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  • Freewheeling, po'boy, hobbing.

    Freewheeling, po’ boy, hobbing.

    I have never cut a gear before. This is my first try in aluminum. Although I bought a few sets of

    “Chinese” gear cutters, I have never used them. I have an indexer. I have watched videos

    about how to do it. But, being lazy, I always found it faster and cheaper to buy the gears I

    needed.

    Nevertheless, I have always wanted to cut some gears. I got this idea from watching

    videos of people using a tap to make worm gears, so I bought myself a hob to try out this idea.

    As you can see, I made the gear very wide to leave room

    for errors and experimenting. The leading edge was eaten off trying to get

    the hob to start the gear spinning. Furthermore, a wide gear can be cut into pieces and used to

    make several gears later.

    Here's a video of what I did.


    https://www.youtube.com/watch?v=vqL3...ature=youtu.be



    It seems the secret to this “freewheeling hobbing” here is to have your “gear” completely

    freewheeling. I mean really freewheeling. In this case, I reamed

    the aluminum gear .001 oversized and put it on a .25” shaft with plenty of oil. I really think it

    needs a design so it can run on some bearings to make it turn extremely easily.

    In the future, to get a better start and not bugger up the leading edge, I would try leaving

    the mill off, putting some pressure on the gear with the hob, and then

    start the mill with the two “engaged.” This process is no doubt going to take some time to

    perfect.

    If you had a variable speed mill, and could start extremely slowly, it would work better I believe.

    What looks like chatter between the teeth is not chatter. I moved the hob into the piece in

    spurts and

    this left these marks. This is just an experimental piece and I was in a bit of a hurry. It seems

    that better results could be obtained moving into the gear just a few thousandths at a time.

    This would take patience, but on a thinner gear, not that much time would be involved.

    I am obviously not a pro, just a hobbyist. Disclaimer, please don’t complain about the dirty mill.

    I’ve been using it for a five day project.
    Last edited by davidwdyer; 07-09-2020, 09:09 AM.
    Vitَria, Brazil

  • #2
    Although it's hard to see in the video, the gear actually came out pretty well.

    Here we have a very well formed gear without the necessity of a hobbing machine. What's not to like?

    If you stop the video at exactly 37 seconds, it gives a little bit better picture without the reflections on the chips.
    Last edited by davidwdyer; 07-08-2020, 08:39 PM.
    Vitَria, Brazil

    Comment


    • #3
      Was the spindle inclined to angle of the hob?
      you do know the blank is supposed to be geared to turn with the cutter, and the cutter feeds down ..right ?

      Comment


      • #4
        No. The spindle was completely vertical. I know the blank is supposed to be geared to turn with the cutter.

        That's what's so interesting about this method. There is no gearing required. No expensive equipment. No indexing. It's very simple. The cutter feeds into the work horizontally.

        The slight angle on the hob is what moves the blank. The teeth of the gear are perfectly straight across and well formed.

        I can try to take another little video later of the result off the mill.
        Vitَria, Brazil

        Comment


        • #5
          Originally posted by davidwdyer View Post
          No. The spindle was completely vertical..
          On the end of hob will be etched (at least should be) the helix angle. Tilt the mill head at that angle, probably like 1/2 degree or so, so it needs a bit of care to get right. Its the only way to properly form the tooth - if you look at the hob tilted slightly (at the helix angle) the tooth profile is that of a rack....that's what you need to present to the work

          As you say, the work should driven. No need for mechanical gear trains, many have accomplished this electronically
          in Toronto Ontario - where are you?

          Comment


          • #6
            Try your gear out, cut a slice off that one, or make another. Now mount them close together, so they have no slop on the axis....ie running situation. Now spin them, see what you got.. see how much backlash and do they mesh good ?

            Comment


            • #7
              Since I have no experience with this, please excuse some questions. Are you saying that my gear teeth are not

              correctly formed? I suspect that if I tilt the head, I will lose the "driving force" which is turning my blank, although I would have to play around with it.

              Any diagrams or pictures would be appreciated.

              Some of these concepts are a little hard to grasp.
              Vitَria, Brazil

              Comment


              • #8
                Originally posted by 754 View Post
                Try your gear out, cut a slice off that one, or make another. Now mount them close together, so they have no slop on the axis....ie running situation. Now spin them, see what you got.. see how much backlash and do they mesh good ?
                Great idea. I'll do that. The gear is wide enough to cut into several gears.

                I think I'll first do some very slow passes to improve the finish.

                By the way, how do you judge the depth of the cut? I read that it is printed on the hob. In my case I found the number 10.5.

                Is that .105 inches in?
                Vitَria, Brazil

                Comment


                • #9
                  Step away from the mill, look for a Machinery Handbook.. lots of gearcutting info in there. Maybe do some reading..
                  they look like gear teeth, now see if they run together, it's the only thing they have to do..

                  Comment


                  • #10
                    Originally posted by 754 View Post
                    Was the spindle inclined to angle of the hob?
                    you do know the blank is supposed to be geared to turn with the cutter, and the cutter feeds down ..right ?
                    I was wondering about that too. What's turning the gear?? The hob.

                    That sure makes it simple.

                    JL.................

                    Comment


                    • #11
                      I think you are supposed to gash the gear blank first
                      using an indexer, so the hob will track.
                      If you don't gash it first, you are relying on
                      pure fuking magic (PFM) to get it right.

                      --Doozer
                      DZER

                      Comment


                      • #12
                        Originally posted by davidwdyer View Post
                        Since I have no experience with this, please excuse some questions. Are you saying that my gear teeth are not

                        correctly formed? I suspect that if I tilt the head, I will lose the "driving force" which is turning my blank, although I would have to play around with it.

                        Any diagrams or pictures would be appreciated.

                        Some of these concepts are a little hard to grasp.
                        The hob teeth are on a helix so regardless of the angle they will 'drive down' as it spins.

                        To answer your questions, and some you didn't ask:

                        Will the teeth be correctly formed - no
                        Will they act as a gear if I made two - of a fashion
                        Would I be satisfied with the gears I make - possibly, that depends on your application and expectations
                        Should the blank be turned in time with the hob - yes it should
                        Should the hob be tilted to the helix angle - absolutely it should
                        Will it free hob if I gash it first - very likely it will, and would likely be the best result you'll get without a proper driven-blank setup
                        Will it cut the correct number of teeth on a given blank diameter if I don't gash it - only way to know is try
                        Could I do this in steel - hob won't last long but probably.

                        Hope this helps you a bit David.
                        Peter - novice home machinist, modern motorcycle enthusiast.

                        Denford Viceroy 280 Synchro (11 x 24)
                        Herbert 0V adapted to R8 by 'Sir John'.
                        Monarch 10EE 1942

                        Comment


                        • #13
                          Originally posted by Doozer View Post
                          I think you are supposed to gash the gear blank first
                          using an indexer, so the hob will track.
                          If you don't gash it first, you are relying on
                          pure fuking magic (PFM) to get it right.

                          --Doozer
                          If you have to gash the blank first, you might as well just cut the gear the normal way.
                          Vitَria, Brazil

                          Comment


                          • #14
                            Originally posted by Peter. View Post

                            The hob teeth are on a helix so regardless of the angle they will 'drive down' as it spins.

                            To answer your questions, and some you didn't ask:

                            Will the teeth be correctly formed - no

                            How can you be sure of this?


                            Will they act as a gear if I made two - of a fashion
                            Would I be satisfied with the gears I make - possibly, that depends on your application and expectations

                            Should the blank be turned in time with the hob - yes it should

                            It seems to work well without this. Perhaps it "should" but is it essential?

                            Should the hob be tilted to the helix angle - absolutely it should

                            If the head is tilted any at all, it will cut a helical gear. That much I know for sure. Therefore, the head cannot be tilted in this setup.

                            Will it free hob if I gash it first - very likely it will, and would likely be the best result you'll get without a proper driven-blank setup

                            As stated, if you gash first, there is no advantage to free hobbing.

                            Will it cut the correct number of teeth on a given blank diameter if I don't gash it - only way to know is try

                            I was using a 20 degree 24 DP hob. The outside diameter of the blank was exactly two inches. It cut 48 teeth.

                            Could I do this in steel - hob won't last long but probably.

                            I'm not sure about this "won't last long" assertion. The proof of this would be in the doing. I am 68 years old and this is my first gear.

                            I think I could cut dozens of gears and never wear out this hob. It is one of the sharpest tools in my box.

                            Hope this helps you a bit David.
                            More ideas and opinions are welcome.
                            Vitَria, Brazil

                            Comment


                            • #15
                              Originally posted by davidwdyer View Post

                              If you have to gash the blank first, you might as well just cut the gear the normal way.
                              Yeah, you're right. Gashing is for chumps. How silly of me.

                              -D
                              DZER

                              Comment

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