Are dividing head tables generic or specific to maker?

I posted yesterday about a dividing head I wanted to get back in working order. It needed a part mending and a couple of other bits locating or making. This is now done and it is ready to use.

It was suggested in the replies that for tables, I would need to know the maker because table are specific to the unit.

I had assumed that tables for a DH with 40:1 reduction ratio would work for all dividing heads using the same ratio.

As I have never used one, could someone point me in the right direction for tables please?

Many thanks.

I find it simpler to do the calculations as you may not have the plate with the number of holes specified in the table.

For a 40:1 dividing head, divide 40 by the number of intervals/teeth etc you wish to machine. Reduce to an integer plus a fraction. The integer part is whole turns, the fractional part leads you to the number of holes to advance in addition.

So, for example, to do 24 teeth on a gear, 40/24 = 1 + 16/24 = 1 2/3. The plate hole circle needs to be a multiple of 3, for example, 39 is a commonly available circle, so 1 turn plus 2/3 x 39 = 1 turn and 26 holes.

You'll never need a table again.

Rob

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You’re right, Jim … they do; provided that the set of plates has all the right numbers too.

MichaelG.

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Rob beat me to the post.

Edited By Michael Gilligan on 28/07/2023 17:20:28

What you have is commonly known nowadays as the "BS0" as it is (probably) a copy of the Brown & Sharpe one.

There are copies of the B&S tables on the 'net and plenty of others too. For many divisions there is more than one way so tables may not agree exactly but it is also good to know how to calculate yourself. (there is one mistake in the original B&S tables but I can't remember what it is as it is a count nobody much uses)

Try THIS calculator. put in 40 for the worm and all the plate holes you have, comma seperated. click update and you will have a table of all the possible divisions and all the impossible ones as well!!

Thanks everyone for the very speedy and informative replies. I may download some tables but Rob Cox put it in a way very easy to understand, so I will probably use maths.

First project will be a 1/2" Whitworth left hand thread bolt. Coincidentally the 5C collet blocks I ordered to make a hex head arrived today, but I am now determined to use the DH.

Bizibilder Thank you. I know I will spend an hour checking that against my maths now!

Harold Hall's 'Metalworkers Data Book' is a cheap source of useful stuff like D/H tables and much else; the D/H tables are pretty thorough and IIRC (mine's in the workshop) lists alternative ways of arriving at the wanted division.

Yes, might well be a BS0. If the ration is 40:1, copy the table and change all the 90s mto 40s.

Note the number of holes on each of the plates that you have, and, with a bit of luck, they will appaear on the spreadsheet.

From this you can construct your own chart, showing the divisions available to you.

IF it is BS0,and has a 40:1 ratio, maybe some kind person has one and will send you a copy of their chart.

Howard

First of three videos showing a real Brown & Sharpe one : **LINK**

https://youtu.be/dSzy1dbZKPw

MichaelG.

A 40:1 table will work for all basic 40:1 dividing heads in terms of the mathematics. What matters is whether you have the appropriate hole count in your plate selection. Even if you don't you can easily make one by printing a paper template of your hole pattern onto a disc, centre-punching the pooints and drilling them free-hand. Any error will be divided by 40.

Surely the manufacturers of dividing heads regardless of ratio would be supplying plates that would give divisions most likely to suit the general needs of engineering dividing?

Hole counts are needed for prime numbers, but you are not going to bother with a circle of just say 7 holes. So the lowest number is eg 3x7 but it might be 2x13 and so on, picking multiples of the lowest primes. Plates often have 6 or 7 rows of holes and a set of 3 will probably give all the divisions up to 50 and lots more but with gaps in the sequence.

This covers most normal work but manufacturers would have a couple more plates to give some more prime numbers covering almost everything up to 100 though they probably hardly ever got used. A larger more fully equipped machine shop would have a universal head enabling differential indexing to get those big primes, like 127 for metric conversion gears.

They do, but the worm ratio and the number of holes in any particular circle are not independent.

The (useful) number of holes depends on what prime numbers are contained within the worm ratio. Consider a 40:1 ratio and a 90:1 (or 60:1). There is a factor of 3 in these latter two ratios which is not in the former ratio, so plates supplied with the former have to provide the missing 3.

Just fit a stepper motor and Ward controller and forget about plates.

no thanks john give me a solid worm and worm wheel any day. Most dividing practice is based on the Brown and Sharpe dividing head as they were I believe the inventor/developer of dividing and gear cuting on the universal mill,the major manufacturers used the 40:1 worm wheel and most tables in Machinerys Handbook and other literature are B & S tables. possibly the most common variation is the Myford head which uses a ratio of 60:1. B& S mounted their dividing head on the left hand end of the table,possibly because lathes had their chucks to the LH side, Cincinatti mounted theirs on the RH end of the table,it seems an unusual position but at the time of these developments and patents ,its possibly a way of avoiding patent infringement.

Agreed. But drive the worm from a stepper.

It's fair to say that some rotary tables have been supplied with bad printed dividing tables by the makers.

It's also fair to suspect that the same dividing plates end up on BS0 heads. Which explains why the internet has so many tables available

Personally I wouldn't trust any supplied tables and I always run a complete gear marking each position with a felt tip before fitting a cutter. It's tedious, but a lot less so than messing up a gear cut.