# Dividing Head Question



## stomp10 (Jan 6, 2019)

Hi All!
Several years ago I to picked up a very old, very  tired, and quite beat up, NEWS, Yamatokoki Mfg Co Ltd dividing head for not a lot of $$$.  It does have a 40:1 gear ratio. No tailstock, no chuck and only one dividing plate.  The dividing plate is kind of a morphodite in its own right.  3 7/8" diameter, with a 13/16" center hole and 3 counter sunk mounting holes.  The plate holes are 21, 23, 27, 29, 31 and 33. I seem to have a knack for finding goofy stuff like this.  I guess this comes from trying to get stuff on the cheap.  You should see my rotary table.
All of my stuff is very much a work in progress....
I also found a very beat up Union Mfg, 5", 3 jaw chuck, class "S" (?) the same size as the backing plate that came with the dividing head.  Which are both actually 5.5" in diameter. Also for not a lot of $$$
All of this sat in the basement for a number of years until I decided it was time to move forward on this project.  This past weekend I managed to get the backplate cut to fit to the chuck and mounted on the dividing head.  By some miracle everything seems to be perfectly centered and true when mounted on the dividing head. Lucky me! (At least it appears so to my inexperienced eye.  )  Prior to mounting the chuck on the dividing head I also skinned the outside diameter of the chuck to make it true as well.  I found it odd that the outside of the chuck was so far off of true.  But I think this chuck had seen a lot of crashes in its lifetime and attributed it to that. 
So, now I am wanting to scribe, or engrave 360 degree markings around the outside of the backing plate and maybe on the chuck too.  IDK yet as I am still working all of this out in my head.  It will probably wind up being a Rube Goldberg affair with a crosslide to mount the engraver onto.  Too bad that I have to keep all of this within a tight budget.  If money was no object, the possibilities are endless!

So much for background info.

Now my question for you is if one turn on the crank equals = 9 degrees arc at the spindle, then one turn on the crank and 40 degrees of arc on the crank SHOULD equal 10 degrees on the spindle? Or am I mistaken in this assumption?
Some, I am sure will suggest to use the rotary table to mount the backplate onto and use the table to scribe the marks.  I had thought of this but as it turns out, the table also has some kind of morphodite T slots that I haven't gotten around to making T nuts for yet.  The T slots also seem to be tiny in comparison to the T slots on my lathes. So I am hoping for a way to do all of this while mounted on the dividing head and using the crank to set the divisions for the scribing operation.  I was thinking that I can set the little divider arm thingy (Apology, the correct name for this thing escapes me at the moment...) on the crank\plate at 40 degrees, then do one turn + the 40 degree arc on the crank SHOULD arrive at 10 degrees at the spindle.
I was planning on scribing all of the 10 degree divisions first, then mark all of the 5 degree divisions. then scribe the individual degree marks. 
I realize that this probably isn't the preferred method to get this accomplished.  I'm just trying to get this done with what equipment is available to me.  The time involved to get it done doesn't matter to me, as long as it gets done right the first time.

Appreciate your time to even read this long winded post.


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## benmychree (Jan 6, 2019)

On that dividing head, the angular marks were on the quick indexing plate that screws onto the step where the chuck screws onto the spindle, with 3 small screws.  Save your time and effort, dividing heads are rarely used for angular work, mostly all dividing for such as gears, etc.  For angular dividing there is a special dividing plate, it works with both the sector arm and it's  pin, and also the pin that secures the plate from rotation in the back of the plate.


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## jcp (Jan 6, 2019)

stomp10 said:


> Now my question for you is if one turn on the crank equals = 9 degrees arc at the spindle, then one turn on the crank and 40 degrees of arc on the crank SHOULD equal 10 degrees on the spindle? Or am I mistaken in this assumption?


Sounds right..


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## f350ca (Jan 6, 2019)

One turn of the crank is 9 degree at the spindle, your 27 hole ring on the plate will work. 3 holes on the plate is 1/9th of a turn or 1 degree at the spindle, so one turn plus 3 holes for 10 degree, or 15 holes for 5 degree increments, or 3 holes for 1 degree increments.

Greg


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## stomp10 (Jan 7, 2019)

Thank you everyone for your responses!

Ben, sadly the quick indexing plate was not included in this particular EBay deal, which is why I wanted to scribe these marks on the existing backing plate. I figured if I can make a perfect 360 degree scale on the backing plate it would both familiarize me with the operation and that I would have a point of reference for the resolution that is capable on doing divisions via the hand crank.  This kind of thing is kind of outside my wheelhouse, so I thirst to learn.
jcp, it is also good to hear that the grey matter is still working in this old brain of mine so, many thanks for your affirmation on my crude calculation. 
Greg, I gotta say your answer blew my mind.... It might have taken me years to figure that one out, but instead you have just cut a lot of time out of my learning curve.  I have no idea how you figured that one out other than you must be a machinist by trade? Anyway, I can't thank you enough for that answer!
Brad


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## P. Waller (Jan 7, 2019)

benmychree said:


> Save your time and effort, dividing heads are rarely used for angular work,



Gears and splines are not radially angular? Please explain.


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## Bob Korves (Jan 7, 2019)

P. Waller said:


> Gears and splines are not radially angular? Please explain.


It was clear to me.  Dividing heads are for setting divisions of a circle, tooling like rotary tables are for setting angles directly.  Sure, both can be used for each other, given an integer division ratio (or some "close" substitute), but they are not designed for that use and are usually clumsy for getting the results you want.


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## P. Waller (Jan 7, 2019)

Dividing plates were created in order for a machinist to set up multiple machines then have them run by unskilled operators.
Turn the crank X number of times then place the pin in this hole every time and here is a simple guide to help you do so, a sector arm.

Pre Automation

If indeed you possess a dividing head you may produce accurate divisions without dividing plates, this is slow and cumbersome at best but you are a hobbyist and time is not a major factor.

If I were to suggest buying a $5000.00 dividing head that will produce virtually any number divisions required many would point out that they are not pros but hobbyists and do not require speed, you can not have it both ways unfortunately. Cheap and good do not dance well together.


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## Bob Korves (Jan 7, 2019)

P. Waller said:


> Dividing plates were created in order for a machinist to set up multiple machines then have them run by unskilled operators.
> Turn the crank X number of times then place the pin in this hole every time and here is a simple guide to help you do so, a sector arm.
> 
> Pre Automation
> ...


OK.  I need to set an angle of 2 degrees 10 minutes, but don't have a rotary table.  I have a B&S standard dividing head.  I divide 360 degrees by 2.16666(7) (approximate decimal value of 2 degrees 10 minutes), then divide that into 360, which gives me this many -166.1538205917199- (roughly!) divisions of a circle.  Tell me what plate to use and what count circle and how many divisions of it, and how close the result will be.  I do understand how to pick something that is roughly correct, but how do I find the best choice among the three dividing plates I have?  Not asking for an numerical answer, instead asking how you would get there with my B&S standard dividing head and plates.  No fair switching to sine plates. Won't do this job...


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## P. Waller (Jan 7, 2019)

You want a 12 decimal place solution in decimal degrees?

You could not do that with a very high end rotary table or a CNC indexer.
That is 2° 9' 13.75413" Deg. Far from 2 Deg 10 Minutes (-:


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## Bob Korves (Jan 7, 2019)

P. Waller said:


> That is 2° 9' 13.75413" Deg. Far from 2 Deg 10 Minutes (-:


How did you get to that number, if I may ask?


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## RJSakowski (Jan 8, 2019)

Actually, 2º 10' is equal to 130' and 360º is equal to 21600'.  Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel. (Bob, you got caught in rounding error)

However, the question was how do you set up a dividing plate to produce a rotation of 2º 10' (+/- 5 ", the typical resolution of a rotary table)?


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## Bob Korves (Jan 8, 2019)

RJSakowski said:


> Actually, 2º 10' is equal to 130' and 360º is equal to 21600'.  Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel. (Bob, you got caught in rounding error)
> 
> However, the question was how do you set up a dividing plate to produce a rotation of 2º 10' (+/- 5 ", the typical resolution of a rotary table)?


Well, a standard B&S dividing head does not do differential indexing, and 166.153846153846, even if 166 divisions can be done, will not be within the 5" tolerance.  Perhaps on a differential indexing head, with all the attachments, but I think this confirms that the dividing head is not equal to the rotary table for the randomly stated sample angle.  And that is what I had guessed.  If the boss told me to make it with the dividing head, my answer would have to be "not with the tooling on hand."


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## Janderso (Jan 8, 2019)

Insubordinate employees always give me headaches.


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## Bob Korves (Jan 8, 2019)

RJSakowski said:


> Actually, 2º 10' is equal to 130' and 360º is equal to 21600'.  Dividing the former into the latter give exactly 166.153846153846 divisions, according to Excel.


Well, likely not "exactly."  Notice that the long number has repeating groups of 5 digits after the decimal point.  That will repeat on and on, never reaching an end.  Still, close enough for anything we are doing by calling it 166.15 divisions.  Measure it with a Moore Special Tools rotary table, mark it with a carpenter's pencil, cut it off with a hardy (hardie) and a hand sledge.


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## RJSakowski (Jan 8, 2019)

Bob Korves said:


> Well, likely not "exactly."  Notice that the long number has repeating groups of 5 digits after the decimal point.  That will repeat on and on, never reaching an end.  Still, close enough for anything we are doing by calling it 166.15 divisions.  Measure it with a Moore Special Tools rotary table, mark it with a carpenter's pencil, cut it off with a hardy (hardie) and a hand sledge.
> View attachment 284366
> 
> View attachment 284365
> ...



Good catch, Bob.  I didn't notice the repeating sequence.  When I used Excel to do the math, I set the number of decimal places to the maximum which was 30 decimal places.   It gave all zeroes after the 12th decimal place and the implication was an exact answer.  Apparently, Excel has rounding errors too.  To put things in perspective though, a 5 second error in laying out an agle would amount to .00012" on a 5" radius.


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## tcarrington (Jan 8, 2019)

To turn the dividing head 2 degrees 10 minutes, a 54 hole dividing plate should get the job done. with a 40:1 reduction
13 holes out of 54 holes is 360*13/54 = 86-2/3 on the dividing plate, 2-1/6 on the head. 
Not the easiest way to get there, but It would work.


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