No announcement yet.

SB 10k lathe underdrive mechanism

  • Filter
  • Time
  • Show
Clear All
new posts

  • SB 10k lathe underdrive mechanism

    I just bought a 1980's South Bend 10k lathe (the Korean version). However, the bench/cabinet containing the underdrive mechanism and motor was not included (of which I was aware). Apparently it was accidentally disposed of...

    A decade ago I bought a 9c lathe from 1936, so I have an existing, working, horizontal drive mechanism to stare at and play with; I'll likely sell this lathe when the new one is up and running. Between the two lathes I have most stock accessories; the 10k of course has a gearbox (and thread dial indicator), larger feed dials, cross feed, and much less wear. The 10k also came with a collet closer and 6k collets by 1/16" (but missing the 1/2" size).

    I can build an underdrive bench, but what should I do about the flat belt pulleys? Google has not turned up a picture or diagram of the original arrangement. I see SB 9" parts for sale on eBay, so I've pondered buying a horizontal drive setup and adapting it to mount beneath a benchtop. Any other ideas?


  • #2
    I'd check with to see what he may have available or may know of one elsewhere.

    You could find the speed chart, measure the spindle pulley diameters, the RPMs of the motor you will use to calculate the size of the pulleys on the underdrive. If you make your own pulleys keep in mind they should have a slight crown to help keep them centered. I'd also use a automotive serpentine belt instead of a leather one as they transmit power much more efficiently. If you cannot find a serpentine belt of the correct length they can be cut, overlapped and glued very successfully with the two part plastic adhesive made by Loctite.

    I recommend obtaining the SB manual so you can see the various drive set-ups used over the years and select the one best suited for you. Tony at sells manuals for numerous machines and his site has an index for SB lathes. He's not the cheapest source, but very reliable and only sells legible ones, not blurry poor copies.

    There is also a Yahoo user group for SB's at

    BTW, welcome to the asylum as you apparently have OIS (Old Iron Syndrome). It is not curable, but needs an occasional infusion of new to you old iron.


    • #3
      I have a 10K and could text or email a picture with my phone--PM me the cell number or email to send it to.


      • #4
        There's an excellent exploded parts diagram at
        It's a PDF of a US Army document.


        • #5
          There are some good pictures here, maybe older than your machine?


          • #6
            Unless you are trying to make this a "restoration" and not just a working machine, an option worth exploring, and maybe money better spent, would be to run a DC or 3 Phase motor with a belt to the spindle and vary the motor's speed. In the long run it may be less expensive that purchasing all the parts necessary for an original drive and give you variable speeds.


            • #7
              Thanks for all the replies! Yes, I am aware of the website, and already had downloaded the Army manual (page 16 shows the underdrive unit). Already use a serpentine belt on my 9", would be happy to do the same for the 10k. Not too concerned with restoration of the 1980's Korean sourced 10k, and I'm definately interested in what I've read of VFD and 3 phase motors. Since I've really no machining experience, I'd prefer to start with some existing pieces (pulley assembly) and limit most of my fabrication to welding or woodworking, or what I can do with files and a drill press, until this 10k lathe is operational. Lost Creek Machine looks like a good resource, but I'm up in the Pacific Northwest. Shipping would seem costly, though I'll check with them. All the good salvage yards here have gone away in the past few decades...

              Thanks again! Yes, the Old Iron Syndrome has no cure... beyond the next acquisition!


              • #8
                Since this isn't a restoration and you have an interest in VFD and 3 Phase you might also consider DC. While not having all the merits of VFD/3 Phase, it may be less expensive. I have purchased new surplus industrial 2 HP DC motors and DC controllers for under $125 complete. If you shop around they are available and fairly simple to get up and running.
                Maxheadroom and others here are great resources for info on DC and 3 Phase.