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Trying to understand the Worm Gear Cradle on a series1 step head

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  • Trying to understand the Worm Gear Cradle on a series1 step head

    I'm trying to debug a Handwheel feed problem on my mill.

    So far, things seem to point to a problem with the Worm Gear Cradle and/or related mechanisms.

    Can someone enlighten me on the following Questions:

    Worm Gear Cradle (17) pivots horizontally, in a shallow arc, at Feed Driving Gear (36), correct?

    The Worm Gear Cradle (17) raises and lowers by action of the Shift Crank (23), correct?

    This raising and lowering of the Worm Gear Cradle (17) is what should engage/disengage the cluster Gear Input Shaft (38), correct?

    The Shift Crank (23) rotates the Worm Gear Cradle throwout shaft (18). The pin sticking out the end of the Worm Gear Cradle throwout shaft (18) engages the Feed Engage Pin (16), correct?

    The Feed Engage Pin (16), is free to move vertically in its' bore on my mill, so how would this assert any change in movement in the Worm Gear Cradle (17)?

    The Worm Gear Cradle seems to be wet enough with oil, and has some movement when lightly prying with a screwdriver, but I don't know if it has enough movement, or the correct movement.

    Any ideas gratefully received.
    Last edited by jmarkwolf; 03-18-2013, 08:41 AM.

  • #2
    Looking at the drawing and from what I remember from stripping and cleaning the head on my Long Chang BP clone;

    The feed is engaged by moving the worm wheel into mesh with the worm cut into the spindle.

    The worm gear cradle only moves horizontally to achieve this mesh.

    I'd suggest running the head with the gear cluster cover removed. You should then be able to see if the feed gear (36) is moving.
    Paul Compton
    www.morini-mania.co.uk
    http://www.youtube.com/user/EVguru

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    • #3
      Originally posted by EVguru View Post
      Looking at the drawing and from what I remember from stripping and cleaning the head on my Long Chang BP clone;

      The feed is engaged by moving the worm wheel into mesh with the worm cut into the spindle.

      The worm gear cradle only moves horizontally to achieve this mesh.

      I'd suggest running the head with the gear cluster cover removed. You should then be able to see if the feed gear (36) is moving.
      I already know that nothing in my gear cluster is turning, but I'm not sure of it's an engagement problem I'm having with the shift crank, or something else.

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      • #4
        I do not have a drawing at hand and it has been a while since I was into a Bridgeport drive but these are my recollections. The cradle at the top moves horizontally to engage the feed with the spindle and does not move vertically. From the cradle, the drive goes through a pair of bevel gears down into the feed selector transmission. If the cradle moving lever is not timed right the movement will be reversed and the limits will be wrong so that may be what is preventing engagement. About the only other thing that could prevent any movement in the gear clusters would be stripped gears or broken shafts. I think you can remove the cradle lever mechanism and reach in there to move the cradle in and out of engagement.

        Hope this helps.
        Don Young

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        • #5
          Found the problem.

          The feed pinion bevel gear had broken off (see pics) which explains why the gear cluster was not turning.

          Further, the broken gear had jammed in such a way to prevent the worm gear cradle from pivoting as it should, which, I hope explains why the crank handle was turning above it's pivoting point instead of below, as is correct, and likely explains why the crank handle couldn't "reach" both detents!

          Haven't found the two broken teeth, saving that for tomorrow.

          Maybe the broken teeth explain the little intermittent rattle I hear when the spindle is turning. Man, that would be a Grand Slam!





          Last edited by jmarkwolf; 03-22-2013, 09:25 PM.

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          • #6
            I don't know just how common that breakage is but I do know that the whole Bridgeport down feed system is rather light duty. It is intended mainly for boring and Bridgeport specifies 3/8" maximum for drilling in steel. I am sure that with maximum feed and/or a dull drill even that might overload the system. If the overload clutch is set properly it should prevent breakage unless something seizes for lack of lubrication.
            Don Young

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            • #7
              Wow I've worked on BRPT for over 40 years and have never seen that break, it almost appears the large gear was jammed (some how) and then the drive was engaged. TJMHO

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              • #8
                Could this happen if the quill lock was tight and the down feed engaged?

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                • #9
                  I can't believe that gear............... and the force that it took to split it. Any other damage done internally as a result???????

                  JL...............

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                  • #10
                    Originally posted by jmarkwolf View Post
                    Could this happen if the quill lock was tight and the down feed engaged?
                    I would think the the quill lock would be overidden by the reduction of the drive assy.
                    It did split across the key slot which is the weakest point....... but still!!

                    JL................
                    Last edited by JoeLee; 03-24-2013, 03:42 PM.

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                    • #11
                      As far as I can tell, nothing but the shaft and the little bevel gear were damaged. The mating gear still looks nearly new to my eye, as do the all the cluster gears for that matter. Apparently they were never engaged very often. See pic below.

                      I found the two broken teeth right nearby, they hadn't migrated anywhere else from what I could tell. There wasn't any other debris other than grime and oil.

                      I'll order the specific replacement parts plus some related parts, like screws and keys, etc. to be safe.

                      I wonder if they (Bridgeport) made this the "weak spot" so that if it did break due to overload, the pieces had somewhere to go without getting "injested".

                      Last edited by jmarkwolf; 03-24-2013, 05:18 PM.

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                      • #12
                        I've been inside a lot of BP heads and never seen that. The overload clutch stops that gear damage. Look at your clutch. Maybe someone monkey'd with it.

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                        • #13
                          When I first got my Webb Milling Machine (Large BP Clone) the down feed worked but it would pause in a regular phase. I was going to disassemble it anyway to clean the head and replace both belts. When I got it apart, the problem became evident. The small pinion on the nose of the worm cradle had lost several of its teeth. This was no doubt caused by a ham-fisted prior operator using the down feed to drill a large hole in a piece of steel. The Webb, like the original BP has a limit of 3/8" sized drills in the manual when using the downfeed.

                          Since repairing it, I don't do any drilling with the downfeed. I use it now and then for boring where the vertical loads are light and the safety clutch has been set to protect the gears. The entire design is rather weak and is not intended for heavy loads. When I need to drill holes with the mill, I do them manually with the hand feed lever on the quill.

                          If I were the OP here, I would replace both gears unless there is some way to make sure that the mating gear is not cracked. I took no chances and simply replaced both gears.

                          The manual states that grease should be injected into the worm cradle area now and then, but most people simply give a few drops of oil in the cups.
                          Last edited by GNM109; 03-25-2013, 12:14 AM.

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                          • #14
                            Originally posted by lakeside53 View Post
                            I've been inside a lot of BP heads and never seen that. The overload clutch stops that gear damage. Look at your clutch. Maybe someone monkey'd with it.
                            Hi Lakeside53

                            I wondered the same thing, why the clutch didn't save the gear.

                            When I purchased the machine, it was missing the "outboard" clutch assembly entirely, so who knows the condition the clutch was in. I've since replaced them.

                            The Quill Stop Micro Screw and the Feed Trip Plunger were so dirty, they were badly stuck, and unable to "teeter" at all. So maybe the clutch was unable to kick out or something.

                            Before I found the broken gear, the handwheel had some serious "draggy" spots. Maybe I'll find something wrong in there as well.

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                            • #15
                              Originally posted by GNM109 View Post
                              If I were the OP here, I would replace both gears unless there is some way to make sure that the mating gear is not cracked. I took no chances and simply replaced both gears.
                              .
                              Good advice.

                              I will do so.

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