Roger,

The instructions sound entirely logical

(5×16)+10 = 90

… So I really don't know what's going wrong.

MichaelG.

You need five complete turns plus 10/90th of a turn. Thus you need one hole in a 9 hole plate, 2 holes in an 18 hole plate etc. You will have to find a plate where the number of holes is a multiple of 9.

I dont agree with 18 holes.

You can do it with the 16 hole plate as I said above.

Or you can use 5 full turns and 15 spaces of a 24 hole circle

Or you can use 5 full turns and 20 spaces of a 32 hole circle

18 holes does not work.

Phil

Edited By Phil P on 03/11/2015 17:24:21

Hello Roger,

It is the gaps you count, not holes and the sector arms are moved as a locked pair after each cut. You don't need to release the chuck, in fact you could easily lose count or position that way.

I found a cocktail stick on the other side of the sector arm when it has been moved into contact with the pin as a useful reference to return to if you lose count. Move it up to that arm again after each resetting of the sector arms.

Try another 'air-cut' to check it through as you did.

Brian

Going back to thw original post:

I am trying to cut a 16 tooth gear. The Warco chart for 16 teeth on a 90:1 ratio shows 5turns and 10/16 extras. I set it up as instructed with 11 spaces between the sector arms.

Surely with a 16-hole plate it should be 11 holes or 10 spaces?

But the only way to get 18 with 90:1 ratio is to make 5 full turns + NOTHING, so I am sure that LUigi has the real problem – the sector arms aren't being advanced after each division is made.

Neil

Does anyone know what the advantage of 90:1 is?

I wonder if there is one really. Coming from industry I had used 40:1 for dividing plus compound at times. I went to buy a worm and wheel and they only had the 60 as that is what people want so bought that. Turns out that with the usual standard plates 60 is ok. On the other hand I saw some new Vertex bits available and do want to make a bigger dividing head or maybe / rotary table at some point I wondered about buying them to save making a few bits and pieces. When I checked the hole counts in the plates I found that they wouldn't cut 2 primes that I will probably want. Leaves me wondering if 90:1 is just bigger number must be better. 90 also needs to be a bigger wheel to achieve equally strong teeth,

John

–

On the Arc site there is a link to a guide by Cletus Berkeley on setting up and using a rotary table.

**LINK**

No, you need 90/16 turns = 5.625 turns

So 5 turns plus 5/8 of a turn (or 5 turns plus 10/16 of a turn) …. a plate with a multiple of 8 divisions.

I think the 90:1 has got more to do with the physical size of the actual worm gear under the table.

By default the rotary table is usually larger in diameter that a dividing head, so the gear will also need to be bigger, if it only had 40 teeth they would need to be huge ones, so they went up to 90 as standard on most commercial rotary tables I have come across.

In reality it does not matter too much what the ratio is so long as it is an even number that can be divided into easily.

I tend to use plates from my 40:1 dividing head on the 90:1 rotary table and vice versa when required.

The GHT dividing head is 60:1 and that is quite a useful bit of kit as well. But to be honest most times for general use I use a 24 hole direct indexing plate on the back of my Tom Senior dividing head.

Phil

Do it all in division plate hole steps.

Multiply the 90 by the 16 of the division plate giving you 1440 for 360 degrees.

you need 16 teeth so divide by 16 which is 90.

you have 16 holes on your division plate so 90 is 5×16 + 10

or 5 whole turns plus 10 holes for each tooth.

regards Martin

Edited By Michael Gilligan on 04/11/2015 11:34:57