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

I think I'll go for half-mod (or 48DP it won't make a difference thats
worth talking about) and a 30 degree PA or bigger if I can find it, I'll
need one cutter for 16 teeth for the sun and one for about 50 teeth for
the planets. for the transfer drives I can use something coarser so will
prolly go for 24DP because I have a set of cutters for it..... 
chrisc

> -----Original Message-----
> From: modeleng-bounce@xxxxxxxxxxxxx
[mailto:modeleng-bounce@xxxxxxxxxxxxx]
> On Behalf Of Alan Stepney
> Sent: 27 September 2007 08:06
> To: modeleng@xxxxxxxxxxxxx
> Subject: [modeleng] Re: Calculating gear form of very low tooth count
> gears
> 
> At recent Midlands ME exhibitions I have picked up several 12 v
motors.
> The
> next one (ME exhib) is coming up shortly so that could be a (another!)
> good
> reason to go.
> 
> As for the gears, gear cutting of the larger ones in metal isnt too
hard,
> but I imagine that plastics, depending upon the type used, might make
life
> difficult.
> Can you not search round for something that will do the job?
> This seems to be a case where a comprehensive "odds" box is
worthwhile!
> 
> You can often find small gears in laser printers, 5 1/4" floppy
drives,
> and
> similar older computer items.
> http://www.alanstepney.info
> Alan Stepney's Model Engineering, steam, and workshop pages.
> 
> 
> ----- Original Message -----
> From: "Chris Crosskey" <chris.crosskey@xxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Tuesday, September 25, 2007 9:40 PM
> Subject: [modeleng] Calculating gear form of very low tooth count
gears
> 
> 
> 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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