12 Apr
2013
12 Apr
'13
10:37 a.m.
On Thu, 11 Apr 2013 21:29:30 -0400, Ethan Dicks <ethan.dicks at gmail.com> wrote:
I didn't really think so (for the same reasons), but I haven't kept
up-to-date with today's additive manufacturing capabilities.
If you find the photos or make the scans, please send them. If
possible, scan the gear next to something with a known scale such as a
6-inch machinist's scale or equal.
Sounds like a "non-standard" gear. I can see why you (cctalk)
couldn't find one in a catalog.
> Mention of
the Alps plotter reminds me that we've had various discussions
> about all the plotter mechs with broken gears but we've never worked out
> the details...
I may be able to draw up a gear like this, but
like the "gear
generator," I'd have to have the correct gear data to know what to
draw.
Understandable. If I had more numbers up front, I would have given them.
What specs should I try to draw a gear to? I
have access to both 2D &
3D drafting/modeling software (AutoCAD & SolidWorks).
Do you intend to use a 3D printer to try to manufacture the gear?
I do not. I was contemplating trying to laser-cut some out of Delrin sheet,
something I did not have access to the last time this conversation made
its rounds. As before, FDM printers do not have the resolution for such
a tiny part, and other technologies (sintered powder or UV-cured resin)
are likely to be too brittle, especially with such fine features.
I suppose
these gears are spur gears with involute gear teeth.
As far as I know that is true.
What is the pressure angle?
I do not know.
What is the total number of teeth?
What is the pitch diameter?
I do not know without digging out a printer to check. I used to have
4MP close-up pictures (taken with my gear in 2003 back when
Electronic Goldmine was surplusing the bare Alps printer mechs
for a few dollars) but I don't know exactly where those photos
are at the moment. My best approach right now would be to
drop one on a high-res flatbed scanner (1200 dpi) to get a
reasonable "to scale" picture, but I don't have a gear in front
of me at the moment (I do have them in town).
You said the
face width is 1/8-inch and the shaft hole fits a 1.27mm
diameter shaft.
That's what I've scraped from previous conversations about this
gear. I now own a micrometer so with a gear in hand, I have
a chance of confirming that to better accuracy.
Wikipedia (https://en.wikipedia.org/wiki/Gear)
has all this info and
more -- I'm pretty sure that you are interested in only spur gears
right now, so you can skim over the other gear-type information on
that page.
*nods*
Knowing the gear specs may even allow someone to
go to the "small
gear" catalogs and maybe even be able to select an "off-the-shelf"
gear for each needed gear. It's possible.
I think we (the cctalk community at the time) looked into that and nobody
had such tiny gears with so few large teeth in their catalog. There were
calls to remove a gear and make castings (most gears are already broken
making that difficult) or using a lathe to make a fresh brass gear, etc.
Someone apparently did take a stab at a homemade brass gear but
declared it too expensive to warrant starting up a small run. Perhaps
hobby CNC has evolved to the point now where one could do a gear
with less labor and make an individually cut gear easily enough to
justify selling it for around $5. Or not.
The hobby CNC world seems to have drastically increased in popularity
in the last few years. A lot of the (mostly) guys are retired now and
*may* be willing to make a small run for a reasonable cost just for
the challenge. We'd still have to be able to give them full specs so
they can program their machines. I recommend we wait on approaching
the hobby CNC community until the gear specs can be determined and you
have a go at the prototype with the laser.
If I have a DXF or EPS of the face of the gear, I can see if the laser
cutter can make an approximation out of Delrin for nearly free (I just
spend a few minutes when I'm already working on a run and as long
as I don't work past the quarter-hour billing tick on the tool, the time
is already paid for by the other job). I'm not positive that this will
work, but the cost is so low that it's worth a stab. Just need the
silhouette to scale and I'm good to go.
-ethan
Go ahead and measure what you can and send me the dimensions &
photos/scans. I'll see what I can put into DXF or EPS format for you.
Bob