I’ve come up with some pretty inovative idea to join my two halves. spent almost a day researching methodes for joining at my university…talking to the guy teaching metall, to find something that looks cool and is fun to built…and maybe even works. First I wanted to use 2 snowboard ratchets(?) to hold the halves together… after some thinking we wanted something simpler…not so many moving parts, no plastic maybe… I then wanted to use 2 thick diameter aluminum screws…reaching through the deck of the first half at an angle into the other half…that would have worked and I am keeping that idea for when the other method doesn’t work out… the final idea is to put two tubes between the halves…when you want to join the board you slide a metall (AlMg3) part over both tubes, these have counter threads on both sides and a ring in the middle that has holes every 3cm…there is a slot in the deck…about 9mm wide and 4cm long that is used to reach for the part and screw it into both halves tightening them together… Maybe the picture shows it better… The Carbon/Kevlar tubes used to join the parts are not connected to the metall screw. The outer tube where the C/K tube fits in is glued between a 15mm? Balsa stringer that form an “U” and is connected to the bottom and the deck to pass some stress from the tubes to the shell. Maybe it is overkill and the whole thing gets too heavy…then I will resort to the aluminium screw method… I hope this cross-section explains a little. 
when morey came some years back… his connectors were light weight readily availiable …his bisect utilized toilet seat hardware made of nylonfrom the hardware store…ambrose…and they are white (weiss)
Marcus, keep it up. I’m looking forward to photos.
[smile])) Ambrose, mine is gonna be bullet proof and when you attache weels instead of fins you can ride it to the beach just like a skateboard…even if the next beach is ~700km away like in my case [wink]
Markus, Great hearing about your progress with this idea. Keep us up to date on your research.
Ahm… you might consider that the metal is going to be far, far stronger than it needs to be, so that if you use much smaller stainless steel threaded pieces ( aluminum in a marine environment ain’t so hot, y’know?) left and right threaded that go into stainless steel left and right threaded nuts set into the ends of your carbon tubes, that’d be more than strong enough. It’d also possible to do something with a fixed screw in stud like a hangar bolt with a hard item for it to work agains, much like the way it’s done with stair rails and suchlike. Angled screws, from one piece into the other, well, that’s right out. First wave will bust it, 'cos the hold is kinda tenuous. Now, the whole concept of shaping a board, glassing it and then cutting it in half and adding some hardware strikes me as a kinda questionable. You’re far too dependant on the hardware, which you have to invent. In the words of Monty Python, now for something completely different. But far stronger and easier to do. No hardware need be invented, pretty much plain glassing and standard surfboard skills. Take your shaped blank, ideally stringerless styrene foam, and get out the hot wire cutter. Cut down and forward a little, down and back, down and forward. Remove some material from the cut areas. Glass both pieces and reinforce the cut area heavily. Using plastic or stainless steel hardware ( kinda like the wide-headed threaded fasteners used for bodyboard leash attachments) and plenty of them, put it together. Voila, you wind up with something like that below, viewed from the side. If it’s done right, then you have what we in the large wooden boat trade call a locking scarph joint, where the stress is spread out over a lot of area, the strain on fasteners is minimised and very little specialty hardware has to be invented - I’d imagine the stainless or plastic fasteners are over the counter items. A variation on this with quick-release aircraft-type fasteners wouldn’t be that difficult an adaptation either. The long angled cut is key - your pieces gain a little length but the strength gain is tremendous. Angling the top and bottom cuts serves to take a lot of strain off the fasteners- they act more as locating/locking pins to keep the pieces from moving sideways with respect to one another than anything else. The thing has to be assembled by sliding the pieces together, like a dovetail joint, but that’s no penalty in terms of ease of operation. hope that’s of use doc… 
----------- Ahm… you might consider that the metal is going to be far, far stronger than it needs to be, so that if you use much smaller stainless steel threaded pieces ( aluminum in a marine environment ain’t so hot, y’know?) left and right threaded that go into stainless steel left and right threaded nuts set into the ends of your carbon tubes, that’d be more than strong enough. It’d also possible to do something with a fixed screw in stud like a hangar bolt with a hard item for it to work agains, much like the way it’s done with stair rails and suchlike. ------------ We would use AlMg3 which is ok with saltwater…but I see that it’s way out of proportion…I also thought about the possibility to use nuts at the end of the tubes…but thats way into the board if repair was needed + I don’t want to fix the tubes on the ends. I have also calculated aprox. weight by now…it’s like 300g made out of Aluminium…building it out of Polyamid would be 1/2 to 1/3 lighter. Maybe I will alter the system a little…the same but next to the tubes not over them…M8 threads and Polyamid screws and nuts…would be under 50g. I will also need only one of them in the middle…maybe 20mm Polyamid tube with threads… ----------- Angled screws, from one piece into the other, well, that’s right out. First wave will bust it, 'cos the hold is kinda tenuous. ----------- Don’t know…the angle would be under 15°, using M6-M8 Poly screws… I will do a force test on that…there isn’t much stress left since I have two tubes against torsion forces. ---------- Now, the whole concept of shaping a board, glassing it and then cutting it in half and adding some hardware strikes me as a kinda questionable. You’re far too dependant on the hardware, which you have to invent. ---------- Thats right…but thats what I want to do…invent something new that works well…the risk of failure is given at any time. A scarph joint would ad lenght…i need to avoid every cm. cheers Marcus
I am also thinking of a system that uses excentric(?) parts to thighten the parts together.
I’ve been thinking about bisects for a while (nothing built yet) and I first thougt about using two long aluminium tubes. The board would be a ribs&frame hollow board, 2 or 3 internal ribs would then hold each female tube. The faces where the halves join would be laminated, then covered by a layer of cork. Each face would have an inserted nut that serves both to lock the two halves and act as a vent (see picture below). 
Following the advice from “Surfer Pierre” (the other French Pierre who posts here as well)I went to check how aircraft wings are built and found out that the connecting spars are usually quite small. Most of the forces seem to be located onto the infacing surfaces. So I’m now rethinking the whole idea… I will post some drawings later on. Pierre 
Why don’t you guys borrow an idea developed for racing car connecting rods. You need to make a fracture split surface, probably from a split metal block of appropriate alloy. Join each half of the split block to each surfboard segment. Bolt together with one bolt.
I am at university now…i molded the tubes around the carbon/kevlar tube now and it came out very good, I’ll post pix later. for the screw I will go with one of the above described but a little smaller in diameter, between the two connection pipes and made out of Polyaramid. The tubes have a nice tight fit…they pass on stress perfectly… the screw doesn’t need to be so solid… pope is using two M2 or M3 parts to connect his longboards…I only need one screw cause I have two tubes to eliminate the tosion forces on the screw… i am quiet optimistic… pierre2: I thought about aluminium profiles that you could slide into each other and secure with a clamp only…but connecting the halves with tubes feels a little better…maybe somebody wants to try another method, there should be more people around who need splitboards… cheers Marcus
Ok- lets do a little design critique and consider the possible pluses and minuses of these. First off, Pierre has illustrated what I meant with the hangar bolts, a fixed, threaded arrangement in one half with a nut tightening in a recess in the other half. It’s a good, proven system. A variation on that system, using cammed/eccentric pieces ( think of a rifle bolt) would probably work quite well. There are also hook-on-bell-crank arrangements ( see a sliding glass door latch as an example) that can be used or adapted. If the pieces were large enough to keep the load per square inch ( or cm) down to appropriate levels, then something injection molded would work well. When I design things like this, I tend to think in terms of manufacturing processes in parallel with the design. One-of-a-kind, elaborately machined parts are all well and good, but the economics of mass production need consideration too if the design is successful. I should note that with aircraft wings the small surface of the joining pieces is kind of a function of the overall structure of the wing: it’s all connected framework elements with a skin, not foam with a skin. You could do something similar, yes, but you would need to tie the attaching structure into that skin, which complicates things considerably. If you take a look at how homebuilt aircraft are made, with foam/fiberglass wing structures, you’ll note that they include spars that are quite large relative to the wing itself- see http://cozybuilders.org/chapters/chap14.html and other pages on that site for illustrations. Which brings me to another question; how do you propose to secure the tubes? You’ll need to either tie them into the skin of the board somehow or make the size of them such that the foam will not be loaded beyond where it’ll permanently deform. A good analogy is snowshoes: by increasing the area that carries the weight ( decreasing the load per unit area) , snowshoes allow one to walk on top of snow rather than sinking in. Foam, like snow, will only tolerate a certain compression before whatever compresses it starts sinking in.If the load is enough to permanently compress the foam, then the ends of the tubes are effectively unsecured ( essentially, lever ends) and thus the two halves are free to move with respect to one another: under repeated stress they’ll form slots in the foam rather than cylinders. This, by the way, is one of the reasons incorporating dowels in repairing broken boards is ludicrous. One way around this is to incorporate higher density foam stringers around the tubes, which will tolerate a higher compressive load. Another is the ribs and frame structure Pierre correctly includes ( though I’d also want to clarify that internal framing would be necessary on both sides of the tubes, male and female. Also, both faces of the joint would not only need to be laminated but reinforced a good deal). Another is the four-piece system Pierre has come up with - it eliminates the tubes altogether and the increased size of the bearing surfaces is likely to be well within what relatively light glassing ( again, with considerable reinforcement in the joint area) and foam can tolerate without permanent deformation or failure. It’s also strictly tied into the skin of the board. This is also one of the things I like about the scarph joint - it uses the skin rather than the foam to secure things. A few other thoughts, tossed in. Angled screws are going to be a problem unless you have mating surfaces/stops that are at least nearly perpendicular to the screw or bolt. Vertical misalignment of the two halves becomes probable if you don’t. You’d have to place them beside the tubes or else incorporate some surfaces as described in the joint, lest you wind up with a step-deck board that really shouldn’t be . Also, the greater the angle from the horizontal, the less force is going to be holding the two halves together. At 15 degrees from the vertical, you’re down to around 0.25% ( sin 15 degrees) of the total force exerted by the screw that’s actually pulling the two halves together. Then there is the question of flexibility versus stiffness in the screws or the substructures they attach to - the screws, when under stress, are going to act as levers to break those points free. This would likely be cumulative rather than immediate. These tubes will have to be sealed watertight, though o-rings can probably solve that. Otherwise, you will have foam gettng filled with water, an undesirable situation, plus the weight of water-filled tubes of sufficient diameter will have some effects you don’t want. Another consideration - do you want to design a system that can be repaired and/or fine tuned in a low-tech environment? Say, on a surf trip to Central America or an isolated Pacific island with either easily available materials or a small, simple repair or parts kit? If the purpose of a two piece board is to make it more portable, then a very portable board is inherently going to go to some very out-of-the-mainstream places. Having been the repair guy at an isolated surf camp, I’ll point out that it’s something that needs to be included in your design goals. I have to admit, I miss doing engineering. Keep up the good work. doc…
The idea behind the 4 pieces solution is to have a very strong skin (again, I’m thinking wooden hollow board here). The board I’d like to use for this would be a classic 9’8" noserider (see below). For that reason, it doesn’t have to be ultralight. If the board has to break, then the two the small plates would be the ones breaking. The two halves then split but remainsintact and water tight. You’ll then only have to replace the small plates. Replacement plates wouldn’t take much space in the suitcase and could be easily cut from any piece of wood available. To make sure the plates do break properly and at the right load, they could feature a weak point (such as a small cut). Pierre 
Hi Pierre- I like how you’re thinking, and I’d think that the hourglass-shaped breakable/sacrificial sections you’re describing could work on a more conventional foam-fiberglass board as well, the board suitably modified. In fact, a router jig to carve out the recesses for the wooden pieces could be made and you could modify existing boards relatively easily. The steps I’d use for that would be to rout out the recesses ( oversized to allow for several layers of fiberglass laminate reinforcement), cut the board in half, glass it as needed, reassemble it and you’d be ready to go. This might also be a far cheaper and easier way to work out the necessary dimensions and strengths of the system, rather than building a complete board. While you might want to vary the breaking strength of the wooden pieces for different boards, that would be easy to do by changing the weak point cut somewhat. May I suggest ( if you haven’t already) that you design around plywood rather than plain timber? It’s readily available everywhere I’ve been and more uniform in strength, plus you don’t have any issues with the wood-grain splitting. May I also suggest that the recesses be slightly wider at the bottom than at the top. This would prevent the pieces from popping out under stress, when the board was, perhaps, bent a little. There are easily available router bits ( used for cutting dovetail joints in wood) that would work very well for this. Again, I’m impressed with how well you’ve thought this through. doc…
Hi all. Is your illustration made in Freehand Pierre? The last concept looks very good…try it! I would made the joining faces out of some harder surfaces…maybe 1.5mm plywood? When all the stuff is built in before glassing the surfaces should match good… ---------------------- Ok- lets do a little design critique and consider the possible pluses and minuses of these. When I design things like this, I tend to think in terms of manufacturing processes in parallel with the design. One-of-a-kind, elaborately machined parts are all well and good, but the economics of mass production need consideration too if the design is successful. -------- I try to keep it simple too…maybe I have though too much about it…thank you for all the fresh ideas. …mass production shouldn’t mean cheap… --------------- I should note that with aircraft wings the small surface of the joining pieces is kind of a function of the overall structure of the wing: it’s all connected framework elements with a skin, not foam with a skin. You could do something similar, yes, but you would need to tie the attaching structure into that skin, which complicates things considerably. If you take a look at how homebuilt aircraft are made, with foam/fiberglass wing structures, you’ll note that they include spars that are quite large relative to the wing itself- see http://cozybuilders.org/chapters/chap14.html and other pages on that site for illustrations. Which brings me to another question; how do you propose to secure the tubes? You’ll need to either tie them into the skin of the board somehow or make the size of them such that the foam will not be loaded beyond where it’ll permanently deform. A good analogy is snowshoes: by increasing the area that carries the weight ( decreasing the load per unit area) , snowshoes allow one to walk on top of snow rather than sinking in. Foam, like snow, will only tolerate a certain compression before whatever compresses it starts sinking in.If the load is enough to permanently compress the foam, then the ends of the tubes are effectively unsecured ( essentially, lever ends) and thus the two halves are free to move with respect to one another: under repeated stress they’ll form slots in the foam rather than cylinders. This, by the way, is one of the reasons incorporating dowels in repairing broken boards is ludicrous. One way around this is to incorporate higher density foam stringers around the tubes, which will tolerate a higher compressive load. Another is the ribs and frame structure Pierre correctly includes ( though I’d also want to clarify that internal framing would be necessary on both sides of the tubes, male and female. Also, both faces of the joint would not only need to be laminated but reinforced a good deal). ---------------- You can see the full idea on my drawing…the tubes are joined to the surfaces of the board…I don’t just glue them in the foam. I use 2cm wide Balsa stringers that are “U” shaped and also transfer some stress 45cm-50cm back into each half bottom and top epoxy shell. ------------------- Another is the four-piece system Pierre has come up with - it eliminates the tubes altogether and the increased size of the bearing surfaces is likely to be well within what relatively light glassing ( again, with considerable reinforcement in the joint area) and foam can tolerate without permanent deformation or failure. It’s also strictly tied into the skin of the board. This is also one of the things I like about the scarph joint - it uses the skin rather than the foam to secure things. ----------------- I like that 4 piece system also very much… one of you should built one of these!!! ------------------------ A few other thoughts, tossed in. Angled screws are going to be a problem unless you have mating surfaces/stops that are at least nearly perpendicular to the screw or bolt. Vertical misalignment of the two halves becomes probable if you don’t. You’d have to place them beside the tubes or else incorporate some surfaces as described in the joint, lest you wind up with a step-deck board that really shouldn’t be . Also, the greater the angle from the horizontal, the less force is going to be holding the two halves together. At 15 degrees from the vertical, you’re down to around 0.25% ( sin 15 degrees) of the total force exerted by the screw that’s actually pulling the two halves together. Then there is the question of flexibility versus stiffness in the screws or the substructures they attach to - the screws, when under stress, are going to act as levers to break those points free. This would likely be cumulative rather than immediate. --------------- I havent pictured the screw part now…it is going to be one Polyamid6.6(Nylon) screw (the two counter threads thing) which can be reached by a small slot on the deck between the parts. back in the halfes the female parts will be secured in a wood block behind the front cover. Nothing angeled…you are right that it would make troubles only. -------------- These tubes will have to be sealed watertight, though o-rings can probably solve that. Otherwise, you will have foam gettng filled with water, an undesirable situation, plus the weight of water-filled tubes of sufficient diameter will have some effects you don’t want. --------------- the tubes are going to be sealed…the female tubes are also closed on the back. there is not much space for water left. All the foam is sealed from the water. ------------------ Another consideration - do you want to design a system that can be repaired and/or fine tuned in a low-tech environment? Say, on a surf trip to Central America or an isolated Pacific island with either easily available materials or a small, simple repair or parts kit? If the purpose of a two piece board is to make it more portable, then a very portable board is inherently going to go to some very out-of-the-mainstream places. Having been the repair guy at an isolated surf camp, I’ll point out that it’s something that needs to be included in your design goals. ----------------- That is the hardest one [smile]) I will test the system and we’ll see if it proves to be hassle-free. I hope the board breacks before the system itself. Getting the frontplate, female tubes, nut connection done in one solid befor installing in the board should ensure that everything is watertight…then I only have to glue everything into the foam and glass it as it is (probably one part after the other…the tubeconnections are very, very sturdy…I have built the glass tube yesterday and cut it into pieces already. ---------------- I have to admit, I miss doing engineering. Keep up the good work. doc… ---------------- thx… this discussion is quite interessting. cheers Marcus 
I will certainly build the board, and yes I will use plywood rather than timber. I just don’t have the money for it right now. The good part of it is that it forces me not to rush things and take time to do some thinking… Pierre PS : I use Adobe Illustrator to to my drawings.
Very interesting indeed, Marcus. The illustration clears up a lot in the mental picture I had. The transverse sub-frames ( like formers in an aircraft wing) are the way to go, I think, though you might want to use something a bit harder and less compressible than balsa, perhaps the 1.5mm plywood you mentioned. It occurred to me that an easy way to go with that would be to hot-glue or otherwise stick a piece of the ply to the flat, cut foam surfaceand then run a bottom-piloted cutter along the surface of the foam, using that to cut the thing to the same shape. There are cutters available that are commonly used for Formica and other pressure laminate surfacing materials that’d be ideal for that job. Also, I suspect you might have an easier time of it on the longitudinals with a stiffer, denser foam than with balsa. You could simply glue them in and it’d be fairly straightforward. If you go with a left-right threaded screw setup, and if ( he wrote, enviously seeing the lathe and mill in the picture) you’re going to be making them from bar or rod stock, then a slightly larger diameter toothed wheel ( like a plain gear ) will make a nice, easy way to tighten it up. Are you thinking of using something like an Acme or buttress thread? I think o-rings around the tubes, between the board halves, those might be worth trying. I also like Pierre’s idea of using a thin sheet of cork or possibly a neoprene between the halves, would be a good idea, to keep some tension on the threads, like a lock washer. Otherwise, you might have some problems with things vibrating loose, say on a choppy day. Though the nylon screws would deal with some of that themselves. Aligning the tubes properly and all- a similar problem has been the downfall of many who have tried to reinforce broken board repairs. But, I see you have the answer right there. Attaching the halves to the carriage of that lathe ( you may have to remove the tailstock temporarily) using a simple jig ( and using the centerline and bottom of the board for reference points in attaching the jig to the plywood end-pieces) will not only give you perfect alignment, you can even have power feed. A boring bar chucked into the headstock and there you go. Thius might also be a good way to machine the cavities for the attachment screws, using the carriage cross-feed and milling cutters. heee…this is fun. Cross-pollination, if you will. best doc…
Hey Marcus, Looks good, and as you said…keep it simple. Do you plan on taping up the joint before surfing? If it was me a few years ago, I’d tape the two halves together and hit the first waves I could find. Sort out the fine details later. But you are in a completely different situation. Stay stoked forever. Greg.