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  • Gear cutting

    Help!

    I have need to cut a 127 tooth gear using a mill and a 40:1 dividing head. As it turns out, this is not a simple index, and if I am reading Machinery’s Handbook correctly, it turns out to be a compound index. I haven’t done that, and after talking to five people in “the tradeâ€‌ I can’t find anyone who has.
    If I am understanding the handbook correctly, for this number of divisions, I will make nine turns around the gear to finish, and each index movement will consist of 2 turns, and 23 holes on a 39 hole plate, + 12 holes on a 49 hole plate.
    All sounds good, except how do I keep track of where I may be at each point? Do I move the pin to the 49 hole circle and back to the 39 hole circle, or do I move the index plate without loosing track of where I am?
    Would someone who has done this before give me some advise as to what works so that I don’t have to re-invent the wheel and/or make this gear two or three times?

    Thanks

    JCD

  • #2
    127 indexes per rev? 40 to 1 dividing head? 40/127 = 0.314961 revs per div. How many holes of what hole circle is that? If it doesn't come out how do I gear the index? I have no idea without digging out my books.

    I bought a gadget that indexes for me. It's ruined me as an old timey, pencil chewing, gear swapping machinist.

    I modded the dividing head to drive to take a NEMA 23 stepper motor. I work the ratios and run the stepper with a Division Master. Great gadget. Poke the button, it steps the motor to index one division of the total you selected, and then it stops. Clamp. Bzzz! Cut. Dial back to clear. Unclamp. Poke. Bzzz! Cut. Etc.

    It's only a question of time before I start looking for drapes to match the cutting oil.

    [This message has been edited by Forrest Addy (edited 03-16-2005).]

    Comment


    • #3
      40/127 is very very close to 5/16. The difference between them is, in fact .00246 . I don't know if that amount of error is acceptable in making such a gear, but it's something to consider.

      -Justin

      Comment


      • #4
        <font face="Verdana, Arial" size="2">Originally posted by jburstein:
        40/127 is very very close to 5/16. The difference between them is, in fact .00246 . I don't know if that amount of error is acceptable in making such a gear, but it's something to consider.

        -Justin
        </font>

        To be honest the error may or may not that much to make a difference but when calculating out helical gear cutting ratios the standard we always used was +/-.0000X of the ratio as the gearing equations came out to. For threads (which in some ways can be thought of as a similiar machining operation) the question of error is just how long is the thread in the nut and how tight is the fit
        Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

        Comment


        • #5
          Where are you in MO? I can cut 127 in Des Moines.

          Comment


          • #6
            Hi JCD,
            To cut a 127 T gear with a dividing head, it the dividing head must be a Universal Dividing head with the gears and quadrants and stub spindles, it looks like this when assembled to cut 127 Tooth gears



            The plate has to rotate a fractional amount, it does this by the bevel gear drive, driven from the dividing head spindle, throught the set of compound gears on the quadrent, then turning the bevel gear, which rotates the hole plate.
            Pic of bevel gear drive



            Pic of hole plate rotation after cutting 127 teeth, white mark on plate started at the top to cut the first tooth, then indexing to the next tooth the small gear in the spindle turns the set of gears on the quadrant, witch turn the bevel gears, on witch is mounted the hole plate. The plate has moved approximately 1/3 of a turn, see white mark on the plate.



            ------------------
            Doug

            [This message has been edited by vmil3 (edited 03-16-2005).]
            Doug

            Comment


            • #7
              Without using a universal or cnc dividing head,you can make your own plate with 127 holes in it and then turn every 40 holes. The problem with this is it is almost as much work as making the gear.

              This can be made on a mill with a dro and bolt hole feature. Another problem is that 127 holes are a lot of holes and the holes have to be the same size as the holes in your other plates. Also there needs to be a little meat between holes which may require a larger dia plate than your old ones which in turn may require a longer arm that holds the plunger/pin.Then you may find the larger plate will hit the table,unless you arrange the head so the plate hangs over the edge of the table. I had all of these problems with cutting several 89 tooth gears.

              Maybe you should just buy a gear.

              Jim W.

              Comment


              • #8
                There is an easier way. Just find a gear shop that has a Barber Colman 30-1 hob and have them set it up with a 30 driver and a 127 driven Actually the hobbing ratio is 4.233333333 to 1 driver to driven for a 127 tooth gear. We have neat book at work with the absolutely catchy title of "14,000 Gear Ratios" Comes in very handy for coming up with gearing combos for helical work
                Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

                Comment


                • #9
                  Hey vmil, that head looks a lot like my old kempsmith although I'm missing the gear train parts. Thanks for posting the pics! Now I know what the rest of a universal looks like.

                  ------------------
                  Hoffman in Warner Robins Ga
                  Techno-Anarchist

                  Comment


                  • #10
                    Spin,
                    If he had a 127 driven he wouldn't need a 127

                    There are divison plates on ebay.co.uk with 127 hole circles.

                    John S.
                    .

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



                    Comment


                    • #11
                      If you have a rotary table, you could make a 127-hole plate using that. 2.8346... degrees per hole...
                      ----------
                      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
                      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                      Don't own anything you have to feed or paint. - Hood River Blackie

                      Comment


                      • #12
                        There is an article on the Jan-Feb 1998 "Home Shop Machinist" on compound dividing. I haven't pulled it out to reread yet, so I don't know if it will answer your question or not.

                        ------------------
                        Charles McGough
                        Sterlington, LA
                        Charles McGough
                        Sterlington, LA

                        Comment


                        • #13
                          hoffman,
                          Not a kempsmith, it's a Vilh Pedersen from Denmark. Here are pic's of the complete Universal Dividing head with manual, there are 2 dividing plates.







                          ------------------
                          Doug
                          Doug

                          Comment


                          • #14
                            <font face="Verdana, Arial" size="2">Originally posted by CharlesM:
                            There is an article on the Jan-Feb 1998 "Home Shop Machinist" on compound dividing. I haven't pulled it out to reread yet, so I don't know if it will answer your question or not.

                            </font>
                            Thanks Charles, It looks like my Numbers are correct. I am still looking for procedure.

                            JCD

                            Comment


                            • #15
                              <font face="Verdana, Arial" size="2">Originally posted by vmil3:
                              Hi JCD,
                              To cut a 127 T gear with a dividing head, it the dividing head must be a Universal Dividing head with the gears and quadrants and stub spindles, it looks like this when assembled to cut 127 Tooth gears



                              The plate has to rotate a fractional amount, it does this by the bevel gear drive, driven from the dividing head spindle, throught the set of compound gears on the quadrent, then turning the bevel gear, which rotates the hole plate.
                              Pic of bevel gear drive



                              Pic of hole plate rotation after cutting 127 teeth, white mark on plate started at the top to cut the first tooth, then indexing to the next tooth the small gear in the spindle turns the set of gears on the quadrant, witch turn the bevel gears, on witch is mounted the hole plate. The plate has moved approximately 1/3 of a turn, see white mark on the plate.



                              </font>
                              Thanks for your help,
                              I do not have the gears for diferental indexing, so I must do it with compound indexing.
                              I'm looking for that procedure.

                              JCD

                              Comment

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