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  • Question about dividing plates

    I'm going to be building a rotary table or dividing head soon and can't seem to find any info on building my own plates. There is a set with tailstock on sale at Busy Bee right now but they are designed for there 90:1 tables. I would like to build mine as a 40:1, will these still work or do I need to find 40:1 plates?
    http://busybeetools.ca/cgi-bin/picture10?NTITEM=B2503
    Thanks.

    Clinton

  • #2
    I imagine for nearly all divisions you'd want to do, the 90:1 plates would be perfectly satisfactory for a 40:1 ratio.

    It's all about factors. With either ratio, you end up needing to turn the crank 1/2 a turn, 1/3 a turn, 1/4 a turn, or whatever fraction a particular number of divisions may require. For any given number of divisions, you'll need a different number of full turns and partial turns depending on the gear ratio, but in nearly all cases you should be able to get it.

    For any given number of divisions, you can figure it out as:

    (number of turns required) = (gear ratio)/(number of divisions)

    For example, for 32 divisions, it would be 40/32 or 90/32.

    I think Marv Klotz may have a handy-dandy program on his website to figure all that out.
    Last edited by SGW; 03-06-2009, 06:21 PM.
    ----------
    Try to make a living, not a killing. -- Utah Phillips
    Don't believe everything you know. -- Bumper sticker
    Everybody is ignorant, only on different subjects. -- Will Rogers
    There are lots of people who mistake their imagination for their memory. - Josh Billings
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    • #3
      Index plates are dumb, and don't care whether they are on a 40:1 or 90:1 ratio index head. The BB plates are the standard 3 plate set used with 40:1 dividing heads with 15 to 49 holes.
      Jim H.

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      • #4
        Thanks guys, I've never used either before so I have no clue. It just seemed like a good price so nows the time to buy. I'll go pick'em up for whenever i get around to building.

        Clinton

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        • #5
          This is something I had posted before in response to a similar question:

          The holes in the plates are all about prime numbers. ...... In order to have an exact setup for a given number of divisions you need to have all of the prime factors of that number in either the circle or the worm. A 40:1 worm has 2, 2, 2, and 5. With the 21 (3 X 7) division circle, you can get any number of divisions that can be expressed by a combination of both sets of primes: 2, 2, 2, 3, 5, and 7. Other circles give other combinations and other numbers of divisions. But if the divisions you want contains a prime that neither the circle nor the worm contains, then you can not do it. At least not exactly.

          But there is hope. You can make your own plates on the dividing head itself. This is because the dividing head acts like an accuracy amplifier when drilling a hole circle. The accuracy of the circle you are making is as many times more accurate as the ratio of the worm you are using. Thus, with a 40:1 worm in the head, your work will be 40 times more accurate than the circle you are using. All within the basic accuracy of the head of course.

          You can take advantage of this by using a two step procedure to make your own plates. First make an approximate circle with the number of divisions you want. This can be layed out BY HAND or with a CAD print. This circle is only temporary so it can be just printed on paper and taped over one of the regular plates. Now make a blank plate and mount it for drilling. Use the temporary plate to drill the real one. If you have a 40:1 worm in the head, use 40 holes or lines on the temporary plate for each hole. Or whatever the ratio of the worm is, use that number of holes.

          This new, shop made plate will be 40 times as accurate as your temporary, paper one so, if the temporary one is accurate to +/-1/4 degree, the permanent one will be within +/-1/160 degree or +/-22.5 seconds. Now use this shop made plate to cut a final plate which will be 40 times as accurate again or about +/-0.56 seconds. I really doubt that your indexer is that good or even anywhere close to it so any further refinement would be a totally wasted effort. This plate will be as good as any commercial plate you can buy.

          If the worm ratio on your dividing head or table is even higher like 72:1 or 90:1 then the accuracy multiplier is even higher.
          Paul A.
          SE Texas

          Make it fit.
          You can't win and there IS a penalty for trying!

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          • #6
            Don't matter whether you roll your own or go for shop bought Clinton,a plate with 40 equi-spaced holes on a PCD don't realise what the word "Ratio" means, likewise, if you have 40 equi-spaced holes on a 2" PCD the angle turned between EACH hole is the same for 40 equi-spaced holes on a 4"PCD.

            Regards "Spaced out" Ian.
            You might not like what I say,but that doesn't mean I'm wrong.

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            • #7
              40 :1 chart here for the normal plates although this chart has 63, 25 and 127 on them which is not part of a standard set.

              http://www.stevenson-engineers.co.uk...%201%20new.pdf

              .
              .

              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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              • #8
                Dividing plates

                I have a division plate with one hole in it.

                A bit like the 'I've got a dog with no nose' joke but if you know what you are doing, things get better and better- making division plates.

                Oops

                Norm

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                • #9
                  I wonder with all the cut-price DRO's/digital calipers that are able to be produced nowadays why someone hasn't applied the technology to produce a rotary table with a digital display for a modest price? Is there a limitation to the technology that prevents it?
                  Peter - novice home machinist, modern motorcycle enthusiast.

                  Denford Viceroy 280 Synchro (11 x 24)
                  Herbert 0V adapted to R8 by 'Sir John'.
                  Monarch 10EE 1942

                  Comment


                  • #10
                    Originally posted by Peter.
                    I wonder with all the cut-price DRO's/digital calipers that are able to be produced nowadays why someone hasn't applied the technology to produce a rotary table with a digital display for a modest price? Is there a limitation to the technology that prevents it?
                    Thanks Peter, I guess there is no point in going to the patent office....now that You put My idea on the net .

                    Steve

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                    • #11
                      Hi-res rotary encoders are still quite pricey. You could however, do what some have done in the past, convert rotary motion to linear motion.

                      You could wrap a steel cable or flat steel strap around the table like an old radio tuning dial, and attach it to a digital caliper. You might need to introduce a some tension in-line with this.

                      The problems start when you start cranking the table. An 8" table would need a 24" scale for almost full rotation. A 24" digital caliper can be had for around $100 or less.

                      Doing it with a PC would be easier since you can introduce the angle factor:

                      (arc segment) = (radius) X angle (in radians) or,

                      angle (radians) = (caliper readout) / (table radius) or,

                      angle (degrees) = (caliper readout) * 180 / (table radius) * PI

                      So, a caliper reading of 1" on an (exactly) 8" table platter would represent an angle of 14.324 degrees

                      Den
                      Last edited by nheng; 03-07-2009, 02:16 PM.

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                      • #12
                        BW Electronics in the Uk does such a system

                        http://www.bwelectronics.co.uk/appnotes/rotary.html#top

                        It uses a fine stainless wire to pull an encoder round for rotary work ot pulls it out in a straigh line for linear work.

                        I bought a couple in the early days as they were quite cost effective but unfortunately prices have gone up whilst glass scale units have come down. I notice now he's quoting 0.003" accuarcy when in the early days he used to quote 0.001" ?

                        .
                        .

                        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                        Comment


                        • #13
                          Hmm what about a system that uses an encoder wheel driven off a circular rack similar to how the dial calipers work? That ought to be quite accurate, compact and cheap to produce.

                          EDIT: whoops - just re-read nheng's post about cost of them
                          Last edited by Peter.; 03-07-2009, 02:25 PM.
                          Peter - novice home machinist, modern motorcycle enthusiast.

                          Denford Viceroy 280 Synchro (11 x 24)
                          Herbert 0V adapted to R8 by 'Sir John'.
                          Monarch 10EE 1942

                          Comment


                          • #14
                            Take a Shooting Start (Canadian) DRO and wrap the scale around the table. It is gear based, as far as I recall.

                            added after Peter's last - the hi-res encoders I referred to were those used in precise servo based systems for position feedback. High end ones are in the 20,000 count per revolution, maybe more.
                            Last edited by nheng; 03-07-2009, 02:28 PM.

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                            • #15
                              Clinton, Sorry for wandering off a bit here ... but it could be a way of generating precise angle spacing, perhaps on a par with a good x/y DRO.

                              Peter, There has been lengthy discussion of using PC mice in the past for encoding. I don't recall if it wandered into optical mice but there's an option possibly worth playing with. An interesting basic study of opto mouse movement is here: http://www.contrib.andrew.cmu.edu/~t...ision_Project/

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