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how did they machine it.

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  • how did they machine it.

    Took mi pillar drill apart, an old brit fobco, and noticed that the shaft the driven pulley fits on above the quill has a hole through it with a key, no problem, but on closer inspection what I thought was a hole with a key slot and a key isnt, its all one piece, fobco have machined a hole with a integral key protrusion.
    I've tried to remove what I thought was the key and its deffo one piece.
    How did they machine that one out then.
    Build it, bodge it, but dont buy it.

  • #2
    Well, hmmm.

    It's a degenerate splined hole, of course...
    At home, one could furnace braze the key in place.
    One could imagine a special broach to do such a thing.
    If this were some sort of alloy rather than cast iron, it could be die-cast.

    - Bart
    Bart Smaalders
    http://smaalders.net/barts

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    • #3
      They probably broached it.

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      • #4
        I wondered about a broach, I have little experience of broaching, 'cept for using a rotor broach for bashing big holes in concrete flooring to put machine mounts in.
        Build it, bodge it, but dont buy it.

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        • #5
          It could have been made on a shaper or a slotter, too. Several of my books show rotary-table like devices for standard shapers for doing splined holes, and of course most slotters have such a table built in. Might be more likely than a big broach.

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

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          • #6
            So if you were using a slotter then, you'd drill a smaller hole, and using the slotters cutter and the rotary head slot out the hole bigger, but skip the bit where you'd want the key to be, that makes sense, fobco probably had a slotter with auto feed and adjustable limit switches for semi auto operation.
            When I've been stuck here at work, I have done splines on the lathe, heath robbo but I put felt tip marks on the drive gears to indicate postion with the lathe in a low gear so that the motor did lots of turns per turn of the spindle to improve accuracy, and whilst holding the foot spindle brake used the apron handwheel to drive the cutter through (previously surface ground to the size of the key), sort of a crude shaper, I've done this a few times since to do keyways on pulleys.
            Last edited by dr pepper; 10-21-2009, 08:14 AM.
            Build it, bodge it, but dont buy it.

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            • #7
              Sintered metal,I've seen plenty of sintered steel spockets with intregal keys.
              I just need one more tool,just one!

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              • #8
                I must be a bit fick, whats the issue with sintered, is it cast in the exact shape?.
                Build it, bodge it, but dont buy it.

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                • #9
                  It's powder metallurgy. Metal powder is compressed under extreme pressure and high temperatures in a mold so it forms a solid mass of metal at net required shape. Depending on the process it can produce a close equivalent to cast iron or even hardened steel. It is a very common process.

                  Here is an example of keying two gears together. Powder metallurgy can be so accurate as in this example that it is a perfect finger light press fit. These gears are equivalent to hardened 4140 steel.

                  Last edited by Evan; 10-22-2009, 08:19 AM.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Sintered metal is recent technology and the drill press probably predates it by several decades. If the gear is a casting, the bore would possibly have been rough cast and broached. If it were a steel gear, it would also be broached.

                    Use of a shaper would work, but be too slow for a manufacturing environment. Broaching would be the method of choice. Industrial broaching machines and broaches are quite different than the keyway broaches used in home shops. The broaches can be several feet in length and are used to produce a wide variety of shapes in a single pass.
                    Jim H.

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                    • #11
                      Originally posted by JCHannum
                      Use of a shaper would work, but be too slow for a manufacturing environment. Broaching would be the method of choice. Industrial broaching machines and broaches are quite different than the keyway broaches used in home shops. The broaches can be several feet in length and are used to produce a wide variety of shapes in a single pass.
                      Is it true that "some" automotive engine blocks are "planed" flat with a broad flat broach supported from the back?
                      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                      • #12
                        I don't know for sure, but have little reason to doubt that the procedure could be used.

                        Broaching and broaches represent a whole other machining process not often encountered in the home shop. It is widely used, perhaps less now than formerly due to CNC and EDM advances, but it is a relatively inexpensive and low tech means to produce forms not readily achieved by other means.

                        It is widely used in the firearms industry to produce cuts not possible by other means, the chase for the bolt in a bolt action receiver or a magazine well for instance.
                        Jim H.

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                        • #13
                          Looks like I shoulda searched this B4 askin'

                          This is interesting reading for anyone even mildly intersted in broaching. Not home shop operations, but still interesting...http://books.google.ca/books?id=6PE0...aching&f=false
                          Last edited by camdigger; 10-23-2009, 11:30 AM.
                          Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                          • #14
                            Well thats interesting, I thought I was well versed in manufacturing, I've worked all over maintaining all kinds of machines from junk to aerospace high tek.
                            We had those machines at leyland motors, I remember seeing the broaches in racks, only at the time and untill now I didnt know what they were (showing my ignorance).
                            I do have experience of grinding machines as per the article though, they were one of the most unreliable machines, and being maintenance we were the first to find that out.
                            I'm guessing that my example is broached as the unit is made from steel and the outer edge has witness marks from machining.
                            Thanks for the explanation chaps.
                            Build it, bodge it, but dont buy it.

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                            • #15
                              Broaches were used quite extensively for volume engine block machining. I remember a two or maybe three high broaching machine (could do three blocks in one pass) that finished the sump face and I think one side of the block in one go. This was a massive machine, larger than the one in the book illustration. Every time it made a pass the very substantial concrete foundations would shake. I was working in a reference room (inspection) not far away and that had its own foundations with rubber dampers to try and isolate it from the vibration of that machine and others. It was not wholly successful.

                              The broaches used in these machines were very complex and needed to be reground by very skilled people. Considering that they were cutting cast-iron without much more than initial fettling, the broaches had a hard life, but they were capable of working to close tolerances.

                              Dr Pepper - the mention of Leyland Motors makes me think that you must be fairly close by. I am north of Preston.
                              Bill

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