Author Topic: Dividing With a Rotary Table  (Read 11235 times)

Offline Bryan

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Dividing With a Rotary Table
« on: March 08, 2011, 07:48:01 PM »
Attached is a zip file containing an Excel spreadsheet. Below is a copy of the readme. If you are prompted about macros when opening, you can disable them.

Quote

This spreadsheet is intended to enable divisions with only a rotary table and no division plates. If you want to divide a circle into, say, 16 equal parts, select the sheet labeled 16 and print the page. The last 3 columns are the degrees, minutes and seconds to set on your rotary table for each consecutive step. You may want to tick each one off as you go.

Tables are only included for divisions up to 127, that being the highest number commonly used for lathe change gears. If you need higher numbers it's easy to do.

At the bottom left of the screen, click this  >|  to go to the far right of the tabs. Right click the 360 tab and insert a new worksheet. If for example you're doing 153 divisions, name the sheet 153.

Go to the 360 tab, select all and copy. Paste to your new sheet. Now there are two small edits  needed. First, cell B2 will say =360/360. Change the last number to your divisor, in this case 153. Now just delete all the rows below that number. In our example, delete rows 155-361 inclusive. (There's an offset because of the title row.)

Check that the last row says 360 degrees, 0 minutes, 0 seconds. If it doesn't, something went wrong. Make sure B2 is correct.

Errors, suggestions, comments etc may be addressed to: shed at ptmedia dot com dot au.

This file may be freely distributed.





Offline Artie

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Re: Dividing With a Rotary Table
« Reply #1 on: March 08, 2011, 08:20:47 PM »
Thanks mate, saved... while I do have the plates for my RT... its still 'black magic' at this point, one of the to do list items, learn how to use the plates!  :(
South Wales, wait...NEW South Wales... Batemans Bay.

Offline mklotz

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Re: Dividing With a Rotary Table
« Reply #2 on: March 09, 2011, 10:59:26 AM »
Alternatively, download the ROTARY program from my page and run it.  It will produce a file that looks like this example...

Code: [Select]
Number of divisions = 13

DIVISION      degdec     deg     min     sec
       0      0.0000       0       0       0
       1     27.6923      27      41      32
       2     55.3846      55      23       5
       3     83.0769      83       4      37
       4    110.7692     110      46       9
       5    138.4615     138      27      42
       6    166.1538     166       9      14
       7    193.8462     193      50      46
       8    221.5385     221      32      18
       9    249.2308     249      13      51
      10    276.9231     276      55      23
      11    304.6154     304      36      55
      12    332.3077     332      18      28
      13    360.0000       0       0       0

Print the file and carry it to the shop. 
Regards, Marv

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http://www.myvirtualnetwork.com/mklotz

Offline RichardShute

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Re: Dividing With a Rotary Table
« Reply #3 on: March 12, 2011, 04:55:20 AM »
Thanks mate, saved... while I do have the plates for my RT... its still 'black magic' at this point, one of the to do list items, learn how to use the plates!  :(

Artie,
using the plates is actually not as difficult as it seems at first and for 'direct indexing' you can do the calculation in your head, because there is none, once you know the rule. An example first, then the rule.

Say your rotary table ratio is 60:1 - many are. You turn the handle 60 times to get one table rotation

I'll pick a deliberately peculiar division, say 17. You want the table to turn 1/17 turn for one index, so the handle will move 60/17 per index.

Now, 60/17 is an inconvenient angle of degrees, but if you have a disc with 17 holes, each hole is 1/17 turn and you want 60/17 so you simply count 60 holes round the 17 hole ring. Job done

Soooo... The Rule:
for n divisions, count the number of holes equal to the table ratio round the n-hole ring, that's it.

If you haven't got a disc with n holes then look for one with 2n and count twice as many holes, so in the above example 120 holes on a 34 hole ring. Or if necessary 3n and three times as many.

You set the forks, if you have them, so that the edges indicate the 'extra' holes. Say you were going to do 120 holes on a 34 hole ring. That's 3 turns (=102holes) and 18 extra holes. Set the forks 18 holes apart, bring the trailing fork against the pin, wind round 3 turns and then up to the leading fork, drop the pin in the hole. Before the next move, slide the forks round so the trailing one is again kissing the back of the pin etc.

Hope that helps
Richard
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Offline Artie

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Re: Dividing With a Rotary Table
« Reply #4 on: March 19, 2011, 03:53:44 AM »
Hi Richard, yes it does help and thank you. Ive actually worked out how to use them...just havent taken that 'step' yet.... have had jobs that need the dividing head but have put those jobs to one side.

Lots of excuses.... im in the last 5 days of an extended work trip (jayzus...I left home last month...!!)... get home late Wednesday night and back on the plane Thursday afternoon.....aaaahhhh.....

Be a while before I get cutting fluid in my veins again.... :loco: :palm:
South Wales, wait...NEW South Wales... Batemans Bay.

Offline wildman692

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Re: Dividing With a Rotary Table
« Reply #5 on: December 09, 2011, 02:50:58 PM »
Thanks mate, saved... while I do have the plates for my RT... its still 'black magic' at this point, one of the to do list items, learn how to use the plates!  :(

Artie,
using the plates is actually not as difficult as it seems at first and for 'direct indexing' you can do the calculation in your head, because there is none, once you know the rule. An example first, then the rule.

Say your rotary table ratio is 60:1 - many are. You turn the handle 60 times to get one table rotation

I'll pick a deliberately peculiar division, say 17. You want the table to turn 1/17 turn for one index, so the handle will move 60/17 per index.

Now, 60/17 is an inconvenient angle of degrees, but if you have a disc with 17 holes, each hole is 1/17 turn and you want 60/17 so you simply count 60 holes round the 17 hole ring. Job done

Soooo... The Rule:
for n divisions, count the number of holes equal to the table ratio round the n-hole ring, that's it.

If you haven't got a disc with n holes then look for one with 2n and count twice as many holes, so in the above example 120 holes on a 34 hole ring. Or if necessary 3n and three times as many.

You set the forks, if you have them, so that the edges indicate the 'extra' holes. Say you were going to do 120 holes on a 34 hole ring. That's 3 turns (=102holes) and 18 extra holes. Set the forks 18 holes apart, bring the trailing fork against the pin, wind round 3 turns and then up to the leading fork, drop the pin in the hole. Before the next move, slide the forks round so the trailing one is again kissing the back of the pin etc.

Hope that helps
Richard
sorry but that read incorrectly as the locating pin will already be against the left hand fork you then need to move it 18 holes so the arms are actually set 19 holes showing (number required plus existing location) I am surprised no one has pointed this out yet.

Offline Fergus OMore

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Re: Dividing With a Rotary Table
« Reply #6 on: December 10, 2011, 04:22:33 AM »
One of the most informative( my opinion) articles is the book by GH Thomas called Workshop Techniques. OK, it's a brit book and all that jazz but it takes the reader through not only building a dividing head but actually how to make division plates.

It takes a lot of believing but this guy had at one point, a division plate with ONE hole. He generated -with increasing accuracy, how each plate etc  was made.

And - yes- I have one.  But, GHT -as usuual- wrote up in his other book- Model Engineers Workshop Manual how to make a small rotary table- without gears. His had, however, a set of degree graduations - around the outer edge. Mine has them but has gears as well.

Couple of good books for the Christmas- eh?

Offline Bryan

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Re: Dividing With a Rotary Table
« Reply #7 on: February 17, 2012, 11:57:32 PM »
It has come to my attention that the file in my original post has become corrupted somehow, so I am reposting it. Please let me know if this doesn't work. Thanks.

Offline Fergus OMore

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Re: Dividing With a Rotary Table
« Reply #8 on: February 18, 2012, 02:54:28 AM »
Sorry- maybe it is me- but I didn't get anywhere!

Regards

FOM

Offline Bryan

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Re: Dividing With a Rotary Table
« Reply #9 on: February 18, 2012, 03:11:34 AM »
Fergus, can you elaborate?

Offline Bryan

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Re: Dividing With a Rotary Table
« Reply #10 on: February 18, 2012, 03:25:27 AM »
It's doing everything it should for me. At what stage does it fail? Download? Unzip? Launch? What error messages appear?

Offline Fergus OMore

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Re: Dividing With a Rotary Table
« Reply #11 on: February 18, 2012, 03:32:28 AM »
All I got was a jumble of a few letters on the first and a front piece on the second. Mebbe me- but others will comment.

Whatever, it is a very useful tool to have for most people to use.

Cheers

FOM

Offline Bluechip

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Re: Dividing With a Rotary Table
« Reply #12 on: February 18, 2012, 04:00:53 AM »
Seems to open OK here,

 .xls file with lots of sheets ..

??

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Re: Dividing With a Rotary Table
« Reply #13 on: February 18, 2012, 04:15:49 AM »
Works fine for me Bryan  :thumbup:

Rob

Offline Fergus OMore

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Re: Dividing With a Rotary Table
« Reply #14 on: February 18, 2012, 07:43:44 AM »
No-go! Sorry.

No matter, my maths is still good enough :smart:
Can still do Trachtenburg Maths.

Cheers

N

Offline mattinker

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Re: Dividing With a Rotary Table
« Reply #15 on: March 12, 2012, 09:13:36 AM »
It has come to my attention that the file in my original post has become corrupted somehow, so I am reposting it. Please let me know if this doesn't work. Thanks.

Thanks Bryan,

this one worked for me. It's just the sort of thing I need!

( Modification! I to am a Linux user, opened with open office)

Regards Matthew
« Last Edit: March 12, 2012, 07:59:14 PM by mattinker »

Offline DavidBraley

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Re: Dividing With a Rotary Table
« Reply #16 on: March 12, 2012, 06:02:24 PM »
Thanks for sharing that Bryan! The reposted file opens and works fine in OpenOffice. (I'm a Linux user...)
-David

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