help identifying a gear

[stragenmitsuko]

I took apart a bicyle hub with internal gearing hoping to find a ring gear
to possably build an elmer's no5 geared engine .

It did have a ring gear of aproximately the right size and with an even number of teeth .
So that would be ok .

The orbiting gear needs to be half of the ring gear .
Meaning I would need to make a gear with 30 teeth .
No problem there either .

To determine the gear cutter needed , I've measured the planet gears and the sun gear .
They all are OD 17.03 mm(0.670") give or take 0.01mm .
With z=20 that would make a module of 0.774 or a DP of 32.813 .

Does that make any sense at all ?Is my math correct ?
I mean for a module gear it's an impossible number , andI've never even heared of 32.8 or even 33DP .
Could it be the bicyle company 's have their own dedicated gear sizes ?


Pat

 

[goldstar31]

Wetting my fingers and crossing my legs to point North, I reckon that this is 0.75Module gear.

Beer or wine tokens would be welcomed

Norman

 

[stragenmitsuko]

I guess it's possible .
I know of 0.5m and 0.8m and 1m and 1.5m gears .
Never heard or thought of 0.75 though .

But , recalculating , a 0.75mod 20T gear should have an OD of 16.5mm .
That is only a 3% error on the OD theoretical to actual value , so that ought to be good .

What would be the pressure angle of these gears ?
I'de like to give this method a try
http://david.rysdam.org/machining/gears.html

 

[goldstar31]

Not bad for an 88 year old? At least, I didn't get sarcasm.

Gone for a little of my favourite Chardonnay-- with the rest of my gang of pensioners who face East on the hope of seeing a miracle.
Not even beer money- ah, well?

N

 

[MRA]

These folks are useful, for finding out what gears are normally available:

http://www.hpcgears.com/n/products/12.spur_gears/spur_gears.php

I ordered a couple from them recently for a bending machine at work, where the gears were so chewed that the addendum was no more. Worked out OK in the end.