[LatheCrasher]

I need to machine a spur gear with 106 teeth. I'm not having a problem calculating diametral pitch, addendum, etc. nor figuring what pitch cutter to use. My problem is with the indexing calculations. I'm using B & S plates with 40:1 ratio. Per the machinists handbook, 106 target divisions require 1 full turn plus 7 holes on 39-hole circle + 29 holes on 41- hole circle. I know 40:1 means that 1 full rev of the indexing head = 9 degs and no probem calculating up to 40 divisions. The number of divisions over 40 requiring partial turns is confusing me. Could someone break it down step by step?

Thanks!

[RICHARD ZASTROW]

Try this: http://www.atmsite.org/contrib/JSAPP...e/divhead.html

Dick Z

[LatheCrasher]

Thanks for the link. I can do the easy ones, I wish he had given an example of compound indexing like the one I'm working.

[RICHARD ZASTROW]

Compound indexing?

Dick Z

[Kiwi]

The nearest with a 40:1 Ratio and std plates.
Use 16 holes circle and rotate 6 holes.
This will be 4 holes short at the end so suggest you advance 1 hole at tooth 26,53,79,106.

[Superman]

I'm confused, 106T
If one turn = 9°
& 40 turns = 360°

If I cut at eact turn, I would get 40 teeth ( correct )

then
How many teeth do I get at 1 full turn plus 7 holes on 39-hole circle + 29 holes on 41- hole circle.????? ,,,my guess is something less than 40 teeth

my calc is 40/106 = 20/53 = 20 holes on a 53 hole plate just over 1/3 of a rev.

here's a link page 105

[Kiwi]

Looks like 21.2 teeth.
If this 21.2 cycle is repeated 5 times this gives 106.
Not sure how this works and if all the teeth are evenly spaced?

[LatheCrasher]

That is the way I calculated it Superman. I'm using Brown and Sharpe standard plates with no 53-hole circle. I see in the Machinist's Handbook that Cincinnati plates have a 53-hole circle. Sorry for the confusion but I got my info that I posted from the Machinist's Handbook from the "Simple and Compound Indexing with Brown and Sharpe Plates" chart found in the Milling Machine Indexing chapter. I guessed that 106 target divisions would be the same as "106 teeth."

[Superman]

Finally found what you need - bad news is..... it's a Cincinnati
But it has how it is calculated PAGE 214

http://books.google.com/books?id=dhX...um=7#PPA214,M1

If the link doesn't work, r-click on it, properties, copy the "Address URL" section, and paste into the address bar

[Kiwi]

Here is a good article on Compound Indexing. Also a chart of the Index Movements. Page 143 on.
http://books.google.co.nz/books?id=N...um=9#PPA143,M1

[Charles Lessig]

I posted this before but it is pretty simple.

If you don't have a 53 space circle, print
one out on paper and stick it to a plate and move
your index pin and sector arms by eye.

Any error is reduced by 40 to 1 through your gearing.
Keep going in the same direction to avoid back-lash and
if you do over-shoot, back up some and try again.

Clamp the head while cutting and have no distractions
at all.

Best Regards, Charlie

[HuFlungDung]

...have no distractions at all.

I'm not clear on how you do this last part

[LatheCrasher]

Thanks for the help everyone, I knew I would get help here! Excellent reading in the links you posted Kiwi and Superman! Will start cutting chips tonight.