Chainmail Motorcycle Jacket
(chain maille motorbike shirt) Updated 18/May/2008
I’ve been making chainmail on and off for several years now. Mostly from spring steel lock washers, although a few projects from mandrel wound wire. I favour spring washers because they’re cheap, strong and have a clean cut.
I’ve also been riding motorcycles for about 9 years and a few years ago I had the idea of making a chainmail jacket. Well it stayed an idea and progressed no further; no point in committing to new projects when I hadn’t even finished my hauberk after 5 years. Then in time for my 30th I push ahead and finished the hauberk. The armpits were a bloody struggle, especially with the low aspect ratio of the washers. I’m really pleased with it. 20,000 M8 rounded-square-section spring washers and ~20kg! I then gave up chainmail!
Spring washers aren’t that useful if you want to do re-enactment, but for me it’s the making and creation that’re fun. And they’re cheap!
As I’m going away around Europe in the summer of 2008 (hopefully) I had the idea of trying to create a jacket that would let the wind through (Greece was unbearably hot last year) but keep the gravel out in case of a spill. For speed I decided on the Japanese 4-1 pattern (gusari) with the smaller rings doubled up for extra strength (in an ideal world it’d all be welded). Realising that you could get quite a big spike through the 4-1 I changed over to Japanese 6-1 as it’s denser and would even save weight if I didn’t double up the connector rings. 6-1 is a little more problematic than 4-1 as the weave is different in the x and y directions.
Trawling the internet for information revealed very little other than a few anecdotal opinions until I came across an article on mailleartisans.org posted by Jason
( He’d apparently hit a deer on his bike at a fair whack while wearing a European 4-1 vest with 8mm rings. His arms and legs were ground into the tarmac but his torso ‘merely’ pummled. Certainly no worse than a sleeveless leather jacket. Although my mum has forbidden such a venture this is all the encouragement I needed. Having read various discussion threads I’ve adapted my design to hopefully address all the possible issues. This is a work in progress and I estimate it will take ~90 hours.
Chainmail Motor Cycle Jacket
Material: zinc plated spring steel washers M12 and M6
Pros: cheap (M12@£12.14/1000 and M6@£2.99/1000
strong for butted mail. The M6 washers deform (pull test) enough to let an M12 ring slip through at ~40kgs. I’m not strong enough to pull the M12s apart but guesstimate ~160kgs from the cross section.
Cons: fairly heavy*. Estimating about 10-12kgs for the shirt (heavier than I initially hoped it would be.) ~4800 M12s and ~14400 M6s.
* turns out extra mass is necessary to absorb heat
Design: I just started making sheet! Plan is to draw the panel sizes from my leather jacket onto card and make maille panels to fit, and then join it all together.
Worries:
- M6s protrude verticallyand could dig-in in a crash.
It hurts more than European 4-1 if I stamp on a sample of the material with my heel!
Solution: 1) wear my armour jacket underneath (nylon thing
with pads)
2) double up the M6s on the elbows and shoulders
to give more surface area at impact points. - Removal of jacket by ambulance crew.
Solution: I was going to make a 1 piece jacket with luggage straps to pull it tight, but now I plan to use several luggage straps as buckles up the front and have some overlap. This will allow for extra jumper or me getting fatter! - Rain.
Solution: carry a waterproof jacket - Zinc on skin.
Solution: wear a long sleeve t-shirt underneath. - Attracting too much attention.
Solution: sweatshirt over the top. - Material tearing.
Solution: Maths! A lot of people on threads were worrying about the mail tearing and coming to pieces. That may be more of a problem with mild steel wire. I decided to try and compare the strength of the washers to my leather jacket. Here is my back-of-the-envelope scientific consideration of the problem (feel free to point out )
Tensile strength leather: 2000-6000 lb/inch2 I opted for 4000lb/inch2 as jacket leather is much softer than boot sole leather and it’s in the middle!
So that’s Leather 2.9 kg/mm2
Tensile strength ring: I decided to test this for myself. Using a 50kg spring gauge, the M6 ring deformed enough to let an M12 slide through (2mm) at ~40kgs. The M6 ring is handily ~1mm2
So that’s M6 Ring 40 kg/mm2
Now leather is continuous and the chainmail full of holes so I decided to work out the strength over a 3 inch (75mm) length. Good bike jackets often quote 1.2mm leather. The chainmail had 10 M6 rings in that length. Many of them are at 60o due to the pattern - I just ignored this!
So:
Leather:
75mm x 1.2mm x 2.9kg/mm2 = 261kg needed to shear a 3” leather strip
Chainmail:
10rings x 40kg/ring = 400kg needed to deform a 3” Japanese 6-1 strip
The mail is stronger than leather. Leather is considered safe, and Jason’s jacket held with minimal damage (admittedly a denser weave, but of softer metal).
- Friction Burns: several people (including my mum) have suggested that the mail will get too hot and burn me. I don’t see why really. Ignoring the few extra kgs from the chainmail over a leather jacket, the kinetic energy before impact will be the same. As one slides to a halt the kinetic energy will be mostly converted to heat energy. So the leather and chainmail will have to deal with the same amount of heat energy. Here is my 2nd back-of-the-envelope scientific consideration of the problem (feel free to point out problems )
The amount a material heats up for the energy (Joules, J) put in is called its specific heat capacity.
Specific Heat Capacity Leather: 1500 J/kg/oC
Specific Heat Capacity Steel: 500 J/kg/oC
So the steel jacket of the same weight (ok, mass) will get 3x hotter than leather for the same energy input. However… my leather jacket seems to weigh ~3kgs and if the chainmail is ~10-12kgs so that’s 3-4x the mass to soak up the energy and the temperature rise should be similar, or 1/3 less. Interestingly I had been thinking that welded stainless steel European 4-1 would be a lightweight and strong (and hideously expensive) solution, but maybe you need the mass to soak up the heat. The maille needs to be made of HeavY MetaL!
There may be heat build up in certain areas like the shoulders as they dig in, but this would happen with a leather jacket too. By doubling up the M6s on these areas for extra strength and to stop them digging in, there will also be extra mass to soak up the heat energy and reduce any temperature rise. Also the armour jacket (made of some really dense 10mm foam) should be a good thermal insulator.
- Strong Buckles:Ideally I want the jacket to be cheap, not too stupid looking, durable and adjustable. I think luggage straps may provide the solution. Although the cast material the buckle bit is made of will be weaker than the chainmail, 6 or so of them must be stronger than a zip. The buckles will be clipped to the chainmail on one side and the 1” nylon strapping threaded through the mail and sewn on the other side. This will leave straps that can be pulled to the desired tightness.
Weaving Tips: get a vice, then you can feed the pliers with one hand and twist with the other. Vice can be adjusted to suit various ring sizes. Spring washers are tough and need fresh pliers. Close the M12s and work with open M6s. Although there are 3 times as many M6s, they are so much easier to work with. Make a chain of 100 M12s and then build a square of Japanese 4-1 that’s 10x10. Then make it into a rhombus and fill in the diagonals with M6s.