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  • Gear Cutters

    I have a small gear 1.100" dia. .193" thick with 16 teeth. Came out of a Japanese mortar. How do I determine what gear cutter to buy. Thanks. Riceone

  • #2
    a number 7 involute gear cutter would be required for 16 teeth

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    • #3
      This post will tell you how to calculate what the pitch is.
      http://bbs.homeshopmachinist.net/showthread.php?t=17870
      And then you will need a number 7 cutter in the pitch you determine.

      Comment


      • #4
        Code:
        Outside Diameter = Number of Teeth + 2
                           ___________________
                             Pitch Diameter
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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        • #5
          OD is 1.100" - 16 teeth plus 2 = 18. 18 divided by 1.100 = 16.3636.
          MSC list 14 1/2 and 20 degree pressure angle. What do I order? Is there a difference in this gear made in Japan in the 30's and an American gear made today? Are there different cutters for Metric and would there be a different way to calculate the pressure angle? riceone

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          • #6
            I'm looking in the MSC catalogue; would I order a dimetrical pitch of 18 in a No. 7 Cutter? riceone

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            • #7
              Whoa!!

              The original post was:
              Originally posted by riceone
              I have a small gear 1.100" dia. .193" thick with 16 teeth. Came out of a Japanese mortar. How do I determine what gear cutter to buy. Thanks. Riceone
              Why is everyone going "inch" when the item is Japanese which is probably "metric"?

              A re-work for metric is:

              OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

              For Modular (metric) gears:
              Mod 2

              OD = PCD + (2 x 2) =28

              PCD = 28 - 4 = 24

              (or for DP equivalent) DP = 24/16 = 1.5

              Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

              It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
              - 28mm OD;
              - 24mm PCD;
              - 16 teeth;
              - Mod(ular) 1.5;
              - 5.00 mm (nominal) wide; and
              - 1.5 DP (equivalent).

              The pressure angle is yet to be determined whether it be "inch" (DP) or "metric" (Modular).

              So if it were me, I wouldn't order that gear cutter yet.

              Comment


              • #8
                With these specs and being Japanese chances are it's 1.5 mod and 20 degree pressure angle.

                .
                .

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



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                • #9
                  Is this it??

                  Originally posted by John Stevenson
                  With these specs and being Japanese chances are it's 1.5 mod and 20 degree pressure angle.

                  .
                  Thanks John.

                  That has "closed the loop" and so I'd support what you say:
                  (sizes in mm):
                  1.5 Mod.
                  20 deg PA
                  28 OD
                  24 PCD
                  16 teeth
                  5mm wide

                  It is possible - as John says- that the Pressure Angle (PA) is 14.5 degree.

                  Comment


                  • #10
                    Oldtiffie, your measurements are correct, just used a metric caliper - should have done that first. Now could anyone tell me what to order, I have found several suppliers of metric cutters on the net. But it all Greek to me. Thanks,

                    riceone

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                    • #11
                      Make it

                      Originally posted by riceone
                      Oldtiffie, your measurements are correct, just used a metric caliper - should have done that first. Now could anyone tell me what to order, I have found several suppliers of metric cutters on the net. But it all Greek to me. Thanks,

                      riceone
                      Hi riceone.

                      I guess you have the original gear.

                      I'd also guess that it is on a static (ie non-moving and non-critical) model or original Mortar weapon and perhaps not the "bomb"/projectile.

                      If this is the case, why not use what you have to grind the profile on a fly-cutting tool and make the part/gear from brass or "free-cutting" steel (for "show" and ease of milling). Use what ever you have of the existing gear to grind the tooth/cutter profile from. Its not too hard and not all that "fussy" either.

                      It will cost next to nothing to make the fly-cutter and you will get huge satisfaction and "bragging rights" if you do the whole job.

                      A fly-cut job should work very well in a "dynamic" situation.

                      Just take your time!!! "Hasten slowly".

                      You will always have the "fall-back" option of buying a milling cutter.

                      If buying a milling cutter (MacMaster Carr (Sp?) in the USA?), just quote the details in my previous post and they will identify the cutter you need.

                      If you have any problems - just start a new thread or continue to post on this one.

                      I am sure that you will get all the help you need.

                      Best of luck - enjoy the experience and the satisfaction of "doing it".

                      Comment


                      • #12
                        Thanks for all your help. I will call someone and give them what you have posted. I have made a few of these using a fly cutter every one has a flaw that I can see, however they fit and work and have had no complaints. I just would like to be able to make one exactly like the original on the right. Here is a photo of the last one I made.

                        Last edited by riceone; 05-06-2008, 08:05 AM.

                        Comment


                        • #13
                          problem with the numbers

                          There is a problem with the numbers here,
                          For a 1.5 module pitch gear, the addendum is equal to the module or 1.5mm. If going by the formula in Machinery's Handbook for O.D. of the gear.

                          Rule; for O.D. = "Add 2 to the number of teeth and multiply sum by the module".

                          or (2 + 16teeth) x 1.5 module = 27mm (1.063") not 28mm (1.100")

                          What accounts for the extra .9398mm (.037") increase in the gear's original O.D.of 1.100"?

                          PS; Whole depth of a 1.5 module tooth is 3.250mm (.1279")
                          Last edited by vmil3; 05-06-2008, 09:18 AM.
                          Doug

                          Comment


                          • #14
                            Rice, those are 1.5 Module, which are very close to 16 DP -- the roots of the teeth look like they might be 14 1/2° pressure angle. On a 16 DP gear, the 20° PA teeth have a thicker base, and look more like an isosceles triangle. 14 1/2° teeth have more of an undercut below the pitch diameter.

                            The easiest way to tell would be to scan the actual gear, and then superimpose a CAD drawing of a 1.5 Mod, 14.5 & 20 PA gear on top of it in your favorite Photoshop-type program.

                            You can get the CAD models from Boston Gear, Small Parts, etc...

                            This is from the Boston Gear catalog, 20° PA on the left, 14.5° pitch angle on the right:
                            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                            Comment


                            • #15
                              Error in Mod gear value

                              I incorrectly inserted a Mod value of 1.5 (instead of 2.0) in my original text as I suspect that I confused or transposed it with the equivalent "DP" value:

                              Originally posted by oldtiffie
                              OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

                              For Modular (metric) gears:
                              Mod 2

                              OD = PCD + (2 x 2) =28

                              PCD = 28 - 4 = 24

                              (or for DP equivalent) DP = 24/16 = 1.5

                              Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

                              It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
                              - 28mm OD;
                              - 24mm PCD;
                              - 16 teeth;
                              - Mod(ular) 1.5;
                              - 5.00 mm (nominal) wide; and
                              - 1.5 DP (equivalent).

                              The pressure angle is yet to be determined whether it be "inch" (DP) or "metric" (Modular).

                              So if it were me, I wouldn't order that gear cutter yet.
                              The corrected and Mod value is 2.0:

                              OD = 1.100 x 25.4 = 27.940mm (say 28.00mm)

                              For Modular (metric) gears:
                              Mod 2

                              OD = PCD + (2 x 2) =28

                              PCD = 28 - 4 = 24

                              (or for DP equivalent) DP = 24/16 = 1.5

                              Width of gear = 0.193" x 25.4 = 4.9022 mm (say 5.00mm nominal).

                              It is quite possible and perhaps probable or a certainty that I am wrong, but as it is Japanese I would at least consider that the gear might be:
                              - 28mm OD;
                              - 24mm PCD;
                              - 16 teeth;
                              - Mod(ular) 2.0;
                              - 5.00 mm (nominal) wide.
                              The pressure angle - as advised by John Stevenson is probably 20 degree with a chance that it is 14 1/2 degree.

                              Sorry about the silly mistake on my part.
                              Last edited by oldtiffie; 05-06-2008, 09:01 PM. Reason: Error in Mod value

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