Unit 1: Jacquard and Dobby looms
Advance Weaving notes · PTU syllabus (BSTD 310-20)
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Unit summary
Jacquard and dobby looms allow complex patterns that simple shaft looms cannot. This unit explains how each works, the constraints of warp and weft and the limits of drafting and lifting plans.
After this unit you can
- Compare tappet, dobby and jacquard shedding
- Describe how a jacquard loom controls each warp end
- State the design limits of dobby and jacquard looms
- Relate the number of shafts to weave complexity
PTU syllabus topics
- Understanding and designing on Jacquard looms and Dobby looms
- constraints of warp and weft
- limitations of drafting and lifting plans
Controls
Groups of warp threads via shafts
Each warp thread individually
Design size
Small geometric repeats
Large, complex figures
Shafts
Up to about 24–28
No shafts: hooks and harness
Examples
Small checks, textured shirting
Brocades, tapestries, damask
Topic 1
Shedding mechanisms
- 1Tappet (cam)
Up to about 8 shafts, simple weaves
- 2Dobby
16–36 shafts, small geometric designs
- 3Jacquard
Each warp end or group controlled separately, large designs
| Feature | Tappet | Dobby | Jacquard |
|---|---|---|---|
| Shafts / control | Up to 8 | 16–36 | Individual ends (hundreds to thousands) |
| Control medium | Cams | Pegged lattice or electronic | Punched cards or electronic |
| Design size | Plain, twill, satin | Small geometric, checks, stripes | Large floral, figural, brocade |
| Cost | Low | Medium | High |
Jacquard gives the greatest freedom at the highest cost and set-up time
Topic 2
The jacquard loom
On a jacquard loom each warp end (or small group) passes through its own heddle, hooks and a harness cord; a punched card or electronic signal raises selected hooks for every pick, so any ends can be raised or lowered.
- 1Design on paper or in software
- 2Pattern converted to punched cards or digital file
- 3Cards read by needles and hooks
- 4Selected hooks raise harness cords
- 5Warp ends lift to make the shed
Jacquard fabrics include brocade, damask, tapestry, matelassé and woven sarees such as Banarasi and Kanjeevaram.
Topic 3
Constraints of warp, weft and plans
Limits arise from the number of shafts or hooks, from the repeat size (a motif cannot be wider than the number of ends set on the loom), from floats that must be kept short to avoid snagging, and from the fineness of the reed and yarn. A design is first reduced to a drafting and lifting plan: if it needs more shafts than the loom has, the design must be simplified or woven on a jacquard.
Key terms
- Dobby
- Loom controlling 16–36 shafts
- Jacquard
- Loom controlling individual warp ends
- Harness
- Cords connecting hooks to heddles
- Float
- Yarn passing over several yarns
- Repeat size
- Width and length of the pattern unit
Quick revision
- Tappet < dobby < jacquard in design capacity.
- Jacquard uses punched cards or electronic files.
- Plans must fit the number of shafts available.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What is a dobby loom?
- Q2.How does a jacquard loom select warp ends?
- Q3.Name two jacquard fabrics.
- Q4.What limits the repeat size?
- Q5.Why must floats be controlled?
Long-answer questions
- Q1.Compare tappet, dobby and jacquard shedding mechanisms.
- Q2.Explain the working of a jacquard loom and its design limits.
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