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Symptoms of "worn ways" vs symptoms of worn "screws, nuts and gibs"

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  • Symptoms of "worn ways" vs symptoms of worn "screws, nuts and gibs"

    I have a vintage 1967, 9x42, Series1 J-head Bridgeport, that I've owned for about 5 years. It's been kinda loosey goosey all along, and I was initially thrilled to get it, but now I'm thinking I'd like to have a "tighter machine" for my home shop (plus I'm looking for an excuse to buy myself a retirement gift).

    Backlash is not too bad at 0.012" for both the X & Y (my DRO makes it a minimal issue). But I can grab one end of the table and wiggle it slightly unless the table is locked. And there doesn't seem to be much adjustment left in the gibs.

    The flaking marks on the Tibon chrome knee ways are still quite visible, which leads me to wonder if the issue may be more an issue with the screws, nuts, and gibs more so than the ways.

    I'm wondering if it might be too much to expect that just changing out the rods, nuts and gibs would improve things, or if it is just wishful thinking.

    The choices, after much consideration, I see are:

    1. Replacing the afore mentioned items, as well as exchanging my head with the H&W exchange program, for a grand total of about $3000 or less (if no surprises).
    2. The going rate for a completely refurbed and re-painted Series1 is about $9,000, at least in Detroit.
    3. Sell the Bridgeport to offset the cost of a brand new Taiwan built Acer 9x49 from Production Tool for $8300 delivered.
    http://www.pts-tools.com/cgi/CGP2SRI...93323278563713

    Not interested in a Chinese mill. And the big Precision Matthews is just about the same price, once you consider the trucking charge, etc.

    Any pearls of wisdom?
    Last edited by jmarkwolf; 03-21-2018, 12:21 PM.

  • #2
    I think it really depends on how even the wear is. Try tightening the gibs up to the point you still have full travel but no noticeable binding. If you have split nuts, try tightening them and again check to make sure you still have full travel without binding/etc.

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    • #3
      I think you have to do a lot more info gathering and surveying before picking a course of action. Backlash doesn't matter, except as an indicator of wear. At 12 thou its very little imo; for a 50 year old machine its either been lightly used or diligently oiled. You'd hope the ways would be in equally good shape, but that's conflicted with the idea the gib is fully tightened yet there is still shake.

      screws and nuts have really nothing to do with how well fitting the ways are so I doubt that is the problem. So is its gibs, ways or both, and how bad is it? If you want to avoid guess work, I'd take it apart and survey it - figure out where the way is and why the gib doesn't tighten things. You may need to buy a straight to do so; even you have no interest in scraping it will make assessing wear easier and you can always resell it. Besides, its small dollars compared to what you are thinking of spending. Complete the kit with your version of a kingway tool and a starrett 199 and you'll be able to figure out where the issues are. The 199 is expensive, but can be bought used and resold.

      Complicated suggestion to a simple question, right? well....there's something wrong and you need diagnose what it is exactly before you can have confidence in a solution. In my experience taking one apart and surveying it will give a new appreciation for how the way needs a good fit and bearing to function properly (supporting the cutting force) and it becomes pretty clear it won't get tight like you want it to without first understanding whats going on there
      Last edited by Mcgyver; 03-20-2018, 12:52 PM.
      in Toronto Ontario - where are you?

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      • #4
        I think the classic way to check for wear in the table dovetails is to snug up the gibs with the table centered. Set them for a very slight but noticeable drag. Then try to wind the table or middle carrier to either end. If the travel stiffens up and binds then you've got wear through the most used portion.
        Chilliwack BC, Canada

        Comment


        • #5
          Originally posted by BCRider View Post
          I think the classic way to check for wear in the table dovetails is to snug up the gibs with the table centered. Set them for a very slight but noticeable drag. Then try to wind the table or middle carrier to either end. If the travel stiffens up and binds then you've got wear through the most used portion.
          The middle travel of the x-axis is smooth, in fact I could "whip" the wheel a turn or two before I added the table feed, but tightens significantly at either end, so much so that any tighter would be objectionable.

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          • #6
            Originally posted by jmarkwolf View Post
            ... Backlash is not too bad at 0.012" for both the X & Y (my DRO makes it a minmal issue). But I can grab one end of the table and wiggle it slightly unless the table is locked.
            If you're getting 12 thousands backlash with bronze nuts I think that's OK. If your nuts have a backlash adjustment, don't touch it. You'll just make
            the nuts wear faster.

            And there doesn't seem to be much adjustment left in the gibs. ...
            Some machines use tapered gibs with screws at both ends. One screw does the adjustment and the other locks it down by pushing the gib back
            against the first screw. If you don't loosen the locking screw, it could feel like you ran out of adjustment range.
            Last edited by RichR; 03-20-2018, 02:18 PM.
            Location: Long Island, N.Y.

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            • #7
              When I got my BP, it had about .040-.060" back lash on the X & Y. I could shake the table back and forth in the saddle about 1/8". After cleaning all the moly grease out of everything, installing the table and cross feed nuts correctly (PO had them jammed together--No adjustment) and oiling it up, I get a few thousandths of back lash on the X & Y now (.003-.005" is spec). The gibs just needed a little stoning to get a few dings out. The adjusting screw on the Y gib was broken off but I was able to get the remnants out easily and make a new one. My belt drive J-head is deathly silent compared to the rock-crushers I've heard on YouTube. It came with a brand new Baldor 1.5hp motor and I can hear the motor fan over the spindle bearings at 3000rpm.

              I guess if you have deep enough pockets, you can get someone else to fix it or just buy a new one.

              Comment


              • #8
                Originally posted by RichR View Post
                If you're getting 12 thousands backlash with bronze nuts I think that's OK. If your nuts have a backlash adjustment, don't touch it. You'll just make
                the nuts wear faster.

                .
                That's completely up to how much non-uniform wear is on the length of the lead screw,

                If the lead is in good shape all's that's needed is enough clearance for lube and all will be good, probably not as likely with a used machine but new machines can be set up very tight without wearing anything more so than running one loose,

                I set my Mill up to have .003" on both X and Y over a decade ago, think the X is up to .005 and the Y .004 so no worries about extra wear there,

                He could try .005 and see if it binds at the end of the table travel - any binding at all means your leads are worn and you have to back them off accordingly...

                Comment


                • #9
                  Originally posted by jmarkwolf View Post
                  The middle travel of the x-axis is smooth, in fact I could "whip" the wheel a turn or two before I added the table feed, but tightens significantly at either end, so much so that any tighter would be objectionable.
                  Then you most certainly have wear in the dovetail ways on that axis. And it even sounds like it may be loose if you can make it "glide" like that for a couple of turns worth of the wheel on the oil film. And that's not a good thing for getting accurate work.

                  I'd say that if it's as you describe then it's time to have the ways re-ground on that axis and a new "fatter" gib made if it's a taper style gib. Actually since the gib strip is likely also arced due to the wear from the sliding a new gib isn't a bad idea at all to go with the re-ground ways.


                  ..... or that new machine you're lusting after starts to sound better and better.
                  Chilliwack BC, Canada

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                  • #10
                    If I were you, I'd keep the base you have with the Tibon chrome ways and look around to see if there are any machine shops that can true up your saddle and table for a reasonable price then install new feed screws and nuts for ~$600 or a set of ball screws for ~$1600. You'll wind up with a better than a new BP assuming your head is still good. It's really a no brainier IMO, any machine with excellent Tibon chrome ways is always worth rebuilding.

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                    • #11
                      I would do a combo of both of these shows.
                      https://www.youtube.com/watch?v=mwrarivDsnY
                      then use a mag base and dial indicator like this next one.

                      https://www.youtube.com/watch?v=nqQ3HzoSnUc

                      and adjusting feed screw back lash.
                      https://www.youtube.com/watch?v=YZ3qhMhlzAk

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                      • #12
                        For determining the source of problems, one good way is to move the table to various positions , and attempt to twist it, for instance pushing forward on the right side, and pulling back on the left, or vice-versa. If at some points (but not others, the table can be twisted in that wasy, then there may be worn areas of the ways. If the looseness is similar everywhere, but too much, it may be adjustable to remove it.. But wear in specific areas is not able to be removed by adjustments.
                        backlash:

                        I disagree about backlash on a mill. For a lathe, it is of small consequence. With a mill it may be more significant.

                        For a mill, backlash is a nuisance for one reason because some cuts (slotting cuts, for instance) are neither conventional nor climb, but are instead a "whatever", because there is a bit of both involved. With that, the cutter is capable of taking charge as if you were climb cutting, and pulling right through the backlash to ruin the part.

                        Of course that depends on the mass of the table and work, the friction of the ways, etc.
                        Last edited by J Tiers; 03-20-2018, 07:41 PM.
                        CNC machines only go through the motions

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                        • #13
                          The big issue with making gibb and screw adjustments is the wear is almost always going to be in the area where the most movement is.... the center. So if yo snug up the gibbs at that position your going to find out things start to get tight on the outer ends of the travel. Then you have to find a happy medium and after finding that your pretty much back to where you were. At least that is the way it happened to me.

                          Also if there is any excessive play in the gibb notch where the screw flange holds it the gibb will bind up in one direction and loosen up going the other way.

                          I played with my knee gibb once, thought I had it pretty good and found that after adjusting it the knee started to stick when I lowered it, and it was a litter harder to raise. Actually the screw had to pull it down and it would jump. So.... I ended up back where I started. There was a few thou of play in the gibb notch where the screw flange holds it. Not enough where I could shim it so again...... it was back to where I started.

                          JL................
                          Last edited by JoeLee; 03-20-2018, 07:42 PM.

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                          • #14
                            Add a DRO, removes most issues with warn screws and nuts. You can also split your nuts to make them adjustable, and make a shim that gives you more life out of the gibs. This is what I had to do on my Bridgeport. Also, my head has slack in the spindle, so I get the rattle when the splines hammer


                            Sent from my iPhone using Tapatalk Pro

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                            • #15
                              Originally posted by J Tiers View Post

                              I disagree about backlash on a mill. For a lathe, it is of small consequence. With a mill it may be more significant.
                              how do you see that it matters?

                              I guess it would matter if you are comparing zero vs some amount, but if there is some amount (and there has to be sans anti-backlash tackle) how much is there is doesn't much matter. without a DRO, with any amount of backlash, you always come at things from the same direction for locating, you lock the axis perpendicular to the cut direction if its a heavy enough cut to move things etc, and whether there's 15 thou or say 25 thou is immaterial to that fact that you're going be able to do a heavy climb cut.
                              in Toronto Ontario - where are you?

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