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  • bridgeport drawbar tightening

    Hi,
    I just purchased a bridgeport milling machine and am just learning how to use it. I am familiar with the use of the lathe but the mill is new to me. How tight should I tighten the draw bar in general. I am drilling some 1 inch holes in 1 inch plate steel using the drill bit in a collet and dont want to damage the bit or collet by not getting it tight enough and having it spin. thanks Paul

  • #2
    Hi Paul,

    I usually give it a good shove, with the wrench sticking out the right side and the brake engaged. The R-8 taper is pretty acute. You can generate a lot of force on the tool with very little torque on the leadscrew. If you need a manual you can download it from the MetalIllness site at http://www.bbssystem.com/viewtopic.php?t=62 (but it doesn't tell you much).

    And buy new collets. Your work will only be as good as the quality of the collet in the spindle. Buy Hardinge, Lyndex, or Royal if you can find them.

    Your mill may or may not have a drive screw which engages the collet. They all came from the factory with this installed, but many have been broken off over the years. If your collet rotates freely when almost seated, then the screw is missing. If the collet will only go in one way, with the slot at the rear, then the screw is present.

    You can use the mill as a drill press, but that's not what it's designed to do.

    << edited 11/18 PM to delete potentially erroneous information. Apologies to the OP. >>

    ------------------
    Leigh

    [This message has been edited by Leigh (edited 11-18-2005).]
    Leigh
    The entire content of this post is copyright by, and is the sole property of, the author. No assignment
    of title nor right of publication shall ensue from presentation of this material on any computer site.

    Comment


    • #3
      <font face="Verdana, Arial" size="2">Originally posted by countyrunner:
      Hi,
      I just purchased a bridgeport milling machine and am just learning how to use it. I am familiar with the use of the lathe but the mill is new to me. How tight should I tighten the draw bar in general. I am drilling some 1 inch holes in 1 inch plate steel using the drill bit in a collet and dont want to damage the bit or collet by not getting it tight enough and having it spin. thanks Paul
      </font>
      I use the Handle from my Kurt Vise to tighten the draw bar on my bridgeport. The ball on the end of the handle is also good for tapping the draw bar after you loosen it. You don't need much torque on the drawbar. On my variable speed head, I don't need to even use the brake when I tighten the draw bar (If I'm in low gear around ~200 rpm). I'll use the brake if I'm in a higher gear, otherwise I apply about the same amount of torque that is needed to turn the spindle when in low gear/~200 rpm. I have a set of Enco 1/16th to 7/8" collets in 1/32nd increments and they work great. I only use the automatic quill down feed when I'm boring, otherwise I prefer to to control the downfeed pressure dynamically when I'm drilling.

      -Adrian

      Comment


      • #4
        <font face="Verdana, Arial" size="2">Originally posted by 3 Phase Lightbulb:
        ...I only use the automatic quill down feed when I'm boring, otherwise I prefer to to control the downfeed pressure dynamically when I'm drilling.</font>
        You likely have a bit more experience with it than the OP. You need to tailor your responses to the audience.

        ------------------
        Leigh
        Leigh
        The entire content of this post is copyright by, and is the sole property of, the author. No assignment
        of title nor right of publication shall ensue from presentation of this material on any computer site.

        Comment


        • #5
          VERY LITTLE.. as in *maybe* a quarter turn.
          let the taper do the work.

          i have a kid in the shop that really liked to tighten everything down.. i mean everything. heck the drill chuck key is bent. he pulled the threads right out of my collet chuck.

          from my understanding, the power downfeed on the bridgeports is only meant for boring. and light boring at that. you'll do a number on it if you use it for heavy drilling.

          -tony

          Comment


          • #6
            Depends. I assume you're using Silver & Demming drills having the straight shank. Regardless, a BP quill rack and pinion is not intended to feed 1" drills from the solid. In fact somewhere in the book are word about 3/8" drillign capacity.

            2/3 of the drilling thrust is used to force the chisel edge into the work. Pre-drill a little less than your 1" finish drill's web thickness.

            The quill wrench is proportioned to provide the proper torque. Draw the wrench up formly and give it a final firm pull (or shove.) Anatomy and leverage will do the rest to give you about 50 ft lb. If you're a big strong guy ,lighten up. If you have weenie arms, give it all you got.

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            • #7
              The BP operator's manual states that when drilling only use auto downfeed for bits 3/8" and smaller.

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              • #8
                <font face="Verdana, Arial" size="2">Originally posted by Ted Coffey:
                The BP operator's manual states that when drilling only use auto downfeed for bits 3/8" and smaller.</font>
                Thats a Fact, though it may work it is not recomended,and a B/P with a broken power down feed is like a TV with out a remote.


                ------------------
                The tame Wolf !

                Comment


                • #9
                  <font face="Verdana, Arial" size="2">Originally posted by Forrest Addy:
                  Depends. I assume you're using Silver & Demming drills having the straight shank. Regardless, a BP quill rack and pinion is not intended to feed 1" drills from the solid. In fact somewhere in the book are word about 3/8" drillign capacity.

                  </font>
                  It's in the section about swiss watches and daylight saving time.

                  To be honest it's a joke if it wasn't true.
                  Brilliant design, nice machine totally spoilt by the inclusion of watch gears in the head.

                  Many clones copied Bridgeport without this drawback but are never as well thought about.

                  It's not sour grapes, I own a Bridgeport but to be honest if it wasn't for the transport and hassle of moving it I'd sell it in a heartbeat and buy something the same size but more substancial.

                  I could sell the Bridgy for at least twice what a better mill would cost.
                  Better power feeds, 3 to 5 HP motor and loose than non repeat setting wimpy R8 taper.

                  [EDIT] Iowolf,
                  I robbed the gears out of my bridgy to get another one I was selling working.
                  I haven't missed them for a minute. For one most of my work is above 3/8" and the operation of it, twist , knock, juggle is more like a pantomine than anything else.

                  Sir John.



                  [This message has been edited by John Stevenson (edited 11-17-2005).]
                  .

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



                  Comment


                  • #10
                    <font face="Verdana, Arial" size="2">Originally posted by Leigh:

                    You likely have a bit more experience with it than the OP. You need to tailor your responses to the audience.</font>
                    You're correct, that's why I would never suggest using the power downfeed for drilling holes, and especially drilling 1 inch holes.

                    In fact, I would never suggest a new mill ower use any power feeds of any kind until they've mastered manual feeding.

                    -Adrian

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                    • #11
                      "[EDIT] Iowolf,
                      I robbed the gears out of my bridgy to get another one I was selling working.
                      I haven't missed them for a minute. For one most of my work is above 3/8" and the operation of it, twist , knock, juggle is more like a pantomine than anything else."

                      To each there own,I use my Wells Index power down feed often for bore head setups,and it would be monotinous without it,but Hey, dif'rent strokes for dif'rent folks.
                      I simply like working smarter not harder.

                      ------------------
                      The tame Wolf !

                      [This message has been edited by IOWOLF (edited 11-17-2005).]

                      Comment


                      • #12
                        The BP powerfeed is great for boring and not much else. Everything has it's limits. If you over-do it, like drilling 1" holes, there is a slip clutch that "should" save the gears. Yes, they are small gears. WellsIndex gears are much bigger. I do like the "trigger cocking" action of the power feed engagement. It makes for a repeatable stopping point.
                        --Doozer
                        DZER

                        Comment


                        • #13
                          <font face="Verdana, Arial" size="2">Originally posted by Ted Coffey:
                          The BP operator's manual states that when drilling only use auto downfeed for bits 3/8" and smaller.</font>
                          OK. I'll accept that. My manual doesn't have that notation, but there are several different manuals available. I've never had a problem with the downfeed in the 40+ years that I've used it, but that's not necessarily definitive.

                          Thanks very much. And to the OP, disregard my previous possibly erroneous suggestion. I certainly don't want you to damage your mill.

                          ------------------
                          Leigh

                          [This message has been edited by Leigh (edited 11-18-2005).]
                          Leigh
                          The entire content of this post is copyright by, and is the sole property of, the author. No assignment
                          of title nor right of publication shall ensue from presentation of this material on any computer site.

                          Comment


                          • #14
                            I think it is best to fit a powerfeed to the knee for most jobs requiring vertical feed on a bridgeport...

                            I reckon if they made the head of a bridgeport half as heavy again it would have been a lot better machine....The head seems to be where the lack of ridgidity is, although mine is an asian clone and is of heavier build than a genuine bridgeport...(9X49 table, square Y Ways, heavier main column and all metric dials and leadscrews)

                            Mine has a NT30 taper spindle so I only tighten the drawbar so it won't come undone...



                            [This message has been edited by Ringer (edited 11-18-2005).]
                            Precision takes time.

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                            • #15
                              Paul,

                              The warning on the power feed is correct - I have had to rebuild mine.

                              It is only partially correct to describe them as flimsy, I don't think they were ever intended to do more than power feed a boring head.

                              My manual also says "Maximum loading 3/8" (9.5mm) dia. drill in steel".

                              After drilling pilot holes using the quill and hand feed, you can also crank up the table up to drill your 1" hole, this gives you good control, especially as it breaks through at the end. Plenty of cutting oil.

                              Yeah, and always do up that drawbar tight.

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