SIDE WEFT FORK MOTION
The basic principle of the side weft fork lies in the fork and grate. A metal grate (Fig: 1-c) is placed between the end of the reed and the shuttle box mouth on the starting handle side. A weft fork made of light metal which has three prongs bent at right angles is situated in front of the grate. the complete weft fork motion is illustrated at fig:1-b.
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| A=Weft Fork, B=Weft Holder, C=Fulcrum, D=Knock off Lever, E=Hammer Lever, F=Grey Hound Tail, G=Weft Fork Cam, K=Grate, S=Starting Handle. Fig: 1(a, b, c) Side weft fork motion |
A weft fork A with a single tail hooked at the end is held by a weft fork holder B at C .The other end of the holder is held by knock off lever D, which is in contact with the starting handle when the loom is in running.
The tail end of the fork is slightly heavier than the forked end. A hammer lever E fulcrummed at X is connected to a greyhound tail lever F, the bottom end of which is resting on a weft fork cam G which is fixed on the bottom shaft. During the rotation of the bottom shaft the cam raises the greyhound tail lever on every two picks and causes the hammer lever to rock towards the loom front.
A channel is cut in the wooden race board H opposite the weft fork so that when the slay comes forward to beat up position the weft fork prongs will remain below the raceboard level until it is touched by a weft thread lying across the channel from the selvedge to the shuttle.
In this case the shuttle should be on the starting handle side. If the weft thread is not broken or missing, it will push the weft fork prongs ,thus lifting the hooked tail clear of the hammer lever E. At the same time the rotation of the cam G Makes the hammer lever move towards the front rest. In case the weft is absent either through breaking or from running out, the weft fork remains horizontal and the prongs pass freely through the bars of the grate. Then the hook tail of the fork is caught in the notch of the hammer level E as shown in fig: 1-b and when this lever moves towards the front rest it carries the fork along with its holder resulting in the weft fork lever D pressing against the starting handle S and knocking off the loom (fig: 1-b).
One fault in the mechanism described early is that the weft fork lever and the holder move in an arc of a circle because of the fixed fulcrum of the weft fork lever. This sometimes causes the prongs of the fork to hit against the side wall of the channel in the race board and cause damage. In the British made Northrop looms this arc of movement does not exist since the weft fork acts directly upon the starting handle with a straight backward push.
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| A=Weft fork, B=Weft fork sliding bracket, C=Fixed bracket, D=Knock off lever, E=Starting handle, spring Fig: 2 Weft fork acts directly upon the starting handle |
In the mechanism illustrated in fig: 2 the weft fork A is mounted on a starting bracket B which slides forward and backward in a fixed bracket C.As usual the hook tail of the fork is caught in the notch of the hammer lever on weft failure and the backward movement of this lever will push the knock off lever D, Thus the releasing the starting handle E. The spring S returns the sliding bracket B to its original position.
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