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Free hobbing - a rogue method?

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  • #31
    Some of us are still waiting with open minds for a clear and detailed description of this process and its results.

    So far we know that Robint takes a standard bolt, mills axial grooves into it to form cutting edges, then uses it to mill tooth-like shapes into the face of a soft (aluminum, plastic) blank. We don't yet know the precise shape of these teeth. nor do we know everything about his process in order to try it for ourselves.

    A couple of posts above we learned also to "tilt the work piece in the vice jaws - in my case 2deg up from horizon if you dont tilt then you get a slight helical gear which will show up when you mesh two together and they dont want to rotate in a coplanar manner."

    Is that 2° a precise number, and is it related to the M24-3 bolt you used? The helix angle of a M24-3 bolt should be close to 7°, just wondering where the 2° came from.

    Generating helical gears isn't necessarily a bad thing, especially if they are only to mesh with gears generated using the same process. However but I'm a bit confused why they won't mesh. They will try to push each other away both radially and axially, but that's what helical gears do.
    SE MI, USA

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    • #32
      Originally posted by DrMike View Post
      Generating helical gears isn't necessarily a bad thing, especially if they are only to mesh with gears generated using the same process. However but I'm a bit confused why they won't mesh. They will try to push each other away both radially and axially, but that's what helical gears do.
      They won't mesh if you generate them both using the same hob because they need to be opposite handed.
      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

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      • #33
        Originally posted by Peter. View Post
        They won't mesh if you generate them both using the same hob because they need to be opposite handed.
        Yikes... I knew that, brain fart. Sorry.

        Still looking for the answers to my other questions
        SE MI, USA

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        • #34
          OP has deleted this post
          Last edited by Robint; 10-15-2021, 07:36 AM.

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          • #35
            OP has deleted this post
            Last edited by Robint; 10-15-2021, 07:37 AM.

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            • #36
              Forgive me if this was mentioned before, as I only read some of this thread...

              So for free hobbing to work without gashing, consider this.
              For the spacing of a given number of teeth to be correct,
              this is based on the pitch diameter, not the addendum.
              So make a gear blank thicker than needed, make 2 stepped
              diameters, one bring the pitch diameter and one being the addendum diameter.
              Start the hob on the pitch diameter step and get it spinning, then feed the cutter
              into the larger addendum diameter. That is why people have success with
              quickly plunging in a knurling tool. To get it deep to the pitch diameter quicky,
              so the knurl spacing comes out. Apply the same concept to gear hobbing,
              only create step for the pitch diameter, instead pf plunging quickly in the knurling example.

              --Doozer
              DZER

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              • #37
                OP has deleted this post
                Last edited by Robint; 10-15-2021, 07:37 AM.

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                • #38
                  OP has deleted this post
                  Last edited by Robint; 10-15-2021, 07:37 AM.

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                  • #39
                    Not sure what the fuss is about.

                    Gears should have the right pitch, the right pitch diameter, and the right form.

                    The argument here is as to how "free hobbing" maintains the right form and pitch. Show how that happens and it all disappears.

                    I say the flanks of the hob will drive the work, so it should be close. Not perfect. Likely good enough. The hob does the form.

                    The errors may occur as the cutting edge cuts, because guiding quits during that time.
                    2730

                    Keep eye on ball.
                    Hashim Khan

                    Everything not impossible is compulsory

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                    • #40
                      well - with an encoder and a computer running linuxcnc - you can create real gears with the correct shape...



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                      • #41
                        OP has deleted this post
                        Last edited by Robint; 10-15-2021, 07:38 AM.

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                        • #42
                          OP has deleted this post
                          Last edited by Robint; 10-15-2021, 07:38 AM.

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                          • #43
                            OBTW anyone wanting to make one of these cutters should go for a narrower slot. Mine were 2.5mm . ( suggest 1/16" or 1,5mm) for my 3mm pitch

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                            • #44
                              Originally posted by Robint View Post
                              Gears should have the right pitch, the right pitch diameter, and the right form.
                              Unquote

                              But its not STATE LAW as I keep saying
                              You are, of course correct, it is not state law.

                              In actual fact, it's FEDERAL law, if anything.

                              You can deviate at your own risk, risk of them fitting nothing else in the world.... or even each other.

                              But they all should have whatever you choose or they do not fit and work together. So some sort of fairly precise knowledge of what will result is needed, or it will not go well. Consistency is king.

                              What the standard is, well, that's your problem..
                              Last edited by J Tiers; 10-11-2021, 05:12 PM.
                              2730

                              Keep eye on ball.
                              Hashim Khan

                              Everything not impossible is compulsory

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                              • #45
                                This is a weird thread. Free hobbing has been around forever - we're not discussing some revolutionary discovery & how it works. Nor are we addressing a member's questions about how to free hob. Mostly the thread seems to be a pissing contest.

                                Hobbing's been around forever and yet people still buy gear cutters and cut gears the old way. Must be that hobbing isn't all that great and just an alternative for the desperate without another option. I was once desperate and hobbed a gear - I have other options now.

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