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Flexure Cut Off Blade Holder

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  • #31
    Primo work on both the slick little custom cutter as well as the holder so far.

    Like you I've thought a few times of doing something to permit a rear mounted tool post for some secondary operations. Using the new AXA tool post has taken away some of the urge but I still think it could be a handy feature at times. The top of my cross slide is flat so it's an option. But it's not all that thick so T slots are out of the question. Instead I've considered the option of a few threaded holes probably 3/8-16 to permit mounting a rear tool post in a couple of placement options. But I've never hit a wall where I couldn't do something or where it would save the sort of time that would be needed to justify the operation. On the ToDo List though is removing the cross slide to add ball oilers so I don't have to finger smear the oil on the dovetails. Perhaps while the slide is off I might just drill those holes. They'd be capped off to keep the swarf out with some flat head screws that would be milled off flush with the surface so they don't collect any junk.

    Jackary, nice job of that rear post! It's also pictures like yours that make me think a rear post might be a good idea.
    Chilliwack BC, Canada


    • #32
      Due to an almost comedic series of errors that long bar that was supposed to make 3 blade holders wound up being just one... and a little shorter than target length. Jack screws turned out to be completely unnecessary, and the blade was locked very solidly with just one clamping screw, although the length remaining still held three. I think if I make another (I probably will) I will leave jack screws out. If a blade binds I can always use a wedge.

      I think it was Steffan Gottswinter whose video I was inspired by to make this. I've not gone back through his channel to double check, but that rings true in my mind. I seem to recall him making a flexure holder for an import parting blade insert holder.

      I made test cuts from 1-7/16 to zero in 304 stainless. umahunter had given me two inserts to try with the blade. One was coated with what looked like TiN and one was uncoated. Both appears to be mediocre sintered carbide. The first cut with the coated insert was ok, but as I pushed the insert harder and harder it chipped welded the stainless and chowdered. The uncoated insert was used at modestly low RPM and feed per rev, and it cut from full diameter to zero very well. This is a very rigid blade holder setup inspite of being help in a toolholder. All the flex is in the lathe itself. The blade has more than 3/4 inch of stick out and I was very happy with its rigidity.

      The cut is amazingly good. At first I thought it finished with zero nub, but I can feel a tiny bit of nub with my finger tip. That's really just about center height. I just did the metal scale trick to set height, so its closer to center than I expected. It may even be on center with the tiny invisble nub just being with from me pulling off the part to quickly, or a tiny amount of flex in the machine overall. I would really like to try it with a very sharp polished insert, but I have not been able to find one for this type of turning blade. Of course I can sharpen an insert if I really want to try it.

      I had some issue seating the insert to my satisfaction. Finally I laid a lead bar across it and tapped the lead bar with a mallet.
      *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.


      • #33
        Nothing is super critical if used in a tool holder. Get the insert edge close to the top of the nominal optimum tool size portion. Creep up on the blade fit with the dovetail cutter. Getting the face inside the blade slot parallel with opposing surfaces is nice, but not critical. You can always adjust a few thousands when clamping in tool holder by holding it against a parallel against the chuck face.

        Nothing is super critical except probably the blade fit. A sliding fit when cleaned with light resistance is probably perfect. When you get close take spring passes.

        I considerably simplified the design. I'm not concerned about the "strength" of the flexure. The clamping screws are more than adequate to provide strength. The graph size is not relevant. Its was just the handiest piece of paper. I did work from a print, but I see no reason to publish the print. Everybody's application could be a little different.

        If you wanted to make something like this to use in a 4 way tool post you could leave the nominal tool size clamping bar over size, take test cuts, and then mill a little at a time until you get an acceptable level of near zero nub.

        Click image for larger version

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        Click image for larger version

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        *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.