On Rug Weaving
Although rugs can be woven on just about any kind of loom, the best quality rugs and the most ease of weaving and beating comes from a counterbalance or countermarch loom. You need to have a tight tension on both the top and the bottom of the shed, which a jack loom cannot do. Tight tension requires more pressure on the treadles, and adding very heavy shafts of a jack loom makes jack loom treadling very hard."Because a highly tensioned and often inelastic warp is being used, it is far easier to obtain a given depth of shed with a system that raises some shafts and lowers others than with one that only raises shafts. In the former, the shafts have only to move two inches above or below the normal warp line to give a four inch shed; in the latter, they have to move four inches above the line. In other words, a counterbanlanced or countermarch loom is very suitable. When at rest, the shafts of a jack loom are so positioned that the heald eyes are below the line from breast to back beam. To keep them in this position, when a highly tensioned warp is being used, they have to be specially weighted. Otherwise they will rise and decrease the depth of the shed." Peter Collingwood p.52-53
"Because of the position of the closed shed below the warp line, there is a tendency for the shafts to "float" or hang suspended on a tight warp. Such a condition is the major cause for warp skips when a tight warp is woven with this shedding motion." Fannin p.80
To understand this problem, note that the shafts on a jack loom need to be resting several inches below the breast beam. When a shaft is raised, it must rise to a height which is the same distance above the breast beam. The tension must be kept loose in order to keep the resting shafts down. If the resting shafts do not stay down, the threads on them will become loose, making it hard to throw a shuttle. This gives the shuttle the opportunity to catch threads on the wrong side of the shuttle, causing skips and floats in the weaving. It also results in poor distribution of the weft, poor selvages, and makes wide warps very difficult to weave. It is also difficult to weave weftfaced weaves as every other warp thread is loose.
You may have heard that jack looms are harder on warp threads and cause more broken ends. On a jack loom, as warp threads are raised, they loosen as they reach the center of the shed. Then they tighten again as they reach the top of the shed. The constant loosening and tightening of the warp threads creates a snapping of the warp. On counterbalance looms, the warp is looser when it is at rest. On a jack loom, when a warp is not treadled, it is at maximum tension. This can cause extra stress on the threads. When you are not weaving you should loosen the tension on the warp as there is added stress at the point where the threads are held in the metal heddles.
Jack looms require a looser tension than other looms so you can try weaving on a reduced tension. Lose tension does not support a shuttle very well, so the shuttle can easily fall through the warp threads . Because the tension must be looser, a shuttle race is added to the beater to hold the shuttle. This can interrupt rhythm as the shuttle needs to be placed on the shuttle race and the shuttlerace can get in the way of your hand. Counterbalance and countermarch looms do not have shuttle races unless they have fly shuttles. This is because weaving is done with a tighter tension. If you try to tighten those threads on the bottom of the shed of a jack loom by tightening the tension, the tension is increased on the top of the shed, making treadling more difficult. The bottom of the shed stays looser.
Treadling a multiharness jack loom, or one which has heavy shafts, can be tiring as more weight needs to be lifted. It might be better to have lighter shafts and to weight them if more weight is needed. Sometimes light weight shafts fall too slowly to develop a good rhythm. This is because they are not tied to the treadle used to make the next shed. They fall only because of their own weight.
"Among all hand looms the single tie-up jack-type is the most universal....If built for narrow warps it is not too heavy in operation. But it is a hopeless proposition when economy of time and effort come into consideration. If it is (universal) the weight of heddle frames must be such as to meet all emergencies, which means much too heavy for ordinary weaving." S.A. Zielinski vol.2 p.11
Copyright 1998, Joanne Hall, Elkhorn Mountains Weaving Studio. (jah@montana.com) Used by permission of the author. Citation sources.
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