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What am I doing wrong? Dividing head.

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  • What am I doing wrong? Dividing head.

    I am trying to cut a 26 tooth gear but things are not going quite right!

    Once around the blank and I find it has rotated too far, not much, but enough to be visibly out.

    I am using the 39 hole range, one full turn plus 21 holes. i.e. I have 22 hole space between the sector arms of the dividing head. Is that right?

    My technique is to rotate the handle and put the index pin back in the hole it came out of then turn the sector arms and advance the index pin to the new position of the sector arm.

    ???

  • #2
    you need 21 holes between arms.
    .

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



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    • #3
      The maths sounds right, 40:1 worm and wheel?

      so...
      a turn (39) plus 21 = 60 holes
      (39 x 40) / 60 = 26 alright!

      Hmmm.... Are you coming up short (e.g. 26 and a bit teeth) or long (25 and a bit)? If short, you need to take an extra hole, if long one less - but it sounds like you're doing it right! Are you *certain* the sector arms aren't moving a bit as you crank the handle round?

      Dave H. (the other one)
      Rules are for the obedience of fools, and the guidance of wise men.

      Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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      • #4
        Originally posted by John Stevenson

        you need 21 holes between arms.
        No, 21 *spaces*, surely? that means 22 holes between - f'rinstance, if it was a turn-and-a-half on a 40-hole, you'd need to put on a full turn and 20 spaces, so 21 holes between the arms (you wouldn't count the starting hole)?

        Just my ha'pennorth

        Dave H. (the other one)
        Rules are for the obedience of fools, and the guidance of wise men.

        Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

        Comment


        • #5
          Assuming 40:1 on the drive,
          Code:
           40 / 26 = 1 14/26 if you have a 26 hole plate, or
                     1 7/13 if you have a 13 hole plate, or
                     1 21/39 turns for a 39 hole plate.
          Don't count holes - count spaces. Or be sure you start your count at 0 for the zero'th hole.

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          • #6
            Oh well, I guess I wasnt holding my mouth right or something! Second blank came out OK except some of the teeth are a bit tighter than others, not seriously and I am sure I can fix them.

            Thanks for advice.

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            • #7
              This gadget it the bomb for indexing:

              http://www.divisionmaster.com/divisionmaster.html

              Make some parts bolt it on. Bye-bye index plates.

              Comment


              • #8
                +1 Forrest Addy and the "Divisionmaster". It will cut or drill or what-ever any number - even 127 which no standard set of divider plates will.

                I suspect that the "tight and loose" bit on the OP's gears is due to back-lash creeping in - ie it was not "taken up".

                Always approach the arm in a clockwise direction and alway lock the table at each gear slot as its quite easy to move the table unless its locked.

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                • #9
                  indexing

                  Cranking is fussy! You must be sure to always take up slack in the same direction. If you accidentally go too far, you must back up a ways and come up to the end again. Depending on your machine, you might not be able to return the piece with the cutter in cut position. I have had to lower the knee during return and refeed for the next cut.
                  Hugh

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                  • #10
                    First what is the number of turns of the input shaft for one revolution of the work holding shaft. If it's 5-1 then for a 39 hole plate you have 195 holes. 195/26=7.5. So if you go 15 holes an index that should work. It'll take two full turns of the work to get what you need so you won't be cutting adjacebt teeth until you get to your second revolution of the work. One sector arm aganst the trailing side of the index pin. the other 15 hole away from the index pin. Lock the sector arms. Pull the index pin and rotate to the arm. Insert pin. Unlock sector arms and bring the trailing arm up to the pin. Lock in place. Repeat as required.
                    Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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                    • #11
                      My bet is that its a 40:1 "Vertex".

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                      • #12
                        Originally posted by oldtiffie
                        My bet is that its a 40:1 "Vertex".

                        Maybe a clone, Homge BS-1 semi universal dividing head. 40:1 handle.

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                        • #13
                          P.S. Always ensure chuck is firmly screwed onto dividing head...

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                          • #14
                            Having your head as well as your chuck screwed on tight is always an advantage.

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