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  • Really Stupid Question

    At the risk of opening myself up to massive ridicule.

    Does the "back gear" or low speed gear on your typical manual knee mill turn in the reverse direction of the high speed gear? I've heard the term back gear many times. Is that what it means?

    I was just getting ready to try some chucked up power tapping on the new South Bend 10x54 (SB1028F), and the spindle spun in reverse of the direction indicated on the control panel in the lower gear. It spins the direction indicated in the higher gear.

    I've never owned a real full on full feature knee mill before. The Hurco KMB1 doesn't count because it does what the VFD tells it to do.

    I can write G-code for simple jobs at the control panel, but I don't know all that much about this manual machine. All my previous (all 2 of them) manual mills were/are functionally bed mills with a drill press style pulley sheave for speed changes.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    My experience with older BP knee mill heads it that when back gear is engaged the spindle rotates in the opposite direction.
    However it has been a long time since having used such a machine, memory fades.

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    • #3
      Originally posted by Bented View Post
      My experience with older BP knee mill heads it that when back gear is engaged the spindle rotates in the opposite direction.
      However it has been a long time since having used such a machine, memory fades.
      That is correct, when in low range, what would normally be forward is now reverse.

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      • #4
        Originally posted by Bented View Post
        My experience with older BP knee mill heads it that when back gear is engaged the spindle rotates in the opposite direction.
        However it has been a long time since having used such a machine, memory fades.
        That's the only thing that made sense to me. Thanks. Perhaps due to the mechanical way they shift gears.

        One of the things (of many things) I want to do with this mill is simple second ops like threading holes for handles on lead casting molds and drilling hinge pin holes. Anything simple that only takes a couple tools for a very short run on that particular setup. That way I can just walk those molds back and set them on the table and leave all the CNCs open for more complex machining. Of course the order of magnitude greater setup flexibility of a fully articulating knee mill was part of it too. I've already done several operations on it that would have been difficult or even impossible to do on my CNC mills. So far I haven't screwed up anything important, but I definitely need more experience with the machine.
        *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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        • #5
          Thanks guys. That's what I figured. Just wanted to be sure.
          *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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          • #6
            My BP-clone Grizzly reverses when the back-gear is engaged, but the Spanish-made Exacto rotates the same direction whether the back gear is engaged or not.

            I suspect the latter is the much more unusual situation.

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

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            • #7
              Works that way on my Lagun - I reverse the motor direction to get forward motion at the spindle when in "back gear".
              Johnny

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              • #8
                I began running a lathe today that has a windows based control, this is unusual in machine tools, most are Fanuc based.
                It has a large touch screen with few hard buttons, this will take a bit of adjustment on my part, one may dial up or down the feeds and speeds by swiping the clock in the correct direction.
                Last edited by Bented; 06-24-2021, 08:03 PM.

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                • #9
                  I need to put a stick Z label on the screen of my lathe DRO so I won't get confused when I finally get a CNC lathe in the shop.
                  *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                  Comment


                  • #10
                    Originally posted by Bob La Londe View Post
                    Does the "back gear" or low speed gear on your typical manual knee mill turn in the reverse direction of the high speed gear? I've heard the term back gear many times. Is that what it means?
                    It's been my experience that the term "back gear" is brought over from the early belt drive lathes. The "back gears" located in back of the main spindle were pulled forward into mesh with the main spindle gears (after pulling the bull gear pin) to provide a series of slower speeds. On lathes, pulling this counter-shaft into mesh does not normally cause a reverse in spindle rotation. The counter-shaft rotates in an opposite direction, but the spindle does not. On the step pulley Bridgeport mills, and their knock-offs, the gear reduction mechanism does put a gear in mesh that causes a reverse in spindle rotation if maintaining the same motor direction.

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                    • #11
                      My BP clone mill reverses the spindle rotation in low range and the motor has a forwards/off/reverse switch to correct the spindle rotation.
                      Location: Saskatoon, Saskatchewan, Canada

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                      • #12
                        Bob: Anytime you put an extra gear in the drive line, the direction does change. In post #6, the Exacto would have had to use two extra gears for the reduction and keep the direction going the same .
                        Sarge41

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                        • #13
                          That wasn't a stupid question.
                          A stupid question is "does this dress make my ass look fat?.
                          Like, the orbiting satellites didn't tip you off?
                          Len

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                          • #14
                            Damn good thing that lathes and pillar drills rotate normally when in back gear, the designer of mills that do not should have been put up against a tree and shot.
                            Last edited by old mart; 06-25-2021, 02:17 PM.

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                            • #15
                              Originally posted by old mart View Post
                              Damn good thing that lathes and pillar drills rotate normally when in back gear, the designer of mills that do not should have been put up against a tree and shot.
                              Did the designers of the Bridgeport J head seek atonement with their introduction of the 2J head? Unlike the step pulley design, on the variable speed 2J head the spindle maintains direction when placed in low range.

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