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Old 06-16-2010, 09:52 PM   #1
Brian Rupnow
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Default Rotary table -Divider plates

Today I washed all the cosmoline gunk off my Divider plates which came with my rotary table (which I purchased 3 years ago). I followed the Chinglish instructions, and after slotting the holes in the divider plates so they would actually fit the bolt pattern in the rotary table (Thats a whole 'nuther story) I was able to assemble things okay. I am beginning to figure out how the divider plates are supposed to work---fortunately I am using the rotary table to cut an eithteen tooth gear, which means 5 full rotations of my handle to accomplish the 20 degrees between cutting positions, so I can use any of the divider plates. (Mine is a 90:1 gear reduction).----Now the question---Those brass arms (I think they are called "sectors") have a screw, which when tightened will lock the angle between the sector arms---However, the two arms (now locked at some angle) seem to rotate fairly freely on the center hub.---They shouldn't do that, should they?? If I am doing some exotic pattern that calls for X number of full rotations and then count how ever many additional holes in the divider plates to let my spring loaded handle pin drop into (Which I THINK is supposed to be located by one of the sector arms)---and the arms rotate out of position---then I'll end up dropping my spring loaded pin into the wrong hole. What am I not understanding here---Brian



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Old 06-16-2010, 10:32 PM   #2
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Default Re: Rotary table -Divider plates

Brian,

In the dividing plate set there is a largish spring clip which locates in a groove in the shaft and prevents the sector arms from rotating freely. They will still rotate as they must but with some resistance.

Looking at your picture you seem to have it fitted but maybe it needs bending to tighten things up a little.



The pin should be inside the sector arms and the sector arms should be set to the number of holes required + 1. e.g. X turns + 10 holes, the sector should be set to 11 holes on the appropriate holes circle.

Hope this helps

Best Regards
Bob



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Old 06-16-2010, 11:01 PM   #3
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Default Re: Rotary table -Divider plates

Thanks Bob---I guess mine must be okay then. they don't "flop around" but if you weren't paying attention when you were turning the handle and the pin did hit them, they would move. I guess that just means "Pay attention"!!!----Brian

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Old 06-16-2010, 11:13 PM   #4
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Default Re: Rotary table -Divider plates

Hi brian i have a whole book just on dividing if you would like to borrow it just let me know.

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Old 06-16-2010, 11:32 PM   #5
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Default Re: Rotary table -Divider plates

Brian;
I will try to help if I can.

The two arms should rotate freely around the hub but not too freely.

On my RT there is a half moon spring between the arms and the hub that keeps tension between the two.
If your divider plates don’t have a spring, thy are very easy to lose or it may have came without one you mite be able to put a peace of paper or even some tape between the arms and the hub to give you the friction you need. Or you may be able to dill & tap the ring on the arms for a small set screw to give some friction.

On the divider plate you mite want to put a mark on the top of the plate at the hole that you will be using with something like a Sharpie pen so you will know where you are. When going around the plate for the next tooth if you should go by where you want to stop, you will want to take a full turn in the opposite direction to get red of any back lash then come back to where you wish to be.

You don’t want any distractions, it is very easy to lose count and end up ruing a gear. Cutting gears can be enjoyable (and at times almost as much fun as watching oil base pant dry) Ha, Ha.

Good luck
Richard

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Old 06-16-2010, 11:56 PM   #6
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Default Re: Rotary table -Divider plates

Gee Brian, I thought you said you weren't interested in learning how to use dividing plates.

Let me see if I can explain the use of the sector arms.

With a 90:1 RT, you have to turn the RT handle 90 full turns to make the part turn one complete revolution. Now let's suppose you want to make a 21 tooth gear. That requires turning the part 1/21 revolution for each tooth. That means you have to turn the handle

(1/21) * 90 = 90/21 = 4 & 6/21 turns

for each tooth. That's four complete turns of the handle and 6 spaces (note I didn't say holes) on the 21 hole plate.

Put the pin in one of the holes and bring the beveled edge of one of the sector arms around to touch the left side of the pin. Now, counting the hole the pin is in as zero, count off 6 holes and place another pin. Verify that there are indeed six inter-hole spaces between the two pins. Bring the other sector arm around so its beveled face touches the right side of this last-placed pin. Tighten the locking mechanism that retains this angular separation of the two arms.

Now, when you want to index, swing the locked sector arm assembly so as to put the beveled edge of the sector arm pair against the left side of the indexing pin. Pull the pin and turn it 4 full turns, then continue to the hole that lies next to the other sector arm on the 21 hole ring. Voila, you've moved the handle 4 and 6/7 turns and you only had to count to four. Really, once you understand it, I think you'll agree that it's a very ingenious mechanism.

-----

For any other gear, with N teeth, simply compute:

90/N

and express it in a fraction with a denominator that matches the number of holes in one of your hole circles. Then proceed as above to set the sector arms.

-----

If you do a lot of dividing, it's still easier to use my program. Or, use it to check your calculations if you have concerns.

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Old 06-17-2010, 12:10 AM   #7
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Default Re: Rotary table -Divider plates

Marv---Thank you. I really, really didn't want to use the dividing plates. They seemed like such a black mystery to me that I was afraid to use them. However---once I read enough to realize that with 20 degree seperations I could use any of the plates, not worry about the sector arms, and "hole counting", I decided to at least see if they would fit on the rotary table. Of course, the damned things didn't, and had to be modified, but they are on there. ---Now you have to realize---I was terrified of computers too---Swore I would never use one.---Now I teach 3D solid modelling. I guess anything is possible.---Brian

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Old 06-17-2010, 12:19 AM   #8
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Default Re: Rotary table -Divider plates

It's far simpler than it might appear from a casual glance and it's a valuable tool to have in your arsenal. All that's required mathematically is a bit of diddling with mixed fractions. The rest is simple mechanics and will be obvious.

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Old 06-17-2010, 12:34 AM   #9
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Default Re: Rotary table -Divider plates

I just found this really neat video on "That other" website I hang out on. Its great---shows a man making a gear and using the dividing plates and sector plates. Make sure your sound is on when you watch it.

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Old 06-17-2010, 01:10 AM   #10
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Default Re: Rotary table -Divider plates

Quote:
Originally Posted by Brian Rupnow
and after slotting the holes in the divider plates so they would actually fit the bolt pattern in the rotary table (Thats a whole 'nuther story) I was able to assemble things okay.
Yes my instructions were a bit vague on assembly too and it took me nearly 2 hours to fit the plates correctly on my first use.
I haven't used mine very much yet and I need to concentrate when I am using it not to mess it up, but I do love them


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