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Re: [mlathemods] DIY Dividing Head Question

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  • xlch58@swbell.net
    While this is generally true, it is not precisely true. There are worm gear set ups that allow the worm the be driven by the othe gear. hey generally have a
    Message 1 of 6 , Mar 1 6:08 AM
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      While this is generally true, it is not precisely true. There are worm
      gear set ups that allow the worm the be driven by the othe gear. hey
      generally have a large lead. If you think about it, with high accuracy
      parts and good lubrication just about any worm gear can work in reverse.


      Charles

      e3pi wrote:

      > Note also worm gears lock position on the non-"pinion" main gear
      > axel - i.e.; the main gear angular displacement cannot drive the
      > "pinion" or "worm" - which is a benefit for machinery set up.
    • James W. Early
      At our : Group there is a lot of information stored relating to rough and fine dividing as well as the making of
      Message 2 of 6 , Mar 1 6:58 AM
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        At our :

        <http://groups.yahoo.com/group/mwmills2/>

        Group there is a lot of information stored relating to rough and fine
        dividing as well as the making of gears.
        JWE
        Long Beach, CA


        --- In mlathemods@yahoogroups.com, "e3pi" <e3pi@y...> wrote:
        >
        > I've zero experience with dividing heads, but I am excited with
        > their 40: 60:1 precision leverage and ease for general dividing the
        > circle; and possibly used for linear ruling too; I imagine.
        >
        > I've a Dayton 24:1 Gear Reducer.
        > This has helical gears with negligial backlash that I can tell.
        >
        > It is small enough to be "Taigable".
        >
        >
        > From reading I see 60:1; 40:1 are common for dividing head worm
        gears.
        >
        > Note also worm gears lock position on the non-"pinion" main gear
        > axel - i.e.; the main gear angular displacement cannot drive the
        > "pinion" or "worm" - which is a benefit for machinery set up.
        > This Dayon gear reducer will drive either axel; i.e., 24:1 or 1:24;
        > as desired. This could be a problem.
        >
        >
        > One small grace advantage:
        >
        > "24" is a "highly composite" integer(24=4*3*2*1=4!); ; makes for
        easy
        > arithmetic shared among common fractions of 360 degrees.
        >
        > So aside from half to a third the precision of other DH's - is this
        > a reasonable source on the start of my first DIY dividing head?
        >
        >
        > http://groups.yahoo.com/group/liveaboardlathe/message/81
      • e3pi
        Thank you all for your thoughtful replies. Repeatability seems an easy check by marking the axels and counting spins- or is there something else? DIY dividing
        Message 3 of 6 , Mar 1 9:38 AM
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          Thank you all for your thoughtful replies.
          Repeatability seems an easy check by marking
          the axels and counting spins- or is there something else?

          DIY dividing head plates are discussed in some three
          internet links I've found.

          I'm again amazed at the depth and intensity of
          yahoo group esoteria - the link:

          http://groups.yahoo.com/group/mwmills2/

          with a big following suggests a new standard
          to me of good internet meat and potatoes.

          I'm a micro machinist newbie but have had good
          success cobbling disparate machines and salvaged
          minutiae into something new and delightful.

          My salvaged Hermes engrager alu "X" stand and steel compound
          carrying a Taig headstock into a Taig-scale milling
          machine is beautiful and I hope to have images
          in a week. Alot of options to hang units on; one
          advantage is the milling column dial is at the bottom,
          beneath the Taig lathe - keeping my hands furthest
          away from from a singing endmill or flycutter.

          The cockpit of my sloop that I fabricate in is
          a total tidal mess.


          e3pi
          http://groups.yahoo.com/group/liveaboardlathe/







          --- In mlathemods@yahoogroups.com, "James W. Early" <j.w.early@w...>
          wrote:
          > At our :
          >
          > <http://groups.yahoo.com/group/mwmills2/>
          >
          > Group there is a lot of information stored relating to rough and
          fine
          > dividing as well as the making of gears.
          > JWE
          > Long Beach, CA
          >
          >
          > --- In mlathemods@yahoogroups.com, "e3pi" <e3pi@y...> wrote:
          > >
          > > I've zero experience with dividing heads, but I am excited with
          > > their 40: 60:1 precision leverage and ease for general dividing
          the
          > > circle; and possibly used for linear ruling too; I imagine.
          > >
          > > I've a Dayton 24:1 Gear Reducer.
          > > This has helical gears with negligial backlash that I can tell.
          > >
          > > It is small enough to be "Taigable".
          > >
          > >
          > > From reading I see 60:1; 40:1 are common for dividing head worm
          > gears.
          > >
          > > Note also worm gears lock position on the non-"pinion" main gear
          > > axel - i.e.; the main gear angular displacement cannot drive the
          > > "pinion" or "worm" - which is a benefit for machinery set up.
          > > This Dayon gear reducer will drive either axel; i.e., 24:1 or
          1:24;
          > > as desired. This could be a problem.
          > >
          > >
          > > One small grace advantage:
          > >
          > > "24" is a "highly composite" integer(24=4*3*2*1=4!); ; makes for
          > easy
          > > arithmetic shared among common fractions of 360 degrees.
          > >
          > > So aside from half to a third the precision of other DH's - is
          this
          > > a reasonable source on the start of my first DIY dividing head?
          > >
          > >
          > > http://groups.yahoo.com/group/liveaboardlathe/message/81
        • sauer38h
          ... reverse. ... This is incorrect. A worm gear set with a locking ratio - which is nearly all of them - will strip before the worm will rotate under reverse
          Message 4 of 6 , Apr 13, 2004
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            --- In mlathemods@yahoogroups.com, xlch58@s... wrote:
            > If you think about it, with high accuracy
            > parts and good lubrication just about any worm gear can work in
            reverse.
            >



            This is incorrect. A worm gear set with a locking ratio - which is
            nearly all of them - will strip before the worm will rotate under
            reverse load no matter what the lubrication is. This is one of the
            useful features of worm gearing.

            Locking ratio worm gears have tooth contact at less than the locking
            angle. The locking angle varies with different materials and
            lubricants, but is never zero. Locking action occurs in worm gearing
            because the contact between teeth is entirely sliding contact -
            there's none of the rolling contact characteristic of spur gears with
            involute teeth. Spurs gears do not have locking ratios.

            The static coefficient of friction is the sine of the locking angle.
            It can be measured by putting a block of one material on a ramp of
            the other, and tipping the ramp up until the block slides under its
            own weight, or any other vertical force. The angle at which that
            happens is the locking angle. Strictly speaking, this is Coulomb
            or "dry" friction. The word dry is misleading - it does not mean
            unlubricated. It differentiates this friction mechanism from viscous
            drag, the domininant drag or "friction" force when a fully-developed
            hydrodynamic film separates the parts.

            Worm gears can be modified to be reversing by increasing the lead of
            the worm. To get enough lead you'd have to have something like a 4-
            tooth gear, which won't work for geometrical reasons. Some multi-lead
            worms can be reversed. They're not common - in thirty years in
            engineering I've yet to see one. The other way to make a reversing
            worm gear is to offset the axis of the worm and move it down toward
            the axis of the gear - in which case it becomes a spiroid or hypoid
            gear set, and isn't called a worm gear anymore.
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