Author Topic: Bevel Gear Mill  (Read 6604 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
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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.
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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
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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
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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.
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Steve
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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:
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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
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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 »
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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