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New season, and the moment to start long-postponed projects arrive…
Design criteria
– Minimalist gun, without compromise.
– A tool not a sculpture.
– To be made in max 8 hours without fancy tools.Specs
– Demoltiplied 2+1 direct.
– Long as a standard 75 but with rubbers action of a 90
– Material: Paulownia wood core and carbon shell
– Release mechanism – Ermes Polynesia back type
– Sheaves and hardware from Contesub
– Spear from 6.25 to 7mm with variable ballastHour 0:00… START!
Rescue the last piece of paulownia from the garden hut, draw the gun outline and cut with a jigsaw.
Cut the spear groove with a router and 45 degree pointy tool (mounted on a small hobby table). The 6.5mm spear is only 2mm above the top and will became 3 after finish.
With a hand planer, orbital sander, and wood file, shape the handle till fitting a gloved hand, remove sharp corners from the wood etc.
Apply contact glue on strategic points (spray glue would have been MUCH better than brush) and slide on the carbon fiber sock being very careful to avoid premature sticking to the wood… i managed to make a few wrinkles of course….
Next message follow shortly
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Complete the carbon sock positioning, screw some hook to the ends and apply the lamination epoxy with a brush in 2-3 layers until the carbon is saturated and the wood has absorbed the excess resin: the fiber is totally wet but without excess of resin.
Time needed: 3 hours including dinner in between…
Tomorrow the next steps…
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Interesting project! Looking forward to part two. Not familiar with the wood though. I thought that you had to glue pieces of wood unto each other to make sure it will take the strain? From what I can see from the pictures it is just a single piece of wood…
Laminated wood is necessary if the essence used has the tendency to bend with humidity and you plan to treat it with oil.
With properly seasoned wood or stable essences it is a redundant operation.
In this case the wood is used only as structural core: the carbon skin is what will hold the stress.
The paulownia wood is extremely stable (that piece of wood has been outside in the rain for one year and in the garden hut for another year… slightly moldy but totally straight. It is extremely light (280 kg/m3 ) and with a compressive strength of 20.7 MPa (around 200 kg per cm2 ): perfect as structural core for composite structures, it’s adesion with skin layer is excellent.
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It’s gonna be pretty:-)
As for laminating the wood, it’s not only for strength but also to even out any tendency a piece of wood would have to bend. You would eg. cut one piece into two – turn one around – and glue them together. This will cancel any tendency one piece would have to bend as the other piece would exert an even force in the opposite direction.
Lamberto, did you use kitchen film wrap (Vita Wrap) on top of the CF sock after laying it up? Some people do that in marine and modelling applications. You can add a bit of pressure onto the cloth that way and if the film doesn’t wrinkle too much, you can even get close to a nice finish. Obviously, you would need to insert something in the track to push down on the CF there.
(Just thinking out loud for the sake of others, I know you have done these things before 😉 )Shooter & Shooter - Fotograf & Spearo
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It’s gonna be pretty:-)
Lamberto, did you use kitchen film wrap (Vita Wrap) on top of the CF sock after laying it up? Some people do that in marine and modelling applications. You can add a bit of pressure onto the cloth that way and if the film doesn’t wrinkle too much, you can even get close to a nice finish. Obviously, you would need to insert something in the track to push down on the CF there.
(Just thinking out loud for the sake of others, I know you have done these things before 😉 )No need for surface film in this case: the carbon fibers are braided as a tube (a “sock”) so it is enough to slide the core inside and pull the two ends to get perfect adhesion to the core surface.
The contact glue is used to force the fibers in place where the core has a negative curve (spear track and handle details). In theory i should have built a sock -dispenser that is a PVC tube slightly bigger than the core and where you push the sock in nice and ordered way before sliding it on the core and release the sock straight and nice on the sticky surface…. as i didn’t have the right PVC pipe (actually i may have some in the chaos of my cellar but only God knows where…. :blush: ), I proceeded slowly to the sock job (by turning it in-out and slide it on it’s self): the wrinkles are only relative to fibers alignment in some points where i pushed too much, that means that in some point they are not nice and straight as they can be… only aesthetic issue in this case.
If you use a film on a tubular and complex shape as this one you will end with much more trouble than advantages: the rule “Better is enemy of Good” apply also to spearguns construction… 😉
In composites structures the optimal percentage of reinforcement (carbon) and matrix (epoxy) is extremely important and the film techniques (vacuum or pressure) are used to get a laminate that respond to the design specification: with a kitchen film you can, at best, get a smooth surface of the laminate and often not even that… it is a home-made attempt to replicate at home the peel-ply/breather technique used in industry… and not really successful at that.Today the resin was over gel stage and start hardening (the cellar is quite cold luckily) so, being the resin still “open”, i have given a second layer of epoxy to build-up a thicker cover that then will be finished with sandpaper without damaging the fibers underneath and will protect it from scratches and impacts. One or two more layers of epoxy and then is ready for sanding, opening of the trigger housing and installation of hardware.
P.S. : 8 hours do not include epoxy curing-time… it would be necessary an oven and that goes into the “fancy tools” list 🙂
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I got you on the sock, makes sense that by just stretching it, you don’t need to apply external pressure to the layup.
You are of course also right in that the film trick is used by a lot of DIYers who don’t wanna go into vac-bagging but… it is also used when you roll CF tubes over a mandrel commercially. Actually, they use a heat shrinking material but the idea is the same. And it does indeed squeeze out some resin – though of course it is harder to control exactly how much as opposed to vac-bagging prepreg and/or using a breather layer.
Now, your PC tube sounds like a great idea. Maybe even wet the cloth on the tube, freeze it and then you’ll have your own pre-preg, haha;-). But that would be “better” and likely to mess up.
A slower harder would be better and prolly not mess up for people who are not too used to working within a 30 min or so gel time.It’s a cool project Lamberto – you should run a weekend workshop for people on the Island – you and a small group could build a gun each over a weekend!;-)
Shooter & Shooter - Fotograf & Spearo
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it is also used when you roll CF tubes over a mandrel commercially. Actually, they use a heat shrinking material but the idea is the same. And it does indeed squeeze out some resin – though of course it is harder to control exactly how much as opposed to vac-bagging prepreg and/or using a breather layer.
Commercial tubes need a smooth finish at low cost… but the shrink film has a price: the thickness of the laminate will be thinner at the center and thicker at the ends. Winding the wet roving is a more precise method but even if i’ve been in the composites industry for 20 years i don’t feel like going through that…. a cnc lathe may do but not me :S
A good method, if i ever decide to make them professionally without asking to your neighbors (which actually can be a good idea if you find the right molding company 😉 ), is to use an external mold with internal bladder…. that is what is done by C4 and others. I have also used sometime a funnier method with internal rigid model + bladder for very complex layups and that is really fast as you can layup the layers while waiting for the mold to be back in production… and the rigid model can then be removed quite easily… but how to do that is a little secret 😛
Prepreg is actually used to achieve a higher ratio reinforcement/matrix for particular needs but it is way too far for spearguns where the forces involved are relatively small and the weight is not an issue.
Anyway let’s wait to celebrate because there are still many things that can go wrong in this gun…. Murphy’s laws are always there!
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It’s a cool project Lamberto – you should run a weekend workshop for people on the Island – you and a small group could build a gun each over a weekend!;-)
To make an excellent gun take few hours…. to make it also pretty can take forever…
With a good piece of seasoned hardwood (teak) the gun would be finished almost at picture 7: just open the trigger hole, fit the hardware and go fishing… a layer of epoxy sealer or linseed oil would be enough then as finish if you can wait 24 hours before wetting it.
If the wood is a good cut and well seasoned it will not warp… problem is to find such piece of wood if you don’t have free access to a large timberyard and the forklift guy is not your best friend since childhood :S …. alternative is to take two pieces with the same ring pattern and glue them together with the concavity of the rings facing each other. Epoxy glue is great. Need 24 hours curing for commercial epoxy before it is ready to be handled.
Just in case someone want to try to make a traditional arbalete, there are very few points to remember:
1) rail should be straight.. if not familiar with a router, you can make a beautiful gun without any rail.
2) Extended rubbers should be as parallel as possible to the spear. If there is no rail to sustain the spear then invent a solution to keep the center of the rubbers totally parallel to the spear… a piece of 4-5mm stainless steel shaped as a Y may do the job decently if you have metal-working tools.
3) The handle should be comfortable for you… beautifully shaped or very simple is a matter of taste.
4) The barrel volume should be enough to hold the spear+hardware in the water so be careful if you use the hardwood for terraces… often it’s density is close to 0,9-1, is too heavy and will sink. Teak, lark, oak and ash is a good choice.Tools needed: Jigsaw, wood file, chisel, hammer, drill. A router with hobby-table, angle-grinder and orbital grinder make the job MUCH faster.
Cheers!
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It’s gonna be sexy! 😛
You are right about the female mould and internal bladder, I looked into that for a similar project. It’s the same tech that is used in manufacturing carbon fiber bikes. There are some cool vids on youtube of it. And actually most of the most expensive and advanced frames are made here in China. I suspect, like every high end international company, that Scott, Trek, etc, etc, has very strict quality control staff on the ground here…
But no doubt the technique makes beautiful parts and I had been wondering how C4 did their guns.
Problem is that the moulds are really, really expensive. The setup is rather large with pressurized air systems and the huge heated presses that keep the mould together when the bladder is inflated.
Some also use a silicone core instead of a bladder and of a type which expands when the mould is heated.But if C4 can make it viable, then maybe it is doable. Let me know;-)
Shooter & Shooter - Fotograf & Spearo
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It’s gonna be sexy! 😛
You are right about the female mould and internal bladder, I looked into that for a similar project. It’s the same tech that is used in manufacturing carbon fiber bikes. There are some cool vids on youtube of it. And actually most of the most expensive and advanced frames are made here in China. I suspect, like every high end international company, that Scott, Trek, etc, etc, has very strict quality control staff on the ground here…
But no doubt the technique makes beautiful parts and I had been wondering how C4 did their guns.
Problem is that the moulds are really, really expensive. The setup is rather large with pressurized air systems and the huge heated presses that keep the mould together when the bladder is inflated.
Some also use a silicone core instead of a bladder and of a type which expands when the mould is heated.But if C4 can make it viable, then maybe it is doable. Let me know;-)
An industrial mould for 1000+ pieces can be done for 300-400 EUR.
A heated mould is not necessary unless you need 2-3 pieces per shift with epoxy or 2 pieces per hour with vinilester resins.
Pressure is only 60psi so no press needed if you use a bladder: with expanding core the pressure is higher… but i have my little secret so no costly press needed.
For a heated mold add 500 USD for heating mat and controller.
Overall the cost of mold and consumables shoul not be more than 1.5-2 EUR per piece.
For small quantities (100-200) a much cheaper polyester mold can be done for less than 1000 kr.
Going fishing now so no pics this evening 😉
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[quote=”Diving Gecko” post=14459]It’s gonna be sexy! 😛
You are right about the female mould and internal bladder, I looked into that for a similar project. It’s the same tech that is used in manufacturing carbon fiber bikes. There are some cool vids on youtube of it. And actually most of the most expensive and advanced frames are made here in China. I suspect, like every high end international company, that Scott, Trek, etc, etc, has very strict quality control staff on the ground here…
But no doubt the technique makes beautiful parts and I had been wondering how C4 did their guns.
Problem is that the moulds are really, really expensive. The setup is rather large with pressurized air systems and the huge heated presses that keep the mould together when the bladder is inflated.
Some also use a silicone core instead of a bladder and of a type which expands when the mould is heated.But if C4 can make it viable, then maybe it is doable. Let me know;-)
An industrial mould for 1000+ pieces can be done for 300-400 EUR.
A heated mould is not necessary unless you need 2-3 pieces per shift with epoxy or 2 pieces per hour with vinilester resins.
Pressure is only 60psi so no press needed if you use a bladder: with expanding core the pressure is higher… but i have my little secret so no costly press needed.
For a heated mold add 500 USD for heating mat and controller.
Overall the cost of mold and consumables shoul not be more than 1.5-2 EUR per piece.
For small quantities (100-200) a much cheaper polyester mold can be done for less than 1000 kr.
Going fishing now so no pics this evening ;)[/quote]
That’s good news and I am not surprised you had ideas on a smaller scale, cheaper set up:-).
What I have struggled to figure out, is how to make the bladders custom shaped. Maybe it’s not needed in your idea? With the prepreg bike frames, the layup is done on the bladders and very precisely and then the bladder is placed in the mould.
Curious about your technology;-)I guess you are right about the bike industry. Not only is competition tough leading them to use prepreg and being able to say their frames are 30grams light than the other companies’ – they also need to produce more and faster batches.
Happy Hunting!
Shooter & Shooter - Fotograf & Spearo
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@Geko: The cost of a mold in composites industry is mostly given by the model and by the speed of production and the finish that you need to obtain. A production mold run with carousel skins in RTM with capacity of 4 pieces per hour then is quite costly… but a bike frame mold for 1 piece per day is really not a big deal.
If you refer tho some bike manufacturers that use rigid expanding cores to be able to apply layers of carbon prepreg on the joint area, then it is not cheap… on the other side, a mold for making spearguns (like C4 or others) is very simple and it is not even a vacuum mold.
To make a bladder: take a polyethylene plastic sheet, fold it in two, put it in between two baking paper sheets, put on it a carton pattern with the shape you want to make, run along the edges with a soldering iron ~40W and the game is done! Cut the excess PE and you will have your nice party balloon! The only trick is to learn the speed of the soldering iron and the pressure to apply to avoid melting too much or too few: a bit of practice is necessary.
The mold you need is a standard hand-lamination mold with the two sides matching and two or three half-cones for easy centering and alignment: you can keep it closed with metal clamps.
I would build it with epoxy gelcoat and body for large productions (+1000) and in polyester for small productions.
The beauty of a speargun is that you have many places where you can have a demolding port for compress air and so reduce the demolding damages: if then you use a good release agent it would last forever.
A model is actually a wood gun where the centerline is not glued but hold with removable screws instead: you can make it using two layers of thick popple plywood, shaped nicely (the ply lines will help a lot in getting it nicely faired and symmetric), finish it with car-body filler and epoxy sealer: your model is ready to build the master or the mold for your speargun factory! :cheer:
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Yesterday’s operations:
The hole for the release mechanism has been opened with a Dremel to cut the carbon skin and chisel/hammer. Holes for screws and stopper rods have been drilled.
With an orbital sander the fairing of the surface is fast… finish of the difficult corners by hand. Some ethanol (regular spirit) to get the transparency back and verify the smoothness.
The glue/putty for fixing the hardware and seal the wood core is made with epoxy, colloidal silica, black soot from the chimney.
The trigger hole is laminated from the inside with thin glass tape and epoxy. This is necessary because the paulownia wood is very soft.
All hardware is fixed using the putty. The surface of the gun is then re-wet with epoxy and medical gauze to get back the transparency on the surface and that nice carbon fiber look.
In a warmer room to harden and ready for fixing the accessories!
Total of this operations 2 hours
Overall, 6 hours from the beginning + resin curing time.The gun is going to be equipped with one couple of demultiplied rubbers Ø18mm (or 21mm maybe) and one couple of 14mm directly applied on the spear as a regular arbalete for the initial speed boost. If this setup is not satisfying or give too much recoil, then i will open a notch on the barrel just before the trigger box to hook a second set of demultiplied rubbers instead the direct one.
Ciao!
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Here it is.
16mm rubbers. Waiting for the Sigalsub I’ve been forced to use yakaya that are the worst I’ve seen after bike tubes or office-grade rubberbands (the black in the picture) but luckily they will be out of traction after 30-40 cm max: they are needed only at the start before the others get to speed.
One pair demultiplied and prestressed 150-350% and one pair direct at 350%.
The red ones are fixed with a loop around the rest: very easy to unload after fishing.
Line loop reviewed.
This time, to install hardware, build a few SS parts and set rubbers I’ve used 4 hours: total 10 hours… 2 more than estimated.
Soon test in the water and balancing.
Cheers!
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@Geko: The cost of a mold in composites industry is mostly given by the model and by the speed of production and the finish that you need to obtain. A production mold run with carousel skins in RTM with capacity of 4 pieces per hour then is quite costly… but a bike frame mold for 1 piece per day is really not a big deal.
If you refer tho some bike manufacturers that use rigid expanding cores to be able to apply layers of carbon prepreg on the joint area, then it is not cheap… on the other side, a mold for making spearguns (like C4 or others) is very simple and it is not even a vacuum mold.
To make a bladder: take a polyethylene plastic sheet, fold it in two, put it in between two baking paper sheets, put on it a carton pattern with the shape you want to make, run along the edges with a soldering iron ~40W and the game is done! Cut the excess PE and you will have your nice party balloon! The only trick is to learn the speed of the soldering iron and the pressure to apply to avoid melting too much or too few: a bit of practice is necessary.
The mold you need is a standard hand-lamination mold with the two sides matching and two or three half-cones for easy centering and alignment: you can keep it closed with metal clamps.
I would build it with epoxy gelcoat and body for large productions (+1000) and in polyester for small productions.
The beauty of a speargun is that you have many places where you can have a demolding port for compress air and so reduce the demolding damages: if then you use a good release agent it would last forever.
A model is actually a wood gun where the centerline is not glued but hold with removable screws instead: you can make it using two layers of thick popple plywood, shaped nicely (the ply lines will help a lot in getting it nicely faired and symmetric), finish it with car-body filler and epoxy sealer: your model is ready to build the master or the mold for your speargun factory! :cheer:
I got you 🙂
Thanks so much for elaborating on this.
I had fooled myself into believing that C4s were proabably made by the bike technique and thus, more advanced than they are or need to be.
I guess one good reason is that you don’t have to fight weight and bulk as much in a gun as in a bike. Bulk/mass is more of a friend for us as it counters recoil.Got you on the bag tech as well. It’s the same used by DYI builders of RC sailing planes (gliders). I have seen tutorials in the past on youtube. Again, I fooled myself into believing it was not good enough for us.
Earlier you said:
“Better is the enemy of good”
That’s exactly what I am guilty of. Over-complicating things, over-developing and then not getting my little pet projects finalized because they can always be just a little bit better 🙁
So, for me:
“Better is the enemy of getting it done”
It happened with my own laser sight project as well. And I have a semi-stranded dive torch on my shelve also. Latter is not dead though, just sleeping…For the mould, it all makes sense. Again, I have seen the technique in use a lot when making model RC yachts. You make a plug and then a split mould. And even better if the plug can be split down the middle as well, as you describe – makes it easier to mount on a flat board as a flange for the mould.
Yet another long post from me, but Lamberto the point is, I am so full of respect for you and your getting-it-done ethos.
And… your end product is still better than good:-)Shooter & Shooter - Fotograf & Spearo
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Test done yesterday evening.
Visibility between Hornbæk P. and Helsingør, from poor to bad with a max 5m in the deep waters in Kronborg and 2m in Hornbæk Plantage bath-tub.
The buoyancy is perfect even without any ballast. The gun will float handle-up but in the water it stay totally straight when aiming (means that the barrel is perfectly balanced to the spear) and even after 2 hours swimming my wrist was not tired at all. First goal achieved!
The shoot with 16mm rubbers was ok but nothing compared to the 18mmx2 demultiplied of it’s teak tween.
At 4m was still piercing through the Cocacola can (unfortunately there is a wide choice of soft-drinks and beers cans down there) but not with the burning shot i would expect. The recoil of the 16mm direct was also there and i didn’t like it.Now i have installed two coulples 18mm Sigalsub Brown and both pairs are on demultiplied (@380%). To do so a new notch under the spear, near the release mechanism needed to be opened and laminated with additional carbon fibers.
Here some pic of the operation.
And finally the gun ready for test 2
Cheers!
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Lamberto – det er en fantastisk tråd du har startet her!
…men hvad er det der sker for det der snore-elastikhejs du har bikset sammen?
Er det gearing med snor og talje, eller hvad er det der foregår?It is a demoltiplied gun (or compound or vela or any other name but still same concept): two cm of rubber pull = one cm of wishbone pull. Result is a much more progressive shot and no recoil: absolute precision of the shot. Longer shots also because there are much less losses due to spear spin (bending under compression as it happens in regular guns).
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Result of test #2
As two 16mm rubbers are not enough to reach the speed i have in mind, i now replaced them two 18mm rubbers at 380%.
The first thing i noticed is that i must train more: i can’t load the second pair at 380% :whistle: … the problem is that the rubber at this temperature became woody and rigid (is not a self-pity excuse…).
Reduced at the standard 350% and it is easy to load.
It shoot beautifully with the 6,5mm spear at 5m.
After 30′ loaded another shot has proved good but naturally slower (the rubbers suffer the cold more than i do).Next step is to shoot a 6mm spear with 19,5mm rubbers… when i receive them. My guess is that because the progressivity of the shot it will spin much less, achieving a higher speed both at start and at the 4m distance.
The objective of this gun is to have a ultra-fast and ultra-accurate shot at 3m distance as this is the average max range of local fish.
A fast spear allow to reach them before they sprint away (that happen often with a +7mm spear and fish smaller than tuna-size).Ciao
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