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Thread pitch for segmented boxes

Discussion in 'Woodturning Discussion Forum' started by Larry Copas, Aug 7, 2020.

  1. Larry Copas

    Larry Copas

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    It seems most threaded boxes are chased at 16 to 20 threads per inch. I was thinking with a segmented box its all long grain chasing. It would be easy to thread at somewhere between 8 to 12 threads per inch. In my mind the coarser thread would decrease the chances of cross threading. I could also make it a loose fit (think sloppy) and that would insure the fit doesn't get to tight from seasonal wood movement.

    Thoughts?

    I didn't want to make a coarse chasing tool just to find out it doesn't work.
     
  2. Glenn Lefley

    Glenn Lefley

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    I think a coarser thread might be harder to cut. You would have to move twice as fast if turning at same speed. But I’ve never turned threads before.
     
  3. GRJensen

    GRJensen

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    I don't see any reason why it wouldn't work ... some chase 10tpi threads. For the most part, I chase my threads (I stick with 16tpi) into solid blanks that have been stabilized in Cactus Juice. I haven't tried chasing threads into a segmented ring.
     
  4. Mike Johnson

    Mike Johnson

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    If you are using a powered cutter to machine the threads into the box and lid you can use just about any thread pitch desired. Most of the threading jigs usually offer at least (3) thread pitch spindles and bushings in their thread turning system. I have machined additional bushings for several of the threading systems I have used over the years and purchased short pieces of matched threaded rod to make the matching spindles to hold the face plate or chuck on one end and hand wheel on the other end. I turned several of these bushings out of Delrin material which is easily machined on a wood lathe, a regular machinist tap will cut good clean threads on this material.
     
  5. Don Wattenhofer

    Don Wattenhofer

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    Well I don't chase threads, however for more then 25 years I have been machine cutting threads directly into the base wood of the piece and that includes stacked segment rings. You are correct the courser the thread the better the reason being wood is never completely stable such that the sloppier fit will prevent shrinkage from jamming the thread. The urn pictured is segmented cherry in both the main body and the lid at 11 pitch and I have also made urns like this with a solid body and a segmented lid, which is more apt to jam up due to seasonal movement. The stave segmented piece in my avatar is also threaded at 11 pitch and has seasonal movement similar to solid wood.
    DSC00028 (2).JPG
     
  6. Larry Copas

    Larry Copas

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    Don, what kind of cutter are you using for your machine cut threads? I cobbled up a die grinder mount for my Southbend metal lathe and used a router bit I re-ground for the cutter. Threads were absolutely gorgeous in delrin but had far too much tear out in maple spindle blanks. I tried a segmented ring and it looked better but still not acceptable.

    IMG_2917.JPG

    After getting frustrated, I chased these 18 tpi threads in segmented cherry for the turning I'm presently working on. Your 11 tpi threads look nice. I may make a chasing tool in that pitch to see what I can do.....or fix my machine cutting threader.

    IMG_2939.JPG
     
  7. john lucas

    john lucas AAW Forum Expert

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    Larry you can buy 60 degree for milling but they have a 3/8" shank so usually have to be adapted to fit other tooling. I made an adaptor to fit my 1/2" router but unfortunately they won't fit my smaller 1/4".
     
  8. Don Wattenhofer

    Don Wattenhofer

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    101_1340.JPG The photo shows threading on my vintage LaBlond lathe. The metal lathe has 4C collets that I adapted to hold a 1 1/4"-8 spindle and on the cross slide I mounted a Porter Cable trim router using an angle plate. The cutter is a double angle mill as shown, which is the same one that Bonnie Klein first used and is being used by all of the copy cats since. The shank on the mill is 3/8" so it had to be turned down to 1/4" but you can't see that because it is in the collet chuck. I also have hand ground a two flute HS dovetail bit and a one flute carbide key hole router bit. The work piece and the router must be rigidly mounted. The top slide is set to 30 degrees and the router is then set parallel to the X axis. The top slide is then set to 0 on it's dial, and using the Y axis bring ithe cutter up to just touching the work piece, then advance the top slide for a partial cut. Make sure that the chasing dial is engaged, start the lathe at it's slowest speed, start the router, then when the appropriate line is met on the chasing dial engage the threading lead and be ready to disengage when necessary. When the cut is complete stop the lathe and router, the back the top slide a little past zero and move the cross slide away from the work piece. The partial thread can be inspected and if it is crumbling on the point of the V and or it isn't deep enough soak it with thin CA, then add another 5 - 10 thousands and make another cut. When cutting a mating thread you will need to use steps to ease into the desired fit, which should be fairly loose, thus the need of a coarse thread.
     
  9. Don Wattenhofer

    Don Wattenhofer

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    Obviously I was writing my long winded post as John did his.
    The 60 degree double angle mill does come with a 3/8" shank but if you have a metal lathe with collets such as 4C or 5C the cutter can be dropped into the 3/8 collet from the back end such that the end of the shank can be turned down to 1/4" and that is exactly what I did as you can see in the picture in my previous post where it is shown in a trim router with a 1/4" collet. Also my original PC router purchased when it had the Rockwell name came with 1/4, 3/8 and 1/2" collets and that is what I used before I had an engine lathe to turn down the 3/8" shank.
     
  10. robo hippy

    robo hippy

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    Larry, that cutter looks pretty coarse as in too blunt of an angle, at least to me. I would guess that you already know that you cut the threads down in 3 or 4 passes, rather than just one. I also will lube the threads with walnut oil, letting it soak in for a bit, before taking the final pass. I like that better than the CA glue. Softer woods are always more difficult to chase threads in than harder woods...

    robo hippy
     
  11. Doug Rasmussen

    Doug Rasmussen

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    I've posted this before...to me it's the best type wood thread. It can be cut with a coarse pitch threading jig using a edge rounding router bit as opposed to the 60 degree type. It needs a little hand clean up since all the material that needs to be removed can't be done with the same bit.

    It tolerates a great deal of looseness. And I make mine so they tighten in one turn, 4 threads per inch..

    bottle thread.JPG
     

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