Selectively controllable bobbin thread pull-off mechanism

In a lock stitch sewing machine, mechanism for removing predetermined lengths of thread from a bobbin spool for use in the formation of stitches by a needle including fixed spaced walls between the bobbin spool and needle, a pivoted thread pulling bar having a leg movable between said walls for pulling thread looped under the leg and over said walls from the bobbin spool and into the space between the walls during pivotal movement of the thread pulling bar in one direction, a feed dog, a selectively positionable member, and means for controlling the extent of movement of the thread pulling bar in accordance with the position of the selectively positionable member and thereby the amount of thread removed from the bobbin spool by the bar, said means including a member actuable by the feed dog and in sliding engagement with the selectively positionable member for imparting movement to the selectively positionable member, the said means also including an angular extension on the thread pulling bar engageable by the selectively positionable member at a location dependent upon the selected position thereof.