# 25 Hole index plate



## H. K. Barrows (Jun 20, 2011)

Hello Folks. I'm back with another question about how to figure out the math to make a 25 hole plate for a 72 to 1 R/T. I have tried to work this out but I'm totally missing the use of fractions and reducing them, and how to pick the no. of holes and plate. There are some Rules in my life that I shall Not break ie. No bending conduit, No painting, AND NO Trying to do anything with the computer other than Just opening the web sites that I know. My good friend that knows how to do what MARV has been so generous in making availabie to all of us, when he comes back from a trip he said he would show me how to make it do what it can do. I made the 100 tooth 32 pitch gear it went very well. 
Thank you. Regards Red


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## cfellows (Jun 20, 2011)

Unfortunately, it seems to me you need a 25 hole plate to make a 25 hole plate for a 72:1 rotary table.

You divide the ratio of the rotary table by the number holes you want and place the remainder over the divisor.

So, 72/25 = 2 22/25. You need to crank the worm 2 22/25 turns for each division of the 25 hole plate... no way to reduce that. 

If you had a 60:1 rotary table, it would be 60/25 = 2 10/25 or 2 2/5, so you could use a 5 hole plate to make the 25 hole plate.

If you had a 40:1 rotary table, it would be 40/25 = 1 15/25 or 1 3/5, again, you could use a 5 hole plate.

Chuck


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## Maryak (Jun 21, 2011)

Looking at from degrees

3600= 1 circle

1/25 of 1 circle = 140 24' 0"

To make a 25 hole plate the table needs to be turned 140 24' 0" between each hole.

Hope this helps

Best Regards
Bob


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## arnoldb (Jun 21, 2011)

Hi Red

How did you index the 100 tooth gear ? (or did you perhaps mean 72 tooth gear)

If you have a 100 / 75 / 50 tooth gear somewhere, you can use that with a detent to drill a 25 hole plate.

Or print two copies of the attached document, place them on top of each other with one rotated through 90 degrees and check against light if the circles match up; this is to check that the image is not stretched as it is printed to make sure the circle is round. If they do match up, you can just stick one to the plate and punch on the lines to drill; this works quite well.
If the printed circle is not round, you might have to find some way of stretching the image to get a round printed circle.

HTH.

Regards, Arnold 

View attachment 25divs.pdf


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## mklotz (Jun 21, 2011)

Using my ROTARY program, here are all the settings you will need to generate a 25 hole plate. Since any inaccuracies in setting these values will be reduced by a factor of 72, the final accuracy of your plate should be adequate for most purposes.


```
Number of divisions = 25 

DIVISION   degdec   deg   min   sec
    0   0.0000    0    0    0
    1   14.4000   14   24    0
    2   28.8000   28   48    0
    3   43.2000   43   12    0
    4   57.6000   57   36    0
    5   72.0000   72    0    0
    6   86.4000   86   24    0
    7  100.8000   100   48    0
    8  115.2000   115   12    0
    9  129.6000   129   36    0
   10  144.0000   144    0    0
   11  158.4000   158   24    0
   12  172.8000   172   48    0
   13  187.2000   187   12    0
   14  201.6000   201   36    0
   15  216.0000   216    0    0
   16  230.4000   230   24    0
   17  244.8000   244   48    0
   18  259.2000   259   12    0
   19  273.6000   273   36    0
   20  288.0000   288    0    0
   21  302.4000   302   24    0
   22  316.8000   316   48    0
   23  331.2000   331   12    0
   24  345.6000   345   36    0
   25  360.0000    0    0    0
```


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## H. K. Barrows (Jun 21, 2011)

Hello Folks Thank all of you for your help. Chuck where I get stoped is after I divide 72 into 25 I get 2.88 I don't know where to go from there. I have 2 R/T's booth are 72 to 1 one has a 25 hole plate. I just used your formula it works perfect, but I did not know you could use a 25 hole plate. So much to learn. Bob I got to what you laid out and wondered how accurate it would come out, or is it depending how accurate I can be dialing in the R/T. And as Marv pointed out with his reply the error would be very small with a 72to1 ratio. Marv I just used your R/T print out taking the time to dial each move it worked very well. Arnold I like your idea with the print out, in the middel of the night I laid out a 8 in circle steped off 25 spaces looked ok put it to your layout and it works, love when a plan comes together. As always thank all of you for you'r help. Regards Red


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## tel (Jun 21, 2011)

All this number crunching for a simple job! If you have a 25, 50 or 75 change wheel with your lathe just direct index off that.


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## mklotz (Jun 21, 2011)

tel  said:
			
		

> All this number crunching for a simple job! If you have a 25, 50 or 75 change wheel with your lathe just direct index off that.



Just be glad I didn't tell him how to originate a 25 hole plate if he has no RT or change gears. And, yes, I have a program for it.


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## tel (Jun 21, 2011)

;D


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## H. K. Barrows (Jun 24, 2011)

Good Morning Teachers. Just completed a 25 hole plate for a Little Machine Shop 4 in R/T p/n 1810. I used the 25 hole plate with 2T 22 holes on my other 6 in R/T. While the R/T was set up I follwed MARV'S print out to step off 25 equal spaces, it works perfect.I did this to learn something new that I have not needed to do. Thank all of you Regards Red


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## MachineTom (Jun 24, 2011)

One of the handy things about a DRO is most have a bolt circle feature. Easier than a dividing head, but only for drilling or milling.


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