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Dividing Plate Numbers

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Susan_in_SF

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#1
Hi Guys,
I picked up a 6"rotary table that had a double sided dividing plate on it. As a newbie, I don't know what the two column of numbers on each side mean. When I tried looking up the answer via Google, all I found were the complex explanations on how to use dividing plates, but no simple answer as to what the numbers on the plates mean. Are the plate #'s the # that the row can be divided evenly into?
Thanks in advance for any useful info.
Susan
 

GrayTech

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#2
Number of holes per 360° usually. Pics would help.

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Technical Ted

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#3
On my dividing head (my rotary table doesn't have the index plates) the number on each row is the number of holes in that row. You can look up which row to use and the total quantity of holes needed for each desired division on standard tables in a lot of books or on-line.

Check out YouTube. Here's a quick one I found on a dividing head and I would imagine most, if not all, could be applied to a rotary table as well. I didn't watch the video, just skipped around, but it looks like it explains it much better than I can in a message.


Ted
 

Susan_in_SF

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#4
Number of holes per 360° usually. Pics would help.

Sent from my H3123 using Tapatalk
Sorry about not posting it initially. I will post a pic right now 20181009_092051.jpg
 

Susan_in_SF

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#5
On my dividing head (my rotary table doesn't have the index plates) the number on each row is the number of holes in that row. You can look up which row to use and the total quantity of holes needed for each desired division on standard tables in a lot of books or on-line.

Check out YouTube. Here's a quick one I found on a dividing head and I would imagine most, if not all, could be applied to a rotary table as well. I didn't watch the video, just skipped around, but it looks like it explains it much better than I can in a message.


Ted
Thanks Ted. I will check out the video
 

Susan_in_SF

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#6
Well, I feel silly. I assumed the numbers were 2 separate columns of #'s. It didn't occur to me that the #'s represented the # of holes. Duh!!
Thanks guys for the answers!
Susan
 

Susan_in_SF

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#7
Btw, I did some calculatons, and determined that my vintage rotary table has a 18:1 ratio where with 1 full turn of the handle, the table rotates 5%, or 18 degrees. I got this rotary table from the guy who also sold me Original lathe legs for my baby 6" Craftsman metal lathe. He gets his stuff from auctions. With 1 turn only moving 18 degrees, is this considered a good feature, or a bad thing to have with one's 6" rotary table. Fyi, my female arthritic wrists nearly imploded when I tried carrying this sucker. Bigger isn't always better, lol ;-)
 

Technical Ted

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#8
OK, let's check this... if turning the crank 1 time equal 18 degrees then the ratio is 20:1 not 18:1

Just to double check, count how many full crank turns it takes to make your table turn one complete turn (360 degrees). This number would be the ratio to one.

I don't know what the ratio of my Phase II 10" rotary table is, but my diving head is 40:1 which is pretty much standard. I don't really use my rotary table all that much.

Ted
 

T Bredehoft

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#9
What you will eventualy find, by moving the handle one and 1/3 revolutions, (20holes on a 60 hole plate) You'll get 24º, and other needed numbers. ie., more than one way to use an RT.
 

Technical Ted

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#10
Google is your friend! Did a quick search for common gear ratios for a rotary table and came up with 40:1,72:1 or 90:1. So, the number of turns and number of holes you use on any indexing plate with vary with the ratio of your table. Make sure you know the correct ratio and use that to determine the correct plate/hole spacing to use.

Again, mark your table with a reference line or use some other means of establishing a base line. Count the number of turns it takes on the crank to make one full 360 degree rotation of your table. The number of cranks will be the ratio. So, if it takes 90 full crank revolutions for one full table revolution your ratio is 90:1. BTW, 90:1 must be pretty common because my little Black Book has one table in it and it is for 90:1 ratio rotary tables.

Ted
 

Susan_in_SF

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#11
OK, let's check this... if turning the crank 1 time equal 18 degrees then the ratio is 20:1 not 18:1

Just to double check, count how many full crank turns it takes to make your table turn one complete turn (360 degrees). This number would be the ratio to one.

I don't know what the ratio of my Phase II 10" rotary table is, but my diving head is 40:1 which is pretty much standard. I don't really use my rotary table all that much.

Ted
 

Hawkeye

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#12
Here's a page out of a 1967 high school text book. It tells how to use the plates and the sector arms to get the right angle for your task.
 

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Susan_in_SF

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#13
Hi Ted,
I just saw your message now, but I now have to run out the door to pick my son up at school. So, until I have a chance to read your post and reply, for nor I will quickly post this picture that I took earlier today. I had the pointer on the dial set to zero before I did my one rotation of the handwheel. After one full rotation, the pointer was set at 5. The dial has 4 sets of 0-90 for each quarter of the dial. Regardless, it would still be 5 out of 360, right? Gotta go now 20181009_124616.jpg before I get in trouble for being late in picking up my kid
I appreciate your feedback and correction of any of my mistakes.
Susan
 

Technical Ted

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#14
Hi Ted,
I just saw your message now, but I now have to run out the door to pick my son up at school. So, until I have a chance to read your post and reply, for nor I will quickly post this picture that I took earlier today. I had the pointer on the dial set to zero before I did my one rotation of the handwheel. After one full rotation, the pointer was set at 5. The dial has 4 sets of 0-90 for each quarter of the dial. Regardless, it would still be 5 out of 360, right? Gotta go now View attachment 277293 before I get in trouble for being late in picking up my kid
I appreciate your feedback and correction of any of my mistakes.
Susan
OK, looks like your is a 72:1 then. (360/5=72) So, make sure you use look up tables for 72:1 ratios.

The post by Hawkeye is very good, but looks like it's for a 40:1 ratio so the math won't be the same for yours, but the example is great!

Ted
 

Hawkeye

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#15
The math is the same. Just substitute the number of turns your dividing head uses for the 60.
 

Susan_in_SF

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#16
Special thanks to Ted and Hawkeye for clarifying my foggy wrong calculations. I will print out Hawkeye's high school textbook page, keeping in mind the ratio difference. Hopefully I will eventually really understand how to use dividing plates correctly, especially since I'd like to make some spur gears, to start off with. I have a special project i'd like to try out that involves lots of gears.
 

Technical Ted

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#17
The math is the same. Just substitute the number of turns your dividing head uses for the 60.
60? Yes, the formulas are the same, replace the "40s" with "72". That's what I meant by the math is different. Thanks for the clarification.

I did a quick search for a look up table for plates with 72:1 and didn't come up with anything. Lots of 40:1 and 90:1, but no 72:1. If you search more you may be able to find one. There are on-line calculators where you specify the ratio and desired divisions and those might end up being your best bet. For simple divisions, i.e. ones involving full turns of the crank, you can use the formulas in the post by Hawkeye.

Ted
 

Hawkeye

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#18
I just noticed my slip in the last post. Guess I was thinking about my rotary table. I built it around a 60-tooth gear I found at the scrappers.
 

Susan_in_SF

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#19
Thank you guys. I can use your anseers as a future reference when I finally start using the dividing plates
 
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