack form tool either in a shaper or mill. A multi toothed mill has the advantage, as usual, of speed, as this method will also create faceted teeth, and the more facets the better the profile, but the longer it takes to complete a tooth.

If I simplify the machine concept, just for visualization's sake, to a fly cutter of rack shape, I can imagine having a horizontal mill spindle which can be positioned around the vertically oriented gear tooth being cut, with the cutter arranged to spin tangential to the bevel gear's tooth cone. And to cut along that axis. It would have to be narrower than the tooth space. As before it would cut only one facet on one tooth face at a time. Multiple passes per tooth side would be required to generate a faceted involute form.

How to move that mill spindle mechanically, vs via cnc and an equation is an interesting puzzle I'm still thinking about.

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Lew_Merrick_PE

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Re: Bevel Gear Mill
« Reply #39 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

Offline timby

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Re: Bevel Gear Mill
« Reply #40 on: August 28, 2020, 03:33:04 AM »

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.

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.

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #41 on: August 28, 2020, 10:07:44 AM »
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

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?
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Steve
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Offline awemawson

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Re: Bevel Gear Mill
« Reply #42 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:
Andrew Mawson
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #43 on: August 28, 2020, 10:31:54 AM »
That's pretty cool timby.  :beer:
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Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #44 on: August 28, 2020, 10:40:41 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:
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: )
I love it when a Plan B comes together!
Steve
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Offline RussellT

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Re: Bevel Gear Mill
« Reply #45 on: August 28, 2020, 11:06:48 AM »
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
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #46 on: August 28, 2020, 11:21:40 AM »
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."

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #47 on: August 28, 2020, 12:43:53 PM »
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.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #48 on: August 28, 2020, 03:54:29 PM »
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:
I love it when a Plan B comes together!
Steve
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Offline mattinker

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Re: Bevel Gear Mill
« Reply #49 on: August 28, 2020, 05:31:28 PM »
Two piece plaster moulds would be quit easy to make! Grease as a release agent.

Cheers, Matthew

Offline Joules

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Re: Bevel Gear Mill
« Reply #50 on: August 28, 2020, 05:44:06 PM »


Now this is intriguing to watch, note the hob seems to have two teeth offset so it can machine each side, not sure about the profile at the end.  As the gear is very broad the tooth profile almost looks like a tapered Acme form.  A blunt Meccano gear
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #51 on: August 28, 2020, 08:51:59 PM »
It doesn't look like the spindle changes its vertical angle. If so and there are two teeth they would have to move towards each other as the mill rotated into the cut, making a tapered space.

One possibility for achieving that might be a rotationally fixed core spindle acting as a tapered cam, inside an outer rotary spindle holding the teeth. The inner spindle driven by a linear actuator. That might force the teeth together or apart at a timing and degree determined by the CNC program feeding that cam.

I dunno, maybe something like that......
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #52 on: August 28, 2020, 09:01:03 PM »
I wonder if you could have a cnc "wobble spindle" to cut both sides of the tooth space in one revolution?  :loco:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline WeldingRod

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Re: Bevel Gear Mill
« Reply #53 on: August 28, 2020, 10:17:04 PM »
I think spiral bevel gears can be hobbed...  not totally sure, though!
That would be even more complicated  ;-)

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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #54 on: August 29, 2020, 10:59:55 AM »
It might actually be easier.

But this is getting to the point where my brain hurts!

I'm pretty sure the two things I will be trying out are a mill (possibly mounted on my new lathe) with involute profiled teeth (probably with a homemade cutter) and a zinc alloy casting from an existing bevel gear. Those seem like the simplest (and quickest) for what I have on-hand for equipment and capabilities.

The rack tooth generation method has great appeal, so maybe some-day I'll try that, and likewise building a hobbyist gear hobbing machine like the Jacobs or the JS Eley machines -- both shown in older Model Engineers, has always been something I wanted to do.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline WeldingRod

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Re: Bevel Gear Mill
« Reply #55 on: August 30, 2020, 02:52:16 PM »
It looks like face milling spiral bevel gears is done with a shaped cutter (normally multi-tooth) moving in a circle and cutting on the end.  Think hole saw.  This is tipped and tilted to get the geometry to work.  You plunge it in once per tooth space.  It looks like a single tooth cutter would be ok, just slower metal removal.
Actually sounds pretty straightforward for what you are interested in.  One setup, two cutter head angles for the right and left spirals you need, and tooth indexing.
This gets away from the tapered tooth generating problem nicely!

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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #56 on: September 04, 2020, 01:59:23 PM »
Look what came in the mail today! A brand new, in ancient metal cornered unopened box, still factory taped closed, inside Cosmolined, and anti-rust paper wrapped, National #5 20P bevel gear mill w/7/8" arbor hole.

I believe (not absolutely sure) that this will cut bevel gears in the size range and tooth count I'm interested in. Which is about an inch dia 16 tooth, more or less.

Even if it doesn't, it was way cool to just crack that box open for the first time after who knows how many years since manufactured! The first person to look inside and unwrap that little treasure! Fun.....!  :ddb:

I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline awemawson

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Re: Bevel Gear Mill
« Reply #57 on: September 04, 2020, 02:48:24 PM »
Well don't tease us man - open the box and SHOW us  :clap:
Andrew Mawson
East Sussex

Offline Lew_Merrick_PE

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Re: Bevel Gear Mill
« Reply #58 on: September 04, 2020, 03:11:31 PM »
I think spiral bevel gears can be hobbed...  not totally sure, though!
Hi WeldingRod  --  Yes, I served my Apprenticeship in a Tool & Die shop "across the alley" from Western Gear.  Making hobs was a (moderately) common task.  The set-up to use such hobs was fr from trivial.  --  Lew

Offline tom osselton

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Re: Bevel Gear Mill
« Reply #59 on: September 04, 2020, 05:36:20 PM »
OPEN THE DAM BOX ALREADY!  :D Ebay find?

Offline vtsteam

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Re: Bevel Gear Mill
« Reply #60 on: September 04, 2020, 06:28:43 PM »
Jeepers! :whip:



 :beer:

yes, Tom, the Bay
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Steve
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Offline shipto

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Re: Bevel Gear Mill
« Reply #61 on: September 06, 2020, 04:49:14 PM »
Sure I read somewhere these can do bevel gears: http://www.lathes.co.uk/jacobs/
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #62 on: September 06, 2020, 06:23:42 PM »
Yes, Shipto, that's the machine I've always wanted to build -- the version in Model Engineer, not the College Engineering version, which does not do bevel gears.

But on the second page of this thread, engjas mentioned a second Model Engineer gear machine by JS Eley, that I hadn't seen before. I like that one. too. Some day I'm going to build one of those two.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #63 on: September 22, 2020, 10:04:27 PM »
Well my two bevel gears arrived from China finally today. I must say they do look shiny, and I was particularly pleased to see they threw in an extra gear with the pair!
I love it when a Plan B comes together!
Steve
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Offline Joules

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Re: Bevel Gear Mill
« Reply #64 on: September 23, 2020, 12:40:49 AM »
WOW, just don’t be tempted to plant them and grow more....   They could be “Bevel Not Gear Weed”
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #65 on: September 23, 2020, 09:52:11 AM »
I find I can pretty much get by with just two words these days: "What the.....?"
 :bang:
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Steve
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Offline vtsteam

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Re: Bevel Gear Mill
« Reply #66 on: September 23, 2020, 10:02:20 AM »
Obviously, I'm going to have to make them myself. I'm slowly working my way back to getting a usable shop, and the time to work in it.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg