IV. FabLab tools#
A. 3D Printing for repair#
In this first part of the fourth module, the goal is to repair a broken object using 3D printing. Using 3D printers to repair an object involves a certain number of restrictions as well as a detailed thought process. This process and restrictions are extensively described in this guide. I will describe here below how I put it in use.
Very shortly, the guide helps you to analyse the feasibility of repairing your object and how to do it. Indeed, 3D printed parts are in plastic (PLA, …) and cannot be as resistant as a metallic part or a conventionally thermoformed plastic. Moreover, modelling the broken part can be challenging if part of it is missing or if it is entirely missing.
According to those principles I chose to try and repair a radio handle.
Analysis#
As you can see, it is not exactly the handle that is broken but rather the hooks of the handle. Both of them are broken, but at different spots. One of them is broken in its main part (as you can see on the first and second picture) while the other is broken at the groove of the cylindrical part that rotates inside the radio. This groove actually is supposed to hold an E-clip (a sort of circlip) avoiding that the rotating part of the hook slides out of the radio.
The parts had previously already been temporarily repaired with superglue, but it did not held on. Hence, this was not an option anymore. Hence, the obvious solution was to redesign a new hook part and printing it twice.
Redesigning#
I worked with Diane BILGISCHER on the redesign, remodelling and printing of the parts, I therefore invite you to look at her documentation as well.
As you can see on the previous pictures, the hooks had several grooves on the outside. As those were decorative, we decided not to loose our time trying to reproduce them. The angle in the previous hook made the radio more ergonomic and esthetic. However, foreseeing that it would probably create stability issues during the printing process, and need support, we decided to bypass it. In our design we simply replaced it by a right angle.
Here are some plans I draw :
Please do not mind the slight proportions variations, as I draw freehanded. The little dotted lines are meant to represent the decorative grooves. As you can see on the second plan, we also decided to remove the different surface levels when we did not see their necessity.
All in all, we tried to make the appropriate design the simplest possible, as it would be easier to model and to print.
Remodelling#
We modeled our design using OpenSCAD, as we were both more familiar with it than with FreeCAD.
The main hook is composed of three main “cubes”, numeroted on the first plan.
- A long and thin one, like a strip, linking the cylindrical rotating part to the piece going inside the handle.
- A more cube-shaped one, going up against the handle and the first cube.
- A long and mildly thick one, going inside the handle.
We measured the different dimensions and distances of those 3 pieces to code them :
// Authors : Diane BILGISCHER & Louis JONAS
// Date : October 2023
// License : Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-nc-sa/4.0/)
//Parameters
dim_strip=[60.75,15.17,4.22];
dim_rectangle=[14.95,15.17,12.62];
dim_attache=[9.78,9.78,32.62];
// Main script
cube(dim_strip);
cube(dim_rectangle);
translate([2.65,2.75,0])
cube(dim_attache);
We then had to add the cylindrical rotating part. After measuring its size and position, we divided it in 3 parts :
- The base of the cylinder.
- The groove for the circlip.
- The end of the cylinder.
The first and third part have the same diameter but not the same height. We therefore added new parameters as well as some lines in the script. This is the final version of our model :
// Authors : Diane BILGISCHER & Louis JONAS
// Date : October 2023
// License : Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-nc-sa/4.0/)
//Parameters
$fn=50;
dim_strip=[60.75,15.17,4.22];
dim_rectangle=[14.95,15.17,12.62];
dim_attache=[9.78,9.78,32.62];
diam_cyl=6.68;
diam_rondelle=3.90;
h_cyl1=3.50;
h_cyl2=2.80;
h_rondelle=0.79;
// Main script
cube(dim_strip);
cube(dim_rectangle);
translate([2.65,2.75,0])
cube(dim_attache);
// Adding the cylindrical rotating part
translate([49.88+diam_cyl/2,4.44+diam_cyl/2,4.22])
union(){
// First part of the cylinder
cylinder(h=h_cyl1,d=diam_cyl);
// Groove for the circlip
translate([0,0,h_cyl1])
cylinder(h=h_rondelle,d=diam_rondelle);
// Extremity of the cylindrical rotating part
translate([0,0,h_rondelle+h_cyl1])
cylinder(h=h_cyl2,d=diam_cyl);
}
Here below you can see the final render :
Printing#
The first printing was kind of a draft. There were some issues as we expected and that is why we chose to use low quality printing settings and to only print one copy.
Firstly, when we tried to fit the piece inside the handel, we realised we had made it slightly too big. It was extremely difficult to get it in and broke as we tried to pull it out. Secondly, as it is quite small we hoped it was not necessary to support the gap created by the smaller diameter of the cylinder where to circlip has to fit. Unfortunately, that was not the case, and even if it is not that clear on the picture, the remaining of the cylinder upside that part was skewed.
To resolve those issues we simply slightly increased the gap between the dimension of the inner handle and that one of our part, as well as we added support around the cylinder. Despite the error that occurred during the printing, this proved to be working :
You can see on the first picture that the last layers of the part that goes inside the handel seem a bit blurry. This was due to the filament adhering too much to the reel, making it hard for the printer to convey the matter.
B. Computer Controlled Cutting#
Lasercutters use 2D design files to get their instructions. Thus in order to cut something you have to be able to design using 2D softwares such as Inkscape.
Inkscape#
Inkscape is a free and open-source vector graphics editor that is available for GNU/Linux, Windows, and macOS. It offers a rich set of features and is widely used for both artistic and technical illustrations such as clip art, logos, typography, diagramming, and flowcharting. It uses vector graphics to allow for sharp printouts and renderings at unlimited resolution. Inkscape uses the standardized Scalable Vector Graphics (SVG) file format as its main format. It can import and export various file formats, including SVG, AI, EPS, PDF, PS, and PNG. It has a comprehensive feature set, a simple interface, and is designed to be extensible; users can customize Inkscape’s functionality with add-ons. It also provides you with integrated official documentations and tutorials.
On the left pane, you will find the basic tools, allowing you to easily draw a rectangle, an ellipse/a circle, polygons (star-shaped by default) and spirals. The colour bar underneath displays numerous shades of colours; when an object is selected, clicking on one of those will set it as the filling colour of the said object. The upper toolbar has two displays, a generic as you can see on the screenshot and a specialised. The generic one allows you to do simple operations on an object or a path : translations, rotations, changing its level on the canvas, … The specialised one will display the settings specific to the type of object you selected; to display it you have to select in the left pane the corresponding type of object. The right pane is customisable, with more detailed settings and operations. You can also find most of those in the differents menu tabs, above the upper toolbar.
Objects can be converted in “path” : the vectorial form strictly speaking. A path can also be edited but not in the same way. For example, you can also display text on your canvas (available in the left pane), it is then a “text” object. While it is considered a text object you will be able to easily change the displayed text (correcting a spelling mistake, …), but as soon as you convert it into a path, you cannot edit the text anymore.
To create more complex designs, you will most likely use the basic objects and assemble them in different ways. All of the boolean operators are available, you can make unions, differences, intersections, exclusions, divisions and other things as well. I recommend you try by yourself.
The different official tutorials are available in the “Help” tab. They are interactive : the tutorials documentation has been made in Inkscape and provides objects you are invited to test upon along the tutorial.
Lasercutting#
On a lasercutter you can generally choose both the power and the speed of the laser. Your choice of these, as well as the type and thickness of the material you are using will determine the result of the laser. You can engrave your material by going fast at low power to create patterns, or choose a lower speed with higher power to make sure to cut through it (vector cutting).
In most of the softwares of the lasercutters, having different colours in your SVG file will allow you to choose a different configuration of power and speed for each present colour.
The kerf#
When cutting on lines you draw, you should know that the laser will position in the middle of it, so that the thickness of your lines are of little importance. However be wary that the laser has a certain thickness or diameter, called “kerf”. As you know, lasercutters work by burning part of your material, so when you cut a piece its dimensions will be reduced by the size of the diameter of the laser. If the size of your piece is important, you should remember to add it in your design dimensions !
The tricky part is that this diameter varies with the thickness of your material and your choice of speed and power (closely linked to the type of material). Before cutting your piece you should establish how big that diameter is. To do so, you should test the power and speed you want to use on the same material you will be using. Once you have made your choice, with those settings cut this pattern in your material :
When all of the rectangles detach, fit them in the frame and push them all on one of the sides. You can now easily measure with a caliper the gap created by the several transits of the laser. In this instance, there are 9 rectangles and 10 lines. Hence, by dividing by 10 the length you measured, you get an average kerf for that material at those settings.
Precautions and safety#
Lasercutters are equipped with several safety mechanisms to make sure you cannot touch the laser. Nevertheless, some risks remain. You should for example never stare at the laser for a long period, unless you wear special glasses. All materials cannot be cut, there are lists of recommended, allowed but not recommended and forbidden materials. You should always check them to be sure but in general, if it reflects the light well, do not try it ! Some materials are forbidden because of the chemicals they emit in their smoke when burned. You should always stay next to the cutter while it works to prevent any issue.
Regarding smokes, be sure you always turn on the smoke extractor corresponding to your cutter. You should also know where the emergency stop button and the extinguisher are. You will find more details and references here.
The lasercutters#
I mainly used the Lasersaur, and although the positioning of your material as well as that of the laser are not easy, it works quite well. Here is a short guide (in French) describing how to use it. And here is the guide for the Epilog Fusion Pro 32.
My construction kit#
After our formation we had to design a construction kit of a 3D object that could be cut by the lasercutters. As Christmas is slowly coming and I love nature, I unoriginally (so I have been told) decided to design a fir tree. I created it by using Inkscape.
Designing#
I first designed the trunk of the tree, with a simple rectangle. I then added a sort of root, that would provide stability to my object. To design this base I started by a rectangle, then removed 2 circles from its upper corners, added two smaller circles next the base (left and right). I then united them and converted it into a path, which allowed me to create a smoother curve with the “Node tool” by removing and changing the type of nodes composing the curve. I then stacked and united the trunk with the root.
For the branches I used the “Pen tool” to make a triangle with a vertical line. Then with the node tool, I curved the lines in what I considered to be an esthetic way. I copy pasted that first branch, flipped horizontally its copy and put them next to each others. With the node tool I removed the 2 vertical lines. This is done by pressing the “Delete segment between two non-endpoint nodes” button, after you selected the two node delimiting the vertical bar. My next step was to rejoin the 2 branches by selecting the nodes facing each others and pressing on “Join selected nodes”.
I placed that finished branch centered on top of my tree, after scaling it to match the trunk. To cover the whole tree, I copy pasted that branch rescaling it each time by 120% as I lowered it down the trunk. You can easily rescale an object with the right panel :
Once I covered the whole trunk I used the “Shape Builder Tool” to unite them all together.
To assemble my kit I decided to make two of those tree surfaces and dispose them perpendicularly, forming like a cross (from the top view). They would have slits (you make them by removing a long rectangle in the center of the tree) that would combine : one in the upper part of the first copy and one in the lower part of the other copy.
Cutting#
Of course the width of the slits had still to be determined, depending on the thickness of the material I would use and the corresponding kerf. Moreover, for the two parts to hold together, the slits should be slightly thinner than calculated.
For the Lasersaur, using 95% power at 500mm/min on a 3.35 mm thick MDF board (actually the one you saw in there), I measured a 0.49 mm kerf. Thus I made slits 2.80 mm wide (I rounded down 3.35-0.49; we subtracted two times half the kerf, as the kerf is the diameter and you only loose the radius on the piece you keep, but you cut on both left and right). With this information I was able to make my final design :
Here are some pictures of the cutting :
Results#
To my great surprise, it fitted very well at the first try.
