Longitudinal cut in a grown mast

  • 20 Jan 2013 10:24
    Reply # 1184071 on 1183419
    Anonymous member (Administrator)

                                                                        Stavanger, Sunday

    Shear tension and shear load; just google Shear Load and you will find it explained. Anyway, don’t make a big issue of this; I may well be wrong here so you could fit the split where you like. My hollow masts have the join in the fore-aft direction

    You may well scarf join the battens to make use of its tensile strength. If you use epoxy glue, the scarves need not be perfect. The batten filling the gap should not be bigger than necessary so don’t open the gap too wide and deep with the router.

    The link to that scanned sample: If you go to my personal photo album, it is the last photo.

    Arne

    [Webmaster edit: To go to a member's personal photo album, click on his/her name (above left) then click on Photos (top right).]

    Last modified: 20 Jan 2013 17:23 | Anonymous member
  • 19 Jan 2013 22:45
    Reply # 1183816 on 1183589
    Deleted user
    Arne Kverneland wrote:

                                                                           Stavanger, Sat.

    ...the shear tension (as a result of the weaker side forces) will be working on the re-glued split.



    I don't understand that sentence.

    , he opened it to an even gap with a router, inserted a tube for electrical wiring and finally glued in battens to close the gap. .



    Butted or scarphed battens. Somehow you remove some of the integrity of the outer layer of the mast. It worries me. Shouldn't the battens be 20% of the mast diameter

    Now I just scanned an inch-thick sample of Malena’s first solid mast. It shows what happens if the mast dries too fast and without that tension-relieving split cut into it.



    The link doesn't work for me, did you really upload it?

    Cheers, Arne


  • 19 Jan 2013 14:51
    Reply # 1183589 on 1183419
    Anonymous member (Administrator)

                                                                           Stavanger, Sat.

    The position of the split is not that critical, but I guess I would put it in fore-aft direction as the shear tension (as a result of the weaker side forces) will be working on the re-glued split.

    I haven’t used the split method on my masts, but I closely observed the drying process of a friend’s 32cm mast with that split cut in it. The owner measured the width of the split on 3 positions every week, and noted the value. When the gap stopped opening any more, he opened it to an even gap with a router, inserted a tube for electrical wiring and finally glued in battens to close the gap. No splits more than nail-thick could be found on that mast (easily filled with preservative oil).

    Now I just scanned an inch-thick sample of Malena’s first solid mast. It shows what happens if the mast dries too fast and without that tension-relieving split cut into it.

    Cheers, Arne

    Last modified: 19 Jan 2013 20:13 | Anonymous member (Administrator)
  • 19 Jan 2013 12:01
    Reply # 1183545 on 1183419
    Deleted user
    Arne

    Would you put the cut fore and aft knowing that the righting moment is higher in the longitudinal axis? Have you done it yourself or have you always built hollow masts?
  • 19 Jan 2013 08:47
    Reply # 1183520 on 1183419
    Anonymous member (Administrator)

    Thierry

    This isn’t rocket science. Just measure the diameter of the mast on 4-8 places ("waypoints"). Then you start cutting in the thin end and adjust the dept of the cut at each waypoint. BTW I would shape the trunk into a mast first and make the cut afterwards. Thickness of the blade is not critical. The cut will open fairly unevenly as the mast dries. When the cut doesn’t open any more, after a few months, the mast is supposed to be dry enough.

    Good luck.

    Arne

    PS: As long as it is cold and the bark is still on the log, the wood will not split, so you are not in such a hurry. Just don’t debark the log before you are about to shape it into a mast. Then make the longitudinal cut right after that.

  • 19 Jan 2013 02:20
    Message # 1183419
    Deleted user
    I cut a spruce for my mast this afternoon and I am wondering if someone here has ever done the longitudinal cut. After Arne's instructions depth is a quarter of the diametre. What about the width of the kerf? I use thin kerf blades. How do you keep the depth reducing along the length of the mast? How important is the depth of cut? Does it matter if I step the depth, like changing the depth every foot or so?

    The tree is still in the forest in the snow. I need to cut it to length and debark it, then carry it out of the woods with a few strongmen.

    Thanks

    Thierry
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