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  • #31
    Originally posted by mickeyf View Post

    But, but...! There's no lathe on top!
    yeah.... I do not see as much advantage in a concrete bench for just bench work.
    2730

    Keep eye on ball.
    Hashim Khan


    It's just a box of rain, I don't know who put it there.

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    • #32
      That's a pretty nice way to build up a concrete bench with less form work. So for that a good thanks. But yeah, total overkill for bench work. Or did you have other plans for it originally?
      Chilliwack BC, Canada

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      • #33
        Are the concrete benches cast upside down? Or is the top surface fine if casting upright?

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        • #34
          bc, if your talking to me, the idea was that i can attach stuff like benders to the bench. one goes on horitontally and the other one on the bolts you can see. also the vise stays put, of course. i made it when building the house, so the effort was limited, everything was on hand. the ss edge protetion was probably the most expensive part.

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          • #35
            Originally posted by dian View Post
            bc, if your talking to me, the idea was that i can attach stuff like benders to the bench. one goes on horitontally and the other one on the bolts you can see. also the vise stays put, of course. i made it when building the house, so the effort was limited, everything was on hand. the ss edge protetion was probably the most expensive part.
            It was more a general idea but with focus on a reply to you as well.

            Use with benders and other high force items clears up why you went with the heavy and well secured bench. It's really nice to have something immovable for such things.

            My own center island with drill press and bench vise serves the same function for me. It's done in plywood but it's way overdone. And through the scrap steel in drawers, heavy milling machine tooling and the other side being filled with fasteners I make good use of gravity to hold the bench in place when using my own Hossfeld clone for bending things.
            Chilliwack BC, Canada

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            • #36
              Silly question, hopefully someone can elaborate with some engineering knowledge. What kind of loading does a lathe have on a work base. Would it be torsional or eccentric? These was briefly touched on by The Metal Butcher, and from his explaining of moment of polar inertia it would seem it’s all torsional?

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              • #37
                Use with benders and other high force items clears up why you went with the heavy and well secured bench.
                Makes sense. My main workbench was originally built for musical instrument repair and is pretty solid - 2x6's and heavy plywood top. But it still wiggles a bit when yanking on something big in the vise.
                "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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                • #38
                  Originally posted by ikdor View Post
                  Are the concrete benches cast upside down? Or is the top surface fine if casting upright?
                  I expect mine was cast upside down. All surfaces appear to have come out of the forms with fine finish.

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                  • #39
                    Originally posted by Bds60 View Post
                    Silly question, hopefully someone can elaborate with some engineering knowledge. What kind of loading does a lathe have on a work base. Would it be torsional or eccentric? These was briefly touched on by The Metal Butcher, and from his explaining of moment of polar inertia it would seem it’s all torsional?
                    My take on it is that it is mixed. The reasoning is as follows:

                    The forces are "contained" to some degree in the "path" between the parts that have the forces on them, normally the spindle/work, and the carriage/bed subsystems. That is assuming work held in a chuck.

                    if the work is between centers, then things are a bit different.

                    Assume you bolt it to a piece of steel, and are turning a piece of work in a chuck. The work is being rotated by the motor, and the cutter is held to the bed. So what are the forces?

                    The headstock is being forced up, forced off the bed to the left, and also away from the tool toward the back to a varying degree. Because the work has some diameter, and the tool is likely cutting out on that diameter somewhere, there is an off-center point of action of the upward and leftward forces, tending to twist the headstock clockwise as viewed from the tailstock and as viewed from above. So the headstock is being lifted, twisted, and pushed backward away from the operator ( which is also a twist vs the mounting points).

                    The bed is being forced down, and away from the work toward the operator to a varying degree. Most of the pressure is coming on the front way, so there is a torsional force on the bed, CCW vs the headstock. That torsional force causes a bending downward of the bed, and a bending outward toward the operator from the outward force, and from the off-center force pushing leftward on the work.

                    If the work is between centers, then the work is being bent upward and toward the rear, and the bed downward and toward the front. The tailstock is being forced upward, so the bending of the bed is more "contained" within the lathe and work system.

                    Bending the bed downward tends to spread the feet outward in the direction along the bed. Twisting the bed due to the off center forces forces the feet at one end to be twisted in relation to the other end.

                    If you were to hold the bed feet solidly to a perfectly rigid surface, the downward bending of the bed would change to more of a beam restrained at both ends, vs one just sitting on points which it is more like if the mounting is soft or flexible, like wood, sheet metal, etc. Also the torsion would be changed so that both ends of the bed would resist the torsion, instead of just one end if the mounting is soft, etc. Both effects would stiffen the bed considerably.


                    2730

                    Keep eye on ball.
                    Hashim Khan


                    It's just a box of rain, I don't know who put it there.

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                    • #40
                      That's a very nice explanation.

                      There is one other effect not mentioned though. If the right material is used it can also help to damp out any vibration that tries to get started. Metals have a tendency to ring like a tuning fork. Even cast iron which is more dead then steel still has some of this. If we tie the lathe to a big steel tube it will add to the rigidity but it might still find a frequency where it can ring. Filling that tube up with a loose heavy material can do a lot towards damping out any mechanical resonance before it starts. Or we can form a mounting pad from reinforced concrete and get both functions from the one feature.

                      Imagine walking up to a metal I beam or hollow tube support column. Give it a sharp rap with a hammer. Then walk over to a concrete support column and give it a the same sort of rap. That's vibration damping in action right there.

                      Chilliwack BC, Canada

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                      • #41
                        damping is important. many big machines are made from epoxy-granite. the bench for my 3-in-1 also. made a huge difference.

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                        • #42
                          Originally posted by BCRider View Post
                          That's a very nice explanation.
                          ...........
                          Imagine walking up to a metal I beam or hollow tube support column. Give it a sharp rap with a hammer. Then walk over to a concrete support column and give it a the same sort of rap. That's vibration damping in action right there.
                          Well, maybe.

                          It can be damping, but it can also be "stiffness". Stiffness RAISES the vibrational frequency, which can be good, as it may move it out of the area which can be "driven" by some vibration as from cutting etc. That is what hapens with that concrete support column. Instead of a dull clang, you get a sharp "tap" noise, which is high frequency VIBRATION. That vibration can be better damped, and is also is out of the way of the frequencies the machine can generate. Not an issue.

                          As long as the frequency is either raised, or lowered, so it is far away from the frequencies the machine can generate, you will not have an issue. Vibration "damping" is a bit over-rated. "If it is damped, it was there". You would prefer it not even to "be there".

                          If it has to be there, then yes, damping is better than ringing.
                          2730

                          Keep eye on ball.
                          Hashim Khan


                          It's just a box of rain, I don't know who put it there.

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                          • #43
                            I'd call that a separate functional mode. So now we're up to three things that a good bench provides to a bench lathe. One- Added rigidity just from the added beam strength. Two- Added mass that along with the rigidity that alters the resonance. Three- A good degree of damping by using the right material(s) for the added bench or beam.
                            Chilliwack BC, Canada

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                            • #44
                              maybe it should be pointed out that not all cast irons have the same damping properties. nodular ci (pherodised graphite) only has about 30% of the damping of proper* gray iron (lamellar graphite). the others are inbetween.

                              yes, its desirable to prevent vibrations and resonnance, thats why they balance stuff. unfortunately vibrations are inherent to material removal. in slow motion an endmill looks like an mixer and even smooth turning will produce chatter under unfavourable conditions. hence all the active vibration management strategies on computer conrolled machines.

                              * fine, homogenous and random orientation. (e.g. "meehanite" certifies foundry processes that achieve this.)
                              Last edited by dian; 05-11-2021, 05:08 AM.

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                              • #45
                                That's true. And to be fair when I tap a cast iron brake disc top hat it rings like a church bell. But as you say it's a case of finding the iron with the right properties.
                                Chilliwack BC, Canada

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