In article , James Harris
writes
If you guys wanted to buy some simple but reasonably substantial gears
where would you go?

I am needing two gears about half an inch thick, and preferably made of
metal, to drive the soil sifter I mentioned in another thread. If you
haven't seen that other thread, the sifter looks like this:


Snip
I wonder if you could cannibalise an old manual sewing machine?
--
Chris Holford

On Tue, 11 Apr 2017 09:49:01 +0100, James Harris
wrote:

If you guys wanted to buy some simple but reasonably substantial gears
where would you go?

snip

I might not, I might design the ratio I want using a toothed belt
drive and print the pulleys on a 3D printer. ;-)

If the big gear ended up bigger than 200mm diameter (as big as I can
print on my printer) than I might print it in 4 quadrants and mount
them on a common hub?

FWIW, a guy called Cedric Lynch used to hand make smaller rear
sprockets for the local lads mopeds from a sheet of nylon and
apparently they used to outlast the steel ones?

Along similar lines, I build a fairly large reduction stage on my
electric racing bike (moped size). I used a (small) camchain sprocket
off a Honda 90 welded to an adaptor I turned on my lathe on the motor
to a hand made 1/8" thick dural sprocket. I drilled the holes for the
teeth and cut the teeth from a sheet, mounted in place of the bottom
gear on a 5 speed cycle sprocket, running on a lay shaft. From there
the std cycle chain when back to a 5 speed derailer system. This meant
I could manually choose one of the remaining gears on the front block
for the particular track and the rear changer for dealing with the
course bends / hills etc.

24V PM Motor, small sprocket big home made gear on layshaft manual
pre-set cycle sprocket block on layshaft derailer cycle sprocket on
rear wheel. Six one hour races, one (lucky) win and not one
transmission failure. ;-)

Cheers, T i m