aluminium extrusion spear gun

[davidmoodie]

Hello all

I have been trawling this forum trying to glean info on diy spearguns. Seems like not many people attempt Aluminium extrusion guns? I am looking at making a small gun myself and have got some basic drawings. As I have discovered, the trigger mechanism is a touchy issue. Please feel free to comment on what I have so far - Constructive please!!

Cheers
David

 

[foxfish]

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Hi David, welcome to db.
Your are right that not many folk build guns that are so readily available in the shops.
I apologise for not studying your drawings but short rubber powered guns say under 750mm are only really suitable for extremely close range fishing or hunting inside holes.
Guns in the 750 - 1000mm are very popular worldwide & therefore very reasonably priced.
However you can buy all the components separately & put one together yourself.
Home made trigger units & spears are best left to the main manufacturers because of the specialist materials required, there are some members who have made trigger but they usually have access to a fully equipped machine shop & facilities to heat treat the components.
Maybe not the constructive answer you wanted but you can still build a fantastic gun using a commercial trigger & spear.
We have some of the words best known gun builders on this site many who will be willing to help you put together your gun but very few of us build the type of gun you have drawn preferring to use either wooden barrels or shop bought components.

 

[DivingDane]

you will find that most main stream manufacturers use aluminium pipe for there middle of the range and guns can be had in almost any size and setup.

if you are after a small gun with rail and a nice handle trigger mechansim then the Omer Cayman Cave is an excellent example and very well priced.

the reason that most people do not use this way of manufacture for their own projects is that this style of materil really limits the amount of custimisation a builder can make the the strength or hydrodynamic of the gun barrel. where as with would or carbon fibre more advanced shapes such as cuddle bone, tear drop etc can be used.

looking at your pictue there are obviously no issues with the barrel or muzzle really they are factory available parts so thats easy. the trigger mechanicm will wprk in prinscilpe but i think that you will have issue with the shaft not being released when the shaft is loaded up with power bands, this will put ALOT of pressure on the "scear' system you have and even after pulling the trigger the spear notch putting so much pressure on the square pin will not allow it to reliably release. in either way the addition of the spring and the tension from the bands will make the trigger pull very stiff, which makes smooth pulling fo the trigger and therefore accuracy more difficult.

as mentioned above small guns of 40cm in rubber have very little range and are only really suitable as a cave gun for shots of less than 1m distance.

on a gun this short a track/ or rail is not necessary as the spear is short and ridgid an does not need support over such a small distance, in reality a rail doesnt really effect accuracy noticably until barrel length exceeds about 90cm or so in my opinion.

DD

 

[davidmoodie]

Hi thanks guys.

DivingDane that was really helpful - I couldn't see why everyone makes these complicated trigger mechanisms when a 'pin in a track' is so simple and will not let go no matter how much force is applied horizontally. I see now that the trigger will be really stiff. Ok, more to think about!!
Im an industrial designer so I love the challenge of designing the gun and mechanism. I didn't want to reinvent the wheel - just thought I could simplify it a little!

Do you think trigger stiffness would be an issue for a smaller gun? There are not going to be multiple large rubbers on this? I am looking at overall length of about 800mm.

I have been using a hawaiian sling and see this as a next step into the spearo sport. The sling is a challange to aim and also has minimal range - so this couldn't be too much worse!

Anyway - half the fun is the designing/building.

Thanks for your answers

David

 

[Old Man Dave]

It's always fun to design things. It's not often however that anyone comes up with a totally new idea. I am afraid your trigger design has more than a few flaws and could be dangerous (IMHO).

The problem with your trigger mechanism is that the slot in the spear needs to be a very accurate rectangular slot as any angle on the sides of this slot will cause a lateral (downward) force. Wear on the slot with use will quickly worsten the problem. This force will need to be resisted by the spring which will need to be very strong. This will make the trigger release too heavy as it has to overcome the spring pressure.

My other main concern is the trigger does not positively lock as it is the spring pressure that is the key locking mechanism. If the spring weakens or even breaks then the gun fires. More worryingly what about if you drop the gun? Any shock load could cause the gun to fire.

Keep up the good work but keep safe .

Dave.