3. 3D Printing#

This week we 3D printed the FlexLinks we designed last week.

How to use the 3D printers#

The software#

I installed Prusa Slicer from the website. In order to correctly print, we have to give the software the specifications of the 3D printers available to us. These are MK3S & MK3S+ Prusa printers. We should select the usage of PLA filament, with a profile of generic PLA, using a 0.3mm nozzle. Then, click on “Slice now” and “Export to G-code”.

First try#

The first piece I printed was using the following parameters:

Parameter	Value [mm]
Height	1.7
Width	7.8
Space	3.2
Radius of hole	2.4
Edge Space	1.6
Bar Width	0.5
Bar Length	50

This piece turned out to be too fragile. Within 5 minutes of testing the flexible bar the slotted pieces had detached from the bar. The actual flexible properties of the bar were very good. But, the fragility of the piece led me to reconsider some of the parameters.

Second try#

The next piece was printed with the half circle bar instead of the straight bar and with these parameters:

Parameter	Value [mm]
Height	5.0
Width	7.8
Space	3.2
Radius of hole	2.4
Edge Space	1.6
Bar Width	1.0
Bar Diameter	40

The most important parameters that I changed were the width of the bar and the height of the slotted pieces. This would, in theory, make the piece more sturdy, having more contact between the bar and the side of the slotted pieces, and it would give the bar more solidity. In reality the new piece was way more durable than the first one. But, still, when testing its flexibility, the slotted piece broke off from the bar. When looking at the OpenSCAD file that defined the new piece. I noticed that at the edges of the bar, there was only one point of contact with the side of the slotted piece. Therefore, only superficially attaching the bar to the slotted piece, which made the joint very fragile.

Third try#

This final interation was printed using what I learnt from the first two, with the same parameters as the second one. But, now I modified the code for the creation of the straight piece, so that the bar would overlap with the slotted piece. This would give the joint more durability:

else { // straight bar FlexLink
        l=length(n);
        union(){
            piece(n, w, h, x0, y0, z0, a_x, a_y, a_z);
            piece(n, w, h, x0+l+bar_r, y0, z0, a_x, a_y, a_z);
            translate([x0+l-1, y0, z0]) // the origin of the bar is translated by -1 to have an overlap between the bar and the piece
            cube([bar_r+2, bar_w, h]); // bar_r is the length, just easier to use this within the final code
            // I added 2 to the length in order to have more overlap between the bar and the piece than just surface contact
        }
    }

This modification worked. Indeed, the piece is more sturdy and did not break at the joint. Instead the only real limits of the design is the material used to print it, which is still only plastic.

Fourth try#

In this try, I wanted to modify the diameter of the holes to make them fit into a lego piece. I added a small “error” variable that I could modify independently from the code:

for (i = [0:space+r*2:l]) {
        translate([x0+i, y0, z0-1]) cylinder(h+2, r+error, r+error);
        }  

This allows me to change on the diameter of the holes and keep the center of their defining circles at the same points.

In the end, this resulted in the same strength piece, but with holes that could fit into a lego bump. I printed a lego piece with an error of 0.5mm.

This was done by printing a piece with an error of 0.3mm and realising it still did not fit on my lego brick. Then, printing a piece with 0.7mm error and finding that it fit on the lego, but was a bit too loose. Therefore, trying something in between those values, I printed a piece with an error of 0.5mm. This fit on the piece well enough to snap in place easily and not move. On the following image, you can see the three pieces. The one with the 0.5mm error is in the middle and is the only one that fits on the brick and snaps into place without falling.

Working mechanism#

An interesting way to combine these pieces would be to place the pieces in different directions, allowing for two different rotations.