# Thread: How to use a rotary table and dividing plates

1. ## How to use a rotary table and dividing plates

Hi All
I have just purchased a rotary table and indexing plates as i would like to lean how to cut some gears.
The instructions which came with it are useless as to the setting up and working out which plate to use.
I want to make a timing belt gear which is about 5" dia whith 82 teeth, the gear ratio on the table is 90 to 1 can any one point me in the right direction or suggest any sources for informationon on useing dividing plates and rotary tables .
The table is a vertex 6".
Many thanks Bill

2. What The 90-1 Ratio Is For 90 Turn Of The Handle The Table Will Rotate 360 DEG. The Index Plate A For Indexing If You Have A Plate With 8 Notches Each Nocth Will Be 45 Deg. So Take The # Of Notches And Divide By 360

3. ## How to use a rotary table and dividing plates

It is pretty simple. Take your table ratio and divide it by the desired number of divisions. Take the result as a fraction and find a plate which has some multiple of the fraction deminator. Your example: 82 divisions
90/82=1+8/82
This gives one full turn plus 4 holes in your 41 hole plate.

If you had a common 40 turn head, the problem would become: 40/82 which reduces to 20/41 - 20 holes in your 41 hole plate.

Most machinery handbooks will have tables for this sort of thing..

4. Originally Posted by lvanduyn
It is pretty simple. Take your table ratio and divide it by the desired number of divisions. Take the result as a fraction and find a plate which has some multiple of the fraction deminator. Your example: 82 divisions
90/82=1+8/82
This gives one full turn plus 4 holes in your 41 hole plate.

If you had a common 40 turn head, the problem would become: 40/82 which reduces to 20/41 - 20 holes in your 41 hole plate.

Most machinery handbooks will have tables for this sort of thing..
Maybe that should read 90/82=1.097*nearest equal divider hole plate(41) =45 holes.

Another format for the sake of the discussion would be that for a full revolution of the table 360/90 turns of the handle=4degrees/turn. 1.097*4deg=4.39 degrees, which is the same as 360/82.

That brings up a problem with prime numbers of division. Unless you already have an index plate with prime numbers pre-made, like say 83. You can still do this without an indexing plate. Just use the turns factor to calculate the index manually. 90/83 =1.084*4deg would be 4.337 degrees for each index. A servo indexer is a great asset for this type of setting to reduce the chances of operator error. It makes it pretty tough to hit 4deg 20.22minutes consistently depending on the quality of the handwheel scales. This has made me consider mounting a rotary encoder to the RT. That can be done for reasonable cheap.

DC

5. If The Ratio=90/1 The 0n Turn Is = 4 Deg 4X90=360 ON THE PLATE IS THERE MORE THAN ON HOLE OR A SCALE THE MATH CAN GET CONFUSING THERE MAY ALSO BE OTHER PLATES FOR YOU TABLE FROM THE MANFACTOR

6. Hi Guys
many thanks to you all for coming back with the information its has been a great help.
The time has come to play, i think i will try it out on a peace of MDF or paxaline to get the feel of things before cutting chips with the metal ,and make up a spread sheet with
all the holes on the indexing plates and mark them up so i know what is what.
Many thanks Guys
Regards Bill

7. Hi guys
I've just unpacked and degreased my 90:1 RT and plates. I read the posts on a couple of sites and have the general drift of how to operate the RT. Being challenged in the math dept ,I'd like to source the set of tables/charts for the RT. The kit didn't include a destruction manual.

8. ## 82 tooth division

Since your rotary table has a 90:1 ratio divide 90 by 82.
This reduces to 45/41 or 1 and 4/41. That would be
1 whole turn and 4 spaces on a 41 hole circle on a
division plate.

If you don't have that circle, print
one out on paper and stick it to a plate and move
your index pin and sector arms by eye.

Any error is reduced by 90 to 1 through your gearing.
Keep going in the same direction to avoid back-lash and
if you do over-shoot, back up some and try again.

Clamp the table while cutting and have no distractions
at all.

Best Regards, Charlie

9. ## Rotary table instructions

Thanks Charlie

The 82 division tip with a "paper plate" will come in handy

I've been scratching in all nooks and crannies on the net and finaly found instructions with tables and math instructions.

So other newbies to rotary tables (with a 90:1 ratio), try this link:

http://www.minitech.com.au/images/PD...le%20Guide.PDF

Beyers

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