Making a gear cutting Hob

[fcheslop]

Maybe a daft question but this muddled model engineer canna figure out
When making a hob for example 48 dp 20 degree pressure angle how do you work out the the spacing for the cutting teeth
Iv made several single point cutters using the button method but fancy trying a hob as it will save making several cutters
Thanks

 

[Charles Lamont]

48 DP means 48 teeth round the circuference of a 1 inch diameter circle. The circumference of a circle is pi x D.
So the pitch of the rack or hob is pi / 48, or 3.142 / 48 which equals 0.06546". The pressure angle has nothing to do with the pitch.

 

[Cogsy]

Here's a great site full of all the info you need for our calculations - LINK

 

[fcheslop]

Many thanks gentlemen, So just treat it like a rack pretty obvious now the fog has cleared
cheers

 

[mc_n_g]

Here is a PDF of information from Chris Heapy's site (now defunct)
It is good information with formulas.
Also shows racks and spacing of gear teeth.
You can use the rack style to cut the gear teeth if you have a dividing head.

 

[fcheslop]

Many thanks for the data mc ng