A 7 metre variant of SibLim

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  • 11 Jun 2018 12:47
    Reply # 6303443 on 6302868
    David Tyler wrote:

    Interesting, and encouraging, Gary. I'm having difficulty spotting which errors are due to the plywood being thicker (the difference between 9mm and 12mm at full size), which due to the CNC cutter not using the latest drawing, and which due to you having to enlarge slots and ease the fit of the tabs by hand. 

    How should we proceed? Perhaps if you send me the dxf file back, with the points that you think need adjusting ringed or marked up in some way; and a sketch of the tab and slot arrangement that you think we should use, with sizes?

    Yes of course David,

    At this point I suspect the majority of the issues are down to the CNC folk, well except for the ply thickness of course. I think there are issues where they have just busked it. 

    They said something about trying to get the tabs to fit which makes me think they knew what was up.

    Clearly they did not just copy the stuff you sent or there would not have been 2 station 2s !! 

    Having said that the structure is around 90 % spot on so far. 

    SO I am quite pleased so far but there are a few points of issue. 

    But of course thats why we did this. 

    Will send you full details direct - BUT what we have now looks really good. 

    A very fine effort on your behalf.

    Hopefully we can tune this so it becomes idiot proof 

    (as a certified idiot I hope so :-) )



  • 11 Jun 2018 09:00
    Reply # 6302868 on 6010674

    Interesting, and encouraging, Gary. I'm having difficulty spotting which errors are due to the plywood being thicker (the difference between 9mm and 12mm at full size), which due to the CNC cutter not using the latest drawing, and which due to you having to enlarge slots and ease the fit of the tabs by hand. 

    How should we proceed? Perhaps if you send me the dxf file back, with the points that you think need adjusting ringed or marked up in some way; and a sketch of the tab and slot arrangement that you think we should use, with sizes?

  • 11 Jun 2018 07:49
    Reply # 6302855 on 6010674

    Well not everything went as smoothly as it might, for which I take full responsibility.

    Firstly I managed to get the cut plywood wet - this required trying to dry it without getting inordinately warped. It was still a bit wobbly but I decided it was time for a fitting exercise. This was short lived as I discovered that the 1.5 mm ply I bought sight unseen and had shipped direct to the CNC folk was in fact about 2.11 mm thick. So nothing would fit in the slots. Fortunately I had precisely the right dremmel bit to sort the slots - you can see a half cut slot in the middle.

    Of course the tabs were now too short with only a tiny amount of tab hole poking through which meant my wife got her cocktail sticks back ..... but lost some dressmaking pins :-(

    Assembly did allow us to spot a few errors such as station 4 which required its slot enlarged

    Also discovered that most of the interlocking tabs required trimming 

    There were also a few cuts missing such as this one for the cockpit seat Ooops. Easily fixed with the dremmel. 

    The astute boatbuilders here will note that at this stage the structure is not attached to its jig. I was really only checking fit for which the flexibility helped lot.

    What was interesting to feel was that the hull is almost self jigging. The strength that appeared once the bunk assembly was in place was quite striking. 

    The good news is that once we have ironed out all these little errors, those who follow should be able to progress much more quickly, and with more confidence. 

    So we are learning some lessons about CNC. One is that for sure the CNC folk have messed about with things. For instance I got two station 2s. And some issues which had been corrected early on became magically uncorrected. 

    I also feel we need a different type of tab - square section like the original mirror dinghy tabs with angled wedges that could be cut from the spaces between stations. Tabs through the bottoms and topsides will also prove extremely useful, especially if hull planking is to be a single person job. I think that tolerances for tabs could also be readily increased. 

    Thats what I think so far. I will let you know how things progress.


    Last modified: 11 Jun 2018 07:52 | Anonymous member
  • 18 May 2018 08:59
    Reply # 6241617 on 6240496
    Annie Hill wrote:

    Well now you know the set up for cutting things and that it's all feasible, why not just saw up the plywood for the model by hand? Treat yourself to a nice, 1/2mm wide blade Japanese hand saw and it won't take long.  They are a delight to use, anyway.  Then all you'll have is the cost of the plywood and the glue.  Also, sawing up the different components will give you a closer sense of the boat.

    But that would do very little to prove the accuracy of the CNC - there are also some very small bits involving the tabs and such. 

    If making the model works then not much can go wrong on the real size version and people with limited skills and infrastructure should be able to knock one up.

    Oh and right now I am rather busy building a house so anything that saves me some time is fine by me. 

    And I certainly don't plan to mess about carrying 30 sheets of ply up 100 steps from the road to my workshop so that I could carry the parts back down to the garage where assembly will take place. 


  • 18 May 2018 08:26
    Reply # 6241608 on 6010674

    In the UK, the leader in the field of production of plywood kit boats appears to be Jordan Boats, in Somerset. They will take any design, and produce a kit of the plywood parts. So, when we're a little bit further on in proving the design by CNC-cutting a model, this would probably be the place to go, for UK builders,  as they already have a lot of expertise.

  • 17 May 2018 21:56
    Reply # 6240496 on 6239049
    Gary Pearce wrote:
    Gary Pearce wrote:And the answer for the cutting is: AUD 387.50 PLUS the cost of the ply.

    The "sweet spot" for the ply looks like the Birch at $136 so thats $272 for the ply so thats AUD 659.50 total. 

    Which is a very large amount for a 1.2 (ish) metre model boat that will never get wet but one needs to consider this as a "design cost" from which others may hopefully benefit in future.

    We shall see.


    Well now you know the set up for cutting things and that it's all feasible, why not just saw up the plywood for the model by hand? Treat yourself to a nice, 1/2mm wide blade Japanese hand saw and it won't take long.  They are a delight to use, anyway.  Then all you'll have is the cost of the plywood and the glue.  Also, sawing up the different components will give you a closer sense of the boat.
  • 17 May 2018 11:34
    Reply # 6239049 on 6149723
    Gary Pearce wrote:

    Ironically the CNC for a model will be quite a lot higher pro rata as the cutter needs to be around 1mm or less, you have to move much more slowly or you snap the bit. 


    And the answer for the cutting is: AUD 387.50 PLUS the cost of the ply.

    The "sweet spot" for the ply looks like the Birch at $136 so thats $272 for the ply so thats AUD 659.50 total. 

    Which is a very large amount for a 1.2 (ish) metre model boat that will never get wet but one needs to consider this as a "design cost" from which others may hopefully benefit in future.

    We shall see.


  • 11 May 2018 23:28
    Reply # 6149723 on 6149707
    Annie Hill wrote:
    Gary Pearce wrote:

    Brunzeel (Brookvale) have 1220x2440x1.5 hoop pine for AUD 80

    Crumbs - I'm paying about that for 6mm okoume plywood I'm putting into my boat!
    Ironically as the ply gets thinner past a certain point the price increases rapidly. I was given some 0.6 mm 3-ply samples yesterday which cost a whole lot more again. 

    6mm "BS1088"Gaboon  (Okume) is AUD 110, 9mm is AUD 129 - regular 1088 is 72 and 95, but thats list price. 

    Oh and you are right about grooving the bulkheads,  one might get away with a shallow groove, or one just might not be bothered.Especially as when you pay for CNC you are effectively paying for the length of the path and the speed it takes to run that path. They run a simulation and it tells them how long the machine will take. Adding grooves could add a huge amount to the cutting cost. 

    The other CNC shop I have used did a flat AUD 75 per sheet last time, but that was for kitchen cabinets and doors. Those machines rip through 18mm HMR MDF

    Ironically the CNC for a model will be quite a lot higher pro rata as the cutter needs to be around 1mm or less, you have to move much more slowly or you snap the bit. 


  • 11 May 2018 22:57
    Reply # 6149707 on 6148739
    Gary Pearce wrote:

    Brunzeel (Brookvale) have 1220x2440x1.5 hoop pine for AUD 80

    Crumbs - I'm paying about that for 6mm okoume plywood I'm putting into my boat!

    BTW: your thought about routing grooves on the plywood: it looks effective, but you need to be using quite thick plywood if you do this, otherwise you will be substantially weakening it.  Especially if the grooves happen to match up on either side.


  • 11 May 2018 13:34
    Reply # 6148870 on 6148859
    Gary Pearce wrote:

    I wonder if tabs on the case ends (fore & aft)  into the bulkheads might make things more foolproof but need to think if thats possible for assembly. 


    Yes, I thought of that, but it doesn't look easy. Stn 3 and stn 4 need to be slotted into the berth sides first, and then stn 1 can be slotted onto the forward end and the berth sides can be sprung inwards enough to slot in stn 6. If, then, the berth flat is to be slotted in, there needs to be enough give in stn 4 to permit that. It may be that the board cases can be slotted into stn 3, which would get the angle and position right, but not stn 4. It may be that with only shallow tabs for positioning, not wedged tabs, stn 3 and stn 4 can be sprung apart far enough to get the board cases in.This is what the model is going to do - prove what can and cannot be reasonably easily done. On Annie's boat, we built the cases in situ, having glued the fore and aft ends onto the bulkheads at an early stage.
    Last modified: 11 May 2018 17:48 | Anonymous member
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