Notes for left-handers mak­ing thread

On a shoe and boot­makers for­um I read someone was hav­ing trouble with their threads unwind­ing at the slight­est pro­voca­tion. They knew the thread and code were good because both of them had been used by oth­er people before.

The pic­ture they pos­ted showed that the thread had been plied up using the oppos­ite twist than would nor­mally be used, which made me real­ise that a left-hander might end up doing the same thing if they were mir­ror­ing instruc­tions writ­ten by/for right-handers.

When I ply up a thread I twist it up by rolling it down my right thigh, away from my hip towards my knee, with my right hand res­ult­ing in a clock­wise twist if you look at the end of the thread. If you rolled the same ply down your left thigh with your left hand you’d end up with an anti-clock­wise twist to the thread, which won’t want to stay plied up because the res­ult­ant plied cord is an S/S twist instead of an S/Z twist and cords plied with the same twist as their strands won’t stay plied.

If you are left-handed and you make threads on your left thigh, you need to break the thread by rolling it up your thigh, knee-to-hip, and ply the cord the same way.

When you ply up a cord the twist of the ply has to be the oppos­ite of the twist of the com­pon­ent strands, in oth­er words the twist you ply the cord with should be the same as the twist you use to break the indi­vidu­al strands.

The reas­on for this is that if you ply with the oppos­ite rota­tion from which the strands were spun, then the fibres in the final cord lay straight. If you ply with the same twist you are pla­cing addi­tion­al twist on the already-spun fibres, which is then going to nat­ur­ally want to untwist.

The dif­fer­ence between an S-twist and a Z-twist can be a bit hard to explain, and google wasn’t vend­ing with any­thing use­ful so I drew this pic­ture: [update: It has been poin­ted out to me by someone who knows far more about fibre work and spin­ning than I do (thanks CW and AdW) that this pic­ture is back­wards. What is labelled S should be Z and vice-versa. I will fix it as soon as pos­sible.]

I’ll fol­low this up with some pic­tures of S/Z and S/S plied cords that show the fibre dir­ec­tions which will hope­fully cla­ri­fy this explan­a­tion.

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