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Bridgeport mill: How many turns on the return spring on the quill downfeed handle?

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  • Bridgeport mill: How many turns on the return spring on the quill downfeed handle?

    The spring on the downfeed handle on the Bridgeport mill at the school got disconnected somehow, and we need to get it working again.

    I can get the hole in the spring back on the pin on the downfeed shaft. It takes a lot of grip to turn the spring holder after the first two turns, so I'll probably need to make some sort of tool. Any suggestions on what the tool should look like? I'm thinking something with a pin to engage one of the two holes, leaving the other hole open so I can put the screw in.

    What I don't know is how many times I need to turn the spring holder to get the right tension. I can't come close to enough turning it by hand.

    Roger
    Any products mentioned in my posts have been endorsed by their manufacturer.

  • #2
    Originally posted by winchman
    The spring on the downfeed handle on the Bridgeport mill at the school got disconnected somehow, and we need to get it working again.

    I can get the hole in the spring back on the pin on the downfeed shaft. It takes a lot of grip to turn the spring holder after the first two turns, so I'll probably need to make some sort of tool. Any suggestions on what the tool should look like? I'm thinking something with a pin to engage one of the two holes, leaving the other hole open so I can put the screw in.

    What I don't know is how many times I need to turn the spring holder to get the right tension. I can't come close to enough turning it by hand.

    Roger
    You won't need two turns. If you can get the spring reconnected as you say, then turn just enough to balance the quill and give a slight upward pull. If you go too tight, it will be coil bound.

    I made a tool out of a large washer with two pins that connect to the spring holder to make the job easier.
    Last edited by gnm109; 11-24-2009, 12:37 PM.

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    • #3
      Wow, that few? I could get that by hand, but it didn't make any difference at all. The quill just stayed down. I had the quill lock lever loose, too.

      What else could be keeping it from working? It moves smoothly and almost effortlessly up and down. It just won't come back up by itself.

      Roger
      Any products mentioned in my posts have been endorsed by their manufacturer.

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      • #4
        "It moves smoothly and almost effortlessly up and down. It just won't come back up by itself."

        Good!

        Use a pin spanner, like on a surface grinder wheel nut.
        Tension on Bridgeport quills is usually lighter than on a drill press.
        Generally set so the quill does NOT forcefully retract, but rather just counter-balances the weight of the quill, plus just a bit more.
        I like to install something heavy in the spindle, like a boring head, and set the spring tension so it just barley holds the quill in position with the boring head in there. If I had the quill lock set, and I released it, I would not want the spindle to drop, but rather it stay put or retract just a little bit.

        Hope this helps. It is sort of a personal preference, but this is how I have always seen them set. I have seen import mills with way too strong of a quill spring, and even if you backed off on the set tension so you had some sensitivity at the beginning of the quill travel, it would still spring back like a drill press from longer quill extensions. Not good.

        I think having the right spring, and having it adjusted just right, is a big part of the happy operation of a mill.

        --Doozer
        Last edited by Doozer; 11-24-2009, 06:54 AM.
        DZER

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        • #5
          Thanks, that's making more sense. With about two turns, the quill will stay where I put it.

          Roger
          Any products mentioned in my posts have been endorsed by their manufacturer.

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          • #6
            compilation of answers Ive given about this subject from forums here and there.

            its the grub screw that holds it
            ...the heads come off probably .
            pics below of new one i made..well its the spare one .the best one is in the bridgeport
            this has three threads ...you need two and a half ...
            you can guess the other dimensions of it ...just by looking
            the threads are 5/16s UNC ....and it is made out of a HT cap Allan bolt ...for strength.
            saw the cap Allan head off off a 2.5 inch long bolt ..and put rest in a collet in the lathe.
            use carbide tool to turn it......a grooving tool to make the groove .........and hack saw to put the slot in for the screw driver..............
            even with 2.5 threads ...you are still going to be filling the heads ,...as it will stick out of the drum somewhat ...and will stop you pushing the drum back intro the machine .





            when installing and tensioning ...having trouble !

            you think its coming off the shaft ...in fact it is .....but only because its slipping off the outer grub screw

            i spent an hour trying to figure this out the couple of years back .....
            taking the drum out ..every time it slips ...the outer ends up at the same place .................and you think its still attached to the grub screw.... it ain't ...
            after ten goes you will catch the little bugger out ...and you will see that it hasn't landed in the same position again ...making you think its still held by that grub screw
            BTW ...the first coil that you attach to the shaft is untempered ...and can be formed so it fits the shaft a lot closer.........dont fart about with it too much ...as you may end up cracking the spring .
            the outer clock spring has a hole shaped like this :-



            head of grub screw goes through large hole ...
            and then you manipulate the spring ...so that it pulls it into smaller slot ...BEFORE you put the drum into the machine .
            and before putting the drum back into the machine ,once the grub screw has been dragged into the slot .....unscrew the grub screw a little bit and it will tighten the head onto the spring.....that's why you have to file it ... because it comes out a little bit ...

            all thew best.markj
            Last edited by aboard_epsilon; 11-24-2009, 07:45 AM.

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            • #7
              Thanks, Mark. I'll check that out, too.

              Roger
              Any products mentioned in my posts have been endorsed by their manufacturer.

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              • #8
                Im able to just take out the 3 screws that hold the entire cover/boss and then I just rotate the unit a 120 degree's at a time --- my spring was too weak at first and now its perfect.

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                • #9
                  The J head is not too bad, being a cartridge design.
                  The M head, ya have to wind the spring into the head casting.
                  I made friends with a local clock maker finding a spring for my M head.
                  Good info on the little screw that grabs the spring in the cartridge.
                  I have fixed a few of those, no fun.

                  --Doozer
                  DZER

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                  • #10
                    I always use just enough tension so the quill don't move up or down on it's own. I can't tell you how much tension, just adjust as needed.
                    It's only ink and paper

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