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  • Get me started making gears

    In my recently-aquired Stockbridge, there's an interesting power-downfeed mechanism, as shown here:



    There's a trip on the outside of this plate, which contacts a dog that mounts to the T-slot in the way cover, seen right below the plate (which is upside down, of course.)

    There's a watchspring mechanism in and under the righthand gear, and that causes the other two to cycle (possibly even adjustably) which then turns the pinion which turns the tool slide.

    Note, however, the smaller portion of the center gear is missing at least three teeth, and there's a half-broken tooth in the righthand gear.

    I know that I could just closely grind an HSS bit to the shape of the existing teeth (and use it in either the Stockbridge itself or the little Lewis) but I also have the new-to-me and still-being-rebuilt Nichols horizontal mill.

    Say I wanted to buy a cutter for the horizontal, and use it with an indexer of some sort. How would I determine just exactly what sort of cutter to purchase? And, for that matter, who carries gear cutters like that?

    Doc.
    Doc's Machine. (Probably not what you expect.)

  • #2
    start by searching dimetral pitch cutters. I guess first you would need some gauges.

    here is the setup http://jeep534.smugmug.com/gallery/2...14871220_Sgh5Q

    also http://www.ashgear.com/singlefull.htm

    and another way would be to use something like this
    http://www.jeffree.co.uk/divisionmaster.html
    be sure to look at the examples of use

    Happy hunting
    archie =) =) =)

    Comment


    • #3
      Two key specs for a gear: diametral pitch and pressure angle. (If metric, it's mod, which is the inverse (in metric, of course) of the diametral pitch, and pressure angle, but I assume these gears are imperial.)

      Diametral pitch defines the tooth size. It's the number of teeth that will fit on a gear with a 1" diameter pitch circle. So a 16dp gear 1" in diameter at the pitch circle will have 16 teeth. To calculate the dp of the gear, count the teeth, add 2, and divide by the outside diameter. For a 16-tooth gear then, you'd add 2 to the tooth count, getting 18, and divide by the o.d., say 1.125":

      18/1.125 = 16dp.

      Of course, things being what they are it will come out more like 16.035 or 15.991 because the o.d. won't be exactly according to theory, but one can assume with some confidence that the diametral pitch is the nearest whole number.

      Now the pressure angle...is, unfortunately, not so easy to calculate. I don't know a good way to do it. Maybe somebody else does. Old gears, and change gears, tend to be 14 1/2 degree pressure angle. Newer gears are more likely 20 degree pressure angle because it's a stronger tooth form. But it's not guaranteed.

      Places like Travers www.travers.com and MSC www.mscdirect.com sell gear tooth cutters. There is typically a set of 8 cutters to cover a full range of teeth from 12 to a rack, since the tooth form changes on a gear according to the number of teeth it has. Happily, you don't need to buy a full set of 8 cutters, you can buy only the one you need.

      Before you start this project though, buy a copy of "Gears and Gear Cutting" by Ivan Law. It will tell you everything you need to know.
      Last edited by SGW; 06-16-2008, 08:12 AM.
      ----------
      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

      Comment


      • #4
        Isn't there a way to set up to Hob gears on a horizontal mill? or do you need and absolutely have to have a universal mill? Gear hobbing let's you cut a wider range of gear teeth with a single hob (cutter).
        Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

        Comment


        • #5
          This is a sort-of way to hob a gear: http://homepage.ntlworld.com/peter_h...ting/index.htm

          It could be done on a shaper, too.
          ----------
          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

          Comment


          • #6
            Originally posted by SGW
            Now the pressure angle...is, unfortunately, not so easy to calculate. I don't know a good way to do it. Maybe somebody else does. Old gears, and change gears, tend to be 14 1/2 degree pressure angle.
            You can't really calculate the pressure angle without a gear caliper, but you can compare it against a PA chart, or take a digital photo of the gear and overlay it with the CAM drawings from Boston Gear, Martin Sprocket et al.

            I posted this screenshot of the Boston Gear identification chart here for the guy trying to identify the Japanese mortar gear. 20° Pressure Angle on the left, 14.5° Pressure Angle on the right:



            If you have a mating rack, you can measure the pressure angle directly off the rack by taking a picture and measuring the angle with software. I did this for the rack and pinion I needed to repair on my Bridgeport slotting head. This is the picture of the rack on my Daughter's Intel Blue Digital Microscope.

            I had to adjust the rotation of the picture to get the rack form exactly straight (the yellow lines), and the red line is calculating the angle with "Meazure" Freeware from CThing software:

            http://www.cthing.com/Meazure.asp

            It's basically a Poor Man's optical comparator



            I any event, a shaper of that age is almost certainly 14.5° Pressure Angle.

            So just measure the DP the way SGW described: OD / (Number of Teeth +2), count the number of teeth, and buy the correct numbered gear cutter from MSC et al.

            Good luck!

            Robert
            Last edited by lazlo; 06-16-2008, 01:25 PM.
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

            Comment


            • #7
              My guess from past experiences is the gear will be a pressure angle of 14 1/2 degrees. The reason I say that is that is an old machine and all the old stuff I have worked on ALWAYS had 14 1/2 degree gears. Get you a gear pitch gage and check the gears to find the right D.P.
              I have a extra set if your are interested. PM me.
              Every Mans Work Is A Portrait of Him Self
              http://sites.google.com/site/machinistsite/TWO-BUDDIES
              http://s178.photobucket.com/user/lan...?sort=3&page=1

              Comment


              • #8
                Originally posted by camdigger
                Isn't there a way to set up to Hob gears on a horizontal mill? or do you need and absolutely have to have a universal mill? Gear hobbing let's you cut a wider range of gear teeth with a single hob (cutter).
                I guess you did not look at the first link I posted. That photo was taken at the local Votec of a Horizontal mill set up to cut gears with an Dividing head. there is also an atlas accessory that uses atlas change gears to duplicate the number of teeth needed to cut a gear instead of using a Dividing head. both still need a Dametral pitch cutter.

                and hobbing is a different process altogether. and I have lost all the links to john stevenson's home built gear hobb.
                oh well

                Happy Hunting
                archie =) =) =)

                Comment


                • #9
                  Thanks guys, good info to start. I've never had occasion to make gears before, but I do have a couple of proposed upcoming projects that may require a very good custom gear (adapting an old Borg-Warner overdrive to a different manual transmission) and will almost certainly require custom splines or an internally-splined collar. So I'd best start readin' up.

                  Jeep- That first link takes me to a picture of a guy's Rockwell drill. I looked around his gallery for something relating to a gear or hobber, but didn't see anything obvious.

                  But I happen to have those Atlas acessories, both the headstock and tailstock. They'll be a bit undersized for my considerably-larger Nichols horizontal, but they'll work. If I'm recreating an all-new gear (rather than doing a braze/recut of the stock gear) I can just use the original gear to get the tooth spacing.

                  SGW- Thank you, those are both good bits to start with. I'll have to try to see if I can find a copy of that book.

                  Doc.
                  Doc's Machine. (Probably not what you expect.)

                  Comment


                  • #10
                    Doc,
                    I guess i should have been more Specific. when I bring up this page
                    http://jeep534.smugmug.com/gallery/2...14871220_Sgh5Q
                    it shows the K&T Milwaukee 2HL Set up to cut gears (i did re word the caption a bit as I have another mill like the one in the picture) also if you look here
                    http://jeep534.smugmug.com/Hobbies
                    you can see my machines on the shop equipment page.

                    the "hunt list" are pictures of things I do not own. I do however Now own a 2HL =-) and it has all the bit's and pieces with it including a 3 Axis DRO.

                    I also just loaded pictures of my dividing heads (even though they are a little rusty) and they are on the shop equipment page as well.

                    I hope this helps

                    Happy Hunting
                    archie =) =) =)

                    Comment


                    • #11
                      Nope, I still just get a photo of a Rockwell drill. There's only two photos in the "Hunt List"- the Rockwell and a P&W punch. Is there another photo I'm missing? The only photos I can see show the K&T horizontal out in the "shed", in your "Shop Tools" gallery.

                      Doc.
                      Doc's Machine. (Probably not what you expect.)

                      Comment

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