• posted
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
• posted
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
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.
• posted
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
• posted
This seems like a way to make a simple problem HARD! 5 holes in a 12 hole circle is so much easier.
chuck
• posted
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....
• posted
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
• posted
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
• posted
Yep, you're screwed. Standard plates are:
#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.
• posted
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.
• posted
As I mentioned, compound indexing is possible with this number of divisions, but it requires that the dividing plate be "movable." Not all dividing heads have this capability.... beyond that, it is a monumental PITA.

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