Bulking up a Lightweight Lathe with a Concrete Cart

When it comes to machine tools, a good rule of thumb is that heavier is better. A big South Bend lathe or Bridgeport mill might tip the scales at ludicrous weight, but all that mass goes to damping vibration and improving performance. So you’d figure a lathe made of soda cans could use all the help it could get; this cast concrete machine cart ought to fit the bill nicely

Perhaps you’ve caught our recent coverage of [Makercise]’s long and detailed vlog of his Gingery lathe build. If not, you might want to watch the 5-minute condensed video of the build, which shows the entire process from melting down scrap aluminum for castings to first chips. We love the build and the videos, but the lightweight lathe on that wooden bench never really worked for us, or for [Makercise], who notes that he was never able to crank the lathe up to full speed because of the vibrations. The cart attempts to fix that problem the old fashioned way – more mass.

There are a few “measure twice, cut once” moments in the video below, as well as a high pucker-factor slab lift that could have turned into a real disaster. We might have opted for a countertop-grade concrete mix that could be dyed and polished, but that would be just for looks. When all is said and done, the cart does exactly what it was built to do, and there’s even room on it for the shaper that’s next on the build list. We’re looking forward to that.

18 thoughts on “Bulking up a Lightweight Lathe with a Concrete Cart

  1. Just for theory’s sake… this works as mostly a low pass filter in mechanical space, no? The higher frequencies that shimmy and wobble in the lathe still do to the same degree but are greatly damped by the increased mass giving a better surface finish – and a “resonance rigidity” above a certain point, but if say there were resonant subharmonics of the motor at let’s say 20Hz less so. In practice probably a non issue.. but just wondering.

    1. It’s a spring+mass system, so if you increase the mass you lower the resonant frequency.
      Concrete has also a better damping than aluminum so it increases also losses (lower Q).

      That’s why most machine tools are good old iron: big mass, high damping.

  2. Or, instead of the concrete outside the lathe, do as the Taig does and use it internally in the lathe bed for rigidity.
    The concrete looks way-out too top heavy for that table and perhaps overkill – he could have saved himself a deal of trouble by just buying a solid piece of 3″ or 4″ thick vintage hardwood instead of all that fuss with the concrete.
    I also wonder what the longitudanal accuracy became after tightening the lathe bed directly to his hand-leveled concrete without some soft shimming in between.
    Nice Gingery build, BTW!

  3. Cast iron is still significantly better for vibration absorption than concrete. I suppose using epoxy concrete could have given better results.
    Also, he can’t level the lathe using this table, which will influence the quality of work done, along with the lathe being rigidly bolted to this massive lump of concrete this build fails to impress.

  4. For all the time that machine tools have existed, there’s been little, if any, application of scientific principles to them for reducing vibration while reducing weight.
    Make it heavier. Make it thicker. Lighter weight machines get relegated to hobbyist class or in some cases all but spat upon, like the Atlas and Craftsman lathes with flat ways – or as they’re called when the exact same design is used on bigger iron – box ways.

    Since Hardinge bought Bridgeport and built a new factory with much improved manufacturing in less space, I’d like to see them tackle using processes like FEA to rework the venerable Series 1 Bridgeport knee mill which has seen very little change since its origins in the 1930’s. I bet they could shave a few hundred pounds of iron off AND improve its vibration characteristics to make it a better machine.

    Then there’s the J Head. That’s the part that does all the work, rotating and moving the cutting tools up and down. Largely unchanged since its origin, it’s a crazy complex piece of machinery and contains some rather delicate components for a machine meant to carve through steel. Chuck it out and do a new design from scratch, erasing every weak point and needless complexity. Keep the mounting bolt pattern so it can be retrofitted to any old Series 1 mill and others that use the same pattern.

    Next up, a head specifically designed for a CNC Z axis. The design can be far simpler than a manual head, with a smoother, less complicated and thus lighter casting. The only areas that need be the same as the old J head are where it mounts to the ram and where the drive mounts to the head. Everything else, a clean CAD drawing. Basically an iron tube with a vertical hole for the quill and a slot on the left or right for the drive to attach for moving up and down. That would also provide opportunity for making the quill movement longer. But Hardinge being Hardinge, they’d probably charge 2x the price of a manual head for the less costly to produce CNC head.

    Such a purpose built CNC head would seem like a no-brainer, but Bridgeport/Hardinge and the clone makers all make their CNC heads by bolting a servo or stepper drive onto a manual head. Sometimes they’re purpose built and leave out all the useless manual and mechanical power feed parts, but most often they just take an already built manual head and remove a few items like the quill lever and levers that engage the mechanical power feed. I stripped all the useless manual parts out of the head on my Acra mill and sold them. They were in new condition because they had never been, and could not be used on a CNC mill.

    1. They’re probably a bit busy with making VMC’s for huge markets to make a profit than to retrofit a old design of which the number purchased would be magnitudes smaller and the design cloned by everyone and their dog within a few years anyway.
      The rest of your post reads like your describing how a interact cnc head is put together on the rigid ram bridgeport interact BOSS machines that followed the J head models. They have redesigned more rigid heavier castings without bosses for the feed handles (you drive them in manual mode with joysticks), pumped oiler lubrication, a more rigid quill that doesn’t tilt or nod (hence rigid ram) and attempts to get away from the r8 spindle fitting into something more cnc friendly, qc30 on some, iso standard later on, only downsides in there now are both something that has changed with time, namely the lack of spindle brake, encoder and the varisheath design instead of a vector vfd.
      I’ve replaced my interact’s varisheath drive with a vfd and 1:1 belt and added a brake and encoder too (but kept back gear because low speed torque occasionally matters) while I was converting it to run linxuCNC. Do I expect there’s any commercial reason for a manufacturer to fiddle round retrofitting a replacement head assembly so I didn’t have to machine my own conversion up? not really in the real world no. Nor would anyone be willing to pay for it.
      If you want to see new tech and lighter machinery, buy a newer machine, cnc machining centres are getting lighter all the time.

    2. IMHO: Machinists are generally conservative and they want heavy machines as they know weight helps in reducing vibrations. They generally want cast iron as the construction material too, not a bad choice – good damping, reasonable strength and hardness etc. plus relatively cheap.
      But I can’t agree that scientific principles aren’t used in machine construction, FEA is used for everything and some machines have complex construction to avoid warping due to heat and cutting forces.

      I have ranted here and elsewhere that properly constructed a lightweight machine can be as sturdy as a much heavier cast iron construction. E.g. the Taig lathe (and mill too for that matter) is one example of a lightweight machine that without complicated design or materials can be much sturdier than a traditional cast iron lathe several times its weight, the Taig lathe uses an extruded aluminum bed (filled with concrete), a wide steel dovetailed way and an extruded aluminum headstock. Aluminum have very bad dampening properties, steel have pretty bad damping properties and concrete have less damping compared to cast iron.
      By using the same design but with Zamak for the bed and headstock and replacing the concrete with epoxy granite the result would be both stiffer and have higher damping.

    3. I think what you see as a lack of science, is the intractable nature of the problem. The lathe is only part of the system. Whatever it is turning is the other, and that means big differences in mass, in angular momentum, in off-center masses, etc. To scienceify this you need a machine with more degrees of freedom than a lathe, and active control of tool position.

  5. A bag of concrete mix is like $6 at Lowe’s, but adding in all the material to build the form and the labor, you might find it cheaper to buy. But would you get a 4″ thick slab weighing 260 pounds? I doubt it. The most common “stone store” is probably the local granite countertop fabricator, but they generally work with slabs in the 1.5″ thick range. I suppose the mason supply yard might have granite for landscape projects; they might be able to fix you up with a big, thick slab. Or even (gulp) a visit to the local cemetery monument carver. They work in all kinds of stone, and some pretty thick.

    Protip: My brother-in-law visited a big granite countertop fabricator and got permission to dumpster dive for scraps. He came away with a truckload of pieces, some up to 2’x3′. Perfect for the machine shop granite plate, although not ground flat enough as-is. Still, useful stuff – even small scraps make good surfaces for sharpening chisels and plane irons.

  6. I would be doing an epoxy laminate of granite countertop offcuts long before I was caught dead using concrete. There’s a reason concrete isn’t used in machine tools (or any precision surface, really), and that’s because it’s not dimensionally stable.

    1. Concrete have been used in machine tools… The main problem in this project is that the lathe is rigidly mounted to the concrete. Using concrete as a damping mass with something else as the fixture (e.g thick steel plate) there wouldn’t be too much of a problem. OTOH I doubt the lathe is used for precision work anyway.

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