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Frequently Asked Questions

Troubleshooting Harness Systems

(Commonly referred to as Shaft Systems)

Two types of harness systems can be found on most AVLs; harnesses for polyester heddles and harnesses for metal heddles. Each harness structure is distinctly different.

Harness systems for polyester heddles utilize transverse harness sticks, top and bottom and frequently have harness wire or rod at each stick end loosely tying the top and bottom sticks together.

The harness system for metal heddles utilizes a rigid structure with top and bottom harness sticks firmly connected by vertical struts. Heddles are suspended via heddle rods at top and bottom running parallel to the harness sticks. The metal heddle harness structure is the same, whether twisted wire or flat steel heddles are used.

In all cases the harnesses are hung from the top via harness cables and stabilized from the bottom by a series of spring-tensioned levers, Spring Levers, or in some cases by springs. These hold the harnesses down and prevent your heddles from floating.

Some weavers like metal heddles because they believe they are easier to thread; others prefer the lighter and quieter polyester heddles. On occasion you will find that one or more of your harnesses will misbehave. That is more likely to happen with harnesses with Polyester Heddles. There are a finite number of things that can cause these problems.

Take a look through these common issues and solutions:

One or more top harness stick collapses; it assumes a diagonal angle and one leg of the harness cable from which it is suspended goes slack.

Possible Cause How to fix it
Your heddles are bunched together towards the center of the harness or on one side only. For polyester heddle-type harnesses, the heddles are actually part of the harness structure. Move a few heddles to each end of your harness sticks; just to the inside of the harness wires that connect the top and bottom sticks. That way your harnesses will be balanced.


The harness cable supporting the shaft has come out of its pulleys at the top of the loom.


Trace the cable back through its pulleys in the Harness Pulley Support and make sure that the cable is properly seated. Check the action of the Dobby Cable as well. Make sure that it moves easily up and down. If the Dobby Cable seems to bind, check for debris in the hole where it comes through the Dobby Top. You may need to use a very thin piece of wire to dislodge accumulated yarn dust or other debris.

AVL Looms

The heddles float; they are lifted upwards by the warp thread when you tension the warp and your shed is not even or not large enough.

Possible Cause How to fix it
 The tension in your warp is greater than the tension in the springs that hold the harnesses down. Take up a link or two in the chain that spans the Harness Spring Levers for that particular harness. Check the result and take-up more links if you feel you need more hold-down tension. Do not try to make all chains the same size. The size will depend on how much tension is required for each harness depending again on the number of threads going through that harness.

AVL Looms

One or more harnesses that are supposed to raise don't.

Possible Cause How to fix it
 1) Left treadle isn't being pressed all the way down. Concentrate on getting both treadles all the way through their travel.

2) Dobby arm out of adjustment.

Realign the dobby arm according to the assembly instructions.

3) Dobby cables out of finger slots. Rearrange the cables according to the assembly instructions.

AVL Looms

Harnesses don't raise properly.

Possible Cause How to fix it
1) Harness cables have been hooked to the wrong harness. Rearrange the cables.

2) Chains from the spring levers have been hooked to the wrong harnesses.

Rearrange the cables.

3) Copper hooks on the spring levers have been bent. Straighten the hooks with pliers.

AVL Looms

Harnesses jam up on each other.

Possible Cause How to fix it
 1) Heddles are not distributed evenly over the harness sticks. Redistribute the heddles evenly on both sides from the center of the harness sticks.

2) Harness wire that connects the harness sticks has jumped out and got stuck in the heddles of the other harness.

Pull the wire out, make sure it does not catch any heddles, and replace it to just connect the top and the bottom harness sticks. If you have a large number of extra heddles on each side, you might want to tie them in bundles to prevent getting caught by the harness wire.

AVL Looms