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Involute gear tooth template

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  • Involute gear tooth template

    Is there such a thing as an involute gear tooth template (guage?). I just purchased a shaper and want to be able to grind a single point cutter to be able to cut gears for different projects I have in mind. I don't have gears to match up the cutter to so am looking to find a template-guage to use. Anybody know of a company or supplier for such a beast? TIA for your response.

  • #2
    No, not really. The involute is a generated form that varies with tooth count, pressure angle, and pitch. The trick is to see your tool's profile and tune it to suit the closest approximation to the actual infolute form. OPtical enlargement of the tool is a good starting point. An overlay of the desired form accurately drawn 10 to 20 times the size of the tool is the next step. An older drawing text will give you directions for drawing a true involute from starting data.

    If an optical comparator is unavailble, you can extemporize one from a 35MM slide projector and a screen on which you've attached a scaled up involute. Or you can use a pawn shop enlarger or anything with a suitable lens. There's ways if you really want to mess with it.

    A formed involute has to be very accurately made if it's to run quietly at any speed. Generated involutes from hobs, reciprocating rack sections, Fellowes Cutters, and the like are far more accurate but tha's a long way from your question. There are also several geometric approximations like Grant's Odontograph where radii are swung from construction circles. There are others which may be found in older handbooks dealing with foundry practice.

    Many shaper hands use formed gear tooth space milling cutters postioned to present a single tooth to the work in a shaper clapper box. When one tooth dulls it's indexed to the next.

    It's possible to cut pretty good gears in a shaper but you have to jump through some hoops if they are to run smoothly.
    Last edited by Forrest Addy; 12-21-2006, 02:46 AM.

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    • #3
      This may work for what you need Gear Tooth Pitch Gauges. Look near the bottom of the page.

      So what kind of shaper do you have?
      Wow... where did the time go. I could of swore I was only out there for an hour.

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      • #4
        Forrest's answer, no, is correct. The stick type gear templates can only be used to duplicate a cutter for rack gears only. For proper tooth form, a series of cutters is needed to accomodate various tooth counts. Eight different cutters are typically needed.

        The cutter profile can be generated by using the two disc method described in Ivan Law's book, Gears and Gear Cutting. It is also described in this article by John Stevenson;

        http://www.metalwebnews.com/howto/gear/gear1.html

        The procedures involve making cutters for use with a milling machine, but are easily adapted to making single point cutters for use in a shaper.
        Jim H.

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        • #5
          You can generate templates programmatically.

          See here: http://hobbing.com/

          You can also download the free version of Allycad. It will generate spur gears.

          http://www.allycad.com/

          Example:

          Last edited by Evan; 12-21-2006, 08:48 AM.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            ...use a pawn shop enlarger or anything with a suitable lens.

            The germ of an idea. Been wondering about what to do with that unused enlarger I have been hanging on to. Thanks, Forrest.
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

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            • #7
              It is possible to generate the involute tooth form on a shaper, using a rack-shaped cutter (straight sides). The approach is more or less as described here http://homepage.ntlworld.com/peter_h...ting/index.htm

              It would take quite a while, but it would be do-able.
              ----------
              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.
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              • #8
                At one time, Boston Gear Co. published the profiles of several different tooth forms for identification purposes. You laid the gear in question on the profiles and were able to identify the pitch. If you can find an old catalogue with these shapes illustrated, perhaps this can form your template.

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                • #9
                  I do exactly what Al Messer suggests. I have a Boston Gear catalog showing gear tooth profiles. I copy the desired gear with my scanner and compare the outline to the tool as I grind it to shape. I can also enlarge the tool image to better see the contour. I neither have the finances or room for every involute gear cutter so this method works best for me.

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                  • #10
                    If you register at Boston Gear (free) you can download cad 2D and 3D drawings of thier products.

                    http://www.bostongear.com/
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      Thanks for all the great responses. I was away from the computer for a bit while I went down to Montana to pick up my new-to-me Ammco shaper. Didn't expect it to arrive this soon but was pleasantly surprised when it did. Now all I need to do is get it cleaned up and serviced to start making chips. Getting this shaper was one of the reasons I asked about a template/guage for gears. I am going to need to make some cutting bits to make gears for some projects I have in mind. Thanks again for all your help.

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                      • #12
                        Marv has a program on his site that may help
                        http://www.myvirtualnetwork.com/mklotz/
                        it is called cutters it is designed to design gear cutters.
                        Tin
                        Ad maiorem dei gloriam - Ad vitam paramus

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                        • #13
                          Originally posted by Tin Falcon
                          Marv has a program on his site that may help it is called cutters it is designed to design gear cutters.
                          The program on Marv's site (by Joe Smit of South Africa) has a lot of potential, but it makes a vague reference to an article published in Model Engineering Workshop Nuber 41, April 1997.

                          I typed in a 14.5°, 16 DP gear, and it gave me the correct gear blank diameter, tooth depth, et al, but it gives "pin diameter" and "pin centre" -- which apparently is reference to a table in the MEW article.

                          I'm guessing the pins centers and radii are the radius of the involute form.

                          Anyone have this article?
                          Last edited by lazlo; 12-23-2006, 07:35 PM.
                          "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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                          • #14
                            I believe I have read the Model Engineering article and I have it on my home computer. Unfortunately, I am out of town and can not access it now. But, if it's what I am thinking of, the idea goes something like this:

                            An involute can be approximated by a circular segment of the appropriate diameter. So a tool for cutting a gear tooth cutter can be made by placing two disks of tool steel an appropriate distance apart on a support with a notch cut between the disks. This tool is used to form the milling cutter.

                            I know that a close approximation can be had in this manner, but it will not be 100% accurate and small errors in the gear shape can cause noise, etc.

                            I suspect that Marv's program calculates the diameters and spacing of these disks on the tool.

                            Frankly, I do not trust any of the approximate methods, including grinding the tool to a template. Can you see tenths? I sure can't.
                            Paul A.
                            SE Texas

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

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                            • #15
                              Lazlo,

                              I still have a copy of the MEW article - 4 pages. If you want a copy PM me with an e-mail address and I will scan it for you.

                              franco

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