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Jack Looms part 1

by Joanne Hall

&   What is a jack loom?
&   Understanding how a jack loom works
&   Weaves which are difficult for a jack loom to accomplish
&   Creating a smooth weaving rhythm

What is a jack loom?
A weaving instructor I met a few years ago said in relation to jack looms: In the 70's we had jack fever. I remember those years. Weaving had become very popular, and new weaving shops opened up everywhere. They wanted to sell inexpensive looms, and many new loom makers went into business making table looms and small jack looms. When they wanted to make larger looms, they simply made their looms wider. Beginners liked the idea of the lower price and smaller size. Many of these looms were very small and not very deep, making weaving on them sometimes difficult and producing fabrics with poor selvages and an uneven beat. Now jack looms can be purchased with large frames, many shafts and a variety of features.

Jack looms are good for taking to workshops, designing and experimenting. They work very well if you are weaving narrow warps, short warps, four shaft plain weaves, balanced weaves, open setts and smooth warps.

"...They are best for experimenting, demonstrations, teaching, designing." S.A. Zielinski vol.2, p.15

But when you ask a jack loom to weave a combination of more difficult weaving tasks such as a close sett the full width of your loom, or a tight weave with a sticky warp, or an unbalanced weave on more than four shafts, you will encounter varying degrees of difficulty with your loom.

"Tying up a jack loom is very quick and easy." Deborah Chandler p.26

"Single tie-up (jack-type) are easy to set up and adjust, but hard to operate." S.A. Zielinski vol. 2, p.15

There are some things you can do to adjust your jack loom and make it work better, but you also need to learn what kinds of weaving you should avoid. To do this you need to understand how a jack loom works.

Understanding how a jack loom works
A jack loom is sometimes called a single tie loom, as only some of the shafts are tied to a treadle. This simplifies the tie-up, but causes problems in the weaving. The resting shafts which are not tied to the treadle cannot be controlled by the weaver. They must be heavy to stay down against the pull of the warp.

A jack is the part of the loom which is attached on a pivot and is used to raise a shaft. There are usually two jacks for each shaft. When you press on a treadle, the jack pivots, one end going down and the other up, raising a shaft. Shafts only move up and so a jack loom is sometimes called a rising shed loom. Jacks can be placed under the shafts pushing them up, or can be above the shafts on a castle pulling them up. Retaining the castle makes a better loom, but having the jacks under the shafts allows the loom to be made without a castle, making it much shorter and lighter weight. Workshop looms, made for folding and transporting to workshops are jack looms. Although these small looms have many limitations, they are portable and are designed for learning.

Styles come and go, and when the jack looms were designed, modern meant low and compact. Today we are more accepting of the advantages of a castle. In her 1961 book, Harriet Tidball wrote:

"The handsomest of all looms is the push-up jack loom with no superstructure. With four or six harnesses this loom is one of the most satisfactory, but for a loom with eight, ten or more harnesses, there should be overhead jacks." Tidball p.8

"Present day loom builders, with few exceptions, make the harness motions an integral part of the loom frame and so deny the weaver the facility of changing easily the type of harness motion according to the nature of the job... Unfortunately, this does not usually permit modification except by a complete rebuilding of the loom frame." Fannin p.80

Shafts are held down on jack looms by their own weight. This weight comes from the shaft frame, metal bars and metal heddles. Do not replace your heddles with string heddles or wire heddles unless you are weaving more than 8 threads per inch per shaft. The manufacturer of your loom has planned on their weight when designing the loom. Each loom manufacturer needs to decide how heavy to make the shafts. If they are too heavy, the weaver will find it difficult to raise them, especially when a treadle is tied to more than 2 shafts. If the shafts are too light, the resting shafts will not stay down when a shed is made, since the warp threads, when tensioned will be pulling them up. The weight of the treadles will also be pulling on the shafts and helping them to move up, especially if many treadles are tied to one lamm as in unbalanced multiharness weaves. Often the shafts need varying amounts of weight when an unbalanced weave is tied up.

"This kind of shed can be very large or smaller depending on the pressure there is on the warp threads and how many threads we have. For example, it will be easier to have a nice shed with a 36" loom with 20 threads per inch than with a 60" loom with 40 threads per inch. Here you have to understand that we may have to raise half of the threads; so the more threads and tension you have the more difficult it will be to raise them." Francois Brassard, www home page

"Unless you are strictly interested in fairly light-weight multi-shaft weaves, you should not get a jack loom for your only loom. It is not as versatile as the other two types. It is unsuitable for rug weaving and many tightly packed weft-faced weaves, and light-weight jack looms are undesirable for close warp-faced weaving." Rachel Brown p.120

"These looms should be used only when the cost of equipment is of primary importance because a double-tie-up loom although more expensive is much more satisfactory, and if necessary it can be used as a single-tie-up." S.A. Zielinski vol.2 p.13

"A loom is a piece of equipment designed to facilitate the textile process. There is little pleasure and no profit in trying to weave on a loom that will not do its share of the work willingly, accurately and easily." Mary Atwater p.30

The noise made by a jack loom comes mainly from a jack loom which does not have a castle. The shafts make noise when they fall onto the jack box, as the shaft frame and its metal heddles shake as they hit. There usually is some cushioning foam here to muffle the noise. The lower beater also makes noise when it lands on the upright on its return. This also can have rubber bumpers to help soften the noise. Sometimes other family members are more aware of this noise than the weaver.

"The large number of moving parts contributes significantly to a high noise factor.... the noise simply must be accepted as a part of the mechanism." Fannin p.83

"The noise of harnesses returning to their resting position can be quite an item if you do not have a loom room away from the rest of the household." Thorpe p.16

To make weaving on your jack loom successful, learn which weaves are difficult for your loom to weave and how you can adjust problem sheds.

Weaves which are difficult for a jack loom to accomplish
If your loom is large, very wide, or has heavy shafts, most light weight fabrics can be woven with little difficulty, although more pressure is required to do the treadling. If you do not weave the full width of the loom or you do not have many threads per inch, you will be more successful. You will have more problems on a shallow loom (one which is less than 40" deep). The most troublesome things to weave on a jack loom are tapestries, rugs, warp faced and weft faced weaves, fuzzy warps and close setts such as with doubleweave. You may also have trouble with unbalanced weaves such as summer and winter and other multiharness weaves where many warp threads are threaded on one harness and many treadles are tied to this lamm. There are a number of things you can try to help alleviate problems when weaving these, but the jack loom is not the best choice for weaving them.

Part of the problem is that the weaver only controls the top of the shed when pressing the treadle. The rest of the warp is on the bottom of the shed and it is unaffected by the foot pressing on the treadle. So, threads that stick together are a problem as the treadle will not separate a sticky shed. Jack loom weavers have been known to push shafts down with their hands and this should not be necessary. The bottom of the shed is often looser than the top of the shed. Tightening the tension to attempt to get more tension on the bottom of the shed means the top of the shed is tighter making treadling more difficult. But the bottom of the shed is still looser than the top and the shed is smaller. Add to this heavy shafts, and the treadling is tiring. And having to press so hard on the treadles can mean you will be uncomfortable on your bench.

"Right away you can see that a warp of extreme tension may not be stretched on this type of loom - making it unsuitable for tight weft-faced weaving, especially rugs. Besides this limitation, there is the fact that the rising action of any harness (or harnesses) does not force the opposite action of other harnesses..... For this reason a close-set warp for warp faced weaving may tend to lift all the harnesses when one is raised.... The loom is, however, superlative for light weight multiharness weaving....I suspect the jack loom is losing its popularity somewhat to the ancient counterbalance loom and counter marche loom." Rachel Brown p.120

"A very tightly stretched non-resilient warp (such as for rugs) can cause the shafts to float.....adversely affecting the shed. Additional weights can be added....but unfortunately... that weight also must be lifted.....In general, the action of a jack shed is lighter in a loom which lifts the shafts from above than in a loom which pushes them up.... however, both are considerably heavier than a counterbalanced or counter marche shed, a serious consideration..." Constance LaLena p.31

On rug weaving "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 counterbalanced or countermarch loom is very suitable. When at rest, the shafts of a jack loom are so positioned that the heddle 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

Treadling on a jack loom does not control the size of the shed as it does on counterbalance and countermarch looms. So when you need a larger shed, you must loosen the tension on the warp. But a looser tension may not be what you need. A warp which tends to be sticky needs a tight tension.

Creating a smooth weaving rhythm
Rhythm in weaving which comes from smooth, even, fast weaving, can be achieved with most looms with practice. But the loom must have clear sheds, a tight tension and easy treadling. This is best done with a one shuttle weave and by tying up the treadles so that you alternate feet while treadling.

Several characteristics of a jack loom must be considered when you want to weave with a good rhythm. One is that the shuttle race might be in the way. Placing the shuttle on the race and throwing it along the race will often be awkward and difficult to learn. But if you take it off, you may have to weight the shafts to get a tighter tension on the bottom of the shed to support the shuttle. This makes the treadling heavier and that also affects your rhythm.

Treadling a shed which has more than two shafts tied to it, or one with heavy weighted shafts, can be tiring as more weight needs to be lifted. It might be better to have lighter shafts and to weight them only if more weight is needed. But light weight shafts can affect your weaving rhythm too, as sometimes light weight shafts fall too slowly. This is because they are not tied to the treadle used to make the next shed. They fall only because of their own weight.

The following quotes will give you an idea of what others can achieve with a good rhythm. It is easier to do this on a counterbalance or countermarch loom and with a simple weave structure. The size of the weft thread will make a difference in the amount of yardage woven.

"He must be able to weave on a narrow warp (12 to 20") plain tabby at a speed of 60 picks per minute. Check it with your watch. If the loom refuses to work that fast, don't buy it.... anybody can weave 2 yards per hour." S. A. Zielinski vol.2 p.9

At 20 wefts per inch, this would be one yard in 12 minutes. I doubt many weavers today can do that, but obviously he did. I have tried weaving 1 weft per second and it is possible to do it, but I got tired really fast.

" would not be unreasonable for a skilled weaver to be able to maintain a sustained rate of 1500 picks per hour over the length of the warp including time to advance the warp, wind shuttle bobbins, and make any necessary repairs in the weaving." Constance LaLena p.30

At 20 wefts per inch, this would be 75" or just over two yards per hour. This is another weaver who has a lot of experience and I am sure she could easily do this. So, give it a try. Get a timer and see if you can develop a rhythm which will make you more productive. But with the heavier treadling on a jack loom, and especially if you are weaving wide, do give yourself frequent breaks and don't expect this kind of efficiency.

"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 by Joanne Hall. Please contact the author for permission to use any part of this article.

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