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  • Back lash what is acceptable ?

    What would be an acceptable amount of backlash on a cross slide ?
    I started out with about .060 now after some adjustment I am doin to about .015 - .017 should it be less or is this acceptable ?

  • #2
    Not like new, but useable. My first 2 lathes had more than that, and I managed to get by. I’d put a dial indicator on the slide and see how the wear affects the actual travel. That way, you’ll have an idea where the errors can creep in.
    I cut it off twice; it's still too short
    Oregon, USA

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    • #3
      Originally posted by RB140 View Post
      What would be an acceptable amount of backlash on a cross slide ?
      I started out with about .060 now after some adjustment I am doin to about .015 - .017 should it be less or is this acceptable ?
      I was never really concerned with that amount of lash. My SB 10L has some (maybe a good 10 degrees of handle rotation), I never measured it. I do what Tim said and use a plunge dial indicator to get me there.

      Just always remember to "set" the slide when coming up on the cut. Meaning reverse enough so when you go in for the cut the B/L really doesnt matter. JR

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      • #4
        That amount is not bad for a normal hobby lathe and is probably normal for most lathes.
        With the move to DRO's on lathes, It has become a non-issue for most machinists.
        Just follow JRouche's guide for cross-feed use.

        Rich
        Green Bay, WI

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        • #5
          The cross slide on my Clausing had about .100 of lash before I replaced the screw and nut. I was afraid to part anything because the parting tool would pull itself in and break due to the lash.
          No problem now.

          JL......

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          • #6
            Dad's Rockwell had about 20 thou. We just made a new screw and nut today. We'll see how it is when it's all assembled.
            21" Royersford Excelsior CamelBack Drillpress Restoration
            1943 Sidney 16x54 Lathe Restoration

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            • #7
              I'd say that was actually pretty decent for a used machine. I'd not want a new machine to start with that. As long as it is a predictable amount, and reasonably easy to feel, it's fine. It's not too bad until you get to half a turn, or even a full turn or more of backlash. That gets to being hard to keep track of, so it is probably "too much".

              I consider it worthwhile to remove as much backlash as you can. Not because you can get it to zero, but rather because any backlash you can remove is unnecessary slop in the works, something that is likely to result in errors and problems in ways unrelated to the existence of "backlash" itself.

              Getting rid of it will save you trouble, and may result in a machine that is much easier to use, with fewer bad characteristics. Some cuts can result in slides slamming back and forth "through the backlash". With less backlash, that may be less violent, and easier to damp out with a little drag applied to the slide.

              Heh.... the deal with DROs making backlash irrelevant....... Maybe. That depends on what you mean by irrelevant.

              It's true, in that the DRO lets you put the tool where you want it, reliably. That's good.

              The question is, will it STAY there?

              You still need to do all the same things about crossing backlash, etc that you would always do. If you do not, you may find the tool is "pushed through the backlash" to a position you do not want. So, to set to a position, you need always to advance the feed toward the dimension in the direction to deepen the cut, never back it to dimension. That ensures, just as is normal, that the feedscrew is holding the tool against cutting pressure.

              Even then, if advanced to a position without being actually forced against cutting pressure, there may be some slop left which was not bucked-out by friction. The slide may be pushed back through whatever slop/backlash is left and not "taken-up".

              So, the DRO should be viewed as an improved dial, and not as something that allows a different sort of operation of the machine.
              CNC machines only go through the motions

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              • #8
                This like deja vu... There was a pretty long thread about the same topic less than a year ago.

                Backlash of some amount is pretty much unavoidable with normal lead screws and nuts. Some with anti backlash tricks can reduce it but it'll never be totally eliminated without going to something like ball screws.

                For my own machines I try to tune them up so that the total is around an 1/8 of a revolution or less. I aim for that sort of amount simply so I can reset back with just a minor twist of the wrist instead of having to wind back by a lot more. Most of them less than that. But one is just over an 1/8 turn due to the nut apparently.

                And DRO or not we still need to practice proper backlash control or we risk the travel being suddenly pushed away or pulled in if the backlash is not dialed out of the issue.
                Chilliwack BC, Canada

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                • #9
                  I have to agree- the more important aspect is in learning how to work with the backlash.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                  • #10
                    Originally posted by RB140 View Post
                    What would be an acceptable amount of backlash on a cross slide ?
                    I started out with about .060 now after some adjustment I am doin to about .015 - .017 should it be less or is this acceptable ?
                    "“oui, oui…”

                    I told you about my work lathe, the sb 10"

                    My other lathe has excellent dials and cranks. JR

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                    • #11
                      I'll say this... "It depends on what is causing the backlash." Backlash caused by a loose leadscrew nut is never acceptable, because you can't predict where it will end up. Backlash caused by a worn screw and nut can be mostly predicted, up to a point, but it will vary with where the two are engaged. Backlash caused by a loose thrust bearing is usually very predictable and is the easiest one to correct, mostly by shims.

                      You don't say what you did to get over a 0.040" reduction in backlash, but my guess would be that you had a thrust bearing issue that you shimmed out and are left with the worn screw and nut BL. To test whether or not the remaining is acceptable, make a cut in a practice part, measure its diameter, then use your dials to take another 0.010" cut. If you can actually HIT the 0.010" reduction, then your BL is controllable and acceptable. If you CAN NOT hit your mark, then you might want to explore more radical fixes for your BL (like making a new screw and nut).

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                      • #12
                        Originally posted by RB140 View Post
                        What would be an acceptable amount of backlash on a cross slide ?
                        I started out with about .060 now after some adjustment I am doin to about .015 - .017 should it be less or is this acceptable ?
                        Is that throughout the entire travel of the CS ?
                        What I've seen happen with any screw adjustment, lathe, mill or grinder, etc. is you can take some of the lash out and make it feel good in the most used area of travel but when you start moving to either end of the travel it'll start to snug up.

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

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                        • #13
                          Originally posted by SLK001 View Post
                          .................................................. Backlash caused by a worn screw and nut can be mostly predicted, up to a point, but it will vary with where the two are engaged. .................................................. .........
                          Originally posted by JoeLee View Post
                          Is that throughout the entire travel of the CS ?
                          What I've seen happen with any screw adjustment, lathe, mill or grinder, etc. is you can take some of the lash out and make it feel good in the most used area of travel but when you start moving to either end of the travel it'll start to snug up.

                          JL..................
                          If you cannot predict the backlash, which would be the case with an unevenly worn screw, then you will want to be able to "feel" it. You want to be able to feel when the nut "takes up", so that you know the backlash has in fact been taken up.

                          If you cannot, if the backlash takes up "softly", then you have to back out well past the probable backlash, and then crank it forward and hope you have taken it up. That's a nuisance, and you never quite know if things are correct.

                          Also, with unpredictable backlash, you never quite know how much to compensate for when setting the dial to the number you want. That makes it harder to hit the dimensions you need, so you probably have to measure more often. If it is "solid" backlash, then you can feel it, and check the dial for how much there is at the point you have the slide.

                          The whole deal of "just sac up and deal with it" as opposed to fixing as much of it as you can, is kinda counterproductive. Backlash is not a "badge of honor", and nobody is likely to adjust-in some extra backlash just to be "cooler".

                          Yes, you do need to know how to handle it. But all backlash is a nuisance, and not all of it is inevitable. Any you can get rid of is helpful in getting it down to an amount and type of backlash that is easier to deal with.

                          A quarter turn or less is probably fine, particularly if it is "solid" so you can feel when you have taken it up.
                          CNC machines only go through the motions

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                          • #14
                            I was lucky to get hold of a new leadscrew and 2 bronze nuts which could be modified to go in the Smart & Brown model A cross slide. The backlash is now 0.002" or less throughout the 7" of movement. The only downside was the thread was 3mm trapezoidal not 1/8" ACME, but the seller refunded my money and said keep it. A new scale was made with 118 divisions on it as the lathe is imperial, good enough for government work.

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                            • #15
                              So if you have a worn screw and nut assy. does that effect the dial reading ??? Example, if you move in .005 according to the dial did the CS actually move .005. I've never really checked it that way because I have DRO's on my lathe. I'm guessing it doesn't because the pitch doesn't change.

                              JL..........

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