Fun with Treadles and Shafts

Guild member Glenn Davison presented the February program on computer dobby loom weaving at home. When you think of computer assisted weaving, do you envision pressing a button, stepping back, and watching as inch after inch of fabric is effortlessly produced? According to Glenn this is the biggest misconception about computer dobby loom weaving. It actually is hand weaving.

Glenn started with a discussion about the two shaft loom. There are two possible combinations: the threads are up, or they are down. What happens when more shafts are added is rather amazing.

  • 4 shafts = 14 combinations
  • 8 shafts = 254 combinations
  • 16 shafts = 65,534 combinations
  • 32 shafts = 4,300,000 combinations!

(For those with inquiring minds, the mathematical formula is as follows: 2 to the nth power minus 2 when n equals the number of shafts.)

Glenn shares the possible combinations for an eight shaft loom.

Glenn shares the possible combinations for an eight shaft loom.

The addition of shafts to a loom allows for more variety and complexity in patterns. However, using foot treadles to lift the additional shafts becomes increasingly difficult, and the number of shed combinations is limited by the number of treadles and the tie up.

Around 1843 the mechanical dobby loom was introduced. It has no treadles; the dobby controls the warp threads allowing for all the shaft combinations to be available to the weaver. The dobby also keeps track of the pattern sequence.

Today the mechanical dobby loom has been improved with the addition of computer technology. The dobby is controlled by solenoids which raise and lower the shafts. A loom control screen shows where the weaver is in the pattern sequence as well as the past rows and the next rows. The weaver can save and come back to the same spot later.

This is what you might see on the loom control screen.

This is what you might see on the loom control screen.

Mechanical dobby looms are still available. Setting them up is labor intensive, and the patterns are limited to the length of a belt. They are relatively inexpensive but are cumbersome for the home user.

Computer dobby looms have endless program length and can store patterns. The user can design his/her own patterns or can import patterns. They do require a computer, software programs and drivers, and they can be costly.

Click on the link to see a 16 shaft LeClerc Weavebird computer dobby loom in action. The weaver tells the dobby to advance to the next shed using the two treadles. Computer Dobby Loom Video


Glenn’s computer dobby loom is a LeClerc Weavebird similar to the one pictured above. It has sixteen harnesses and is forty-five inches wide. Weavebirds are countermarche looms meaning the harnesses move either up or down for every shot. This results in a good shed and reduces friction on the yarns. It comes with either a traditional or overhead beater and single or double beam. With a double beam, tension can be adjusted for two different types of yarns separately. The harnesses on dobby looms are slender and close together taking up less space than one might expect.

Here are some helpful tips for weavers from Glenn:

  • To improve selvedges, use an end feed shuttle with pirns. The tension can be adjusted, and the speed of weaving is increased.
  • It it helpful to have computer and mechanical knowledge to operate a computer dobby loom.
  • Find a spot with plenty of space and good light when placing your loom. (A remodeling project may or may not be required. 😉)

Our thanks go to Glenn for sharing his knowledge of  computer dobby looms with us.

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