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  • cheap hobs?

    I keep hearing stories of cheap hobs, but can't seem to find them anywhere. Or is my idea of cheap way off? I was quoted over $300 for the smallest size 1 module hob. I know you can find some deals on ebay, but watching and hoping that your size comes up is always frustrating. I am considering making my own, even with the problems of durability etc. seems like less hassle.

    Michael

  • #2
    No such animal as a cheap hob. You can find damaged hobs, and hobes ground back to nothing, and odd-ball pitch hobs for low prices but they won't do you much good.

    The snaggle tooth hobs and the ground-back hobs may self-destruct in the cut.

    Orphan oddball pitch hobs can work very well if the center distance isn't fixed, the PD can be made a variable, and the gears made in meshing sets that don't have to mesh with anything standard.

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    • #3
      What the heck is a hob?
      I figured out that all pans are \"no stick\" if you \"no cook\" in them.

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      • #4
        .

        [This message has been edited by pgmrdan (edited 02-27-2004).]

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        • #5
          Yes, Michael. I know cheap hobs. I too have spent who knows how many hours trying to find hobs of varying sizes, without becoming bankrupt.

          Forrest is on to something there, but not completely. With a bit of luck, hobs turn up on ebay or similar places. Not always ruined; sometimes new in box, for low $. I've bought unused hobs for as little as ten bucks. Mind you, a Mod 1 is a pretty desirable size and might be hard to come by. (I KNOW it is, since I have one. Can you use a left-hand thread?)

          For a long time I've been plagued by not being able to find one of a certain size I need. So, I got fed up with it and decided to make it my own way.

          I went to the Nice-Metals-Dealer and bought a four-inch long piece of top-of-the-line HSS bar stock, for a whopping $40 (not that drill rod or silver steel). Chopped that up into four bits, and threaded them as per the needed CP and PA. Gashed for as many teeth as possible. Trashed all ideas for fancy backing-off devices, and just ground the teeth off manually. At the end of this week they're being sent out to be professionally heat-treated.

          And there you go. Quick, cheap, easy. Four hobs, your size, forty bucks. Quality of execution is up to you. Reduced life span as a result of minimal sharpening margin, but so what?

          More: Several thread taps are of similar size or CP as hobs. For example, an M20 x 2.5 thread tap is very close to a 32 DP x 30* PA gear hob. Probably works just fine for doing 32/64 DP splines, if you grind the tips off the teeth.

          Gotta go,
          Doc.

          PS: Porschenut, a hob is a worm with teeth.

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          • #6
            Yeah, like in Dune
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              Well when you go to auction stand on your head in a barrel or two of misc tooling,you will find them near the bottom.
              I just need one more tool,just one!

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              • #8
                PorscheNut:

                Doc's description of a hob, a worm with teeth, is accurate, but not helpful as an answer to your question. A hob is a special cutter for cutting involute gears. It starts with a thread whose pitch is equal to the circular pitch of the gears to be cut, with sides set at the pressure angle. This thread is gashed at intervals to make cutting teeth which must be relieved so they will actually cut instead of rub. In use, the straight sides of these teeth generate the involute gear tooth shape through the combined rotation of the hob and the gear blank. A single hob will cut gears of any tooth count for a given pitch and pressure angle.




                ------------------
                Rich Kuzmack

                Pi = 355/113 . . . to
                <85 parts per billion
                Rich Kuzmack

                Pi = 355/113 . . . to less
                than 85 parts per billion!

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                • #9
                  Pi?

                  3.141592653589793238462643383279502884197169399375 1058209749445923078164062862


                  [This message has been edited by Evan (edited 02-26-2004).]
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Evan,
                    Is that an aproximate?
                    .

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



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                    • #11
                      So, Doc- I'm going to show my ignorance of metallurgy here. What grade of HSS? I thought you couldn't really machine HSS without exotic tooling. I mean, the only thing I have that will cut M2 is a grinder. And isn't it really hard to heat treat?
                      Thanks,
                      Michael

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                      • #12
                        Yes and no, Michael. The HSS was in its non-hardened state. I think the specific grade is Uddeholm ASP 2030. It may be difficult to heat-treat properly, which is why I opted to have it done professionally. (rather than try to learn everything myself)

                        Machining it was no real problem. Tough stuff, but not so bad.

                        Numberswise, one of the CNC machines here has infinite thread pitches-- useful for dumb numbers like 2.356 and 3.14159 mm pitches.

                        So, no ignorance or dumb questions there at all. You got it right. Good luck if you try it. I'll get back with my own results later.

                        Doc.

                        PS: Indexer, that must be the best hob explanation I've ever seen.

                        EDIT, later:
                        What John says below is among the best explanations of the DIY process I've ever seen-- MEW 56, 57 and 58. Maybe even 56 in particular. Ivan Law wrote it.

                        [This message has been edited by Dr. Rob (edited 02-26-2004).]

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                        • #13
                          High speed steel is available in a soft form.
                          Over here [ UK ] it's known as machinable high speed steel and machines a lot like stainless.
                          Heat treatment of HSS is critical. The people we use for hardening couldn't do HSS until two years ago as they couldn't get the elevated temperatures needed.

                          I believe I have mentioned before that Dr Giles Parkes has wriiten a very good article in MEW no 58 about cutting hobs with relief.

                          John S.
                          .

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



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                          • #14
                            so i went to ebay and looked at several gear hobs. how do you use one of those monsters? do the hob and the part to be cut both rotate at the same speed and mesh together somehow? does anyone have a link to a slow-speed video of hob use in action?

                            andy b.
                            The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

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                            • #15
                              I'm looking. In the mean time check out this gallery.

                              http://www.thegearworks.com/gallery/index.html
                              Free software for calculating bolt circles and similar: Click Here

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