Tuesday, January 16, 2007

Adventures with the Ahrens Fly Shuttle Throwing Mechanism

Some time back, Bonnie Inouye posted a message on WeaveTech with information about a fly shuttle throwing mechanism that she had seen and photographed at the studio of Jim Ahrens (one of the original developers of the AVL looms). Bonnie indicated in her message that only a small movement of the hand was needed to send the shuttle across the race. You can find her original message in the WeaveTech archives, and a photo in the Files section of the WeaveTech site.

Since my husband is a woodworker and an engineer, I asked him to try to duplicate the Ahrens mechanism for my loom. It didn't quite make it into production by Christmas, but before New Years he installed the gizmo on the loom.

First, for comparison, here's a short video showing the standard AVL side-pull fly shuttle throwing mechanism in action:

You'll note that I use my whole forearm and a fair amount of body english to throw the shuttle, so the stress on the body is not limited to my hand and wrist. I try to use the motion I was taught for fly-casting - keep the wrist fairly straight and use the forearm instead. With some degree of arthritis, I'm really anxious to avoid repetitive small-motion stress. (You'll also notice that there's no warp on the loom; at the time, I'd threaded the heddles but not the reed. However, this doesn't really affect the outcome of the experience, as I'll discuss later.)

It may not be immediately apparent, but the cord attaching the handle to the castle is closer to me by about 4 inches than the standard AVL setup. This is because my monitor is mounted in a cradle under the castle, and we wanted to be sure that the cord cleared the monitor to avoid accidental damage. So Mike bolted a piece of wood immediately under the castle, above the monitor, with an eye-bolt on the end, and the fly shuttle handle cord is attached there instead of directly to the castle. These mods were done shortly after I got the loom in 1997

By the way, I really love having the monitor right in front of my face! I don't have to turn to the side of the loom to see where I am in the draft. The PC itself is mounted on a board on top of the castle. Initially, I worried that the constant jarring motion of the loom would wreak havoc on the disk drive, or destroy the monitor, but I've been using the same monitor since I bought the loom, so my fears were unfounded. The PC has been replaced once in that time, but only to have a slightly faster processor, not because of any disk drive damage. The AVL dobby box is also on top of the castle, having moved up from the original position beneath the castle. I never have needed to see the dobby box display, so the location change was no big deal.

Here are a couple of pictures showing the modifications. One shows the pivoting handle, which is attached to the castle so that it clears the monitor (although it does obscure the display somewhat). The other shows the pulleys that route the cord from the pivoting handle to the picker. Initially, the pulleys were mounted higher, about 6 inches below the rocker that supports the overhead beater arm, but in early testing it felt to me like the direction of pull was too vertical, when at the level of the picker, the travel has to be horizontal. So Mike moved the pulleys down about a foot.

And, here's a short video showing the Ahrens fly shuttle throwing mechanism in action:

Bottom line: It's been removed from the loom, and I've gone back to the standard fly shuttle throwing mechanism. After using it for several hours, I felt that the effort required to throw the shuttle was too great. It wasn't just a little tilt of the hand, it was a very strong, sharp motion. My hands and wrists were definitely sore after that amount of time. It was an effort to get the shuttle to travel all the way into the box. Often, it didn't quite make it all the way, and had to be tapped gently to get it all the way to the full extent of the picker so it would be in position for the next throw.

With the standard setup, I can start the motion gradually and pick up speed before ending the stroke. I can also vary the position of my hand, and it's usually farther away from me (toward the monitor) for the right-to-left throw and closer to me for the left-to-right throw, because this is more comfortable for me. With the Ahrens mechanism, the position is absolutely fixed. It's also higher, since it has to clear the top of the beater. The standard AVL shuttle handle can be lower than the top of the beater in rest position, because I typically move the throwing hand closer at the same time as I move the beating hand closer.

After Mike removed the Ahrens mechanism, and I started to weave with the standard mechanism, I found that I was throwing the shuttle way to hard, so the shuttle rebounded out of the box. That told me that I'd been using a lot more effort with the Ahrens mechanism and that body memory of the amount of effort required carried back over to the AVL mechanism. It took a while to re-learn to just use enough force to get the shuttle across the race and into the box and no more. Note that this was with the same loaded shuttle and the same warp.

I don't want to imply that the Ahrens design doesn't work, only that our implementation didn't, at least, not for my hand and wrist. We tried to make the parts as close in dimension as we could to the photos we had of the Ahrens design. When I first tried it, without a warp on the loom and with no filled pirn in the shuttle, it seemed like it would be a workable amount of effort. However, with a loaded shuttle and the added resistance of warp friction, it just didn't feel good to me. Part of that is because I've been using the standard AVL fly shuttle since forever (almost 10 years now) so that any change means retraining both my body and my brain, and part is that my hands aren't particularly strong.

I believe that AVL is working on their own version of the Ahrens throwing mechanism, and it may well be that their clever engineers can fine-tune the design so that it really is "a small tilt of the hand" motion. I look forward to hearing from Bob Kruger that they've come up with a smoother operating version!


beryl said...

Thanks for the blow by blow about the Ahrens flyshuttle system. I, too, hope that AVL comes up with a system that is easier on the body. I'm really sorry to hear that it didn't work the way we had hoped it would.

Jasmine Weaver said...


I say the link on WeaveTech and tried to view the videos but got a message that they are private and you need to receive an email. Sandra, I would love to view the videos.