Re: Toothed pully design information needed.

--- In CAD_CAM_EDM_DRO@egroups.com, "Smoke" <Smoke@5...> wrote:

> Let's see...without even using a book, I would figure the OD of a

3/8" pitch

> timing belt pulley having 40 teeth as follows:
>
> 40 x .375 / PI = 4.774648....diameter. From this I would simply

use a

> cutter made like John mentioned as cut the tooth profiles using a

dividing

> head.
>
> Does that sound reasonable?
>
> Smoke

Not quite, This is where a lot of confusion comes in.
Funny as it sounds and contary to gear technology the OUTSIDE
diameter of a timing pulley is Smaller than the PCD.
Smokes figures are correct for the PCD.
To get the outside diameter you need to subtract a constant from the
PCD. In the case of the 3/8" pitch belts, also known as the 'L'
series this is 0.030" so the OD of Smokes pulley will be 4.775" -
0.030" = 4.745"
This constant is the same for all the 'L' series range regardless of
number of teeth. Other ranges have different constants. I aim to put
some of this on a page and upload it to the files section when I have
a minute.

John Stevenson
Nottingham, England.