Locking Curtain Ring – Vòng treo rèm có khóa

This model came into existence when I walked around my apartment to search for things that could be fixed. I came across the shower curtain and thought to myself that a curtain ring would be an easy start.

Print Instructions

Crank up your perimeter count so that if all layers the bending part of the hook is printed by parallel lines. PETG will give the best results, PLA worked in my testing but is not as durable.

Design Features

I have to admit, that I'm at a point where I can't even design a simple plastic hook without using trigonometric functions. 

Printable Shape

The original I used as a reference are roughly 60 mm tall, 40 mm wide and have a 6 mm cross section. Round objects are not printable and so we get to the first use of trigonometry. 

Strictly speaking we would need to divide that by our layer height, take the integer part of that number (floor) and multiply by our layer height again, so that we get to full layers.

Installability

I've seen on pictures at Amazon that manufactures claim that their product can be bend open to fit over a closed curtain rod. The hooks that currently hold my shower curtain may've gotten fragile over time, but they will most likely not survive bending. I don't want to disassemble anything, so my target was to assure bendability. This is easily achievable by putting the opening at a position where the maximum leverage can be utilizes, thus at the top or bottom. 

But an opening at the bottom would render the hook useless and an opening at the top makes it just as easy to pop off as it is to install--

Locking Mechanism

To come around the beforementioned shortcoming in my proposed solution to “Installability” I added a locking mechanism that can either be placed at the top or bottom. A well placed rake angle at the locking notch utilizes the pulling forces from a curtain to keep the hanger shut.

Pretension

To increase the “Installability” even further and get some tension on the locking mechanism I opened the hook by a few degrees. Doing this get us the problem that the desired target radius ( width / 2 ) can not simply be set as a sketch dimension anymore. In it's opened state the radius is different but the length of the material (at it's neutral axis) stays the same. This is the second time where this design makes use of trigonometry. The circumference of a circle is calculated by it's diameter times Pi.

half of that is what we use in our hooks lower half circle. When we open the hook by 15deg, the arc spans not half a circle but 180deg - 15deg. So our new circle has to be bigger.

Bigger by roughly 9%. With that value we calculate the radius that yields our desired arc length. If you are really interested in this, figure out why we don't need PI in this anymore!

The calculation relies on the fact that the neutral axis is exactly in the centre of our sweep. In reality it never is. In a situation like this I typically apply the math, print a test piece and take measurements from that. If my diameter on a closed hook would be 34 mm instead of 35 mm I address that by simply adding a factor of 35 mm / 34 mm = 1.03

To learn about the usage inside of Fusion 360 aswell as some other nifty details find the source file in the download section.