Which method to reduce cross-slide backlash? - Page 2
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  1. #21
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    So...time to eat some embarrassment "crow"...
    Pulled the cover off the cross-slide so I could run the nut down to where I could get some rough measurements.
    As soon as I put the wrench on the short bolt securing the nut to the cross-slide I discovered it was loose, and the cause of the 2/3 of the "backlash", which was mostly wobble, it turns out. I had done a few quick cuts the day before and was puzzled by sometimes crazy readings on the X axis DRO, this explained it.

    After tightening the nut, dial and DRO confirmed .022 of actual backlash; not great but a substantial improvement.
    To echo Mr. Whoopee, it still bugs the bejeezus out of me "just because".

    Anyway...
    The sleeve nut almost works as-is, but will be to short vertically after milling a flat on top (see pic). Thinking about milling a flat plate "shim" to get correct vertical center for the nut, crazy-glue it to the top of the bronze nut then D&T for the securing bolt.

    What should be the minimum wall thickness beyond the major dia that I need to leave when milling the flat? I considered making a block to house the nut (after turning down to a mimimal OD) but space is tight for that and I don't think it'll need another nut in my lifetime, anyway as Thermite notes...



    cross-slide-screw.jpg

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  3. #22
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    Is your cross-slide marked for diameter (my Sheldon is) or actual DOC? If you're just using the DRO to detect movement and using the dial to determine backlash, you might only have .011" if the dial reads for diameter.

  4. #23
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    The 28$ bronze sleeve nut from Roton would be my choice.

    Optionally:
    Slit it diagonally and squeeze it a tiny bit lengthwise, perhaps half a thou, == 0.01 mm.
    Should get pretty much zero backlash.

  5. #24
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    Quote Originally Posted by Gordon Heaton View Post
    Is your cross-slide marked for diameter (my Sheldon is) or actual DOC? If you're just using the DRO to detect movement and using the dial to determine backlash, you might only have .011" if the dial reads for diameter.
    0-.125 dial, direct-read.
    Pushing/pulling the slide with an indicator on the toolpost shows the same .022 on the DRO as spinning the dial...

    Going to order the sleeve nut, closer look does show visible wear at the most used section of the screw- with a magnifier best I could measure was about ..005 at the top of the crests. Hopefully replacing the nut will take out half the backlash that my OCD will deal with until I can cut out the threaded section on the screw and pin a new section in.

    Appreciate any comments on minimal wall thickness I should leave on the nut when milling the flat, the more I can safely take it down the more contact area I'll be able to get when securing it to the bottom of the slide.

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    Congratulations, you have found and cured a major portion of the problem. Is there a thrust bearing at the back end of the screw? Does the dial move in and out slightly as you reverse rotation?

    What is the distance from the mounting surface of the nut to the CL of the threaded hole? Could you bore the existing nut and turn the Roton sleeve nut to fit or fab a steel housing with more meat? Retained in a bored hole, I wouldn't have a problem with .06 wall thickness. I wouldn't try to super glue to a plate, it will fail quickly.

  7. #26
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    Bit pushing and pulling you should see where the problem is agree with some earlier comments you say .022thou backlash.I measured the gap I had with slips/feelers put a thrust washer in think someone took one out and didnt replace that got it down pretty close but once you start you want rid of it.So in went a shim then a bit thicker shim and eventually it was gone normally you can get rid of it this way

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    You're worried about twenty thou backlash on a cross slide ? Shee-it Where's digger when we need him ?

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  10. #28
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    Quote Originally Posted by MrWhoopee View Post
    Congratulations, you have found and cured a major portion of the problem. Is there a thrust bearing at the back end of the screw? Does the dial move in and out slightly as you reverse rotation?

    What is the distance from the mounting surface of the nut to the CL of the threaded hole? Could you bore the existing nut and turn the Roton sleeve nut to fit or fab a steel housing with more meat? Retained in a bored hole, I wouldn't have a problem with .06 wall thickness. I wouldn't try to super glue to a plate, it will fail quickly.
    I had to face the thrust bearing and dial to get a near-zero backlash on initial disassembly/re-assembly. The super-glued plate is just a shim, I don't see it taking any real load; once D&T'd as one-piece and then secured through the top of the cross slide with the bolt it'd be compressed and held in place by the torque on the bolt.

    McMaster has 1/2-8 nuts that are 1-1/2" dia. (larger than the Roton) that would be large enough to mill/turn down to replicate existing, but not in LH thread. If anyone knows of another source for one that dia please let me know.

    I do agree that sleeving it would be the best way to go absent finding a round nut big enough to work one-piece. As I mentioned (and can be seen in the pic in #21), space is tight in there. I'll take the needed measurements to see if there's the necessary real estate to do it that way.
    Aluminum would be easy machining to use for a sleeve, any reason I shouldn't use it?

  11. #29
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    Done on a Sheldon mill, and looks like it would work for you too.
    Buy the bronze nut, and a piece of threaded rod to match. Use rod to hold nut to turn it down to some recognizable diameter. Small as you can bear.
    Take original nut, drill it out for slip fit of turned down nut. Sweat solder your turned down nut into the hole in the original cross feed nut. Done.
    If it will hold back 6" dia horizontal mill cutters in iron and steel, it will be more than strong enough for a lathe.

    If you feel froggy, you can then use the threaded rod to replace the current screw - which is another "how-to"


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