[modeleng] Re: Calculating gear form of very low tooth count gears

It's about 12mm deep overall, bit thick for photoetching :-), the
problem with the one I have is the wear on it....
 

chrisc

 

> -----Original Message-----

> From: modeleng-bounce@xxxxxxxxxxxxx
[mailto:modeleng-bounce@xxxxxxxxxxxxx]

> On Behalf Of cbrumbelow@xxxxxxxxxxx

> Sent: 26 September 2007 01:39

> To: modeleng@xxxxxxxxxxxxx

> Subject: [modeleng] Re: Calculating gear form of very low tooth count

> gears

> 

> Are you trying to duplicate a gear you already have?  If so, how about

> photo etching its semi-twin from the appropriate thickness of brass?
You

> would probably have to finish the teeth with a fine file.  Charles

> -------------- Original message --------------

> From: "Chris Crosskey" <chris.crosskey@xxxxxxxxx>

> 

> > Hi Folks,

> > I'm trying to clone a very small gear for a slightly off-beat
lighting

> > project. I'm trying to clone an Optikinetics Total Eclipse (see

> > http://www.funky-parrot.com/totaleclipse.html for more info about
this

> > rather insane lighting effect), and I've run into two problems, one
of

> > which is the motor, it's probably about 8W, 12V AC and runs fairly
fast,

> > the other is the sun gear in its planetary gear arrangement is
8-tooth

> > and it has a hole up the centre, it's about 8mm wide (the gear
overall)

> > so it might well be 1Mod. If I could work out the profile without

> > measuring a rather worn one in my possession and trying to copy it
it

> > would be very helpful. Is it worth measuring the planet gears (about

> > 25mm/25 teeth but I'm not being precise here)... it could just as
easily

> > be 24DP, I will need to measure properly, but how would I go about

> > cutting such a gear?.... is there a way to generate a cutter for

> > this?... I've got the WPS book on gear cutting (one of Ivan Law's
IIRC)

> > and I'm happy enough cutting other, rather higher toothed gears but
I'm

> > not up to working it all out at those kind of levels.... Assuming it
is

> > 1 Mod then what sort of pressure angle will get me in the ballpark
for

> > an 8-tooth gear with a 2.5 to 3mm hole in the middle of it?....

> > The effect works by having a pair of rather inefficient drive
systems

> > from a single motor powering up both sides of a planetary gear
system

> > where the gears are clear and have colour section son them. The
whole

> > assembly is spinning so fast that it just colour mixes in graduated

> > bands that change due to differences in the inefficient power

> > transmissions (these can be varied by moving one of the foam covered

> > jockey wheels BTW)..... I'm thinking of cloning it without the

> > inefficient drives and just having a one-tooth variation in a normal

> > gear transmission system..... hopefully a 12V 500rpm sync motor will
run

> > the whole thing fast enough to colour blend..... but I'm still stuck

> > with that minute gear in the middle of the planetary, if I go small

> > enough on the tooth form to get into sensible territory I'm down at
0.5

> > Mod and I'd rather not be cutting gears that fine in plastic then

> > whirling them round in the gate of a projector..... I guess I could
try

> > it though.......

> >

> > Any thoughts on 12V AC motor sources would be welcome too, I've done

> > some googling but not turned up anything particularly useful.... And

> > Optikinetics (and their main dealers Optifanatics) have been very

> > helpful but simply don't have much information (or indeed spare
parts)

> > for stuff that old.... plus the original designer (who was mad as a
box

> > of frogs) died a fair while ago.....

> >

> > Any help gratefully received

> >

> > Chris Crosskey

> >

> >

> >
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