Re: cnc gear hobbing on a horizontal mill *info needed*

> I found a little post made by john stevenson on hooking a encoder to
> the mill spindle then using some kinda divide by chip to make a stepper
> move the dividing head in time with the spindle. does any one now were
> I can find more info on this set up.
> Thanks
>

Ask,

The way it works is that you drive an encoder from the hob spindle, count the pulses and use a divide by chip to then output pulses to a stepper driven dividing head.
From experimentation the magic number id 4000 pulses per rev. This can be achieved by gearing up a lower count encoder with a toothed belt drive.
Any less than 4,000 rpm and the whole operation becoces too coggy and rough, any more and you have problem keeping up on low count gears unless you reduce the hob spped very low.

Because of this limitation low count gears have to be cut at lower speeds than higher count as the pulse train is higher at lower counts.
This isn't such a limitation as it sounds as hob speeds have to be kept quite low anyway to prevent dulling.

The orignal divde by chip layout was devised by a guy in the UK called Brian Thompson, I later had the design altered to use both sides of the encoder to increase pulses.
Brian later wrote this up with circuit diagram for Model Engineers Workshop with the circuit transposed onto vero board or strip board to enable it to be built in the home shop.

Here's a more detailed writeup.

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/Gearhobbing.txt

Pictures start at

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer1.jpg

and go to

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/hob%20indexer26.jpg

Brians article is at

http://homepage.ntlworld.com/stevenson.engineers/lsteve/files/MEW108.pdf

John S.