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Building lathe support. Torsional stiffness

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  • Building lathe support. Torsional stiffness

    This is my lathe PM1236


    The stand is flimsy and lathe essentially sits on top of two stands that connected by thin metal sheet.
    I've bought a 9 x 25.4 steel channel that I'll put on top of cabinets to add stiffness/rigidity.
    I know that closed shape(tubes) provides much more torsional stiffness.
    Here is my question.
    Should I consider welding a steel plate on the channel to make it into a rectangular tube? How much stiffness do I gain? Is it worth the efforts?
    I don't have a welder. I'll have to pay someone to do the welding. What if instead of welding I build bolted webbing in the channel to increase stiffness and weight?

    Here is the specs for my MC 9 x 25.4 channel.

    A = 9"
    B = 3.5"
    C = 0.45"

    Any suggestion is welcome except this one: "Your lathe is stiff enough as is, stop screwing around"
    For years I've been suffering from underweight, flexing and vibrating anorexic machinery and I'd rather overbuild than have a chance of having machine flex and vibrate under the load.
    AlexK
    Senior Member
    Last edited by AlexK; 05-23-2010, 04:41 PM.

  • #2
    It depends on how you plan to arrange the pieces of channel, and "...I'll put on top of cabinets..." doesn't really tell us much.

    I'm guessing you are going to put two lengths side by side from one end to the other. That won't get you a whole lot of rigidity unless they're welded and boxed, but the extra mass will probably do a lot to steady the lathe while it's running.

    Do you really want the lathe 3.5" higher than it is now? That seems rather high for working comfort.

    The best approach is some sort of framework that goes between the base of the lathe and the floor. Welded is better than bolted. The cabinets themselves could fit inside the framework, but most of the sheet metal wouldn't be used.

    The stand for my lathe is made of 2" x 1/4" angle welded into a framework that's 24" deep 44" long and 30" tall. It's so rigid that it will rock on uneven concrete with the 700-pound lathe on top and at least a hundred pounds of tooling inside the cabinets. I have to put shims under the legs to level it and keep it from rocking.
    winchman
    Senior Member
    Last edited by winchman; 05-23-2010, 07:57 PM.
    Any products mentioned in my posts have been endorsed by their manufacturer.

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    • #3
      Hi Alex

      I have a lathe which is a twin of yours and I agree it needs more stiffness, mine will twist the bed under its own weight, according to my level.

      The cabinets are rather light weight but being welded boxes they are actually quite stiffer than they might appear, IMHO.

      I suggest the channel steel be at floor level and well bolted to join the cabinets, my lathe is off the floor a little and the working height is just right for me, 5'11".

      John

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      • #4
        I own a HF 12 x 36 that has the two stand arrangement like yours. IF you really want to stiffen it up, bolt the stand(s) to the floor.



        I cast concrete pads to raise the height of the lathe, but this is not necessary. You can use Red-Heads or similar directly into a concrete floor. Actually, I only bolted the headstock, but that was more than sufficient to stiffen up the stand and lathe. If I were doing it again I would probably bolt down the tailstock also, but it is tricky to get the stands aligned so the bolts fit. I have read complaints before about the stands that are used with this class of lathe, but my experience is that the stands are more than stiff enough if you attach them to something solid like the floor.

        Comment


        • #5
          Sidneyt,

          what kind of cement do you use for the base?
          The floor in my garage has a slope so I was planning to pour a 2"-3" high base for the lathe anyway.
          Because of the sloped floor I'll have make the cement base extending to where the operator will stand.
          Otherwise it'll be awkward to stand on the sloped floor while working on leveled lathe.
          AlexK
          Senior Member
          Last edited by AlexK; 05-23-2010, 10:56 PM.

          Comment


          • #6
            If you welded a plate to the channel to box it, that will add more torsional rigidity than doing the webbing. You don't have to have weld all the way along, just do the ends and spot in several places between.

            I was in a store the other day and noticed there was a wider range of premixed cement products than there has been before. One of those was a low shrinkage mixture. Why not fill the channel with that- after the plate has been welded on of course. Won't take much cement, and it will be even stiffer afterwards.

            I never did like those metal stands. My inclination would be to build my own, and that's what I've done for virtually every machine I have. The only machine that's still on the supplied stand is the belt sander. It doesn't need to be any better than it is, so I didn't bother.

            If you were willing to pay for some materials and welding, you could always make up a triangular box beam and fill that with cement. Make the three sides the same width, and wide enough so that what becomes the top plate has enough room to mount some studs to which you can bolt the lathe. Attach all hardware that you would find useful for other things, such as a back splash, or electrical boxes- whatever- before filling it with cement. You might also add some anchors to both ends of the box to give a way to mount legs. You'll end up with a lot more rigid and vibration absorbing structure, and nothing says you can't add storage shelves or drawers underneath that.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

            Comment


            • #7
              Originally posted by sidneyt
              I own a HF 12 x 36 that has the two stand arrangement like yours. IF you really want to stiffen it up, bolt the stand(s) to the floor.
              Hi Sidneyt, we will be moving to a new place soon and I intend to do something like you have done. Are the concrete pads bonded to the floor?

              John

              Comment


              • #8
                Should I consider welding a steel plate on the channel to make it into a rectangular tube? How much stiffness do I gain? Is it worth the efforts?
                The difference is extreme. I think I will do a little demonstration. Back in a while with some pictures.
                Free software for calculating bolt circles and similar: Click Here

                Comment


                • #9
                  Originally posted by AlexK
                  Sidneyt,

                  what kind of cement do you use for the base?
                  The floor in my garage has a slope so I was planning to pour a 2"-3" high base for the lathe anyway.
                  Just make sure your minimum thickness is 2" any where in the pad. Be sure to "Pummel" the existing concrete and throw in a couple pieces of rod bent over into the new pad so it sticks.

                  Of course if your really good at concrete you can always embed a couple pieces of C-channel flat side up where your legs are going to set. That way you can use leveling pads and the screw adjustments, and when the ground shakes as it tends to do in California your lathe can give (move) rather then absorb
                  JoeFin
                  Senior Member
                  Last edited by JoeFin; 05-24-2010, 01:57 AM.

                  Comment


                  • #10
                    Here is a twist comparison of two different aluminum sections. The first is a 2x2 inch H beam and the second is a 1 x 1" square aluminum tube. The total material is much greater in the H beam but the H beam isn't a closed shape.

                    The H beam deflects about 1 inch at the end of the lever arm.





                    The square tube deflects about 0.1" at the end of the lever arm.



                    Free software for calculating bolt circles and similar: Click Here

                    Comment


                    • #11
                      Simply put:
                      You can't stiffen the bed with just two tubes that you put on top of your feet.
                      The easiest way is if your floor is a 3" slab of concrete. Bolt your lathe dwon at every hole (there should be 6) it has. This way, you can twist and even bend your bed in any desired direction.

                      If your floor isn't heavy enough, you have to weld something that has torsional stiffness. I welded something for a friend. In the middle was an I-beam that was closed with two C-channels (left and right). That was as wide as the bed and a bit longer.

                      Whatever you weld, it has to be stiffer or at least as stiff as the bed itself.
                      If you take the bolt-down-route, check inside those cabinets, re-weld them (you'll find a few tack welds) and reinforce them. I did that, and it made a huge difference.

                      Nick

                      Comment


                      • #12
                        Originally posted by Evan
                        Here is a twist comparison of two different aluminum sections....
                        Evan,

                        thank you for the demonstration. It is very convincing.

                        Comment


                        • #13
                          I used Sakcrete that I purchased at HD to cast the pads. It was not necessary to prepare the concrete floor so that the pads stayed in place (OTOH, if I ever need to remove the pads I may have a problem). I had previously poured a pad for my mill/drill stand using 2 x 4s as forms so I knew this would work. For the headstock end of the lathe stand I used cardboard tubes in the form positioned using the lathe base to make the holes for the 1/2" studs that I cemented into place. I used Sakcrete Anchor cement to secure the bolts in the pad.



                          I used standard levelers on the tailstock end of the lathe.

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                          • #14
                            The area that I'll be pouring concrete has 4" difference in height due to slope. Do I need to drill existing concrete and insert some rebars so there is good connection between old and new concrete?

                            Comment


                            • #15
                              Alex, if you have a minimum thickness of concrete at the thin end of your pour, say 2-3 inches, then you won't really need to anchor that to the existing floor. Put some steel mesh into the center of your pour to help keep it an integral 'chunk', and paint the existing floor with a somewhat diluted solution of white glue before casting the new concrete. I was told that and found it a bit hard to believe, but it does work.

                              Because concrete continues to cure with time, it would be best to leave it untouched for several days before you put weight or stresses on it.

                              I don't know what you're thinking to make the form of, but you might also consider leaving it in place. Call it a kick plate or whatever- just make it look decent and be done with it.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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