[modeleng] Re: sprockets

  • From: "Terry Lane" <tel@xxxxxxxxxxx>
  • To: <modeleng@xxxxxxxxxxxxx>
  • Date: Mon, 30 Aug 2004 20:45:54 +1000

Thanks Rich - now where did I put that 247 tooth gear wheel to index it
with?


> Hi there Terry,
>
> I'd suggest the following (hoping my maths is correct):-
>
> Guess the number of holes - a good estimate would be to say that the
> circumference of your 500mm sprocket is about pi*500mm, which is 1571mm,
> and your pitch is 1/4"=6.35mm, which goes into the circumference about 247
> times.
>
> Divide 360 degrees with that number - leaving 1.4575 degrees.
>
> Now draw out a right angled triangle in front of you, with one angle very
> small.
>
> Assume that this small angle is half of the 1.4575 degrees (0.7287
> degrees), and that the side opposite this angle is half of your pitch
> (1/8"=3.175mm).
>
> The hypotenuse of the triangle should not be the RADIUS that you should
> form the holes on for your sprocket for 495 teeth:-
>
> hole radius= 3.175mm/ sin 0.7287degrees = 249.633mm
>
> giving a diameter for your holes to lie on of 499.267mm.
>
> This doesn't allow for any clearance between the chain rollers and the
> sprocket though.
>
> Hope this is of some use.
>
>
> Yours,
>
>
> Rich.
> PS 247 HOLES!!! OUCH!
>
> On Mon, 30 Aug 2004, Terry Lane wrote:
>
> > I'm sure the info is somewhere but - have any of you got a quick way of
> > calculating sprocket cutting. I got a job here that calls for a sprocket
> > aprox 500mm diameter to drive 1/4" pitch chain. Now OK - the teeth gotta
be
> > one pitch apart, & the holes gotta be pin dia.+?, but how do I arrive at
a
> > pitch circle for the ring of holes?
> >
> >
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