Page 49 - Shawl Weaving Artisan - TT

In pegging, the upper row of holes in the lug represents
the first pick.
Cross border dobby
Cross-border Dobby is used when two different weaves
are required to be woven using the same number of
healds.
Cross-border Dobby eliminates the high number of
wooden legs that are required in normal dobbies.
Types of cross-border dobbies
1 Two cylinder cross border Dobby
2 Three cylinder cross border Dobby
Dobby faults: The common problem in the dobby is
Jack missing. The heald shaft is not lifted when required
and the weft floats across the warp end giving rise to the
fabric effect called stitching.
Stitching is sometimes caused by shuttle flying. Warp
thread breaks occur because of shuttle fly causing a
major fabric defect.
The causes of Jack’s missing (Heald not lifted) are:
1 Bent wooden peg in a lag.
2 The wooden peg is worn out due to frequent use.
3 The spacing between the lag should be uniform and
the cylinder should be perpendicularly positioned
below the feeler. if the lags are not spaced properly
more feelers may be lifted causing the lifting of
improper jack.
4 The pattern barrel in which the wooden lag rotates
should not move laterally.
5 The needle operating hook may get stuck and the
jack is missed, good oiling is necessary.
Settings 6 The wooden peg will be broken and therefore jack is

1 The driving rod connecting to the crank attached to missed.
the bottom shaft of the loop and T-lever must be set to 7 The hook may come off from the knife in the middle
the appropriate length. If the rod is too short or long, of the stroke, causing a missing jack.
one set of the hooks will travel more distance than the
other. Ruti cam dobby: The ruti cam dobby is negative in
action i.e. the heald are lowered because of the spring in
2 The length of the driving rod is adjusted such that this dobby. The knives are pushed forward by the pair of
T-Lever is horizontal when the crank attached to the cams. The knife will come back and always be in contact
bottom shaft is in a horizontal plane either in the front with the cams because of the spring. Here dwell of about
or back of rotary its stroke. 1/3 pic is achieved. The selection of the hooks is made
3 Crank and T-lever are kept in the horizontal position of paper patterns instead of wooden pegs.
and now two knives are Adjusted by draw bolts so Positive cam dobby: The positive cam dobby is called
that they are equidistant from their slots. The pattern positive because lifting and lowering of the heald is made
cylinder is rotated by a ratchet wheel. The cylinder positively. The dobby has a cam that will give oscillation
is rotated by 1/8th revolution for every 2 picks. the to the griffel and returning bar through the lever i.e.
cylinder is held steady by a flat steadied star wheel. when the griffel is engaged with the hook it will pull one
The Pawl regulates through the star wheel. The T-lever side of the bulk and at the same time return the bar to
is lifting knives in are extreme position there should be push the other side of the bulk. Suppose heald is to be
a quarter-inch clearance between the tip of the pawl kept down on the next pick, the bottom hook will not be
and the teeth of the cylinder ratchet. engaged in the griffel, it is looked in the locking bar and
For right-hand Dobby visible outermost feeler which thus engaged in the griffel, it is looked in the locking bar
operates the bottom drawer hook, the pattern cylinder and thus the other end of the bulk will not move even
rotates clockwise. the upper return bar pushes to the bulk towards the stop
In the left-hand Dobby, the first feeler is a straight feeler and heald will be down. in short, it returns the bar stop
and locking bar together making the dobby positive along
that acts on the top hook.
with grooved cam.
Textile & Handloom: Shawl Weaving Artisan : (NSQF - 2024) R.T. Ex.No 1.3.27 39