How Looms Create a Shed
In the weaving world, there are many types of looms. We quite often get asked which we think is the best. Answering that question is tricky! Each loom has its own quirks and personality and is best suited for different styles of weaving (or different weavers). Before we dive too deep, there are a few concepts that are common to all looms. Understanding these can help you make sense of their differences.
Warp, Weft, & Shed
Every loom provides a frame that helps the weaver stretch the warp out. This can be as minimal as a couple small sticks (as in a backstrap loom) or a large edifice that takes up an entire room. The warp is the length-wise yarn that is attached to the loom. The most simple loom would require the weaver to weave the weft (that's the yarn that goes back and forth) over and under each warp yarn.
This method is fairly time consuming and weavers have devised many shortcuts for separating the warp threads so that the weft yarn can be quickly interlaced. The open space between the warp yarns is called 'the shed,' (think of it as looking a bit like the profile of a shed roof). A shed is usually created by a shed stick turned on edge or a series of heddles that the warp threads pass though and let the weaver manipulate groups of warp yarns all at the same time.
Types of Sheds
A shed can be created by lifting certain warp threads (called a rising shed), by lowering certain warp threads (called a falling or sinking shed), or by simultaneously raising and lowering warp threads. One of the key differences between looms is the type of shed they create and how they created it.
Loom Mechanics, or How to Create a Shed
Many of the smaller looms like inkle, tapestry, tablets, etc are all very specialized in how the shed is created. We'll add more information on them in the future. Now on to the nitty-gritty of how sheds are created.
The Jack Loom is the most common type of loom found in the USA. It works by either pushing or pulling a set of shafts (with heddles) in order to raise or, in a small number of looms, lower the warp.
A jack works on a pivot that is controlled by the treadles. The treadle pushes down, pulling one side of the jack down, which pushes the other side up, lifting the shaft! Schacht and Gilmore looms are great examples of this style.
The jacks can also be placed above the shafts with a system of pulleys to or rods that move the jacks that lift the shafts. Macomber and Harrisville Designs looms are examples of this style of jack loom.
Not sure of you have a jack loom? Take a look at your shed when you press a treadle. Does part of the shed stay still while the rest moves? Unless you are on a table loom, this is likely a jack loom!
Jack looms are straightforward to tie up, and can have a low profile
These next two styles of loom share the same shed type and are the ones people most often get confused. The counterbalance loom works with pairs of shafts that are connected to each other. When one shaft goes up, the other must go down.
When looking at the shed of a counterbalance loom, some of the threads move up and the rest move down. This is the same SHED as a countermarch, but the mechanics of a countermarch are very different.
Counterbalance looms work great for 2/2 twills and plain weave. They start to struggle a bit when asked to weave 3 to 1 or if you add more than 4 shafts. These make wonderful rug looms.
Countermarch looms are very popular in the Scandinavian countries and most of the new countermarch looms you can buy today are built in Europe.
Countermarch looms work by simultaneously pulling some shafts up and some shafts down. Unlike the counterbalance, each shaft is controlled individually. This means that you can tie up a countermarch loom any way you like and it will still work beautifully. Rather than balancing shafts against each other, countermarch looms have two sets of lamms that lift and lower the shafts.
It can sometimes be tricky to tell apart some countermarch looms and a jack loom with upper jacks, but just look at the shed and see if it opens up and down (countermarch loom) rather than only lifting some warp threads (jack loom). You can read more on Glimakra USA's website
Rigid Heddle Looms
The rigid heddle loom is in a bit of a special category as you only thread every other warp yarn through a heddle (the other goes through a slot hole) that is ALSO your reed. When you physically pull the shaft/reed up, those half of the warp threads go up. When you push the shaft down, those same threads go down. This creates an interesting effect where your heddle-hole warp threads are doing all the work.
As long as you are not weaving with a very stiff material like linen, the yarns work themselves out to remain balanced. In order to get fancy sheds with the rigid heddle loom, you need to use pick up sticks and/or extra shafts/reeds. Rigid heddle looms really shine for quick weaving, versatile pick up that is more impractical on a floor loom (the pick up stick goes behind the shafts), and extreme portability.
This is a trick category! Table looms can actually work using any of the previous loom mechanics (counterbalance, jack, etc) and are only truly defined as small looms that can set on a table. Most popular table looms today work through a direct lift style of design. Each shaft (or sometimes a set of shafts) is directly attached to a lever on the loom. The weaver pulls the lever which in turn pulls a cord attached to the shaft. The Ashford and Louët table looms are examples of this style.