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  • Levelling a lathe on my concrete bench...

    Today is the day I mounted my 12x36 Chinese lathe on my concrete machine bench.

    These lathes have 6 mounting points, 4 under the headstock and 2 at the far end.

    I got everything apparently level easily enough but on further checking I found the lathe bed was arched upwards (very slightly of course). I presumed this was due to the 4 jacking nuts under the headstock not being adjusted correctly.

    My level has a vee bottom and does not sit well on the ways (cross wise is OK) so I put it on the top of the cross slide and wound the saddle between the limits of its travel while adjusting the outermost jacks at the head stock end. That seems to have done the trick.

    Now the point is, I have never seen any of the on-line accounts of how to level a lathe ever check for this condition of arched (or swayed) back and I dont think a short test bar would find it either. It might show as a tail stock centre high or low but you would have to check that in two or more places to find if the bed was arched. You migh even be able to get an arch backed lathe to pass some of the common tests perfectly.

  • #2
    Sure your not 'tensioning' the lathe? (Squishing the tailstock and headstock mounting points togethor)

    Also, I used 123 blocks to put my level onto the ways.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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    • #3
      Seems strange to have four adjustable feet under the headstock. Presumable it now only sitting on the two outer ones. Do you have a photo of such an arrangement? I guess an arching (or sagging) bed doesn't get discussed because usually there is no way to adjust for it.

      When checking my lathe I always put the level on the cross slide for checking both the longitudinal and transverse level. After all it's not the bed that matters it's the cutting tool tip moving in the same plane. The documentation for my German built lathe shows the use of the carriage.

      If you can adjust the "arch" of the bed then you have a means of adjusting for wear.

      Phil

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      • #4
        Originally posted by Black_Moons
        Sure your not 'tensioning' the lathe? (Squishing the tailstock and headstock mounting points togethor)
        I dont think so, the holes in the bench are much bigger diameter than the bolts that pass through them.

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        • #5
          Phil, the lathe is nothing special and very many of the Chinese lathes of this size are mounted like this. Four mounting holes, one at each corner of the head stock foot and two mounting holes, one front and back of the tailstock foot.

          These machines are usually mounted on two steel stands which would not give much support against sagging but my solid concrete bench is one solid surface. I have bolts sticking up from the bench top with nuts under the lathe feet as the bench top is not perfectly plane.

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          • #6
            You did it right. releasing the tension on either the two end bolts or the two bolts by the chuck would have fixed it. I suggest you check it every month for maybe 6 months to be sure everything is staying put.
            It's only ink and paper

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            • #7
              Originally posted by The Artful Bodger
              Today is the day I mounted my 12x36 Chinese lathe on my concrete machine bench.
              John,

              Perhaps I missed a post, but I'm wondering how you coped with the misaligned holes?
              Allan Ostling

              Phoenix, Arizona

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              • #8

                lathe fixing by aardvark_akubra, on Flickr

                That of course if the headstock end, the tail stock has just two bolts.

                It looks a bit suspect standing on those bolts like that and I am sure there would be more rigidity if there was tension on those bolts. I did intend to pack with concrete but that would leave no scope for future adjustment. Hmmmm.... I guess it is not going to go anywhere.

                Any ideas of how to fill this gap? Fitted wooden blocks would keep the swarf out and would be soft enough for a bit of future tweaking if required.

                Allan, only the two holes that are overhead the end of the bench have embedded threaded sockets, the other holes are right through and big enough to accommodate the misalignment when I use 12mm bolts. I off-centre drilled and tapped the heads of a pair of bolts for the problem positions and I set those bolts in bog so they are not exactly rattling around in their sockets.

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                • #9
                  Ever think maybe its arched because you jacked up the inside bolts and tensioned the outside bolts?

                  Repeat after me: Metal is as rigid as a wet noodle.

                  Btw: I think theres a serious danger of snaping those bolts when you start doing serious offset/unbalanced turning.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                  • #10
                    No way those bolts would snap. Look up the tensile strength of even common grade bolts for that size.

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                    • #11
                      Originally posted by Black_Moons
                      Ever think maybe its arched because you jacked up the inside bolts and tensioned the outside bolts?
                      More than likely..

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                      • #12
                        Nice looking bench, are you going to paint it before it gets oily. Also have you run the lathe on it and if so, does it seem to give a better finish to the work, less chatter etc.

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                        • #13
                          Use any three mount points to level the lathe on three axes - use all four to take out the warp.

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                          • #14
                            Hmm- I think what I would do at this point is put a piece of wood under the headstock, about halfway between the bolts, then set the bed down on that. Then I'd do the same under the tailstock, except use a slightly thinner piece of wood and lay that of a piece of rod that's centered under the bed. The bed will now be on a three point support and will take the alignment it wants. The thinner wood piece plus the diameter of the rod should have that end of the lathe at the same height as the head end.

                            The lathe would be lined up so all bolts will stand through the mounting holes and the bench top without leaning sideways.

                            At this point I would begin to run the bottom nuts up til they each stop. Once all of them are up, do what you need to to make the studs tight to the benchtop. Then make the rounds again on the nuts, making sure they are all run up about equally. Then I would place felt marker marks on each nut so you can then give each one an extra full turn up. You should be able to remove the wood now, and run the upper nuts down finger tight. Now start checking the bed for warping.

                            If there's an upward warp, lower the two inside nuts under the head end, turning each the same small amount. Finger tight the upper nuts and check the bed again. When you seem to have the bed level, tighten all the upper nuts at the headstock.

                            At this point use only the studs at the tailstock end to make adjustments. You can warp the bed up or down, and twist it. Avoid any twisting except when you have detected it with the sensitive level. Always use both nuts now to de-twist, so the average height at that end stays the same. One set of nuts goes up- the other set goes down the same amount. I'm going to guestimate here and say the most you would need to alter these adjustments would be perhaps a quarter turn, but probably much less than that.

                            If you use this procedure, you can set the lathe bed fairly low to the benchtop. About all the room you need is two threads up on all the bottom nuts, or make what turns out to be the lowest one two threads up. You're never going to need that much adjustment again, once you level it the first time

                            I agree, that's a pretty large gap to fill with mortar or whatever. Just make up something cosmetic that you can slide into place- maybe secure it with a few beads of dap or similar. You will want to be able to remove it without wrecking it, so don't overdo it.

                            I'll make a suggestion for this piece- find a piece of birch plywood, the stuff that has lots of plies in it, about 1/2 inch thick. Make it about four inches longer and wider than the outermost part of the beds mounting plates. Cut a notch where it can slide under the bed at both ends and miss the mounting bolts. Push that under the bed from the front and temporarily block it up. Now you can measure the gap from that to the benchtop and saw up some of the same plywood to become the skirt. Make the front skirt full length, and glue that plus the two side pieces into place. For the back skirt, you want it removable so you can slide this assembly out the front for cleaning and adjusting the bed if and when needed. Sand this assembly up nicely and give it an all-around coating with something durable.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              Originally posted by dp
                              Use any three mount points to level the lathe on three axes - use all four to take out the warp.

                              The level I am using is Czech made 0.17/1000 and I can still get some indication (about a fifth of a graduation) of non flat ways, what should I expect?

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