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Spur Gear - 14T 14P

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  • Spur Gear - 14T 14P

    I have a friend that has a big wood cutting bandsaw. The mechanism that cranks the guard up and down uses a rack and pinion. Well, the rack is a round shaft that has teeth cut in it, the pinion is a Delrin gear that is stripped out more or less. I'm trying to help him replace it.

    So the pinion OD is 1.150", the 'inner diameter' is 0.796". If I guess that splitting the difference gives me an approximate pitch diameter of about 0.973", divide that by the 14 teeth, it gives me approximately a 14 pitch. I havent found an easy way to measure pitch diameter.

    I also haven't found a way to determine pressure angle. So I'm making an assumption that it's 14 1/2 degrees.

    The face is 0.75" and the overall length is 1.1". The ID bore is 0.422" (this doesn't equate to metric.)

    I can't seem to find a 14 pitch 14 tooth gear in any material, much less Delrin. I only have a indexer that will do 24 divisions, and spending $300 on a divider, plus an involute gear cutter seems excessive (though I've done stupider things and ended up with more tools! I have a shaper if I had a divider that could do 14 steps.)

    So, long story short, I'm looking for spur gear stock, or a gear that's too long or hole too small that I could machine to size, and in some kind of soft material (nylon, Delrin, brass, etc). This has not been easy. Any gear experts out there?

    Thanks for any help.

  • #2
    The PA is the angle of the rack - measure that. http://shopswarf.orconhosting.net.nz/spur.html and cutting gears with a shaper is pretty easy. http://neme-s.org/Shaper%20Books/Mic...gear%20cut.pdf
    Last edited by dp; 11-15-2013, 12:10 PM.

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    • #3
      See:

      http://www.gearsandstuff.com/spur_ge...lculations.htm

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      • #4
        Location? You never know who is close by.

        How beat up is the factory gear? Does your printer print accuratly to size? To test draw a 1 inch line and measure it. If close then I can draw you a gear with 14 DP and 14 teeth. You would need a CAD program to open the drawing to print it. This would give you two things 1) It would check your assumption of the DP and 2) It would give you the correct cutter profile to sharpen a shaper bit.

        I have the tooling to cut the gear with the exception of the cutter.

        Pete

        Added information:

        If it is a 14 tooth 14DP gear the Pitch circle should be 1 inch. PC = Number of Teeth/DP of gear
        The Outside Diameter should be Number of teeth + 2 /DP = 14 +2/14 = 1.143
        Last edited by Stepside; 11-15-2013, 01:05 PM. Reason: More info

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        • #5
          Thanks for the quick replies.

          Measure the rack. I didn't think of that, or didn't realize that would be a lot smaller. But, they're relatively small teeth.

          Yes, I think my printer will print to scale.

          Measuring it is a challenge because the teeth are pretty chewed up. 1.143 is probably close enough to 1.150 for them to be "the same."

          I need to update my profile. I'm in Nashville, TN.

          I could probably sell my indexer on ebay and buy a divider. Probably can't do it fast enough.

          I thought about buying a gear that's a multiple of 14, build an "arbor" to hold the stock and the reference gear, and index the piece that way. If it's plastic or brass, shouldn't be hard to do.

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          • #6
            Private message sent check your inbox

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            • #7
              As a hint, if you have a shaper, I got a plastic gear tooth profile template from a Martin Gear distributor when I bought a tiny gear and rack for a project. It would make a reasonable template to use to freehand grind a form tool for your shaper......
              Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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              • #8
                A way to measure rack dimensions is to press modeler's clay into the rack then slice it lengthwise with a razor. At that point you can put it on a scanner bed and scan it at high resolution to get a large image. This will serve to improve accuracy of the measurement.

                Here is a rack and gear from my mill:

                http://metalworkingathome.com/images/rack-and-gear.jpg

                And here is an on-screen way to measure angles:

                http://metalworkingathome.com/images...protractor.jpg
                Last edited by dp; 11-16-2013, 11:19 AM.

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                • #9
                  Where'd you get the cool degree wheel thingy!?

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                  • #10
                    For what you want you are over thinking this.
                    Long short it's a delrin gear that raises a guard up. Not NASA by any means and in plastic as well.
                    Print a division plate out with 14 radial lines, glue this to you indexer so you can eyeball each line.
                    Grind a HSS cutter up from a broken end mill centre drill etc and use as a flycutter. plenty of profiles on web sites to get an idea of the shape you need to grind to

                    It WILL do the job, won't be to micron accuracy but it will work.
                    .

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



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                    • #11
                      Take a look at this: http://homepage.ntlworld.com/peter_h...ting/index.htm

                      No need to buy a cutter -- make your own, fairly easily. Given that you'll be cutting Delrin, you probably wouldn't even need to harden the thing.
                      ----------
                      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

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                      • #12
                        That is a Mac app from the App store (Protractor). A Windows-equivalent is here and works even better:

                        http://www.iconico.com/protractor/

                        Get the whole set here: http://www.iconico.com/index.aspx

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                        • #13
                          I agree with Sir John that it is nothing fancy and we might be "over thinking the issue". His method should work fine for this project.

                          Now if the journey is as important or more important than the destination, then all the dialogue is of value and we all get to see different ways to solve a problem.

                          Pete

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                          • #14
                            Originally posted by SGW View Post
                            Take a look at this: http://homepage.ntlworld.com/peter_h...ting/index.htm

                            No need to buy a cutter -- make your own, fairly easily. Given that you'll be cutting Delrin, you probably wouldn't even need to harden the thing.
                            Thanks everyone for your advice. I think I can do this. I have an oven for hardening (I took a shot at cutting Hirth Couplers one time, still need to perfect that.) Now I just gotta get that indexer figured out!

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                            • #15
                              As long as the sample gear has 14 teeth, wouldn't any gear work to index the teeth for cutting a new one?

                              Probably could use a sprocket, as long as it had 14 teeth in the full circle?
                              Last edited by mikem; 11-18-2013, 06:41 PM. Reason: another thought

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