What is a Lockstitch - my second try at posting this
A lot of the basic ground has been covered but perhaps I can add to it a little. In spite of that I have a problem - where to start?
Most definitions of this term seem to originate from the machinery manufacturers, so perhaps I should start there. When the heavy stitching machines were invented, the ones for stitching soles on rather than sewing uppers, the machinery quickly went in two directions. One group uses a single thread and produces a simple chain stitch, the other uses a second thread in a bobbin and produces a lockstitch. Examples of the first are the McKay (or Blake) machine and the Goodyear Welt sewing machine. The best example in the second group is the curved needle outsole stitcher, known by various names according to which country you are in. These include Landis, USM Goodyear Rapid, Frobana, Pedersen, and many more.
The early developers of the outsole stitcher had to convince customers that their machine could produce a stitch comparable to the hand stitching. This could not be done with a single chain-stitch machine. So they did the next best thing and used two threads looped over each other in the middle of the material. Externally, this looks like traditional hand stitching. Where the two threads loop over each other the machine makers called the “lock”, hence the machine was called a lockstitch machine.
The difference between the lockstitch seam produced by machine and traditional hand stitching is simply that with hand stitching (or sewing) each end of the thread is passed right through the material then loops back through the next stitch hole. With the lockstitch, the thread is pulled (or pushed) through the hole to form a loop on the opposite side of the material, then the other thread end is put through the loop and the first thread is pulled back just enough for the loop to finish up in the centre of the material thickness.
This is hard to describe in words. Below are two cross-sectional drawings. Both are produced by a “lockstitch” machine. The first is a lockstitch where the lock is buried in the centre of the material as it should be.
2309.gif
In the second diagram, the machine tensions are wrong and there is no real lock at all.
2310.gif
As has been mentioned above, this kind of stitching can be produced by hand with a jerk needle. I cannot think of any reason for copying a machine stitch, when the same amount of effort can produce the vastly superior hand stitching (or sewing), which no machine can copy.
Many hand boot/shoemakers speak of “locking” threads. They are nearly always referring to techniques similar to those already described here by DW and others. I personally would very unhappy if such techniques are called a lockstitch. Simply because the term has been used for over 100 years to describe the machine-made stitch spelt out above.
However, as always in our trade, words mean different things to different people. All I am quoting here is the common usage in a number of countries by many hundreds, if not thousands, of individual people.
Frank Jones
frank.jones@shoemaking.com
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