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Bridgeport Leadscrew and Nuts

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  • Bridgeport Leadscrew and Nuts

    My new to me Bridgy has about .012 and .014 backlash in the x and y respectively. I have taken up all of the adjustment in the leadscrew nuts. I have been thinking of replacing the brass nuts with new ones from http://www.machinerypartsdepot.com/ Is it worth the effort, or should i live with it? BTW it is a hobby shop machine that gets used infrequently.
    Arbo & Thor (The Junkyard Dog)

  • #2
    Originally posted by Arbo View Post
    My new to me Bridgy has about .012 and .014 backlash in the x and y respectively. I have taken up all of the adjustment in the leadscrew nuts. I have been thinking of replacing the brass nuts with new ones from http://www.machinerypartsdepot.com/ Is it worth the effort, or should i live with it? BTW it is a hobby shop machine that gets used infrequently.
    Hmmm, I lived with 0.090" of backlash on my X-axis since I bought mine. When I installed the DRO I took all but about 0.010" out of it.
    If you can live with that amount on your projects then that answers your own question. I have a project that will require multiple bolt patterns on one plate, so it would get almighty confusing to keep track all the moves with that amount of backlash.

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    • #3
      It's a lot of work to replace the nuts and then there is the wear on the screw. Does it have the same slop at each end of the travel as it does in the center of the travel. Most the wear will be in the center area of each screw. I'm betting it gets hard to turn the crank at each end of the travel.
      It's only ink and paper

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      • #4
        feedscrew my man, feedscrew

        what would replacing it accomplish? sans an anti backlash nut there has to be some clearance or the screw would jam in the nut....so whether you have .004 or .020" doesn't much matter.

        so far as accuracy goes, wear in the screw can absolutely affect things, but wear in the nut not really. If you trying to move exactly 10" and are going from a worn part of the screw to a unworn, the lead will change and you won't be exactly 10". But wear in the nut does not determine how much you move; for that matter you could stick a pin between the threads it would be just as accurate (but not as strong or long lasting)

        Unless you're replacing it with an anti backlash ball screw, I'd leave it
        .

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        • #5
          I would put a DRO on it before replacing the screws and nuts. The DRO reads the movement of the table regardless of how worn the screws and nuts are.
          It's only ink and paper

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          • #6
            Arbo first did you just tighten the screw holding the nut in, or did you take the nut off the screw and split it like your supposed to do. After cutting the nut in 2 grind the cut ends flush, reinstall them with a gap in between, remember that there is more wear in the middle of the screw than the ends , set your back lash near the ends. Now as an aside does your machine have a 1 shot lube system, if not you have to manually lube the nut housing on the saddle or table there is a line that says "OIL NUT" on the saddle or table there is a line , line the 2 up remove your vise if its mounted in the middle of the table, now in the middle "T" slot look for a set screw in the middle of the table that is the lube point for the nuts.

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            • #7
              Replace nuts with Evanuts ( search this forum for them )

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              • #8
                Originally posted by Carld View Post
                It's a lot of work to replace the nuts and then there is the wear on the screw. Does it have the same slop at each end of the travel as it does in the center of the travel. Most the wear will be in the center area of each screw. I'm betting it gets hard to turn the crank at each end of the travel.
                You can get the same result with worn dove-tails as well.

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                • #9
                  Originally posted by Lu47Dan View Post
                  Hmmm, I lived with 0.090" of backlash on my X-axis since I bought mine. When I installed the DRO I took all but about 0.010" out of it.
                  If you can live with that amount on your projects then that answers your own question. I have a project that will require multiple bolt patterns on one plate, so it would get almighty confusing to keep track all the moves with that amount of backlash.
                  "Back-lash" is not only between the lead-screw and the nut but at the thrust plates at each end of the lead-screw and the mill table ("X" and "Y") which are additive.

                  If you "come onto" each hole position from from the same direction (ie from "clock-wise" on the"X"and "Y" hand-wheels) you will largelyor entirely eliminate the effect of back-lash.

                  A lot of the "positioning" problems can be reduced if all the required postions are re-calulated to an ordinate system (ie "X" and "Y") with a known reference/zero point. This is very easily done in CAD but its even easier with a DRO - with or with out CAD.

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                  • #10
                    If it we me and more than a couple of holes were involved I'd mark it out and centre-punch it to minimise the risk of individual or cumulative error.

                    Marking out with a height gauge or a surface gauge as well as an angle plate and perhaps a rotary table will work just fine - on your mill table is quite good enough - or a surface plate.

                    Your eye will soon detect even a small amount of misalignment error between the mill quill centre and the drill on the one hand and the centre-punch marks on the other.

                    A properly sharpend small drill will soon self-centre in the centre-punch marks - with care.

                    In my case, unless there were compelling reasons other-wise, I'd drill the centre-punched holes on my pedestal drill.

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                    • #11
                      See pic 55 here on a Sieg X3/SX3 mill lead-screw nut - which is typical for many mill lead-screw nut adjustments for "back-lash".

                      http://www.arceurotrade.co.uk/machin...ly%20Guide.pdf

                      I'd be very wary of over-tightening that nut as the "bend over" bit may be a bit fragile if over done.

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                      • #12
                        According to a BP factory rep I talked to in the 80's, factory set new X/Y backlash is .006 to .007".

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