Loading ...
Sorry, an error occurred while loading the content.

Interchangeable spindles

Expand Messages
  • Pat
    Any of our machine designs involve spindle choices. We have to choose between a slow turning spindle with a huge spindle bore, a conventional lathe spindle or
    Message 1 of 3 , Feb 1, 2012
    • 0 Attachment
      Any of our machine designs involve spindle choices. We have to choose between a slow turning spindle with a huge spindle bore, a conventional lathe spindle or a higher speed milling spindle. Swapping spindles types is difficult to do in a simple and affordable way because the spindles need to be both easily removed from some kind of a housing and without any play at all (especially at the spindle end).

      I had a idea last night. Make the removable spindle a few thousandths smaller that the outer housing and then evenly centerpunch a 1/2" band of punchmarks around the inside of the outer end of the outer housing.

      To insert the inner spindle, just slide it in until it hits the raised humps (upsets?) caused by the center punching and then force the spindle over the humps with a big hammer.

      This could also work with an MM with a cast iron bore if the center punches were replaced with very thin tapered shims.

      Pat
    • keith gutshall
      Hello Pat Could you explain the reasoning for the two spindles?  How fast would a milling shaft have to turn?    I would think a hollow shaft could turn  a
      Message 2 of 3 , Feb 1, 2012
      • 0 Attachment
        Hello Pat
        Could you explain the reasoning for the two spindles?
         How fast would a milling shaft have to turn?
         
         I would think a hollow shaft could turn  a milling cutter to a good speed.
         
         Te limit speed is how fast the bearing are rated at,or how much HP you have.
         
         Keith
         
        Deep Run Portage
        Back Shop
        " The Lizard Works"
        From: Pat <rigmatch@...>
        To: multimachine@yahoogroups.com
        Sent: Wednesday, February 1, 2012 10:47 AM
        Subject: [multimachine] Interchangeable spindles

         
        Any of our machine designs involve spindle choices. We have to choose between a slow turning spindle with a huge spindle bore, a conventional lathe spindle or a higher speed milling spindle. Swapping spindles types is difficult to do in a simple and affordable way because the spindles need to be both easily removed from some kind of a housing and without any play at all (especially at the spindle end).

        I had a idea last night. Make the removable spindle a few thousandths smaller that the outer housing and then evenly centerpunch a 1/2" band of punchmarks around the inside of the outer end of the outer housing.

        To insert the inner spindle, just slide it in until it hits the raised humps (upsets?) caused by the center punching and then force the spindle over the humps with a big hammer.

        This could also work with an MM with a cast iron bore if the center punches were replaced with very thin tapered shims.

        Pat



      • David G. LeVine
        ... Sorry, Pat, good idea, bad implementation. The place you need precision is on the front of the spindle, this moves the precision back AND each spindle
        Message 3 of 3 , Feb 2, 2012
        • 0 Attachment
          On 02/01/2012 11:47 AM, Pat wrote:
          Any of our machine designs involve spindle choices. We have to choose between a slow turning spindle with a huge spindle bore, a conventional lathe spindle or a higher speed milling spindle. Swapping spindles types is difficult to do in a simple and affordable way because the spindles need to be both easily removed from some kind of a housing and without any play at all (especially at the spindle end).
          
          I had  a idea last night. Make the removable spindle a few thousandths smaller that the outer housing and then evenly centerpunch a 1/2" band of punchmarks around the inside of the outer end of the outer housing.
          
          To insert the inner spindle, just slide it in until it hits the raised humps (upsets?) caused by the center punching and then force the spindle over the humps with a big hammer.
          
          This could also work with an MM with a cast iron bore if the center punches were replaced with very thin tapered shims.
          
          Pat

          Sorry, Pat, good idea, bad implementation.  The place you need precision is on the front of the spindle, this moves the precision back AND each spindle must (by definition) be of a different diameter.

          There are two tricks that work, however:
          • Put a taper on the front and pull it tight with a drawbar -- pretty common in the machine world for tooling.
          • Use a collet with cantilevered segments (look at the ER series for a good example) -- can be accurate if the spindle is either very accurate or is held with a key/keyway to ensure precise rotation on assembly.

          How can a spindle be off if it is round and the spindle itself has little runout?  Imagine a 2D spindle cross section with the center of rotation offset from the spindle OD.  The spindle now is offset from the center of the workpiece or cutter by a different amount (or in a different direction) for each insertion.

          Inserting the spindle with the same rotation (via a key) tends to give a fixed offset every time, which can be compensated for from a lookup table.

          Tapers like the R-8 and CAT series tend to be very accurately made and very repeatable.  In the sizes we would want, they also are very expensive.  Unfortunately, common tapers (like the Morse taper series) tend to be too small, the biggest Morse taper in common use is the #7, you can buy a lathe for the cost of the reamer (it is 10 inches long and the small end is 2.75 inches, roughly.)

          A better choice might be a sub-spindle in something like a 5C or R8 taper.  A 5C (or Cataract #5 for historical reference) taper only goes to 1 1/16", so tiny, high speed spindles could be built in that envelope.  5C collets are very common and relatively cheap.  This means a good workholder and a way to accurately hold work.  An ER50 collet goes to 35 mm (1.339"), and has exactly the same advantages and limitations, but is more expensive.

          R8, CAT and NMTB tapers do not go through, hence through spindles don't use them.

          HSK type shanks MIGHT work, but we are getting into some pretty esoteric tooling.

          On the other hand, having multiple spindles permanently mounted is not such a bad way to go. 

          So let's assume a flange and a taper (not such a bad approach, it is used in several tool shanks).  Given a precision taper (so the flange is precisely located just above the mounting surface when seated) and precise torques on the flange fasteners (so that source of warpage is minimized), a precisely located spindle is practical, but the precise machining may be impossible with hand tools.

          It would appear that interchangeable headstocks might be simpler and easier.

          Make a bed ala Yeomans, and have the headstock reference the ways and a locater pin or two.  On many 7x lathes, the headstock bolts to the bed and the ways are cut into it, with the headstock sitting on the ways a few thousandths above the bed.  The smaller the clearance, the harder it is to manufacture, the larger the clearance, the easier it is to get swarf in the gap, making accurate assembly impossible.

          It would be poor engineering to try to locate on more than one way, the machining gets too difficult, and more than one locating pin will mean slots to allow for thermal effects.

          Dave  8{)

          --
          "Political Correctness is a doctrine, fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."
          (quoted from http://www.wattflyer.com/forums/showthread.php?t=30060)

          NOTE TO ALL:

          When forwarding emails, please use only "Blind Carbon Copy" or "Bcc" for all recipients. Please "delete" or "highlight & cut" any forwarding history which includes my email address! It is a courtesy to me and others who may not wish to have their email addresses sent all over the world! Erasing the history helps prevent Spammers from mining addresses and viruses from being propagated.

          THANK YOU!
        Your message has been successfully submitted and would be delivered to recipients shortly.