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Dan D'Silva





Joined: 28 Apr 2007

Posts: 163

PostPosted: Mon 01 Apr, 2019 12:40 pm    Post subject: Calculating design weight         Reply with quote

Hello again. I've been asked to design an all-metal akinakes for a custom build and I'd like to make sure the design I've come up with isn't going to be a crowbar. Could any give me an estimate for a realistic weight and balance?

The design is to be all-bronze. I would prefer it to have a bronze hilt and steel blade but I'm not sure that's feasible given the client's budget.



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Andrew Gill





Joined: 19 Feb 2015

Posts: 105

PostPosted: Thu 04 Apr, 2019 3:36 am    Post subject:         Reply with quote

Hi Dan

You need to calculate the volume of the dagger, and then multiply by the density of the material.
Break up the shape of the dagger into solid forms which are easy to calculate the volume of. The hilt-side half of the blade (the strong) is roughly a diamond-shaped prism (formula V=l*t*w/2), from half-way to the tip is roughly a flattened pyramid (V=l*t*w/6 I think). The grip, pommel and even the guard could be roughly approximated as equivalent rectangular boxes (V=l*w*t).
Calculate each one (where l is the length of that part, w the width and t the thickness) then add all together.
If you multiply the volume of each bit by distance from the back of the pommel to its center, then add them and divide by the total volume, you'll get a rough idea of the distance from back of the pommel to the center of gravity.

As an aside, surely a steel blade is cheaper than a larger bronze casting? I was under the impression that bronze-casting was very expensive, and the more so the bigger (and more complex) the piece. By mass, bronze is certainly more expensive. A steel blade could be fabricated entirely by stock removal using hand tools, I'd have thought? I am an amateur, of course, so I'm not familiar with the economics of professional knife-making.

I hope the formulas help

Regards

Andrew
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Dan D'Silva





Joined: 28 Apr 2007

Posts: 163

PostPosted: Fri 05 Apr, 2019 9:11 am    Post subject:         Reply with quote

Thanks, that's very helpful.

Pommel: 6 cubic centimeters
Grip: 19cm³
Guard: 10cm³ (a rectangular prism would be 15 but I reduced it by a third because of its taper in various directions)
Forte: 12.25cm³
Foible: 4cm³

That should make for a total volume of 51.25cm³. Bronze varies depending on the alloy. I chose 8.9g/cm³ which is on the heavy side, resulting in a weight of 456.12g or a hair over 1 pound, not unreasonable I think.

Going by that formula, the balance would be somewhere around 12.69cm from the top of the pommel, either right at the guard or a little bit inside it.

Now that you point it out, I realize that the notion of a whole bronze casting being cheaper than bronze and steel sounds strange, but he was originally going to contract the work to an overseas caster who can do casting much cheaper than in the States. However, that deal fell through yesterday.

Actually, at the moment I'm discussing with him the idea of getting a steel blade and allowing me to make a wax hilt that we'd have cast domestically.
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