Those curved swords again

I had another thought on cores for curved swords.

9.5mm diameter 6061 T6 (tempered) aluminium alloy rod.

I’ve seen crossbow prods (bows) made from this stuff and it’s very very strong.They also build airplanes from it, because it is strong, light and has excellent resistance to metal fatigue.

This aluminium alloy weighs 2.7g/cm3, so a 9.5mm diameter rod 1m long would weigh around 190g

Fiberglass varies in density depending on the glass/resin ratio.
Glass has a density of 2.6g/cm3
Resin 1.1-1.2g/cm3.
Rods, would probably be around 2g/cm3

So aluminium rod is maybe 50% heavier than fiberglass, but it can be curved and then tempered to remain in that shape.

Just a thought…

I’d be surprised if the yanks aren’t doing it. I know there are a ton of SCA fighters who make armour from it because it’s light and almost indestructible.

Do not make a weapon with an aluminium core - alloy or otherwise.

Too heavy too hard and it does not flex which means there is a far greater chance of injury. Carbonfibre and fibreglass cores will at least give a little bit of flex.

Metal cores will just punch though the foam and impail somone.

Actualy I wouldn’t rule it out straight away. Looking at some of the supposed specs (ah Boundy how we love you and your database)… Its a relitivly good material.

The problem I can see is the tempering process.

WARNING SCIENCE CONTENT FOLLOWS!!!
If home done you can get localised precipitation hardening leading to enbrittlement of the material and increasing its suseptability to brittle fracture during the cores flexture during a strike. Brittle fractures leave sharp edges.

Also over time the metal will age, once again leading to the precipitation of the aging elements.

On the other hand the factor that this will effect the over all strength…unknown.

I’m not convinced either way.

This is my fencepost and I’m staying here till I see some reliable tests.

The mass of aluminium is higher than fiberglass / carbon fiber, but if you reduce the diameter to slightly less than the fiberglass rods in use, the weight will be the same or less than as fiberglass.

Likewise, the flex will be determined by the diameter.

Fiberglass, carbon fiber and aluminium are all vastly harder than foam. There is no reason why one should be more likely to punch through foam than another.

Except possibly that fiberglass has glass in it and glass is sharp, to it’ll likely go through foam quicker than aluminium. Aluminium can easily have the tip polished so there are no sharp bits.

I personally would rather be impaled with aluminium than fiberglass, because of how fiberglass splinters don’t show up on x-rays…

What is the standard diameter fiberglass rod in a weapon these days anyway?

the difference is that carbon fibre flexes alot when put under pressure thus reducing the risk that it will come through the foam and also the risk of injury if somone were to fall on it.

You totaly have flex in aluminium…depending on the amount of heat treating.

All points made by derek are valid.

Remember your talking about an alloy of aluminium not nessaceraly the stuff your used to in gazebo frames, so your perception of its characteristics may not be clear. I mean Copper is soft and maluble but alot of copper alloys are tough as hell…look at brass and bronze for instance.

Still not budging from my spot in the fence post though. I’d have to see test results and be assured the heat treatment is done right.

Exactly, kind of how fiberglass and glass have very different characteristics :smiley:

Or Cross Bonded PVC (the pipe) and Non Cross Bonded PVC (those tight snake skin pants you own)

:stuck_out_tongue:

Can you point me at this “Boundy”? My only experiance of 6061 aluminium is from actually using it to make stuff, so having some numbers would be good.

I’m highly dubious about this. The arguments for it are certainly logical, but the usual characteristics of aluminium would surely stack against it? What I’m thinking here is that yes it’s very strong, but if it’s tempered that way as a weapon core then as Adam says there will be no flex. That or it’s weight will betray you. If it’s tempered so there is a bit of flex, it won’t be strong enough and will bend, ruining the weapon.

Convince me why this wouldn’t be the case, and I might budge to the fence.

Also, what about cost? Even if there is a specific way the metal can be made to tick all the boxes, won’t getting purpose made metal extrusions cost a packet if not done in insanely bulk numbers? If they’re going to cost a significant amount, I would suggest looking at primalforge.co.uk and emailing them about special shipping rates to NZ for a number of units. Which they will be happy to sort - I know, because I’ve asked them in person :slight_smile:

Can you point me at this “Boundy”? My only experiance of 6061 aluminium is from actually using it to make stuff, so having some numbers would be good.[/quote]

Its an online database I have access too through my student account at AUT through the university servers. You enter some formula and it gives a graph that Tells you its relitive properties for certain uses Canterlever, plates, columns etc (if you know how to read the graphs). It seems to be similar to fiber glass (If I have my column and canterlever material variables right, although i just looked quickly). I only have acess to the limited version from home but I’ll see the numbers I can get on the full program at university.

Imagine for a moment, two pieces of tempered aluminium rod 1m long.

  • The first is 20mm thick and has too little flex (for larp purposes)
  • The second is 1mm thick and has too much flex (for larp purposes)

Somewhere in between these numbers is a diameter of tempered aluminium rod that has roughly the same flex as a piece of 8-10mm fiberglass. We just don’t know what that diameter is.

Extruded aluminium of this sort comes in a selection of diameters in 5m lengths. I can get it through my mum, who owns an aluminium window manufacturing company. Not sure of cost at the moment, but they typically pay by the kg, and a 5m length would be less than a kg.

I’m not sure if flex is much of an issue. I don’t use fibreglass rods in my swords, I use battens. In cross-section, they are eliptical. Which means that are more sword-shaped. i.e. fatter in the middle and thinner at the edges.

Dave used one at the most recent St Wolfgang’s weekend game. When I handed it to him he laughed at me. You see, it’s quite flexible along the “flat” axis (i.e. if you hold the sword with the flat facing you and waggle it up and down, it will flex a lot).

However, it has no flex whatsoever along the edge. i.e. when you are fighting with it, there’s no give in the core.

Which leads me to think that the key factors are shape rather than flexibility. Battens have more surface area, so the contact adhesive has more area to work on. Rods have a smaller surface, so less area for the adhesive. More importantly, rods, because of their shape, are suseptible to torque (twisting of the surrounding foam). A circle is perfect for allowing the foam to twist, and thus increases the likelihood that the foam will loosen.

Once the foam is loosed, I posit that this enables the end to start poking through the foam.

Ergo, it may not be that the choice of core is the issue, rather the shape of the core.

Maybe, Derek, you should make a prototype and we can see how it goes ?

Even along the straighter edge, they still flex slightly. And yes, I did laugh - it was an interesting weapon to fight with, but I’m sorry Mike that waggle was a little disconcerting (but it did allow for some interesting under-shield action! :smiley:).
Furthermore, for what Derek is trying to achieve, a curve along that thinner edge might make the overall project significantly trickier, because you’d be bending against the stronger cross-section. I certainly agree though - maybe a prototype is in order.

As for twisting - I wouldn’t want to see any weapon “twisted” around it’s core. That’s just inviting damage, and any weapon that twisted like that during construction should be considered DOA anyway. Plus the battens only have more surface area to the sides - the total surface area is probably very very similar. The “punchthrough” discussion is interesting. Really, if a core is going to punch through foam it’s going to be from stabbing, which is banned across the board. For normal strikes, a round core that has foam directly between it and the surface (thinking three layers of foam here), shouldn’t punch through except in the case of misuse, or (more commonly) defects in the manufacture.
The flip side though is that if a weapon does twist, and somehow the core separates from the foam to which it is bound on the entirety of it’s surface, then at least it would still be sheathed in the foam outer. In the instance of a flatter core, sandwiched between only two layers of foam, if the core separates it’s more likely going to split the foam apart entirely.

Regardless - prototype!

We could just make one of each, then test to destruction and compare.

That’s what I’m thinking. I’m just trying to figure out how to temper 6061 aluminium. I think heating to to 200C for a couple of hours and then quenching in icy salt water will do it, but I really need to see some instructions.

While aluminium has its merits Derek, one thing to bear in mind is that there is nowhere else (in the world) that would allow a metal cored larp weapon. This is probably based on historical issues where homemade weapons containing metal were pretty horrendous. Even so most of everyone I’ve had contact with is nervous about metal in larp weapons.

Sure, and a few years back you weren’t allowed fiberglass either. Now it’s standard.

We could just rehash all the old conversations about fiberglass, do a find and replace on the word “fiberglass” with “aluminium”, take out the bits about splinters and x-rays, and save ourselves a whole lot of time.

Just to backtrack - have you considered two smaller fiberglass rods, held curved and bonded with contact adhesive in a similar manner to your laminated idea? (just a thought)

Duct tape would be much more effective at holding two narrow fibreglass rods together in a curve. Glue wouldn’t cope with the constant tension. A combination might work. Or is there some even better and more permanent way to bond fibreglass to fibreglass, perhaps by painting resin on to join them?

They would have to be quite narrow rods, to minimise the amount of tension on them. Like 4mm or something? It’s an interesting idea that could work. But it would probably work even better with flat lengths of fibreglass, as you’d be bonding two flat surfaces together.