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  • Terminology

    I've been reading along here for a bit and there's some words/terms/procedures I'm still not understanding.

    This one's probably the dumbest. What's a drawbar?

    Trepanned and trammel are 2 more and for awhile I thought they might the same thing!

    And we "hob" a gear?

    Thanx for any info. I'm learnin'.

    Bill

  • #2
    Okay, I'll take a shot...A drawbar is used to secure tapered tooling in spindles. They range from the elaborate to plain old all-thread. Trepanning results in holes in plate/sheet similar to a holesaw, but is usually accomplished with a single point cutter similar to a flycutter.

    I'll let some of the experts fill you in on the rest...

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    • #3
      Very good. Trammel is 2 adjustable sharp points attached to a bar in order to find locating points for any large radius.

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      • #4
        and that leaves 'hob' which yes is about gear making. 'Hob' its not slang for making a gear, a hob, a gear hobber and hobbing refer specific cutting tools, machines and operations used in gear generation. for the ball to drop on this one you need to know what an involute is and a tiny bit about gear geometry - lots on the web including some good animations which i just can't seem to pinpoint right now.

        this is what a hob looks like
        http://www.turnerelectronics.co.uk/p...mages/hobs.jpg
        .

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        • #5
          Hobbing is not just about gear making, it has been used for years in building molds and dies.
          "Hobbing is the process of forcing a pre-shaped, hardened die into an unhardened mold insert, cold-forming the resulting cavity."
          I have worked on several molds we had cavity's hobbed in, they are finished as good as the hob is polished. No further work was needed other than to clean up the parting line of the mold.

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          • #6
            didn't know that Mcruff, sounds like a different op though, hobbing as it relates to gears is a cutting action not a forging action
            .

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            • #7
              When I 1st joined up hear and heard you guys talking about hobbing gears I thought you were nuts, I had never heard of that and had seens mold cavity's hobbed 35 years ago as a kid hanging around a friend of my dads shop. Die and mold cavity's have been hobbed this way for probably 65 years or more that I know of.

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              • #8
                Hobbing is another one of those universal terms for "Milling"

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                • #9
                  I thought hobbing was when you want your horse to graze but you dont want him to run away so you "hob" his two front feet together and he can still hop around to feed but cant get very far away from camp...

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                  • #10
                    LOL on the horse bit! But that's hobbling. You hobble a horse, not a gear.

                    I guess I knew a drawbar gets used to tighten a collet, I'm just not knowing how that works. Does it go in from the side, back, front? The reason I'm asking is these 2 lathes I'm looking at both have collets in them and I'm not sure how to get them out.

                    Bill

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                    • #11
                      A drawbar is used through the spindle. To loosen, back the drawbar out a turn and give the end a tap with a brass hammer. The collet will release. I use a brass bar instead of the drawbar and tap the collets or centers out.

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                      • #12
                        drawbars

                        A drawbar runs along the length of the spindle. One end is threaded into the collet, the other usually has a threaded portion that sticks out of the back end of the spindle. A nut and washer are used on the threaded portion to draw the collet into the nose of the spindle. Ideally, the washer will match the inside chamfer at the end of the spindle to provide a good bearing surface and reduce wear and tear.

                        Karl
                        At a certain point in the course of any project, it comes time to shoot the engineers and build the damn thing.

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                        • #13
                          I've been puzzled too how we got to use the same word, hob, for two completely different machining operation. I don't know if there's some real etymological relationship or if they originated in two completely different fields like independent languages that sometimes wind up with the same word sound that has no connection, like oui and we.

                          We used to hob small punches for powder metal dies for electrical contacts so they'd have a pattern on them.

                          For the gear hobbing process, think of a worm gear that has a spiral several inches long. If you cut longitudinal slots in the worm it would form teeth so there would be a cutting action as another part is brought up to the rotating hob. If you held the rotating cutter against a stationary part it would simple chew its way in since you've got successive teeth in different positions - the spiral, remember. However, if the part to be cut is also rotating in the same direction the spiral appear to move down the hob, you would start to cut successive gear teeth. The cutting tool and the gear blank are geared together to get the correct number of teeth on the blank.

                          Interestingly, there was an article a while back in the British magazine Model
                          Engineering Workshop where a guy had done the gearing electronically by putting a stepper drive on his gear blank arbor, and used an encoder on the cutting spindle with the computer doing the ratio calculations to pace the two together. Clever I thought.
                          .
                          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                          • #14
                            According to a language dude. Hobbing is where the cutter gives the form to the result. Milling is where the movement of the work and a generic tool gives the shape.

                            The word hob originally clown, prankster, fairy, time waster. Hence hobby, hobble and Hobnob. It sometimes came to also to refer to the devil and/or his work.

                            Hobbing got its name from the machine. No ones sure, but the hobbing machine may have been a reference to doing the devils work eating the metal.
                            Murphy was an optimist

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                            • #15
                              Interesting. Hob seems to be a rather multipurpose word with not a lot of obvious connection between the various meanings.

                              Hob:
                              • goblin: (folklore) a small grotesque supernatural creature that makes trouble for human beings
                              • elf: (folklore) fairies that are somewhat mischievous
                              • a hard steel edge tool used to cut gears
                              • cut with a hob
                              • a shelf beside an open fire where something can be kept warm
                              • A hob is a term used in Pennsylvania Dutch Country to describe a cast iron griddle. A remnant of the Victorian era, the hob originally kept beds warm during cold winters, but to the present day serves as a metal pad that provides additional insulation for casserole dishes.
                              • A master model in hardened steel. The hob is used to sink the shape of a mold into a soft metal block.
                              • an unneutered male ferret.
                              • Hang On Back Filter. An External Filter which is hung on the back of the tank.
                              • An induction hob is a cooker hob that uses electromagnetic induction in the hob to heat a metal cooking pot.
                              Free software for calculating bolt circles and similar: Click Here

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