Part 3: A Fairy Tale to Explain the Automatic Tension System
Order Warping Your Loom & Tying On New Warps HERE
When I was writing the book, I wanted to explain the tension system on the Ahrens looms I had and on AVL looms. Since Jim Ahrens is the “A” part of AVL and I was consulting with him when writing my book, I had to make sure I made it clear. I could never explain right. Finally, Jim said, “You still don’t understand it, I’ll tell you a story that I think can explain it. The system was used centuries ago; in fact, all the looms in Diderot’s Encyclopedie (1751-17172) show it. It might have been discovered like this story.” Hence “A Fairy Tale” on pages 140, 141 repeated here.
Once upon a time long, long ago before there were ratchets for looms, ways to tension the warp were very primitive. One day a weaver found a new way to put tension on the warp beam.
He put a sturdy stick, like a peg, vertically in his warp beam, hooked a rope on it, wound it around and around the beam, and hung a big rock on it. With the weight off the floor, he had full warp tension, and he was very pleased with himself. As he wove along and advanced the warp, the rope wound up on the beam and the rock rose higher and higher off the ground. Prety soon he had to stop because the rock was up on the warp beam, and he had to unwind the rope to let it down. Then he wove along until the rock got too high, stopped to unwind some rope and let it down again. This worked fine and he was very, very pleased with himself.
One time when he was unwinding the rope, he pulled out the peg and the rope slipped off the stick into his hand. He was surprised when he held the end of the rope, that he didn’t have to pull hard on it at all to keep the rope from slipping around the beam. In fact, he could hold the loop in the end of the rope with one finger and the rope around the beam didn’t slip. The big rock still hung in place putting full tension on the warp!
He had been winding the rope, say, ½ dozen times around the beam, so he decided to see if he could wind fewer times. He found with only 3 turns on the beam there was still not much weight needed on the end of the rope. So he hung a small rock on the end of the rope and began weaving.
As he wove along, the big rock rose and the little rock fell until it hit the floor. Then the most amazing surprise came.
When the warp threads were lifted to open the shed, the beam rolled forward slightly, raising the big rock and lowering the small rock to the floor. The little rock touching the floor took the tension off that end of the rope for an instant. As soon as it did, the rope slipped a bit on the beam. As soon as the beam slipped, the big rock put tension back on the rope pulling the small rock up off the floor again. The slippage let the warp move forward a few thousandths of an inch—just enough to compensate for the take-up of the warp for the weft!
The big rock was off the floor, obviously, while the small rock dangled just above the floor, where it bounced and dangled on and off the floor as he wove along.
Not he didn’t have to get up and unwind the rope to let the big rock down! He could weave along continuously, and the big rock would hold the full warp tension. The little rock would let the warp beam slip a bit with each weft and also would let it slip when he advanced the warp. The two rocks remained in these positions all during his weaving. This pleased him very, very, very much.
When the shed closed, our weaver realized that the beam rolled backwards to its starting place. The tension on the warp threads never changed even when the warp threads were lifted to open the sheds, because the wight (the big rock) was always the same. This was perfect for fine silk warp threads that couldn’t stand the stress of stretching with old locked beam systems. He was enormously pleased with himself!
Rocks (with on rock ten time heavier than the other) and the weaver’s invention are still used today! (Peggy’s note: I’ve seen this over and over in my travels.)
When Jim Ahrens began using the wight-counter weight system he tried the two weights and noticed the two weights jerked when the rope slipped. Then he got the idea to use a small spring in place of the counterweight. The spring let the rope slip slowly so there was no jerk or sudden change, just smooth weaving. He came up with the idea on his own, but never claims to have invented it; he said, “I always found someone else had done the things I worked out on my own.”
When he needed to make smaller looms, there wasn’t enough room for the big weight so he substituted a heavy spring for the weight. “It was no big advance, there was no place for the weight,” he said. It works the same way as the weight and small spring. Today some AVL looms use the two-spring system, and some use an arm with a weight and the small spring.
The heavy spring (or weighted arm) puts the tension on the warp; the small spring is the counterweight. When the shed opens, the warp beam rolls forward a bit loosening the tension on the other end of the rope at the small spring. The rope slips a little. The heavy spring takes over again, putting the rope back under tension. When the shed closes the warp beam rolls back to its starting point. The slippage is a few thousandths of an inch, and the warp stays under constant tension.
As you crank the warp forward you exert more force on the warp than the force of the weight or heavy spring, causing the cord to slip. This allows the beam to turn and the warp to unwind.
Jim prefers using the combination of a heavy weight and the small spring because he can beat harder than with just the two springs. But the double springs are a good enough substitute if you don’t beat too hard.