Part 22 - Aspect Ratios
by Lord Thomas the Black
A while back, the Kingdom Largesse Coordinator for my local SCA (Society for Creative Anachronisms) group tasked me with creating “Kingly largesse”: tough, manly stuff for His Majesty to hand out in court. You see, there were already loads of “Queenly” largesse, such as hand-made pillows, embroidery, soaps, etc, but the Largesse Coordinator wanted something for the King.
So, I began work on an order of 21 knights’ chains. Knight’s chains, for those who don’t know, are made of brass welding rod, and are meant to be heavy to remind the knight of their responsibilities of office. Brass welding rod is used because it can be polished to shine like gold, but is a harder alloy than pure brass (which is too soft to work for chains). The goal was to make three chains each of seven different weaves. I began the project optimistically, finishing two chains in a weekend before running out of brass rods.
My lady suggested we go to The Yard in Wichita, Kansas for more brass. The Yard is a metalworker’s paradise, with wire, plate, and scrap metal available for a song. I found fifteen-foot brass rods for $1.00 per pound, so I bought a mess of them. Upon returning home, I began coiling and cutting my new brass. This is when I discovered that the new brass was @ 2mm larger in diameter than the brass I’d been using. It’s only 2mm, no biggie, right?
Wrong. Upon trying to weave the next chain, I soon found out that weaves and ring sizes that worked with the old brass didn’t work with the new brass. I was forced to move everything up one ring size. So, the weaves I used to do in 5/16” rings now had to be done in 3/8” rings. 3/8” got bumped up to ½”, and the ½” weaves became impossible. It was a frustrating experience, to say the least.
I tell you this long story to illustrate a point: knowing your aspect ratios can make or break your maille project. What do I mean by “aspect ratio”? Mathematically speaking, the aspect ratio is the relationship between a given ring’s wire diameter and its inner diameter. It’s calculated like this:
(Aspect Ratio) AR = -----
WD (Wire Diameter)
The important thing to remember is that both the ID and WD measurements must be in the same units (inches, millimeters, etc) so that the units will cancel properly.
The Aspect Ratio (AR) determines how loose or tight a weave will be. Each weave has an optimal AR, or a range of possible AR’s. If the AR is too small, you won’t be able to fit the rings into the weave (which is where I was having problems). If the AR is too big, the weave will be floppy and may not hold its shape. To use my problem as an example, the optimal AR for a Full Persian weave chain is 4.88. The original brass I’d started with was @ .08” WD, coiled into a .390 ID. This put the AR right at 4.88. With the new brass (WD = ..09), the AR got dropped down to 4.3, which didn’t work (way too tight). This is why knowing the AR is important.
Fortunately, for people bad at math (like me) there’s help available. The Maille Artisans International League (M.A.I.L.) website (www.mailleartisans.org) has a number of AR tables and charts that list the optimal AR’s for most maille weaves.
Now, before you dive right into your next chain project, there’s something else to keep in mind: spring-back. Most metals have a certain amount of spring-back to them. If you wind wire around a mandrel, instead of staying tight against the mandrel, it will naturally attempt to return to its natural state, i.e. it will “spring-back”. The result is rings with a slightly larger ID than the diameter of the mandrel, thus increasing the resulting AR. The amount of spring-back depends on several factors, such as the alloy of the wire, the temper of the wire (how hard it is), and the speed at which it’s wound. So, it’s important to start planning your projects with the actual measured values of your rings, and be careful comparing ring sizes of different materials. To use another example from my catalogue of mailling mishaps, in my riveted maille projects, I’m using 3/8” rings in mild steel. I wanted to trim this in brass, so I got some 3/8” overlapped brass rings. Brass has greater spring-back than steel, so the rings I got were slightly larger than the steel, and now have to be reduced before being useable for my project.
So, to sum up:
¨ For the same wire gauge, smaller ID = smaller AR; larger ID = larger AR
¨ For the same ID, thicker wire = smaller AR; thinner wire = larger AR
¨ Smaller AR = tighter weave; larger AR = looser weave
¨ Smaller AR = stronger ring
¨ Because of spring-back, rings made of harder wire will generally have a slightly higher AR than rings made with softer wire, when the wire thickness and mandrel are the same.
As always, thanks for joining me for another month of Blackmaille! Any mail-related questions or comments can (and should) be sent to:
c/o Tom Beckett
13628 Belmead Ave
Grandview, MO 64030
Next month: How to survive large demos!
See you next month!
“Aspect Ratio (AR)”
by Theresa Olin (Vacacita)
“Aspect Ratio Studies”
“Everything You Ever
Wanted to Know About Aspect Ratios, But Were Afraid to Ask”
Ring Sizes for Weaves” by Venom
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