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Best Design for Connecting Two Pieces of Collet Adapter

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  • Best Design for Connecting Two Pieces of Collet Adapter

    I am designing a 5C Collet Adapter for my South Bend 9. In order to get a sufficient diameter to hold the collet on the external threads, the drawbar extension piece needs to be too big to pass through the 1 1/2-8 threads and definitely too big for the collet end of the main body. So a two piece design of the main body is definitely called for: a backplate and the front which actually holds the collet.

    I have worked on this for several nights and done some research. I am concerned about the alignment between the two parts. Both the initial runout and any changes that may occur if it is disassembled for maintenance. One published design used a circle of 5 cap screws and 5 dowel pins for alignment. I am also considering a thread mount similar to the lathe's spindle thread but bigger in diameter and with a finer thread. I would use a tight fit at a raised boss area similar to that on the rear of a 3 or 4 jaw chuck. And yes I am aware of the differing opinions about this fearure but if I control both male and female parts, I think I can use it for centering.

    My question is this, Which of these methods is likely to produce the better, more lasting fit? Which will provide the best runout when taken apart and reassembled? Or does anyone have a better suggestion for assembling these two parts and maintaining consistency. I would be tempted to use some kind of tapers but what and how to precisely match them? Or should I consider a "Set-Tru" feature?

    In any case, I would save the final cuts on the taper and hole for the collet until all other work had been done and they would be made on the fully assembled adapter. This should provide the best runout, at least initially.

    I did see and read the recent article in HSM. It started this project. I have also reviewed a couple of other published designs. And I have gotten a suggestion for three dowel pins in perpendicular slots on the other board. But dowel pins in slots would rest on such a small area. I would rather match drill, ream and insert the pins in tight holes.

    All suggestions and opinions will be appreciated.

    Paul A.
    Paul A.
    SE Texas

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

  • #2
    Metal Lathe Accessories sells a casting kit for a 5C collet chuck. There was a build article in HSM earlier this year.

    Another method of using the 5C in the smaller lathe was to make a screw on adapter, and use collets with an internal thread. an adapter was made to use the internal thread with a drawbar. This will not allow material to pass through the collet, but does have some utility.
    Jim H.


    • #3
      Something like this looks possible,
      Just scale it up. The ring with notches is a nut that grabs the outside thread of a 5c.
      I would take a 4 inch faceplate from here,
      They have a 4 inch face plate that is threaded for a SB that you could mount an adapter like the Sherline one. If machined in place on the spindle should be very accurate.

      Just my thoughts.....