Washing Line Prop Hook

The following project was created due to the necessity to make a repair and at the same time save money.

Created with TinkerCAD Block Code and 3D printed.

The broken prop* head to be replaced is small in comparison to the over size of the item being repaired and after an internet search which drew a blank for a replacement, it seemed a waste to consign the metal pole which made up the bulk of the prop to the scrap when the pole was perfectly fine.

*A prop is a support and in this context is used to support a washing line.

TnkerCAD

Cura

3D Printer.

Filament (SUNLU PLA+ Black), although other options with regard to robustness exist such as ASA, ABS or PETG.

M4 nut

M4 Bolt 40 mm

Tools

Allen keys

Vernier calipers

4mm drill bit

Needle files

Sanding paper

Know your tools and follow the recommended operational procedures and be sure to wear the appropriate PPE.

No affiliation to any of the suppliers used in this project, feel free to use your preferred suppliers and substitute the elements were appropriate to your own preference or subject to supply.

Links valid at the time of publication.

A number of considerations were required in the design process.

1: Fit the existing pole.

2: Decide on a method to fix it in the tube.

3: Fit the existing clothes line.

4: Be able to support a weighted clothes line.

5: Easy to print without supports.

6: Simple to assemble.

7: Simple in form.

Being aware that the commercial product was also made of plastic and became brittle over time.

The first iteration of this design has survived one season of use in all weathers using PLA+ (as this is what I had to hand), in the relative short term there has been no issue, only time will tell how well it will fair in the long run.

Be aware that filaments of the same type may have a wide degree of robustness to the weather subject to formulations, colour and thickness and some material types may be more suitable in the long term.

Measure the internal pole diameter. This is 13.5 mm.

Measure the width of the line. This is 3mm.

Now to the shape of the head.

This needs to be some form of hook. (Defined as a curved or bent tool for catching, holding or pulling something).

This needs to catch around the line but not fall off due to swaying.

To improve strength decided on a rigid form with no moving parts.

Ultimately, a spiral was chosen making it easy to hook on the line and manipulate the hook to position the line in the centre of the spiral.

Being a spiral it can be expressed mathematically and lends itself to be created in code in this case using Block Code.

If we consider a circle and how it can be generated in code.

Any point on the circumference of the circle can be referenced from the centre using Pythagorus theroem.

Where: Radius = Hypotenuse, Base = X and Altitude = Y

Radius = sqrt(X^2 + Y^2)

Therefore, all points are equidistant from the centre, this distance being the radius.

However, in order to generate a circle the values for X and Y are required.

From a trigonometric perspective:

X/Radius = Cosine(angle) and Y/Radius = Sine(angle)

With one revolution equal to 2Pi radians or 360 degrees, sin(angle) or cosine(angle) will range from -1 to +1.

Knowing the Radius and the angle, X and Y can be calculated.

Circle

Applying this in an OpenSCAD code example:

for (i = [0 : abs(1) : 360]) {

 translate([(sin(i) * 10), (cos(i) * 10), 0]){

  cylinder(r1=1, r2=1, h=1, center=false);

 }

}

This executes a loop where the angle starts at 0 and ends at 360 with 1 degree increments.

The point on the circumference is defined by the function of the angle multiplied by the radius = 10.

At the point is plotted a vertical cylinder (Radius =1 & Height = 1), these overlap creating a solid perimeter.

Spiral

This is all well for a circle but we need to create a spiral.

This is created in a similar manner to a circle however the perimeter does not meet, starting from the centre with progressively larger twists gradually increasing the radius.

for (i = [0 : abs(1) : 360]) {

 translate([(sin(i) * (i / 32)), (cos(i) * (i / 32), 0]){

  cylinder(r1=1, r2=1, h=1, center=false);

 }

}

The main difference between this code and the previous code for the circle is in the multiplier. Rather than a fixed value equal to the radius there is now a value equal to a fraction of the radius. (i/n) where n = 32. Therefore, the radius gradually changes from 0 to 11.5

This gives us the basics of the spiral but we may wish to make adjustments with regards to the size (i/n), number of spiral loops (i), the rate the spiral moves out from the centre (n), the eccentricity of the circle due to different values of (n) applied to the X and Y co-ordinates.

Securing the hook to the prop simply requires an M4 Allen key.

This was achieved using a wedge nut, this is a cylinder with an inclined end that contacts another incline.

As the nut is tightened and due to the wider diameter bore of the peg the nut is forced to try and slide away from the other inclined cylinder. This offset presses the peg and wedge nut combination against the side of the pole in opposing directions wedging it in place.

The code for the final object is created using TinkerCAD Block Code.

Spiral

The first part of the code creates the basic spiral that forms the hook.

This is made using a cylinder with radius 2.5 mm and 13 mm high, which is within a loop.

Start and end points from the basic spiral adjusted to create alignment with the pole for easier engagement.

Step increment of 3 rather than 1 due to primitives limitation of 200, this creates a ridged textured on the hook due to the effect of the overlap of the cylinders that make up the spiral.

This creates a total of 170 cylinders overlapping their predecessors to form a continuous spiral of 1.5 loops.

The loop is eccentric in nature to create a slightly less regular sitting point for the line. This is expressed in the multiplier with values of (i/32) and (i/35) for the two co-ordinates.

However, the inner curved surface of the spiral which is horizontal to the line enables the line to move easily around this curve as the pole sways back and forth and therefore possibly work loose.

In order to reduce the likelyhood of this event occuring, ridges are placed at intervals on the inner curved surface to provide additional engagement with the line.

These ridges are also made of cylinders with radius 2.3 mm and 13 mm high also in a loop, creating 16 ridges.

Holes are created on the lower part of the spiral to enable an M4 cheese head Allen bolt to sit at or just below the main inner curve.

Directly in line with this and passing up and through the two spiral arms above, 2 x 4 mm holes are made.

The holes allow an Allen key to pass through and into the Allen bolt head to fix the head in place.

Peg and wedge nut

Attached to the spiral at the lower end is a cylindrical peg with cylindrical wedge nut.

Formed by splitting a cylinder of radius 6.5 mm and 30 mm long with a rectangle of width 3mm placed at an angle of 30 degrees creating two inclinded surfaces and a separate wedge nut.

The hole in the wedge nut is designed to be slightly smaller than the diameter of the bolt such that is self taps the thread as tightened.

However, for extra security, provision is made to fix an M4 hex nut in a recess in the bottom of the wedge nut.

Having created the object, it's exported as an STL file.

Import the STL file into the slicer. (E.g.Cura)

Printer settings:

Filament: Black PLA+

Infill Density: 100%

Layer Height: 0.15 mm

Build Adhesion: Skirt

Support: No

Overall Size: 65 x 40 x 13 mm

Filament length: 4.85 m

Weight: 14g

Print time with these settings : ~2.5 hrs

The hook is aligned horizontally to the printing surface which adds strength as each layer runs the full length of the object. Effectively a stack of flat spiral springs with the grain running at 90 degrees to the line.

Post processing may be required to remove any aberrations, inparticular the peg and wedge nut which may obstruct insertion into the prop or the holes for the bolt and Allen key access hole.

The 3D design can be found below and on TinkerCAD: Prophook

Feed the M4 bolt through the hole at the top of the spiral and down to enter the peg.

Feed the Allen key down through the same hole into the M4 bolt head.

Whilst holding the bolt in place screw the wedge nut (incline aligned to incline), onto the bolt.

Once the bolt starts to bite and hold it in place insert the nut into the recess and continue to tighten the bolt until it holds the nut.

Continue to tighten the wedge nut until it is in close proximity to the peg but still inline.

Roughen the surface of the wedge nut with sanding paper.

Remove any grease or oil from the end of the pole and roughen the inner surface with sanding paper.

This will help reduce the likelyhood of the head slipping in the prop.

Insert the peg/wedge nut assembly into the prop and continue to tighten the Allen bolt until the head is locked in place.

With washing on the line, hook the open end of the head over the washing line and move it around the spiral gap toward the centre of the line to rest on the upper curve of the final spiral.

Push the prop up and plant the pole into the ground.

Thanks for reading and hope you found it of interest.