I recently bought a dividing head and in an effort to understand
how to use it I went through an example to make a gear.
Machine shop practice covers it pretty well.

I picked a 96 tooth gear because a project I have in mind uses one.

40/96 = 5/12
Which means I need to rotate the handle 5/12 of a turn for each
tooth. Looking at the index plates (A,B,C) I have choices of 15-20
on plate A, 21-49 on plates B and C. There are no plates with
a multiple of 12. I am also puzzled why there are no even numbers
above 20. Plates B and C have only odd numbers. Why?

It seems to me that I need to make an index plate with 12 holes
in order to make this gear. Am I missing something???

chuck

In article ,
Charles A. Sherwood wrote:
I recently bought a dividing head and in an effort to understand
how to use it I went through an example to make a gear.
Machine shop practice covers it pretty well.

I picked a 96 tooth gear because a project I have in mind uses one.

40/96 = 5/12
Which means I need to rotate the handle 5/12 of a turn for each
tooth. Looking at the index plates (A,B,C) I have choices of 15-20
on plate A, 21-49 on plates B and C. There are no plates with
a multiple of 12. I am also puzzled why there are no even numbers
above 20. Plates B and C have only odd numbers. Why?

Hmm ... according to the tables in _Machinery's Handbook_, you
need 3 holes on an 18 hole circle, *plus* 5 holes on a 20 hole circle.
This requires a special setup, so the plate can be rotated (for
alignment) after the first motion and a second motion set up with the
second hole circle. I've never done this, and I don't have the setup
for that, so I can't give more details -- without scanning the whole of
the _Machinery's Handbook_ entry, which would be copyright violation.

The listing in the Handbook for the hole circles available with
the Brown and Sharpe dividing head show the following:

PL
# Holes
------------------------------------------------------------
1 15 16 17 18 19 20
2 21 23 27 29 31 33
3 37 39 41 43 47 49

It seems to me that I need to make an index plate with 12 holes
in order to make this gear. Am I missing something???

That is one option, and it should be easy enough. It also
sounds like the way that *I* would go about it, lacking the extra
hardware to do the compound indexing.

O.K. I just went down and looked at the division plate for my
B&S dividing head, and it skips over 96, suggesting that it can't be
accomplished with the supplied plates.

So -- make a new plate, and start at the outside edge, leaving
room to add other rows as you discover the need.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

So -- make a new plate, and start at the outside edge, leaving
room to add other rows as you discover the need.

Thanks for the help. I will probably start at the inside and save the
outside edge for rows with more numbers. I still find it curious
that standard plates don't cover this, but I guess the other patterns
are probably used more. How many people cut 96 tooth gears anyway!

chuck

Hmm ... according to the tables in _Machinery's Handbook_, you
need 3 holes on an 18 hole circle, *plus* 5 holes on a 20 hole circle.
This requires a special setup, so the plate can be rotated (for
alignment) after the first motion and a second motion set up with the
second hole circle. I've never done this, and I don't have the setup

This seems like a way to make a simple problem HARD! 5 holes in
a 12 hole circle is so much easier.

chuck

BUT there are no multiple of 12 hole circles provided on the 3
standard dividing plates. In fact there are no even numbers
greater than 20. Personally I think its to get you to buy
the differential dividing attachment!
chuck


or......

10/24 of a turn

or......

15/36 of a turn

or......

20/48 of a turn

changing fractions to lowest common denominator, while a way of
getting a good grade on a test, is not always all that helpful....

Keep in mind that back "in the day" when dividing heads were THE tool
for such things shops most likely had all the gears and knowledge to
quickly set up a differential indexing situation.

These days lacking the gears and expereince we have to make a custom
plate for such situations. Some where in my desk I have a 59 hole
plate I made years back for a gear. Never used it but I still have
it!

Errol Groff


On 17 May 2004 21:25:28 GMT, (Charles A.
Sherwood) wrote:

Hmm ... according to the tables in _Machinery's Handbook_, you
need 3 holes on an 18 hole circle, *plus* 5 holes on a 20 hole circle.
This requires a special setup, so the plate can be rotated (for
alignment) after the first motion and a second motion set up with the
second hole circle. I've never done this, and I don't have the setup

This seems like a way to make a simple problem HARD! 5 holes in
a 12 hole circle is so much easier.

chuck

On Mon, 17 May 2004 22:03:16 -0400, Gene Kearns wrote:

On 17 May 2004 22:11:14 GMT, (Charles A.
Sherwood) wrote:



snip


Yep, you're screwed. Standard plates a

#1 15-16-17-18-19-20
#2 21-23-27-29-31-33
#3 37-39-41-43-47-49

You might be able to accomplish the task with compound indexing since 96
isn't prime.

The Machinery's Handbook says the exact division of 96 can be obtained by
moving the handle forward 3 holes on the 18 hole and moving the plate forward 5
holes on the 20 hole. 3/18 + 5/20=5/12. From the table called "Compound
Indexing"

Brent.