# 40:1 dividing head plates - hole numbers?



## just old al (Dec 21, 2018)

I recently obtained a very, very nice Carroll dividing head - older one with a B&S 9 collet boring. Once I cleaned it up and freed up the rotation mechanism it's lovely - smooth as silk.

However, it only came with one plate. Now, I am well aware that I can simply make a plate for any number of teeth or spacing I care to create - but as an anal-retentive I am giving thought to making a 'complete' set of plates for it.

While I have seen the listings of 'A', 'B', 'C' and so on plates for B&S heads, I've never seen a listing for the number of holes accomodated on each plate in the set - and that's what I'm asking for - anyone ever seen such a list? I don;t expect to ever find a listing for what this Carroll ever camew with - that would surprise me no end. So, B&S it is if possible.

Thanks, folks.

                      Alan


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## benmychree (Dec 21, 2018)

Look online for Brown & Sharpe's book "A practical Treatise on Milling and Milling Machines"; I think you could also find the info in Machinery's Handbook.  The Carroll dividing head would use plates with the same numbers of holes, there are three plates to the set, all drilled on one side only.  Machinery's handbook has the dividing tables for both the B&S type and Cincinnati, which has plates with more hole circles and only uses one plate drilled on both sides that is considerably larger in diameter.  If you cannot find the info, message me and I will look it up for you.


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## just old al (Dec 21, 2018)

benmychree said:


> Look online for Brown & Sharpe's book "A practical Treatise on Milling and Milling Machines"; I think you could also find the info in Machinery's Handbook.  The Carroll dividing head would use plates with the same numbers of holes, there are three plates to the set, all drilled on one side only.  Machinery's handbook has the dividing tables for both the B&S type and Cincinnati, which has plates with more hole circles and only uses one plate drilled on both sides that is considerably larger in diameter.  If you cannot find the info, message me and I will look it up for you.



Many thanks, Benny. Never occurred to me to look at Machinery's for that plate data. I'll have a dig about - if I can't manage to locate it I'll message you. Thank You!


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## P. Waller (Dec 22, 2018)

Do the math.
360 Deg, / 40 is 9 Deg. per revolution.
A 9 hole plate will yield 1 Deg, of rotation per hole. To rotate a part 10 Deg. would require 1 revolution plus 1 division.
Scale it up or down.


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## NortonDommi (Dec 22, 2018)

B&S 40:1 listing on the program 'Shop Calc' is:  15,16,17,18,19,20,21,23,27,29,31,33,37,39,41,43,47.


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## just old al (Dec 22, 2018)

P. Waller said:


> Do the math.
> 360 Deg, / 40 is 9 Deg. per revolution.
> A 9 hole plate will yield 1 Deg, of rotation per hole. To rotate a part 10 Deg. would require 1 revolution plus 1 division.
> Scale it up or down.



The maths are not a problem, and that I knew.

What I was looking for was the 'content' (sets of holes per plate) of the set of plates that would have come with a B&S head. When I get bored (and get a chuck mounted on this thing!) I'm going to reproduce a set of plates for general usage. This avoids me having to stop and fab a plate when doing other things.

Thanks, though.


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## just old al (Dec 22, 2018)

NortonDommi said:


> B&S 40:1 listing on the program 'Shop Calc' is:  15,16,17,18,19,20,21,23,27,29,31,33,37,39,41,43,47.



BINGO! Spot on! Thanks!


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## NortonDommi (Dec 22, 2018)

Hello Old Al,
                     Just heading to bed but I as thinking those hole numbers seemed familiar so I checked my dividing head which is 40:1 and I think there may be a number missing in the list I got for the B&S,
  What I have is:  Plate A: 15,16,17,18,19,20
                           Plate B: 21,23,27,29,31,33
                           Plate C: 37,39,41,43,47,49

  Hope that looks good to you.
  Cheers,
  Merry Solstice.


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## just old al (Dec 22, 2018)

NortonDommi said:


> Hello Old Al,
> Hope that looks good to you.
> Cheers,
> Merry Solstice.



Many thanks - many, many thanks. Need to get myself some gauge plate and I can foresee many happy hours of drilling... 

Happy Yule as well.


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## Bob Korves (Dec 22, 2018)

just old al said:


> Many thanks - many, many thanks. Need to get myself some gauge plate and I can foresee many happy hours of drilling...
> 
> Happy Yule as well.


If you can find someone to do the work with a CNC mill, that would be easy and quick, and probably not all that expensive.  Drilling all those holes is a big chore, and every hole drilled is a place for a mistake on a manual machine, scrapping the part.












I highly suggest you talk to Mike Wiggins.  He has been there, done that...  The first one Mike did for Keith, with the fewest amount of holes, *took 7 minutes! *(programming and setup time not included...)


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## just old al (Dec 22, 2018)

Bob Korves said:


> If you can find someone to do the work with a CNC mill, that would be easy and quick, and probably not all that expensive.



Should i choose to go that route I certainly will.


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## P. Waller (Dec 22, 2018)

I would not trust the average NC mill to produce a spacing device that needs to be accurate to minutes of arc when used on a dividing head, rotary table or spacer.
This is what jig borers are for.


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## Asm109 (Dec 22, 2018)

And the 40:1 reduction in the head reduces the errors by the same factor.  Now you are talking seconds of arc error. Or make a second round of plates with your first plates and the error is reduced 40X again.


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## P. Waller (Dec 22, 2018)

It may also increase the error 40 times (-:
Registration errors in printing machinery come to mind, if you are printing 1000 labels per minute and are off by .001" that is 1" per minute error, this would place the picture of the missing person on the corner of the milk carton in short time.


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## Asm109 (Dec 22, 2018)

We are not discussing printing presses. we are discussing a dividing head. So lets just stick to that and leave out the whataboutisms.
if there is an error in the position of one of the holes in the plate the 40:1 gear reduction in the worm gears reduces error of rotation of the spindle by 40 X.  
Make a plate with 1 degree error in a plate. 
Put the plate on the dividing head
Make a new plate.  1 degree error in the plate makes .025degree  (1.5 minutes) error in new plate.
Now make a third plate if you really care.  error is now .025/40=.00125 degree (.075 minutes) or 4.5 seconds of arc error.
This is a case where the tool can improve the accuracy of its self.


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## P. Waller (Dec 22, 2018)

Failed to see the ASCII smiley face did ya?
(-:


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## rock_breaker (Dec 23, 2018)

I am in the middle of making a 40:1 indexer and started exploring home made plates and just off hand it seems the 49 hole row would be approximately 3..9" in diameter allowing each hole to take up 0.25" in the circle. Not having seen or handled a plate it would seem a little conjested. Anyway it is an interesting exercise and I am considering 6.25" diameter plates. Thanks to Norton Dommi I may have  the number of holes per row and number of plates already determined. 
Ray


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## BROCKWOOD (Dec 23, 2018)

I am not familiar with what plates the Carroll came with. There is something to be said for going with stock parts. But at the end of the day, for most dividing heads, only the center hole & the mount bolt circle matter. It also helps accuracy to have the plunger pin & hole size closely matched. Here is a chart of a few different sets & pics of some plates.




Van Norman 7 1/2 plate 'C'



Brown & Sharpe plate '2'


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## NortonDommi (Dec 23, 2018)

At the end of the day if you have a ROTAB for practical purposes you only need the existing scales.  I had to make a plate with 125 holes. Some Mysterium cleaned up on the shaper , turned on the lathe and centered on the ROTAB with a spacer underneath and away you go.  
  I found a link to a good  4 part video on this which I think is worth watching even as a refresher.  As Asm109 has mentioned accuracy increases if you make a second set of plates but careful work will make an accurate set probably as good as what comes with most tables.


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## pstemari (Dec 28, 2018)

Asm109 said:


> ...
> This is a case where the tool can improve the accuracy of its self.



That depends. If the holes are all placed independently, then that's correct. If, otoh, there's any cumulative error in the holes, then you don't get any improvement.

Say the holes are consistently out of place by 0.01°. For a distance of 40 holes, that accumulates to 0.40°, and then you gear that down by 40:1, and you're back where you started with 0.01° error.

That's why you can't just do to same approximation over and over again and make the plates more accurate. An approximation in the dividing ratio creates a consistent error, which simply replicates itself on each iteration. Otherwise I could use a 40 hole circle as an approximation to a 39 hole circle, and it would magically transform itself into a 39 hole circle after multiple replications.

You do get the 40:1 improvement when going from a cnc plate, but that's a one time deal, and it doesn't work if, for example, the plate was cnc'ed in incremental polar mode, where the error accumulates from one hole to the next.

Sent from my Pixel XL using Tapatalk


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## Bob Korves (Dec 31, 2018)

In post #10, I just edited the links to the videos to ones that will actually open!


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