I had a look into how the needle is controlled by the carriage in this video (I’ve removed a few needles to help with the video). Obviously the yarn wouldn’t actually pop up on top (it would be caught beneath the bed), but it shows what happens.
There are four “needle positions” on my machine: A,B,C,D.
- A is the “unused needle” position.
- B is the “use this needle” position.
- C + D appear to be convenience positions to help with the manual operation so you can temporarily “park” needles for the next row. As this will be automated I’m assuming I can ignore these completely.
Imagining what happens as the carriage moves linearly across the bed gives a cosine:
There are two areas of trickiness here:
- The top of the cosine is shown as a shaded area: this is because – on my machine – the stitch size is variable (unsure of correct terminology here!). This translates physically into “how far back do you pull the needle after you’ve caught the yarn”, hence the shaded area.
- To keep the stitches event, the needle needs to be returned to the exactly same position it was before the yarn was caught. Since the carriage runs in both directions the mechanism needs some trickery to deal with this. (This is hard to explain without a carriage model, coming soon)
Note: How the needle catches the yarn is a different area, so I’m going to ignore this for now.