compound and differential indexing/hobbing

Have a question or want to show off your project? Post it! No Registration Necessary.  Now with pictures!

Threaded View
Hi to the group.
This is my first post here and is a request for information.
I have the chance of getting a 127 gear cut if I can figure out the
correct differential settings for a commercial gear hobber.
Please does anyone have a paper or link to information discribing how
to do differential indexing/ hobbing. All that I can find on the web
at present are links to engineering book sales.

Regards Bob


Re: compound and differential indexing/hobbing
On 15 May 2007 11:07:16 -0700, bob wrote:

Quoted text here. Click to load it

Why don't you just buy one - the Sherline 127 is less than $20 US, and the
100 is about the same (the 50 is under $10).  Buy 'em and bore 'em.

Re: compound and differential indexing/hobbing
wrote:
Quoted text here. Click to load it

Yes except that I need 18DP for a boxford(southbend clone)and ordering
from south africa is not so cheap. Freight and inport dutys will more
than double the cost. If I do it this way , I learn about gear hobbing
and differential stuff and the cost is the scrap steel. And besides
I'd rather save my money for the things that I can't make or scrounge.

Bob


Re: compound and differential indexing/hobbing

Quoted text here. Click to load it

Greetings- never used a commercial hob, but think you will find the hob,
assuming it is single lead, must rotate exactly 127 times as fast as the
gear blank. Speed of spindle depends on material, of course. FWIW, I use a
47/37 compound gear for cutting metric threads. I know it is not accurate as
the 127 gear. Regards, Jim



Re: compound and differential indexing/hobbing
On 15 May 2007 14:30:48 -0700, bob wrote:

Quoted text here. Click to load it

Why do you need the 18dp?

Just key the 127 to one gear and the 100 (or 50) to the other.

Or do you want the 127 for somehting other than metric/imperial conversion?

Re: compound and differential indexing/hobbing

Quoted text here. Click to load it
I would think that the required gearing would be unique to the gear train of
the particular hobbing machine and would be found in the operating
instructions for the machine. You might have better luck if you identify the
machine. Compound and differential gearing for the Brown and Sharpe type
dividing head is shown in some machinists reference books but I don't know
if it would help any.

Don Young



Re: compound and differential indexing/hobbing

Quoted text here. Click to load it

Irrespective of what make of gear hobber you won't need differential indexing to
do a spur
gear.
Differential indexing is for helical's on a hobber. To do a 127 on a hobber you
need a 127
in the train, usually supplied in the set.

However if you are talking about doing it on a dividing head then yes you do need
differential indexing to do a 127 as 127 isn't native to standard plates.
Ower Gert sells a set of generic plates on Ebay under the name of Marypoppinsbag
that do
have 127 on them and this allows a gear to be made by single indexing.

However as you are in Africa it's probably not convenient or cost effective to
buy a set.

There are two ways to differential index.
One is where the input from the selector arms drives the spindle thru a set of
gears
chosen for the number of divisions. Looks much like the setup for spiral milling
but not
connected to the bed.
And the second is where you move round so many divisions on one circle and move
the plates
forward or back so many divisions on another circle, according to a chart
specific for
that head.

So the short answer is it depends on what equipment you are doing it on and we
need more
information.
--
Regards,

John Stevenson
Nottingham, England.

Visit the new Model Engineering adverts page at:-
http://www.homeworkshop.org.uk /

Re: compound and differential indexing/hobbing
bob wrote:
Quoted text here. Click to load it
  Differential indexing is AFAIK, separate from setting up a gear train
to use a hobbing machine.

  Are you using and indexing head on a mill, and cutting one tooth at a
time, or a hobbing machine, which is a pretty much continuous movement
process ?

  Cheers
   Trevor Jones


Site Timeline