Using a rotary table

[david gregg 1Participant @davidgregg1]

I have a rotary table with a 90 To 1 reduction and also 4 division plates which cover a wide range of holes can any body tell how to work out the number of holes to use so that I can divide this into 100 so that I can scribe that l can scribe the lines I know that I need to turn 3.6 degrees so less than a full turn of the handle

[david gregg 1Participant @davidgregg1]

I want to put calibration marks on a indexing dial

[EmgeeParticipant @emgee]

David

Please advise the number of holes per circle in the plates, the plate to use can then be calculated.

Emgee

[HopperParticipant @hopper]

YOu need to get a copy of the Workshop Practice Series book Dividing. All is revealed in there.

Including that 100 divisions on a 90:1 ratio dividing head can be achieved by moving 18 holes at a time on a circle of 20 holes. Or a multiple thereof, such as 36 holes on a 40 hole circle. Or 72 holes on an 80 hole circle.

Or you can work it out: 90/100 x number of holes in the circle. Answer of course must  be a whole number as you cant move half a hole etc.

It gets complicated. Best to get the book. Also there are online spreadsheets and charts. Be wary of the Vertex chart, it contains errors but I forget for which divisions.

Edited By Hopper on 02/02/2022 23:43:33

Edited By Hopper on 02/02/2022 23:45:02

Edited By Hopper on 02/02/2022 23:46:19

[noel shelleyParticipant @noelshelley55608]

18 holes in a 20 circle, 27 holes on a 30 circle, 36 holes on a 40 circle , 45 holes in a 50 circle, 54 holes in a 60 circle. Etc ! Hole circle divide by 10 then X 9 = holes needed to be moved. Good luck, Noel.

Edited By noel shelley on 02/02/2022 23:53:01

[Thor 🇳🇴Participant @thor]

Hi David,

There is an online calculator here, that you may find helpful. As others have mentioned, you need a 20 hole (or multiple thereof) division plate.

Thor

[SillyOldDufferModerator @sillyoldduffer]

If the table is one of the HV6 family, Howard Lewis gave us this corrected table. For 100 holes he gives Wheel A, with 20 holes, then 18/20, which agrees with Noel.

As many of us find keeping count painful, driving the table with a micro-controlled stepper motor is a popular alternative. The software does all the hard sums, keeps count and there's no need to mount the division wheels. Ask again if that's of interest.

Dave

[not done it yetParticipant @notdoneityet]

Posted by noel shelley on 02/02/2022 23:45:23:

18 holes in a 20 circle, 27 holes on a 30 circle, 36 holes on a 40 circle , 45 holes in a 50 circle, 54 holes in a 60 circle. Etc ! Hole circle divide by 10 then X 9 = holes needed to be moved. Good luck, Noel.

Edited By noel shelley on 02/02/2022 23:53:01

S’easy when you know how! Noel is spot on with any one of his multitude of options, but you are maybe trying to start at the wrong end of the calculation.

It does not matter how many times you turn the handle, you just need those extra spaces for that extra 3.6 degrees on top of the multiple of 4 degrees. You would need to turn that same amount 100 times for a full revolution at 3.6 degrees each time.

For 3.7 Degrees, you would need 37/40 of a turn. For 3.9 degrees you would need 39/40ths. For those prime numbers (37 and 39) you cannot use a plate with fewer holes than forty.

Your 3.6 degrees would be for a 100 tooth gear, or whatever you might be machining, so you need a plate hole number that when multiplied by 90 is divisible by 100. End of problem, really, in this instance. 90/100 = 0.9. Any plate which has a hole at exactly 0.9 of the way round will do.

Try it and see. 20 space plate: 20*90/100 = 18. 50 space plate: 50*90/100 = 45

This will be how you can calculate any number of spacings required for any integer-number of teeth on a gear, without recourse to tables on the internet (some of which are known to be incorrect).

I’ve never relied on (or even used) tables as the calculation (for gear cutting) is sooo eesy!

The only difficulty might be for someone to pick which plate circle to use when it is not the same as the actual number of increments you want per revolution. Plates are (unsurprisingly) made for prime number (or multiples of primes) calculations. Seems complex at first but is simplicity, if not easily befuddled by maths.

Think simply – each plate circle is that number as a fraction of 40 (rotary tables with different turns/revolution use the same plates but just different fraction denominators).

[david gregg 1Participant @davidgregg1]

Thanks to all those who replied and explained what to do ,I have a plate with 40 holes so I now know that I can move to the 36 hole and go from there and hopefully will remember what to do for any future holes required so thanks to all The forum is such a great source of knowledge

david gregg

[noel shelleyParticipant @noelshelley55608]

If your using dividing plates then remember to set and use the sector arms ! It will make the job easy. Good Luck Noel.

[Brian WoodParticipant @brianwood45127]

David,

Another useful "tool" is to include a cocktail stick so that you have a marker on the last hole from which to index a further 36.

Brian

[Nick HughesParticipant @nickhughes97026]

Grizzly have quite a good manual for their rotary tables, that explains the indexing method quite well:- Grizzly Manual

[DalboyParticipant @dalboy]

Maybe of a little HELP

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