Thursday, 30 April 2020

Yarn slack winder

This is another of the lockdown projects where I'm trying to keep myself occupied during the Covid-19 lockdown by challenging myself to a project per week, using only materials from my workshop junk bin.

I don't crochet or knit, but my partner does, and I often end up watching TV whilst having been delegated to idly unwinding a ball of wool.

So, apparently, when crocheting or knitting, it's important to make sure that there's some slack between the workpiece and the ball of yarn. This usually means stopping every so often to pull more yarn from the ball. It can lead to inconsistent tension in the workpiece, making the work uneven.

This gave me an idea to create a yarn dispenser that could be hands-free, and unwind small amounts at a time, to maintain slack.

The OpenSCAD model
The design

The basic principle is to repurpose two rubber rollers (grey) from a printer. The bottom one is attached to a motor, which is housed in the case (red), and supported at the other wide by a support (yellow).
The top roller is attached to two mounts (blue) and is free-rolling.

The two mounts will be attached to their respective parts of the case by screws, where the tightness can be adjusted to allow more or less gap between the rollers, to vary the grip depending on the thickness/density of the yarn.
The yarn will be sandwiched between the two rollers, so that when the motor is activated by a foot pedal, it is pulled between the rollers.

To keep the two sides of the frame separate, they were mounted to a small piece of scrap acrylic I found. It's not a perfect size, but it's functional enough for this prototype.

The 3D printed models are pretty basic, but should anyone want to use them, they're up on GitHub.

The electronics

The motor is some generic DC motor that, like most things in the junk bin, was probably pulled from an old printer.

Most of the circuit for this was was salvaged from the old Smoke Machine project.

The SN754410 was de-soldered so that it would function in a more conventional way, powered from a 9v wall wart, and a TS7805 regular to provide 5v.

The circuit. The SW1 switch allows the direction of the motor to be easily switched. SW2 is the foot pedal that will be pressed to feed the yarn.

The electronics were built into an old business card box, similar to the USB KVM Switch.

With the circuit hot glued in place, a piece of a disposable pen was glued to the button to extend it's reach, so that it would sit slightly higher than the top of the box lid. This means the the circuit enclosure also doubles up as the foot pedal - pushing down on the lid pushes on the pen, and in turn presses the switch.

Finished product
In initial testing, it was discovered that the yarn would veer off to the side of the rollers and become tangled. As a quick-fix solution, I used a scrap of leather, punched a guide hole in the middle and tacked it to the input side of the rollers.