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3D printed kitchen hook

Problem

A set of kitchen tools had to be stored in an accessible way. A horizontally mounted round wooden shaft was a convenient method. An attachment method for the tools and utensils was required.

Hooks bent from wire were tested and found not satisfying. 3D printing was chosen as an alternative.

Solution

A model was created in OpenSCAD. The drawing is parametric, most to all of the dimensions are specified as named variables that can be adjusted for specific desired dimensions.

Version 1

The first iteration was just a hook with a round ring. This was found lacking, as the fit on the shaft was loose and the hook was not staying in position. This was supposed to be addressed by a small wood screw through a side hole, but this solution would make it less than easy to readjust the position of the hooks, reducing the system flexibility.


First version

Version 2

The second attempt involved more precision and a more complex construction. The ring was split and a pair of clamps was added to allow opening the ring by pressing them against each other. The ring was made a little smaller than the shaft, so the material's elasticity provides a reasonable grip on the wood and hinders free movement. Precision is required here - a little too small and the ring won't fit the shaft, a little too big and the clamping force will be too low or the ring will be entirely loose.

Care was taken to draw the pads. They had to be parallel, separated a little, so pressing them together leads to opening the ring. The top one also had to overlap the bottom one, so the shape is printable - the filament has to have something to attach to when it bridges the gap. (At printing, the first two bridging layers don't maintain shape of the inner edge; this leads to emergence of some thin diagonal filaments. These are harmless.)

The pads must have reasonable length. The ring opening has to be sufficient so the ring fits the shaft. For every millimeter of diameter increase, 3.2 millimeters of pads travel length has to be added. This is easy to underestimate.


Second version

Second version

Second version

Insufficient pad length won't allow opening the ring enough. Excessive pad length consumes space and material, may not sufficiently resist buckling under load, and the degree of opening the ring is limited by the material elasticity and strength. The pads also don't maintain parallelism when the ring is open.


Released ring clamp

Opened ring clamp

The parameters in the variables file have to be tweaked. The file is fairly complex and mistakes could have crept in.

Printing results

At 0.3 mm layer thickness, the printing consumes about 110 cm of 1.75 mm filament and takes a little less than 20 minutes of time.

The first prototypes were printed from naturally colored PLA. After few attempts the correct dimensions were reached. The material is fairly stiff but flexible enough.


PLA-printed, on bed

PLA-printed, on bed

Further parts were made from blue ABS. The first attempt used insufficient bed temperature and too high bed-nozzle distance (poorly calibrated printer). The first layer filament therefore did not fuse properly. Forcing some additional line width for the first layer (from 200% to 250%), and forcing the head 0.1mm closer to the bed, rectified this problem.

The material is a little bit more flexible, which is best visible on response to torsion load of the hook shaft. The pads also require a little less force to open the ring.

The hooks grip the shaft well. When closed, they require significant force for lateral movement, and keep their angular positioning.


ABS printed hooks

ABS printed hooks

ABS printed hooks

ABS printed hooks

ABS printed hook, mildly failed

ABS printed hook, correct

ABS printed hook, levers

ABS printed hook, levers

ABS printed hook, levers

Hooks on shaft

Hooks on shaft

In use

In use

In use

In use

In use

In use

In use, a grill on two hooks

In use, a grill on two hooks

In use, a grill on two hooks

TODO


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