Announcement

Collapse
No announcement yet.

Cross Slide Nut Question

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Cross Slide Nut Question

    Slowly finding the root of many of the issues with my late 1930s Sheldon lathe.
    I may actually get to some of the fixes that had been planned years ago, one of which involves the cross slide nut.

    This is a square thread so I am not about to single point a replacement nut (I want to make first single point threading attempts something a bit simpler) but I will try an Evanut.
    That is the first course, the alternate route will be to replace the screw and the nut with an Acme thread version (and I have the basic parts for those already doing similar to what others have often done with South Bend 10” lathes).

    The question is about the nut itself as I have nothing to compare.
    The current version, which I assume is still from the factory, has been severely ground on the bottom to give clearance at the furthest end of the screw where it is near the end of the “U” shaped channel that crosses/makes up the saddle. This allows for the nut to be unbolted and completely removed from the cross slide screw. It means the screw can be left in place and the cross slide completely removed by pushing it off the back.
    To me too much of this nut has been ground away and using either the Evanut or the replacement Acme nut would mean something similar unless I grind away part of that “U” shaped channel. If I use care and don't make that area too thin, is there anything wrong with grinding that channel?
    Related I guess is if I chose not to grind either the nut or that channel bottom, and the nut can now no longer be completely removed from the rear, have I lost an important detail?

    Thanks, Russ

  • #2
    Russ, Maybe if you post a pic or two showing just how tight it is there in the bottom of the U someone could better see how to help?

    FWIW, I made an Evanut for the Atlas and it was a pretty tight fit clearance-wise on the bottom and sides. What I did using a small chunk of stressproof for the outer shell:









    I'm certain that I could have gone thinner on both the ~+1/8" wall thickness of the acetal surrounding the formed threads. Also could have gone alot thinner on the outer shell part too... I just didn't know. But it does fit now that I very lightly grinded the channel, probably not much more than smoothing out the casting bumps. Had I gone thinner on the acetal and or the outer shell I wouldn't have needed to grind at all. hth

    Comment


    • #3
      Check out Green Bay Mfg as the sell generic acme screws and nuts. I usually cut the original screw off near the threaded section, leaving enough to turn it down then face and drill a hole in the end of the new acme threaded rod , press it in and pin it. You would need to buy a square nut from them and machine the nut's outside. http://www.greenbaymfgco.com/ Rich

      Comment


      • #4
        Richard: a bit more complex than that for me (the way the original screw bears is odd and I have sort of chalked it up to being a very early production model, in a nutshell where one would typically have a thrust washer there is just metal on metal, which is fine except they did not machine it so it would be flat surface on flat surface but rather left the interior apron surface closer to "as cast" so not flat and not round and then rounded the end of that bearing portion of the cross feed screw...the result of which is a poor fit) anyway, the plan is to duplicate the whole thing but with Acme thread etc. so that I can use the lathe itself to do the work, make the corrects to the odd surface mentioned above (flat and allowance for a thrust washer), then mill/spot bore the saddle hole to a flat bottom and use the newly made screw.

        caveBob: thanks a ton for taking the time to post those photos, great detail! It looks very similar to what I envision the nut looking like for the Sheldon.
        The original nut is ground enough on one end that there are what I suspect are "stress" cracks becoming visible and based on the thread depth for the size and type of screw (square thread, 1/2") compared to that a direct measurement says, it is very thin.
        That is the reason for concern...off the top of my head, using your photos as reference, that lower part of the block would not be complete but from the end it would look like a "C" with the open part of the cee being the bottom of the nut.
        I suspect whomever ground the nut realized how close it was on that end and did not go as far with the remainder of the nut; part of the reason I suspect the nut was ground is that it will have been way easier to do that than to work on the saddle. What I don't know is if that nut "needs" to have the capability of removal that way...I mean you can always get to it from the front by removing all the handles etc. its just more work (so that maybe the reason for wanting such a feature)
        [as a bit of a related aside, many of the cast items on this lathe are not the best quality, with lots of small inclusions or air bubbles (?, that is just what they remind me of) and this nut is part of that, the threads nearest the ends are not worn away, they are fragmented]

        Edit: oh yeah, that bushing/spacer on the top of the nut looks remarkably like what I made yesterday [again, related, every so often it was like there was unexpected movement of the cross slide, in my case the hole that bushing goes through was elongated just enough to allow a bit of movement]

        Yeah, at some point I should not be so lazy/procrastinate so much and get a photo account somewhere so I can download stuff here...
        Last edited by RussZHC; 04-24-2014, 08:40 PM.

        Comment


        • #5
          Hi RussZHC
          You can post pictures using tinypic.com, no account required.

          Comment


          • #6
            OK, we try
            that should be cross slide nut view from the end, best quality I could find

            hmmm, see what I can do about making that a bit larger...

            [IMG][/IMG]

            better, see if we can get rid of the first one

            cool, now the whole world can see the junk I own and think is good...

            Thanks Rich
            Last edited by RussZHC; 04-24-2014, 08:22 PM.

            Comment


            • #7
              Actually, it may turn into even bigger thanks to Rich...browsing photos of the lathe to see what else might be useful and it occurs that the nut from the compound maybe exactly the same (hard to tell from photo and I have never measured it)...and I have a second compound since it seemed simpler to have one that uses a tapered gib rather than one that has several horizontal screws when locking the compound in place...it is a bit newer vintage so is Acme thread but who cares as its a separate unit.
              Now to see if it drops into place...

              Edit: drops into place but, AAARRRGH!, 2nd nut correct type and size but WRONG HAND...and, as a bonus, the taper gib for the second cross slide is good too but once again, THE WRONG HAND! (bought on ebay so a bit of a chance, not too bummed but would have been nice if...)
              Last edited by RussZHC; 04-25-2014, 03:59 PM.

              Comment


              • #8
                I have made similar cross slide nuts by single point threading several times and they all turned out. On a couple lathes, though, I found I had to chase the thread on the screw to get it uniform the whole length. Cut it down so the thinnest threads carried through the whole length. Otherwise even an Evinut would have been tight at the ends and loose in the middle of the screw. On a couple very old and worn lathe cross slide screws the threads in the middle were too worn and I had to remake the whole screw. Whichever way, do what you must to the screw first so that the width of the threads on the screw can determine the width of the cutting tool you will single point the nut with.

                Comment


                • #9
                  caveBob, you did a nice job on the nut and metal carrier you made. I was going to do an Evanut on my Clausing lathe but decided it would be fairly tight(maybe too tight, I can't remember) and a bunch of work to make a metal sleeve for it so I went a different route. My screw was shot as well so I bought a length of acme rod and grafted it on to the old one like Richard mentioned. I then made a tap out of a piece of left over rod and used it to make a solid nut out of Delrin.



                  Comment

                  Working...
                  X