dpb wrote in news
On 1/19/2018 12:13 AM, Puckdropper wrote:

How big of gear are we talking? How many teeth and what's the OD?

It's been too long to recall exactly otomh so I'll have to dig one out
to be precise, but roughly 2"OD, probably 60-tooth or so...that's
probably a little high; more like in 40-ish neighborhood probably.


That sounds doable for both 3D printing and flat milling. Most gears are
hobbed from rod, but you can also just cut the gear from flat stock using
a mill.

3D Printing:
Shapeways can probably do that, all you need is the file. (I have not
tried this, but it looks like you'll be well within the capabilities of
their machine.) Here's the trick: That OD is not the OD the gear goes
by. You need to figure out the pitch circle diameter. I usually do that
by plugging in the number of teeth (count, count, count and count again)
and OD where it says pitch circle diameter, then selecting a standard
diametrical pitch or mod and recalculating the pitch circle diameter.

Depending on the tool you use, you can then print at full scale and place
your gear on top of the print out. Any errors will show up.

Milling:
My handy drawing program says for a 60T 2" gear, the maximum endmill is
..050", I run .031" EMs in my mill all the time. It depends on how thick
that gear is as to whether that tiny EM can cut it from flat stock,
though. More than about 1/4" and it'll just be too big. (I might be
able to carefully flip the gear over and get 1/2", but it's hard to get
that exactly exact.

I'd be willing to give it a try, it'll be nice to see a usable gear come
out of the machine. I often work on models with .3 mod gears and the
teeth are just too fine to cut with an end mill. (If you just look at
those tiny mills wrong, they break.)

Puckdropper
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