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  • why so heavy

    Why do rotary tables and large vices need to be so heavy?Surely with todays modern technology the weight could be brought down considerably.I remember reading that old bandsaws and circular benchsaws were always made from massive cast iron then the developed webbed mild steel and thet was just as strong did not warp or vibrate so whay cant this be done with vices and rotary tables.Alistair
    Please excuse my typing as I have a form of parkinsons disease

  • #2
    The weight is calculated by a formulae that takes the distance from a Scotsmans sporran to his wallet divided by how much is in it.

    .
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      I know exactly what you mean, they seem to be getting heavier as I get older! I also think they've been adding a few more steps to the City Hall second floor every year
      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

      It is true, there is nothing free about freedom, don't be so quick to give it away.

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      • #4
        As with all machine tools, mass == stability == rigidity.

        I have one of those 6" Palmgren rotary tables. It's meant for a drill press (not a mill) and it's a lot lighter than the usual 6" rotary table.
        The table lifts up during a heavy cut, no matter how tightly I've got everything clamped down, and it's in near new condition.

        I was thinking of bolting some tantalum pie slices inside the hollow table top, to beef it up a little....

        Just kidding
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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        • #5
          lazlo,

          Where would you get the tantalum?
          Paul A.

          Make it fit.
          You can't win and there is a penalty for trying!

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          • #6
            That's why it was a joke Paul. Did you see the big smiley?

            When I worked at the Army Research Laboratory, the machine shop there had loads of tantalum scrap from making explosively formed projectiles: thin sheets of tantalum that you explosively form into a very heavy dart.

            It's amazing stuff: you'd see a 4" disc laying on a work bench, pick it up, expecting it to be steel, and shocked at how heavy a thin 4" disc could be.

            I once thought about making a set of threaded tantalum rods that I'd screw into a lathe compound to make it a lot more massive...

            Nowadays, tantalum is a lot more expensive than gold:

            http://cgi.ebay.com/ws/eBayISAPI.dll...m=220150236349
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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            • #7
              Because

              They don't use much computerized stress analysis software in CHINA!
              James Kilroy

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              • #8
                You know, when people have a metal plate in their skull, odds are it is tantalum.
                Stuart de Haro

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                • #9
                  >"You know, when people have a metal plate in their skull, odds are it is tantalum."<

                  Titanium. A bit lighter than Ta--makes it easier to keep yer head above water---!
                  Gold is for the mistress - silver for the maid
                  Copper for the craftsman cunning in his trade.
                  "Good!" said the Baron, sitting in his hall
                  But iron - cold iron is the master of them all.
                  Rudyard Kipling

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                  • #10
                    Strangely, the density isn't directly related to atomic number. For instance, tungsten is denser than uranium. Tantalum is about twice the density of iron
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      I like heavy tools Makes me feel like I bought something for all that money. On a more serious note, I agree with Lazlo regarding mass and rigidity for fixturing.

                      Another way to approach it is to think in terms of mechanical solutions to the problem. My plan is to make a sort of "boom crane" mounted on the back of the Bridgeport as John Stevenson was so good to post here some time back. I believe Lane showed one similar but differently mounted. I have a BP 12" rotary table and also an angle plate to turn it upright. I would guess that the combined weight is 200+#....not at all good for my back.

                      My intent is to buy a big hydraulic press to sit behind my lathe. By mounting it to the floor, I can take the same "head" with the winch attached off the mill crane and stick it on a similar crane I will fabricate and mount to one of the uprights of the shop press. A guy can gain a lot out of careful planning and a sort of "interactive placement" of tools.

                      Paul
                      Paul Carpenter
                      Mapleton, IL

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                      • #12
                        Originally posted by Benesesso
                        Titanium. A bit lighter than Ta--makes it easier to keep yer head above water---!
                        Check this page out:

                        http://theodoregray.com/PeriodicTabl.../index.s7.html

                        The skull plates are near the bottom along with the screws to put them on. Look around the rest of the site too. Lots of cool stuff on there.

                        Stuart
                        Stuart de Haro

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                        • #13
                          Adding weight by means of more cast iron, specifically, increases overall rigidity. Not so with other material choices.

                          The more non-damping but stiffer material you add, like hardened steel, will reduce total deflection but increase chatter. If you were able to use a stiffer material than cast iron while retaining the same damping, the weight of the table would go down. That option is not economical at this point.

                          There are two kinds of rigidity a person cares about in machine tools: static and dynamic. Static stiffness is resistance to deflection under a load. Dynamic stiffness is resistance to vibration. A machine tool needs to have both, but materials that are good at one are not usually very good for the other. Silly putty has great dynamic stiffness, but isn't all that rigid from a static standpoint. Hardened steel may not deflect under great loads, but it likes to pretend it's a wind chime when you hit it with something - clear, bright ring that does not attenuate for a long time. High static stiffness, low dynamic stiffness.

                          So everyone uses cast iron, as it's one of the few materials that falls in the middle category of "okay at both."

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                          • #14
                            >"The skull plates are near the bottom along with the screws to put them on."<

                            You're right! I had no idea they made some of them from Ta. Only $61 too. Guess I should buy one to cover the hole in my head!

                            I know the docs are now avoiding the popular Ti "aircraft" alloy Ti-6Al 4V because the V can cause problems in people. Maybe that's why they use Ta?
                            Gold is for the mistress - silver for the maid
                            Copper for the craftsman cunning in his trade.
                            "Good!" said the Baron, sitting in his hall
                            But iron - cold iron is the master of them all.
                            Rudyard Kipling

                            Comment


                            • #15
                              Originally posted by Benesesso
                              You're right! I had no idea they made some of them from Ta. Only $61 too. Guess I should buy one to cover the hole in my head!
                              Tantalum is so friggin' dense -- wouldn't your head tip to the side?

                              By the way Benesesso, if you want that Norton wheel, you need to tell me what grit you're looking for...
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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