A 7 metre variant of SibLim

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  • 08 Aug 2018 10:19
    Reply # 6422222 on 6422039

    Yes, I think this would be worthwhile, consulting with your CNC man to see what his view is, and what kind of offset would produce an easy sliding fit, but with no appreciable amount of play. 

    with the topsides and middle panels, I'd put biaxial glass tape on the inside of the joints, as though they were a chine or a major bulkhead, and of course there will be glass on the outside as well. A bending test on a glued, glassed and cured sample, maybe 200mm wide, would be good.

    OK, I'll have a chat with the CNC folks and see what they say. 

    Presumably a test with 2 mm stock would be a waste of time ?

    Oh and while the folk I use can not mark a part with a pen they can put on a sub mm groove in the ply which should be OK

    And thanks for the B&B update. I did watch the video and it looked a bit like 3 guys juggling jelly, glad to hear it works in the real world, and yes it does produce very nice fair bows. 

    Cheers

       

    Last modified: 08 Aug 2018 10:21 | Anonymous member
  • 08 Aug 2018 08:07
    Reply # 6422039 on 6418868
    Gary wrote:

    I wonder David if some experimentation might be in order. I still have half a sheet of 2.2 (!) mm ply and could get a lump of 6 or 9 mm. 

    I think maybe a bit of trial and error of different offsets might shed some light.

    Could also try some stress testing of you think that might be necessary.

    What you think ? 

    Yes, I think this would be worthwhile, consulting with your CNC man to see what his view is, and what kind of offset would produce an easy sliding fit, but with no appreciable amount of play. With 6mm, we have some narrow joints in the bottom panels, where excessive free play would cause misalignment; but if there is a marked centreline, this may not be a problem. With 9mm we dont't have a problem with most of the joints, as they are wide, but some would benefit from a marked waterline or buttock line, to be able to sight along and check alignment.

    with the topsides and middle panels, I'd put biaxial glass tape on the inside of the joints, as though they were a chine or a major bulkhead, and of course there will be glass on the outside as well. A bending test on a glued, glassed and cured sample, maybe 200mm wide, would be good.

  • 07 Aug 2018 14:42
    Reply # 6420307 on 6418868
    Gary Pearce wrote:

    Always nice to hear from someone who has actually tried something.

    The CLC stuff looks rather nice, and the B&B stuff also looks nice, although I remain to be convinced about the B&B origami assembly method. Can't see it saving much and it is definitely not a one man operation.


    Not to get too off topic - but I can vouch for the B&B assembly method if you're talking about the butterfly technique for getting that great bow curve- it definitely was one man operation (just me) and only took a few hours.  


  • 07 Aug 2018 09:58
    Reply # 6418868 on 6414421
    Anonymous wrote:

    Thanks, Scott. I'm gaining confidence in the puzzle joint, so I've converted the drawings to all-puzzle joints (full size) and also made all puzzle joint drawings at 1/4.25 scale, so that a model can be made from 2mm plywood, and the tab and slot joints should fit exactly (I hope)

    yes thanks for the input Scott,

    Always nice to hear from someone who has actually tried something.

    The CLC stuff looks rather nice, and the B&B stuff also looks nice, although I remain to be convinced about the B&B origami assembly method. Can't see it saving much and it is definitely not a one man operation.

    I wonder David if some experimentation might be in order. I still have half a sheet of 2.2 (!) mm ply and could get a lump of 6 or 9 mm. 

    I think maybe a bit of trial and error of different offsets might shed some light.

    Could also try some stress testing of you think that might be necessary.

    What you think ? 

  • 05 Aug 2018 17:02
    Reply # 6414421 on 6010674

    Thanks, Scott. I'm gaining confidence in the puzzle joint, so I've converted the drawings to all-puzzle joints (full size) and also made all puzzle joint drawings at 1/4.25 scale, so that a model can be made from 2mm plywood, and the tab and slot joints should fit exactly (I hope)

  • 01 Aug 2018 19:32
    Reply # 6408762 on 6402438
    David Tyler wrote:

     ...pending further information and thoughts from anyone who has used puzzle joints. I've retained the all-scarphs drawing.

    I've built a few of the CLC craft, and we are building their Teardrop Camper right now, believe it or not - my first kit ever, and therefore my first puzzle joint panels.  The panels in place do have some good bends and twists.  Nothing like the bow of my Core Sound 17, which was designed by the Graham Byrnes that David cites below of B&B Yacht Designs, but a fair amount good 3D shape develops.  Incidentally, the CS17 didn't use scarfs:  the panels are carefully butt jointed with glass tape on both sides, all the panels in one shot in big stack screwed right through to keep them from moving during setup.  They've never had a failure if done by spec.  Concerns about the strength of the puzzle joints may be like worries about whether nuclear fusion or fission is a faster way to boil water for tea.

    I haven't done destructive testing, but boy the puzzle joint seems strong if glassed on both sides - even just one side is impressive. The fit is tremendously close, nearly idiot proof even.  It also forces any crack propagation along the join into a circuitous route that takes it across 90 degrees plus of turn, forcing its way through glass fibers sometimes running with the weave, others with the weft, and often 45 degrees to them both.  Not that we want any crack to start, of course, but propagation is quite frustrated.  

    Like I said, I haven't destroyed any of them, but I am pretty sure that when twisted or bent it would break outside the joint.  If I were planning on using them in a design of my own, I'd keep them in flatter runs just like any other joint in order to keep the changing properties of the wood from ruining a fair turn. 

    Visually... meh.  It looks a bit too mechanical for my tastes, but that's only an issue if finishing bright anyway.
    Last modified: 01 Aug 2018 19:41 | Anonymous member
  • 01 Aug 2018 07:24
    Reply # 6407852 on 6403350
    Anonymous wrote:
    Gary wrote: - unless you are the type who inserts their jigsaw puzzle pieces with a hammer. 
    The CNC company takes my dxf files of the profiles, and then sets a toolpath at a certain offset from those profiles, according to the radius of the cutter to be used. How would it be to specify that that offset is just a little less than the radius of the cutter, so as to avoid too tight a fit and consequent brutal hammering together? Say 0.1mm or 0.15mm?
    I think this might be a case for a  couple of small experiments. 

    Its just possible as well that the appropriate gap for 9 mm ply will differ from that for 5 mm. 

    I like the idea of cnc holes and pins for the scarfs - not certain how one could screw that up ...... maybe if you did not cut the angle quite right - but it has to be better than a guess.

  • 29 Jul 2018 15:25
    Reply # 6403350 on 6403148
    Gary wrote: - unless you are the type who inserts their jigsaw puzzle pieces with a hammer. 
    The CNC company takes my dxf files of the profiles, and then sets a toolpath at a certain offset from those profiles, according to the radius of the cutter to be used. How would it be to specify that that offset is just a little less than the radius of the cutter, so as to avoid too tight a fit and consequent brutal hammering together? Say 0.1mm or 0.15mm?
  • 29 Jul 2018 10:24
    Reply # 6403229 on 6010674

    Jordan Boats have a good trick for aligning scarphs. They make three holes across the scarph, into which pins can be inserted through both parts. It would be easy enough to CNC-cut 10mm holes for dowels, through scarphs in the hull panels.

    http://bandbyachtdesigns.com/ Has been suggested to me as users of a mix of both puzzle joints and scarphs

  • 29 Jul 2018 06:43
    Reply # 6403148 on 6402438
    Anonymous wrote:

    One school of thought says that puzzle joints are not as strong as scarphs, but are quite strong enough. Further, that they may not be the very best option when the panel is stressed in bending, as for a hull panel, but are fine on straight, unstressed panels such as the internal, longitudinal components.


    That sounds like a good compromise to me. 

    I think any type of join will create a hard point in a panel that will be bent, but the question is to what degree, and whether or not it is material. The answer to that will be determined on a case by case basis I think.

    The main point is that speed and accuracy will be hugely improved this way, and the opportunity for error will be greatly lower - unless you are the type who inserts their jigsaw puzzle pieces with a hammer. 

    Scarfs are not a huge deal if you set up a jig for your router. The large Makita is readily adapted using a couple of long rods and a frame. But I am of the school that says that machines should do everything they are capable of. I would rather be sailing than building.





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