Announcement

Collapse
No announcement yet.

Gear Cutter via 2 button method

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Gear Cutter via 2 button method

    I would like to make an involute gear cutter using the 2 button method as described by Ivan Law's book Gears and Gearcutting , p 114-.
    No problem with the method, which is fully understood, but I need a 20 degree PA, No8 gear cutter for 12-13t. The book only gives the table of dimensions for cutters from No1 to No6. Can someone supply the remaining part of the table, or alternately define the equations which define these dimensions?

    Possibly Ivan derived these best fit dimensions by drawing the actual involutes, in which case I will do the same, but a calculation method would be best. It is also possible that the deviation from the involute form becomes too great with the lower tooth counts and this is the reason why they are omitted.

    Can anybody help?
    Bill

  • #2
    Hi Bill,

    I have derived a table for button sizes , button spacing and infeeds that goes down to 12 tooth gears, see:
    http://mikesworkshop.weebly.com/desi...r-cutters.html

    I would also point you to another page on my website that shows an alternative way of making the cutter which is much simpler to do. The methods was invented by John Stevenson who posts on this bulletin board.
    http://mikesworkshop.weebly.com/maki...r-cutters.html

    I hope this helps

    Mike

    Comment


    • #3
      Three or four years ago, I posted an Excel spreadsheet for determining the button sizes. I sent a copy to a couple of board members. A year ago, I lost my hard drive, and one of the lost files was that spreadsheet. None of the guys I sent it to has been able to find a copy, unfortunately. I haven't had time to come up with a new one.
      Jim

      Comment


      • #4
        Mike -

        Many thanks for those links - they should give me just what I need. I must be getting old, because I now remember the thread where John S introduced his improved method and you suggested some improvements. I actually contributed to that thread but had forgotten that I had done so.

        I need to do the calculations for an 8DP cutter which is a lot bigger than those for which the original method was defined. Have you any thoughts on the feasibility of the method with bigger gears and lower tooth counts?
        Bill

        Comment


        • #5
          Hi Bill,
          I have no experience of cutting gears that big but I cannot see any reason why it should not be possible using the same techniques if you have a big enough and powerful mill to chew the metal. You will need a thicker cutter to withstand the increased cutting forces and you will have to watch that there is sufficient clearance at the back of the tool or it may rub.
          Cutting forces are much lower if you use plastic such as acetal (Delrin) for the gear blank but whether this would be suitable will depend on the application.
          Mike

          Comment


          • #6
            Mike -

            Delrin would be nice, but not possible in this case. The gear is for a small hydraulic pump which will be driven by line shafting from one of the smaller mill engines in our museum. (http://www.nmes.org/) I don't think Delrin would be strong enough, and ideally we like to stay as close to the original materials as possible. The pump will not be under any great load, it is just so that we can show what line shaft drives looked like and how they worked. The pump is missing this critical gear so I am working out how to make it at a reasonable cost. To add to the interest, the gear is non-standard. A considerable degree of profile shift has been used, probably because of the rather small number of teeth.
            Bill

            Comment


            • #7
              Bill you need two buttons 0.612" diameter, 0.746 apart.

              Start off with a 0.500" wide blank, touch the buttons on the outer edges and infeed 0.253" to form a 12 tooth 20 degree PA, 8 DP gear cutter

              I have shifted and stubbed this slightly as you wrote but the OD is still the same as a standard gear.
              .

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



              Comment


              • #8
                John, thanks very much for that. Did you use Gearotic to help with the calculations? If so, how well do you feel it works with non-standard, profile shift type situations?
                Bill

                Comment


                • #9
                  Yes Bill, based the calculation on the 2D output from Gearotic.

                  I find it a brilliant program. works well with all types of spur gears and helicals, bevels are still untested to a big extent, on paper they look OK but not enough users are beta testing.

                  As regards profile shift gears, last year I was given the engineering drawings for a 4 speed vintage car gearbox. This was a complete new design where aall the gears had been changes from crash sliding gears to sliding dog to give a better change, different ratio's and a stronger box.

                  The design was approved by the VCC in that these type of boxes existed in the relevant years so everyone stuck to form.

                  My customer bought in to the design for an undisclosed sum but wanted different ratio's for hill climbing. The original designer wasn't interested so I ran the figures thru Gearotic, added a tooth here, dropped a tooth there and got the ratio's he wanted.

                  All the details of the project screen was sent to the gear cutters and they fitted all fine.
                  .

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



                  Comment


                  • #10
                    John, that sounds great. I will put Gearotic on my Christmas list.

                    I worked in the automotive industry for some years. Very few gears were standard or even close. Lots of odd specifications to get the right ratios or perhaps stronger gears.But those companies had some extreme gear specialists and the backup of the big gear cutting machine suppliers to help get it right.

                    In our museum we sometimes need to work with gears where there are definitely no drawings, no spares, no money to buy expensive tooling and we are not gear specialists. Gears that date from about 1840, sometimes not even involute and in the extreme cases weighing 30 tons and 18 feet diameter. Some of those big gears are 'as cast' - no machining, just general filing to fit. They tend to rumble a bit when they run.

                    The current job is fairly simple in comparison, but I would like to cut a gear that runs well and doesn't damage its mating gear.
                    Bill

                    Comment


                    • #11
                      Not to discourage you but I went this path and personally found it 'finicky' to get everything set up. I also wanted to cut mulitple gears so I need to make a new buttons and possible holder each time. The other thing that drove me nuts was the 'banging' while making the cutter if you are relieving the cutter any.
                      I finally went the rack design because I had a nice divding head to use. That is what sold me on make a rack type cutter.
                      Both methods have their pros and cons. It just depends upon what equipment you have available to you.
                      The rack is simple as you only have to grind the angle of the gear you need and determine the proper depth for the cut.
                      http://i10.photobucket.com/albums/a1...ps9c1024fe.jpg
                      http://i10.photobucket.com/albums/a1...ps43446c03.jpg
                      http://i10.photobucket.com/albums/a1...ps16ff59f3.jpg
                      http://i10.photobucket.com/albums/a1...psca606afd.jpg
                      http://i10.photobucket.com/albums/a1...psd2c3dcbf.jpg
                      http://i10.photobucket.com/albums/a1...ps8d836b29.jpg
                      http://i10.photobucket.com/albums/a1...ps9c1024fe.jpg
                      http://i10.photobucket.com/albums/a1...ps585ffafa.jpg

                      I also like the following link for formulas.
                      http://www.astronomiainumbria.org/ad...h/geardata.htm
                      This one may help you with the buttons also
                      http://mikesworkshop.weebly.com/desi...r-cutters.html

                      Dean's page is also a great alternate method to make cutters. Heavy picture warning bet well worth it. It has been posted here before.
                      http://www.deansphotographica.com/ma...ultipoint.html

                      Comment


                      • #12
                        Originally posted by mc_n_g View Post
                        Not to discourage you but I went this path and personally found it 'finicky' to get everything set up. I also wanted to cut mulitple gears so I need to make a new buttons and possible holder each time.
                        That is a fair point, but in this case I will make just one gear (hopefully) and probably never use the tool again. It will go into stores just in case someone in our museum, 50 years on, needs to make a replacement. The method that John S introduced is very attractive because it reduces the number of tool cutting stages essentially to one.
                        Bill

                        Comment

                        Working...
                        X