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

Dimensions/ new narrow lathe carriage

Expand Messages
  • rigmatch
    Maybe a design for carriage for a small lathe. attached . Only 2 bolts attach the cross slide base since there probably not be room for more. The cross slide
    Message 1 of 7 , Jan 31, 2014
    Maybe a design for carriage for a small lathe. "attached". Only 2 bolts attach the cross slide base since there probably not be room for more. The cross slide would be aligned over wet grout and then removed after the grout stiffens. 


    The cross slide base would be tapped for 2 through bolts that would pass through the narrow carriage center section and be used to attach a larger lead or concrete "dumb bell" weight on the bottom.

    The cross slide base would then be epoxied into the "socket" left in the grout. 

    In this way a large cross slide could be securely aligned and attached to a narrow  but heavy carriage practical for even a 6" lathe.
  • Pat Delany
    Does anyone see a major problem  with the narrow carriage base concept? Optional weight on bottom? Cross slide base with just 2 bolts? Base epoxied into an
    Message 2 of 7 , Feb 1, 2014
    • 0 Attachment
      Does anyone see a major problem  with the narrow carriage base concept?

      Optional weight on bottom?

      Cross slide base with just 2 bolts?

      Base epoxied into an aligned and grouted "socket" (can't think of the right word)?

      A small design change that makes it easy to scale the machine down down to the common 6" lathe size with 1" ways on 5 or 6" centers.

      Pat


      On Friday, January 31, 2014 5:29 PM, "rigmatch@..." <rigmatch@...> wrote:
       
      [Attachment(s) from rigmatch@... included below]
      Maybe a design for carriage for a small lathe. "attached". Only 2 bolts attach the cross slide base since there probably not be room for more. The cross slide would be aligned over wet grout and then removed after the grout stiffens. 

      The cross slide base would be tapped for 2 through bolts that would pass through the narrow carriage center section and be used to attach a larger lead or concrete "dumb bell" weight on the bottom.

      The cross slide base would then be epoxied into the "socket" left in the grout. 

      In this way a large cross slide could be securely aligned and attached to a narrow  but heavy carriage practical for even a 6" lathe.


    • David G. LeVine
      ... Pat, Conventional wisdom says that narrower ways lead to more chatter and poorer accuracy. Dave 8{) -- A word to the wise ain t necessary - it s the
      Message 3 of 7 , Feb 1, 2014
      • 0 Attachment
        On 02/01/2014 04:23 PM, Pat Delany wrote:
        Does anyone see a major problem  with the narrow carriage base concept?

        Optional weight on bottom?

        Cross slide base with just 2 bolts?

        Base epoxied into an aligned and grouted "socket" (can't think of the right word)?

        A small design change that makes it easy to scale the machine down down to the common 6" lathe size with 1" ways on 5 or 6" centers.

        Pat

        Pat,

        Conventional wisdom says that narrower ways lead to more chatter and poorer accuracy.

        Dave  8{)

        --

        "A word to the wise ain't necessary - it's the stupid ones that need the advice."

        Bill Cosby
      • kwolson2002
        All - Actually, if I m looking at this correctly, it seems OK to me. Try searching the web for narrow guide principle - it s generally accepted that you want
        Message 4 of 7 , Feb 7, 2014
        • 0 Attachment
          All -

          Actually, if I'm looking at this correctly, it seems OK to me.

          Try searching the web for "narrow guide principle" - it's generally accepted that you want the longitudinal guide for a way to be "narrow" relative to its length, so that it can't cock and stick.

          Or, I could be looking at it cross-eyed!

          Kevin
        • kwolson2002
          All - As an addendum, I should point out that you want the drive for the slide as close to centered between the guiding surfaces as is possible. Somewhat
          Message 5 of 7 , Feb 8, 2014
          • 0 Attachment
            All -

            As an addendum, I should point out that you want the drive for the slide as close to centered between the guiding surfaces as is possible.  Somewhat off-center is OK, even underneath or inside one of the guides might be acceptable, but outboard is not so good (from the standpoint of stick-slip).  If your bearing material is sufficiently slippery, or has nearly identical static and dynamic coefficients of friction (think Teflon/Turcite or roller bearings), all of these concerns diminish in importance.

            Hey, diddle, diddle, straight up the middle.  Or some such.  That way, you aren't trying to torque the slide around just one of the guides, rather around both of them, but with opposite-handed torques, so this can be taken up as bending in the slide's structure.

            If that makes any sense.

            As a counterpoint to the above, we have all lived with engine lathe carriages being driven (generally speaking) by a screw hanging off the front of the lathe bed, well outboard of the guide ways of the carriage.  So, it might not be as big a deal as I am suggesting!

            With modern machine tools tending toward rolling element bearings for slides, I don't think this is viewed as so important any more.  Certainly, it was never discussed when I was in school 20-odd years ago.  But slightly older books, especially British ones from the 1950s to 1970s, where the sliding surfaces were still largely plain bearings except for some highly specialized machinery, discuss it quite frequently.  The notion has been beaten around in print since the early 1900s, at least.

            For what it's worth...

            Kevin
          • kwolson2002
            All - Doh! I see what David is saying. I was laying under the car, torching manifold flange nuts so as to gently persuade them to decamp themselves from the
            Message 6 of 7 , Feb 8, 2014
            • 0 Attachment

              All -


              Doh! I see what David is saying.


              I was laying under the car, torching manifold flange nuts so as to gently persuade them to decamp themselves from the studs.  It's easier than pulling the what were 12-point bolts which hold the manifold to the head, but have now corroded to exactly zero-point bolts.  In the end, the head needs to come off so it can get a new head gasket.  But I digress...


              Anyway, the epiphany of what David is saying struck me while I was contorted around the front differential, hand cramping, aiming a torch somewhere inconvenient.


              Having a long cross slide mounted to a carriage which is supported by close-set longitudinal ways will allow the cross slide to rotate about the way bearings (or torque the ways proper).  Some form of auxiliary support to kill this torquing tendency may be required, especially if a heavy casting is clamped down off-kilter to the cross slide while line boring, for instance, or when trying to turn a large diameter since the tool will be far from the ways (it will have a long lever arm).


              If, however, you are only contemplating a small lathe (Pat mentioned a 6" size), it might not be such a big deal.  Maybe an extra bit of threaded rod, fished through a hole in the bench back behind the lathe and nutted to a bolt-on torque arm, or some other such expedient, could be used for the odd job which needs the added support.


              The Metalmaster benchtop horizontal boring mill cum lathe had two crossed rods which trussed the end of the lathe bed to the overarm when needed.  By all reports it stiffened everything up nicely.  This was a slightly different scenario for the loading, but I am proposing a similar sort of remedy.


              The "narrow guide" scheme would have an additional way surface parallel to the other two, well set back from them, which only takes the torque loads about the two narrow ways.  A flat way (or two opposed bearing surfaces, top and bottom) would suffice.  But that would ruin the whole narrow layout Pat is aiming for.


              Kevin


              P.S.  Sorry to have been away from the group for a few years.  I have had three new jobs in the last seven years, each of which was engineering related, but in one way or another was unlike anything I had ever done before.  For two of them, I was commuting weekly about 4 hours each way.  I have a very understanding wife, but am just now starting to get caught up on deferred maintenance issues around the house.  Hopefully, I can be a contributing member again, bit by bit.

            • David G. LeVine
              ... Yes, but a lathe puts loads on the carriage which are parallel and perpendicular to the ways, as well as torques. Narrow carriages tend to twist too much
              Message 7 of 7 , Feb 8, 2014
              • 0 Attachment
                On 02/07/2014 04:48 PM, kwayneolson@... wrote:

                All -

                Actually, if I'm looking at this correctly, it seems OK to me.

                Try searching the web for "narrow guide principle" - it's generally accepted that you want the longitudinal guide for a way to be "narrow" relative to its length, so that it can't cock and stick.

                Or, I could be looking at it cross-eyed!

                Kevin

                Yes, but a lathe puts loads on the carriage which are parallel and perpendicular to the ways, as well as torques.  Narrow carriages tend to twist too much and, hence, chatter.

                To reduce it to a minimum, imagine what happens when a zero width carriage has the forces going into it from the cutting tool.  Generally, both wide and long carriages are better.

                Dave  8{)

                --

                "A word to the wise ain't necessary - it's the stupid ones that need the advice."

                Bill Cosby
              Your message has been successfully submitted and would be delivered to recipients shortly.