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  • Involute shaft

    Bear with me this could take a week to do from start to finish as will be explained in the post but I hope to show it with pictures and text.

    Got a job in last week to do some short shafts with an involute spline on the end, even got a drawing that told me the OD, how many splines and how long- wow - but nothing else.
    0.650" OD, 0.875" long and 12 splines.

    Involute splines are just gears but only half the depth and usually have a 30 degree pressure angle and occasionally 25 degrees.
    Because of this gear calculations work the same - to an extent.
    splines are usually denoted by both sizes of the make up, like 16/32 DP.
    This means the teeth are 16DP but the depth is equal to 32 DP

    To calculate the DP you take the number of teeth, add one and divide it by the outer diameter, for a normal gear it's number of teeth plus 2 and divide. splines are plus 1 because the depth is half of a normal gear.
    So in out case 12 + 1 = 13 / 0.650 =20 DP so this is a 20/40 DP spline.

    Run these figures thru the gear generator and we get this.



    Note 12 teeth, 20DP, and the important bit the depth factor has been entered as .5 to allow for the depth of a 40DP spline / gear.
    This then gives us a true involute of the complete spline which can be saved as a DXF file.

    Once this is brought into CAD and zoomed in you can draw two straight lines, one from the root of the tooth to halfway up the involute and another from there to the outer tip.

    Now if two new lines are drawn midway on each line and at 90 degrees to the existing lines they will converge on the centre of a circle that passes thru all three points, standard geometry 101.

    Draw a circle to check and repeat on the other side.



    This gives us four important pieces of information to make a cutter, the size of the circles, 0.277" and the distance apart 0.300", the width of the gear cutter blank at 0.119" and the depth the buttons need to be infed, 0.051"

    Next job is to make what is usually termed a button cutter.



    Just a piece of flat bar with two holes drilled in at 0.300" centres and tilted at 5 to 7 degrees to accept two top hat buttons made of Silver steel or drill rod , hardened and tempered to light straw for cutting steel.
    These are then surface ground on the top face to sharpen them and give a cutting angle.

    This button tool is used to prepare the cutter blank, more of which, with pics in a later post.

    .
    .

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




  • #2
    I don't think that I've ever seen a button cutter-in 3D or in action! I for one am eagerly waiting for more spline teasing!

    Comment


    • #3
      Thanks for posting this.

      I'm not likely to ever need to do anything like it it myself but it's very interesting all the same and I really appreciate that you have the patience to share your knowledge.
      Mike

      My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

      Comment


      • #4
        Originally posted by John Stevenson
        you can draw two straight lines, one from the root of the tooth to halfway up the involute and another from there to the outer tip.

        Now if two new lines are drawn midway on each line and at 90 degrees to the existing lines they will converge on the centre of a circle that passes thru all three points, standard geometry 101.
        .
        John, You lost Me . I only made it to geometry 100.5 not 101

        Steve

        PS and please don't call Me a clumsy bass turd.

        Comment


        • #5
          Great Stuff Sir John!!

          I'll most likely never use it, but it sure is interesting, I also want to say thanks for your time and efforts in posting this.

          best

          rollin'

          Comment


          • #6
            half depth splines

            Where i used to work we had JIS splines that were the half depth you described, but the PD on the spline was actually at the OD per JIS standard as well as using a 20 dsegree pressure angle.

            Is that possibly the case with your splines?

            If so, it makes the spline thicker at the top of the spline and the curvature less on the spline faces.

            Comment


            • #7
              Originally posted by Jpfalt
              Where i used to work we had JIS splines that were the half depth you described, but the PD on the spline was actually at the OD per JIS standard as well as using a 20 dsegree pressure angle.

              Is that possibly the case with your splines?

              If so, it makes the spline thicker at the top of the spline and the curvature less on the spline faces.
              I think when John makes the shafts it will be up to the customer to adapt their parts.
              .
              "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

              Comment


              • #8
                Im intrested in this 'button' method.. However a nagging feeling has struck me...

                How did you align circles to involute curves? Should'nt they be.. involute not circular?
                Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                Comment


                • #9
                  I dont think i get the spline generation but i like the gif, cool animation
                  in time i may yet understand
                  mark

                  Comment


                  • #10
                    Originally posted by Black_Moons
                    Im intrested in this 'button' method.. However a nagging feeling has struck me...
                    The button method is well described in Ivan Law's little red book of gears - I consider it essential reading.

                    http://www.amazon.com/Gears-Gear-Cut.../dp/0852429118

                    Here's Johns' own version: http://www.metalwebnews.com/howto/gear/gear1.html

                    And once you have the gear cutter you need a reliever: http://www.youtube.com/watch?v=kJ8kyC_bpHs
                    Last edited by dp; 05-23-2010, 12:49 AM.

                    Comment


                    • #11
                      Originally posted by John Stevenson
                      Bear with me this could take a week to do from start to finish as will be explained in the post but I hope to show it with pictures and text.

                      Got a job in last week to do some short shafts with an involute spline on the end, even got a drawing that told me the OD, how many splines and how long- wow - but nothing else.
                      0.650" OD, 0.875" long and 12 splines.

                      Involute splines are just gears but only half the depth and usually have a 30 degree pressure angle and occasionally 25 degrees.
                      Because of this gear calculations work the same - to an extent.
                      splines are usually denoted by both sizes of the make up, like 16/32 DP.
                      This means the teeth are 16DP but the depth is equal to 32 DP

                      To calculate the DP you take the number of teeth, add one and divide it by the outer diameter, for a normal gear it's number of teeth plus 2 and divide. splines are plus 1 because the depth is half of a normal gear.
                      So in out case 12 + 1 = 13 / 0.650 =20 DP so this is a 20/40 DP spline.

                      Run these figures thru the gear generator and we get this.



                      Note 12 teeth, 20DP, and the important bit the depth factor has been entered as .5 to allow for the depth of a 40DP spline / gear.
                      This then gives us a true involute of the complete spline which can be saved as a DXF file.

                      Once this is brought into CAD and zoomed in you can draw two straight lines, one from the root of the tooth to halfway up the involute and another from there to the outer tip.

                      Now if two new lines are drawn midway on each line and at 90 degrees to the existing lines they will converge on the centre of a circle that passes thru all three points, standard geometry 101.

                      Draw a circle to check and repeat on the other side.



                      This gives us four important pieces of information to make a cutter, the size of the circles, 0.277" and the distance apart 0.300", the width of the gear cutter blank at 0.119" and the depth the buttons need to be infed, 0.051"

                      Next job is to make what is usually termed a button cutter.



                      Just a piece of flat bar with two holes drilled in at 0.300" centres and tilted at 5 to 7 degrees to accept two top hat buttons made of Silver steel or drill rod , hardened and tempered to light straw for cutting steel.
                      These are then surface ground on the top face to sharpen them and give a cutting angle.

                      This button tool is used to prepare the cutter blank, more of which, with pics in a later post.

                      .
                      John,

                      I have seen your video on You tube, cutting a spiral bevel gear on your X3 under CNC.

                      Just a thought. Using your CNC, it would appear possibe to make a rack shaped cutter and generate the spline teeth by using the the rotary table in the horizontal position, and running the main table back and forth in the manner of a Sunderland gear planer, but moving the workpiece rather tah the cutter? Thinking about it, it would be vital to lock the main spindle, to prevent rotation, if this is where the cutter was mounted!

                      Just a thought

                      Cheers
                      NzOldun

                      Comment


                      • #12
                        Originally posted by dp
                        The button method is well described in Ivan Law's little red book of gears - I consider it essential reading.

                        http://www.amazon.com/Gears-Gear-Cut.../dp/0852429118

                        Here's Johns' own version: http://www.metalwebnews.com/howto/gear/gear1.html

                        And once you have the gear cutter you need a reliever: http://www.youtube.com/watch?v=kJ8kyC_bpHs
                        The involute is a curve with a constantly changing curvature (radius). A circular button will have a single radius.

                        So, the button method produces a cutter that is an approximation of the involute form, not exact. But it can be quite close, usually within a thousanth or less.
                        Paul A.
                        SE Texas

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

                        Comment


                        • #13
                          Originally posted by Paul Alciatore
                          The involute is a curve with a constantly changing curvature (radius). A circular button will have a single radius.

                          So, the button method produces a cutter that is an approximation of the involute form, not exact. But it can be quite close, usually within a thousanth or less.
                          That is correct. In fact though, because the buttons are tipped at 5؛ or so, they produce elliptical shapes. Some years back John produced CAD drawings of the button method profile overlaid on a generated involute for a variety of pressure angles/tooth counts and the differences were withing the error produced by using commercial cutters over the entire tooth count range.

                          Comment


                          • #14
                            ahh tilting the button, that would produce a very close approximation, cool.
                            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                            Comment


                            • #15
                              Might be a couple of days before the next instalment, the tool and cutter blank but some answers first in no order.

                              The circle IS only an approximation as Black Moons has said but the arc length of this spline is only 0.066" long out of a circle who's circumference is 0.870" so we are talking about a 13th part of a circle.
                              To be honest I don't have anything that could measure this error.

                              Finding the centre of an arc or circle for people who got distracted doing Geometry 100.5



                              Draw two lines that touch on the circle at each end, then draw another line at 90 degrees to this from the centre.
                              where these to lines meet is the arc or circle centre.
                              Because the spline is so small it's hard to see the original work without zooming in.

                              NzOldun,
                              That is doable and is worth giving some thought, however now I have started this I will have to continue and as I reckon the job will be a repeat it's worth it to have the cutter.

                              I'll give it some thought and if I do I'll do another unrelated thread on it.

                              JPFalt,
                              I did input various pressure angles but as soon as I got down to 25 degrees the figures were way off. In all fairness I have never seen JIS splines and I'm under the impression they are for newer automotive designs which I won't see for 40 years [ as if ]
                              .

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



                              Comment

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