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Carbon Fiber Speargun Build step by step

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Handle has been trimmed and glued on.
Everything is sanded down with 240 grit then 4 coats of epoxy is applied to everything.
The epoxy application is quite a tricky process and i have still not mastered it and would love any tips people may have.
My process is as follows
1. Sand it all down 240 grit
2. clear it all down with acetone
3. let it dry
4. mix up very small amount of epoxy (for this gun 20grams)
5. let it dry to a tack
6. another coat with even less epoxy repeat 3 times.
I think my coating process is quite good but my prep is not quite up to scratch as i get pinholes in my finish.

i also rigged up the gun to test rear roller height to see if the bands rub, unfortunately they do so i will make some slightly larger rollers for the rear. i have also redesigned the muzzle numerous times to place a bolt anchor for aligning the lines at the right height to stop band and pulleys rubbing on the body.
 
And here is the result.
I wanted a matte finish for this gun so i sanded down the epoxy coating with 400 grit and buffed it with automotive polish using a rotary tool makes it a lot easier than hand buffing.
Fitted with 7.5mm shaft 1 set of 18mm rubber for initial pull and 2 sets of 16mm rubber for 2nd and 3rd pull.
 
The squared off trigger finger guard looks very distinctive, but bear in mind sharp corners concentrate stresses and parts have been known to snap off in plastic and alloy items. I cannot say with carbon fibre as I haven't found guns with sharp corners. Something to think about anyway.

Overall it looks very good for a first gun, a real achievement.
 
Cheers pete will run the gun through its paces and find out what works and doesn't.
first gun for this mould hopefully more to come
 
GRAPHITE SPEARGUNS said:
Cheers pete will run the gun through its paces and find out what works and doesn't.
first gun for this mould hopefully more to come
Click to expand...
Popped another out of the mould. this one is slightly different as it is foam filled. tried a different finish using shiny gold foil pieces in the epoxy coating.
Also this one is a conventional setup another benefit of computer modelling shown where i anticipated multiple setups for the 1 mould

 
popgun pete said:
How is the dimensional stability of the stock over time?
Click to expand...
the stock will not compress, bend or elongate over time as long as the epoxy has been cured hard. this is best done through post curing which elevates the temperature in increments to a final desired temp specified by epoxy manufacturer.

bending of the stock from multiple bands for hours at a time does not effect the body as long as above conditions are meet. maybe if the gun is left in the blazing heat of the sun with all bands loaded there could be bending but after paying copious amount for carbon fiber i doubt they will be treated that rough.

dimensional stability out of mould is extremely accurate. the epoxy coat can add maybe 1 mm but that can also be calculated into the mould design.

Also in general carbon fiber products will either break / explode or go back to there original shape.
 
I only ask because a few carbon fibre guns have been found to have a bend in them, or even a twist. These defects seem to be rare and are not gross distortions, but have been reported on even here. The guns concerned are usually second-hand, so we don't know their history or even if they had been abused. Some evidence of cooking in the sun is shown by a bloom on the resin coat due to surface degradation.
 
i think if the gun had a defect it would have happened when manufacturing, either moulds are not dimensionally stable or parts pulled to early or put together in a distorted way?
maybe if it were an extreme unlucky case were uni directional carbon was used and most of the fibers aligned in one direction resulting in a weak shear or torsional output concluding in a twist?
 
From memory both were C4 spearguns, one had a long thin forward barrel which was a feature of that model and it had a bend in it. The other had a lateral twist on the top deck. The cases are both discussed here, but are buried under more recent posts. The owners were not that happy, especially the bent barrel as I think that gun was new. The problem was put down to the undesirable movement of material as the internal bladder squeezed the gun up into the mould. As for the gun with the twist, it might have been a Urukay, I can't remember the outcome. Resin is a thermoset substance, but its strength is given by the fibres in it, resins can develop cracks on their own.
 
That's an amazing built! I know fusion and you must have spent quite a bit of time working on this project
How does it shoot? Have you compared it to commercial spearguns?
 
Gjoss said:
That's an amazing built! I know fusion and you must have spent quite a bit of time working on this project
How does it shoot? Have you compared it to commercial spearguns?
Click to expand...
Hi Gjoss Thanks for the kind words. It sure is many hours of work in the computer before anything physical is actually made I think lots of people underestimate the time that needs to be taken to account for all the small intricacies that go into designing anything.

I could say it shoots like a laser 4m plus with mega power but I think listing pros is probably better.

list of pros of the custom carbon invert roller.

line of sight. Some conventional guns can have good line of sight when the band are inline with the shaft but you will never actually see the shaft from tip to tail like an invert with only a single line on top. A invert also has no bridge which can be ever so slightly in your way when aiming a roller.

Recoil. there is always some. And because this is a full carbon build it is very light which amplifies the recoil. But in saying that it is only a small push no sudden jerk to push the aim off like some conventional guns can do.

Carbon. Light out of water and the shapes that you achieve with carbon makes them feel light in the water, by a combination of ballast and shape. The stock is also extremely stiff almost no bending with 18,16,16 bands.

The gun is quite short for the in my opinion powerful shot it produces. I also made it for NZ so unless I'm hunting marlin I don't see the point in making it any longer.

If i was to compare it to a carbon tube invert.
The main advantage would be the bands being hidden within the body structure of the gun without rubbing on the body, better hydrodynamics when tracking, im going to guess less strumming of bands when tracking also.
There is also the possibility of intentionally making the gun heavier but still only slightly negatively buoyant something a fixed tube gun cannot achieve without being very negatively buoyant.
With a custom gun i can also position the carbon laminates in correct orientation to the forces a speargun produces, for example a invert has a bending force on the carbon stock that push the middle of the speargun up this means the tension forces are acting on the top skin of the speargun, so i can add more strength to parts of the stock that need it.

Visually looks bloody good!
 
That sounds amazing. I'm UK based so no real need for power over here as we're more fighting for viz than long shots, but I like the idea of something that has less recoil. Also I will assume that the flat front face will help with recoil, the physics of inverts are beyond my understanding, but for a simple gun I like to picture it as a "torseur" (I think you call it screw theory in english) where as the spear is released there is a screw effect twisting around where you hold the gun.

I can relate to that feeling, having done something yourself feels bloody good.
But doing something that works just puts the the best smile on your face for quite a long time.

I was thinking of the possibilities that carbon fiber brings but I have way to many ideas Vs time. Maybe one day I'll try
 
I think if your fighting for vis and want the line of sight as an invert you could do a rear roller standard roller. so the gun is a standard roller with no pulley under the gun so the pull would be 1 to 1 but the top deck will only have a dyneema line for better sight picture. I think a guy called @Black_Reef_Co is using the concept but he is also splitting the load at the muzzle for easier loading.

Building something from the ground up is always fascinating and i think the lessons learnt along the way is often more important than the final product.

share some ideas maybe I could make them become reality?
 
Reactions: Black_Reef_Co and Gjoss
Thanks, at the moment I'm trying to keep things simple... I'm not the deadliest hunter tbh. I tend to use a standard 75 single 16 band and a 90 double 14 band for the lucky days where I see further than a few meters. One of the reasons is that I really want to avoid the "fear of reloading" factor, where you're not sure about your shoot and you have this moment of hesitation because reloading your speargun is a pain.
Thanks for the offer, I need to do some research on the idea myself, but I'll reach out if I think it's worth investigating.
 
popgun pete said:
Rollerguns have been analysed here.
Click to expand...
Thanks, I've seen it its quite fascinating all the potential variations. I quite like this master thesis which highlights some of the maths behind it: https://www.researchgate.net/publication/349350884_Modelling_Speargun_Dynamics
Sadly its purpose was not to assess the recoil from the shooter point of view and it does not apply the screw theory to the various forces engaging in the speargun (which will make the model much more complex).
 
Correcto. Minus the easier to load part as my "black reef style" true fusion band design has excessive stretch profile to take full advantage of the smaller platform. I build stout guns not meant for most people. But there's a reason for it: Latex has a terminal velocity that is dictated by many factors but most importantly by acceleration which is confined by distance in our speargun application. And Latex has a parabolic curve in regards to stretch %. Pete is prob shaking his head to the band stretch I use but people love it and newer rubbers seem to last plenty long even with the aggressive stretch

All of my guns have interchangeable wheels to run a multi stage loading single roller, coined a "mono roller" by Alemanni. So anyone can load them if they're simply strung up differently. I recommend trying out this band design. Inverted is stupid to me because it runs a pulley system on the "hot side" instead of the loading side which is outright silly for the added complexity

My hot take: If you're able to load higher tensioned bands, then roller is the way to go. Rollers are superior in that they can run very high band tension for higher performance, combined with heavier shaft profile capabilities with minimal recoil in a smaller package. Whereas a traditional gun under equivalent band tension would encounter shaft whip and unmanageable recoil... So all comes down to: Can you load 350%+ tension? Go roller.

Hope this helps with something! -- Quade
 
Reactions: Gjoss
I think my next build will be a multi stage loaded roller.

I guess the only draw back that this design may potentially have is
1. a very short band unless rear rollers for top deck of the gun is used, because a roller is 1 to 1 pull on the top and bottom if the top deck is not used you would need a rather large butt for the rubber to anchor onto.
2. because of the 1 to 1 pull on top and bottom the starting point for the rubbers on the bottom deck of the gun has to be inline or less than the connection point of top line to shaft, guess you could call it the ready to shoot position.

I think the two reasons above is the biggest problem with these guns as if you wanted to use this system you need to place the rear roller ideally behind the notches on the shaft because if you don't the rubber will not be on the rear roller when the gun is not cocked making it a pain to load, but because you want lots of force transmitted into the shaft over a period of time you cant just just pull the cords onto the rest tab and shoot.

@Black_Reef_Co looks like your guns solve these problems with a larger butt and larger loading handles? also i can see you designed the guns specifically for this system especially the origami range where the bands are hidden and will not interfere with holding the gun and maybe potential rubbing of rubber on the hand when shot. potential ouchie if your not wearing gloves?
 
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