How would a hobbyist machine gears?

DaveC426913

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I want to play with gears - make my own and such. (They'd be custom, so it's not like I could put in an order for them to be made.) What are my options for getting access to the right machines?
 

Mech_Engineer

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It will depend greatly on what kind of gears you're wanting to make. The machining process for a "standard" toothed spur gear is not too bad, but a tapered-tooth face gear or helical offset ring & pinion like in a car's differential could be pretty difficult.

Doing a search for "gear cutting" in Google came up with this interesting article from "The Boy Handbook":
http://chestofbooks.com/crafts/popular-mechanics/The-Boy-Mechanic-1000-Things-for-Boys-to-Do/Gear-Cutting-Machine.html

As for the fact that they're custom gears, there are many machine shops accross the nation that can make any gear you want, as long as you've got a good drawing/ model of it, and money to pay them.
 
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You could create a solid model and have them printed on a 3d printing machine...they would be plastic but the cool thing is, once the support structure is dissolved, seperate gears in the assembly are able to move. There are several types of polymers used with different strength profiles (depending on what you may need).

I am not sure the cost, I have seen several websites that will make parts and send them out. Try Googling it.

Example of a 3d printed gear assembly:
http://content.answers.com/main/content/img/CDE/_3DPCOLR.JPG

One of many companies that specialize in 3d printing
http://www.3dprintstudio.com/
 

Mech_Engineer

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Depending on the gear application rapid prototyping/manufacturing could be an ok idea. They would have to be pretty substantial in size to be made accurately on a RP machine though, because they usually have trouble making very small features (features smaller than .035 or so, depending on the machine.)

I wouldn't recommend using an SLA (stereo lithography) machine process, but I've had prototypes and functional parts made on SLS (selective laser sintering) and plastic resin machines that were suprisingly durable.
 

FredGarvin

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It depends on the sizes and loads that you are interested in playing with. There are a few companies out there that have huge selections and are pretty cheap. In most cases, unless you really wanted to figure out how to make your own gears, you'd be better off looking for someone to purchase them from and be done with it, especially if you are looking at something other than a spur gear.

http://www.rushgears.com/
http://www.mcmaster.com/
http://www.emerson-ept.com/eptroot/public/prod/dynamic_frame.asp?strMain=http%3A//www.emerson-ept.com/EPTroot/Public/bnames/browning/Browning.htm [Broken]
 
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DaveC426913

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It depends on the sizes and loads that you are interested in playing with.
Inch or two in diameter. They will be almost cosmetic, virtually no load. However, since they may be pretty flimsy, so they'll have to be made of a strong material to avoid binding and distorting, because...

...you'd be better off looking for someone to purchase them from and be done with it...
...when I say "custom", I mean custom. :wink:
 

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turbo

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One word.... WHY?
 

DaveC426913

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One word.... WHY?
An art project.

I want to do things to gears that gears have never conceived of in their worst LSD-induced nightmares being done to them.

I want people to say "that's impossible".
 

turbo

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Well, that certainly is something I never would have conceived of. This isn't a case of "buy this tool to hob spur gears", for certain.
 
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If you want this strong and precise, you might get something useful from the stereo sintering mentioned earlier.

You could do this on a conventional milling machine; I suspect it's fewer than a hundred hours once you get the hang of it.

Something like a 5-axis mill would be great. The problem is the cost, maybe $250k.

If it's just a prototype, think about casting it in bronze and doing finish machining.
 

Mech_Engineer

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Yup, those gears look like a perfect candidate for a rapid prototyping process. The gears would be strong enough to be functional, and part complexity has no effect on price. The other nice thing about rapid prototyping is that you can make parts that would be nearly impossible to machine if you want.

Here are two of the processes I've used before for functional models with good results:

Selective Laser Sintering (note that it is possible to make "metal" parts with this machine):
3D Systems Sinterstation® with available materials.

Printed Polymer:
Objet Eden with available materials.
 
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For the purpose you've described, an inexpensive mini-mill will probably be sufficient if you want to machine the gears. Mini-mills can be purchased new from about $600 (U.S.). Tooling can easily equal (or exceed) that, depending on your requirements. Spend some time exploring hobbiest websites and you can find great deals on used machines and equipment. (I've got a pretty extensive bookmark list -- I'll be happy PM or e-mail them to you if you're interested.)

Here's a great site on making gears from wood:
http://woodgears.ca/gear_cutting/index.html
... including a very slick template generator (Javascript) for tracing the gear profiles:
http://woodgears.ca/gear_cutting/template.html

http://www.lindsaybks.com" [Broken] has a few inexpensive booklets on gear design and machining/manufacturing.
 
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FredGarvin

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I'd second the idea about rapid prototype. You can give them your CAD model and they can stereo lithography them or some other process. Those are NOT what I was picturing. Pretty neat looking gears.
 

DaveC426913

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Mini-mills can be purchased new from about $600 (U.S.). Tooling can easily equal (or exceed) that, depending on your requirements. Spend some time exploring hobbiest websites and you can find great deals on used machines and equipment. (I've got a pretty extensive bookmark list -- I'll be happy PM or e-mail them to you if you're interested.)
Thanks. This sounds great.

What is the difference between "mini-milling" and "tooling"?
 

DaveC426913

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A mini-mill just a small (desktop size) milling machine. http://littlemachineshop.com/info/minimill.php

"Tooling" is a generic term for cutting tools and accessories (end-mills, vises, clamps, etc.)
So when you say...
...Mini-mills can be purchased new from about $600 (U.S.). Tooling can easily equal (or exceed) that...
...you're saying that a mini-mill might set me back ~$600, but all the tools needed to do this "for real" might set me back substantially more. Is that what you meant?
 
They would be really pretty coped out of a hardwood bowl.
 
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... a mini-mill might set me back ~$600, but all the tools needed to do this "for real" might set me back substantially more. Is that what you meant?
The key word being "might". The basic tooling to mill some small spur gears could probably be put together for as little as $200-$300. But, like most endeavors, the more serious you get, the bigger the investment.

You also need to consider your time. For someone who has never operated a machine tool, gear hobbing is pretty advanced work. You're going to need to spend a fair amount of time learning to use the tools.

Have you looked at what gears are available for retail sale? Brass or stainless steel spur gears are only about $20 to $40 (1" to 2" pitch diameter) from http://www.mcmaster.com/" is another great source, but they can be a bit expensive.

You might also try robotic and mechatronic suppliers.
http://www.google.com/search?q=robot+parts
 
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Mech_Engineer

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Let's not forget that the gears you've designed would be very difficult to machine on a manual mill. Sure, it might be possible on a 5-axis CNC machine, but manually machined on a hobbyist bench-top unit, I'm not sure. It would definitely take some rotary stages and pretty fancy clamping, not to mention ball-end bits, etc. etc.

If you bought the material in a hemispherical shape of the correct thickness, your job would be easier; but clamping will still be an issue.
 

DaveC426913

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Have you looked at what gears are available for retail sale?
It's an art piece. If I can buy it, it isn't doing its job.

I would sacrifice high-precision for the sake of labour and costs. As an art peice, it doesn't have to perform under stress, as long as the gears mesh smoothly. (Think of the giant Rube Goldberg clocks you often see in malls and theme parks. On many of them, those giant gears turn, but they're more for show - they don't perform any function. The clock mechanism is usually not dependent on them.) Now, scale that down to about a foot tall.
 

Mech_Engineer

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I would sacrifice high-precision for the sake of labour and costs. As an art peice, it doesn't have to perform under stress, as long as the gears mesh smoothly.
It would be pretty easy to make the gears mesh with an RP model. My guess, they would cost around $100 each, but depends heavily on the company and if you know anyone there. Heck if you knew someone with access to any kind of RP machine you could probably get them made for free.
 

DaveC426913

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It would be pretty easy to make the gears mesh with an RP model. My guess, they would cost around $100 each,
Still: Yeowtch.

For a piece that might have a dozen gears...
 

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