Dobby, (a corruption of “draw boy” refering to the weaver’s helpers who used to control the warp thread by pulling on draw threads), is a type of floor loom that is able to fully utalise all possible sheds ( a 16 shafts dobby loom can utalise 65,534 possible sheds!). “A manual dobby uses a chain of bars or lags each of which has pegs inserted to select the shafts to be moved… Another advantage to a dobby loom is the ability to handle much longer sequences in the pattern. A weaver working on a treadled loom must remember the entire sequence of treadlings that make up the pattern, and must keep track of where they are in the sequence at all times. Getting lost or making a mistake can ruin the cloth being woven. On a manual dobby the sequence that makes up the pattern is represented by the chain of dobby bars. The length of the sequence is limited by the length of the dobby chain. This can easily be several hundred dobby bars, although an average dobby chain will have approximately fifty bars.” http://en.wikipedia.org/wiki/Dobby_loom
Can you believe that, 65,534 possibilities! It actually starts to make my brain hurt just think about all those possibilities, seriously I’m still getting my head around 4 shaft patterns (oh my!).
Right now I want to get my head around how the dobby beg and chain system works. In a future post I’ll go step by step through the warping up of my “teething” warp and thus the various parts of the dobby loom from sectional warp beam to front apron, tie up and my sampler of various weaving structures (that will be a photo heavy post).
Ok, so dobby pegs and chains. The dobby box is made up of bars linked together with a few chain links, forming a long chain of bars. My loom has wooden bars and metal links and pegs, I’m not sure about other dobby looms though. Each bar has 16 holes, 1 hole for each shaft. A peg in a hole indicates that shaft is to be lifted for that rise of the shed, obviously if there is no peg then the shaft stays put. A single bar for plain weave might look like this (with a x indicating a peg): [xoxoxoxoxoxoxoxo]. Incidentally, there are only two treadles for the dobby loom and they turn the gear to move the next bar into position and thus creating the next shed. To continue with a plain weave (or Tabby if your prefer) you would program the next bar to be: [oxoxoxoxoxoxoxox] (the opposite of the first one). The shortest chain you can make is 8, so you would continue to peg all your 8 bars with the alternating pegging:
The AVL manual recommends starting all your projects with this tabby weave for the first inch and or as a header to ensure you’ve got all your threading up error free.
Instead of using a tie-up and treadling plan like you use for other floor looms, with a dobby loom you create a “peg plan”. This is a graph showing the order in which pegs are placed into the dobby bars. Now, lets see if I can explain how to convert a tie-up & treadling plan, into a peg plan! (This is mostly for my own benefit, I could just cut and past the info from the AVL manual, see link below, but I believe I will start to understand the process better myself if I can write it out).
You can see in diagram “A”
that the harnesses are represented down the side of the tie-up, in a peg plan the harnesses are at the top. To convert the tie-up from “A” to the peg plan in “B” simply convert black squares down the left hand side of “A” into pegs going across the top (from right to left) on “B”.
So in “A” you have a black square in harness 2, treadle 1, in your peg plan you would move that square up the top to Harness 2, Dobby bar 1. Continue with 6, 7, 9, 11, 13 and 15. (see chart “C”),
continue to the next treadle and harness sequence (see chart “D”).
Now take a look at chart “E”, see how in dobby bar 30, harness 2 there is no peg? And that continues in a diagonal to form a “V” – compare that to the treadling plan in chart “A” and notice how there is an “x” in the same position, showing when the shed will be formed and thus creating your pattern.
Now, the one last bit that I’m trying to work out is how this all relates to the threading of heddles into shafts. If I was to just see that treadling plan without the words “treadling” I would have assumed it was the threading plan. I would have turned the chart onto it’s side like this:
I would have threaded the first warp thread into the 1st heddle on shaft 1, the second thread into the first heddle on shaft 2 and so on up to shaft 16, I would then thread the 17th warp thread into the second heddle on shaft 15 (so shaft 15 now has 2 threads) and so back down to shaft 1. In this case, shafts 1 and 16 would only have 1 thread each. Somehow this doesn’t seem quite correct to me…
Really useful tips from the manual:
“There are times you will find it helpful to use blank dobby bars to mark your place in your pattern. For instance, if you need to know where the beginning of a pattern is, leave a blank bar just before the dobby bar corresponding to the first shed of the pattern. When you are weaving and come to this blank bar, no harnesses will raise.”
“Keep in mind that the direction the chain moves can be reversed at any time. This feature can save pegging time and dobby chain. One example of its use is with a pattern where the second half is a mirror image of the first half… by reversing the dobby unit, the second half or mirror image is automatically produced. When using this technique, you may want to leave a blank bar as a signal at the point at which the dobby is to be reversed… This feature can also be used where long lengths of tabby are to be woven between pattern borders. Simply peg up part of the tabby and by repeatedly reversing, as much tabby can be woven as necessary. Here again, use blank bars between the tabby part of the chain and the pattern part.”
(Further reading of how this particular loom operates can be found here on the AVL USA website’s manual)