What ever use would this be? Dividing plate question...

[John Hill]

I see a dividing plate I could have but the divisions seem to the most unlikely to be of any practical use.

It has holes 61, 67, 71, 77, 81, 87, 91, 97 / 63, 69, 73, 79, 83, 89, 93, 99.   OK, I can see this would be useful to divide a circle by 3,7, 9, 11,13  but then there is a gap in the odd numbers taking on again at 21,23,27,29,31,33.

So what use are these things?  Am I missing a part of the picture?  Maybe there is some procedure to use some holes from one circle combined with holes in another?

[steve]

when you say there is a gap after 13 divisions do you mean that you cannot get 15 divisions using this odd numbered plate?
  When used on a dividing head with a 40:1 ratio the 99 hole circle could be used as 40x99=3960 (40 turns =360 degrees so that the index pin will cover 3960 holes in one revolution of the dividing head spindle).By dividing 3960 by 15 you get 264 which equals 2 full turns of indexer +66 holes in the 99 hole circle.Many of the other hole circles can be used for 15 I just used 99 as an example.Most other numbers can be obtained this way using the other hole circles.
  Only when used on a dividing head can you get the full use of these plates,when used as a stand alone item I agree they are of fairly limited use.
 
  I hope I have read your question correctly and am not teaching you to suck eggs.

  regards   Steve C.

[bogstandard]

John,

It is a little difficult to explain in a short post, but I think you are getting confused between a dividing plate and an indexing plate.

With an indexing plate, say 60, you count off the number of holes required for each step required, so for 15 divisions, every fourth hole.

Dividing plates work in a totally different way, they work in conjunction with the gear ratio of the dividing head, so after your calculations, you use a certain number of holes ring, and then you will use a series of say three full rotations and 17 holes to get to the desired index. This is just an example, but normally you can either do your calculations longhand or use a chart that is supplied with the dividing head to give you almost any number up to 100, and thousands after it by using just the three supplied plates. for getting the very few numbers that are missing, you either make up the required hole plate or buy ready made plates.

http://www.atmsite.org/contrib/JSAPP/divide/divhead.html

Our John Stevenson specialises in making the missing or very versatile hole plates.

http://www.metoolsonline.com/


John

[John Hill]

Thanks guys..   You have turned the light on, I was indeed thinking of it as an indexing plate.

I get the feeling I was stumbling around in an area completely baffling to me!