This week’s group assignment covers the features of the laser cutter in our lab, such as kerf values, power, speed, frequency through various tests.
While I was searching the internet for laser cutting projects, I came across this “screw reinforced joint”. It was interesting to me because I would like to experiment with combining laser cut profiles with other materials and joining methods. I decided to give it a try.
After last week, I wanted to also try out FreeCAD as an alternative to Fusion 360. It was my first time using this software, so I followed this tutorial.
The default settings for FreeCAD need some tweaking to ensure a smooth user experience. When you open the settings, this is the window that you should see:
Here are some settings I changed with the help of the tutorial:
I wanted to model something simple since it was my first time using FreeCAD, therefore I decided to replicate the screw reinforced joint example I found online.
In FreeCAD, there are several “workspaces” that allow the user to utilize different parts of the CAD workflow. For our purposes, we use the “Part Design” workspace.
The workflow in “Part Design” goes like this: You first “create part”, this is the same as a “component” in Fusion 360. Inside the part, you “create sketch”.
I first started by sketching the profile. In contrast to Fusion, FreeCAD doesn’t provide snapping or automatically make constraints. You have to manually select lines and then select constraints from the upper menu. After making sure that all the lines are defined and constrained, I mirrored the sketch to finalize the profile.
The extrusion command in FreeCAD is called “pad”. To “pad” a sketch, it has to be a fully closed profile. Additionally, it can’t be more than one profile, as FreeCAD doesn’t allow selecting which profile you want to “pad”. I extruded the sketch to be 3mm, the thickness of the cardboard in the lab.
I replicated the same workflow and created another body and sketch. The final component tree and the finished part looks like this:
In order to export this piece as a DXF file, we have to use the “TechDraw” workspace. You select the workspace from the drop down menu and click “insert default page”. After this, we click on the body in the tree, and “insert view”.
At first, the vertices look huge and distracting. We can open settings and set their size to zero. After doing this, we can place the drawings wherever we want on the page. Using the export settings, we then export the drawings as a DXF file.
After my trial with FreeCAD, I wanted to make a more complicated piece to test the “screw reinforced joint”. I had the idea to make a moving part by using the same principle, while also using the screws to create a hinge movement. I decided to design an adjustable phone holder, since I actually needed one.
As always, I started by setting parameters in Fusion to make changes easier in the future. Here is how the process goes:
For this project I also utilized the “McMaster Carr” parts import function embedded inside the software. This is a tool which allows us to import a variety of mechanical parts into our design. I imported the screws and nuts that I wanted to use, to design the part around their dimensions.
I modeled the piece with using the same workflow I outlined in the previous week. I made three seperate pieces, one for the bottom, one for the top which would carry the phone, and a middle piece. Every piece consists of 3mm plywood profiles. There are holes which allow for the “screw reinforced joint” method.
I had never previously exported anything from Fusion for laser cutting. While researching, I stumbled upon an add-in for Fusion. It allows us to insert the kerf value in the very end of the process, and adjusts the DXF files accordingly. This way, we can design the part in Fusion like we want it to look in real life and change the kerf very easily.
After finishing the model, we activate the add-in from the drop down menu. We then select faces to be turned into dxf profiles for laser cutting. After entering the kerf, it exports. We transfer the files to illustrator to collect them into one file.
Before moving onto plywood, I decided to test the prototypes on cardboard. After putting my piece inside the laser cutter, I calibrated the focus of the laser. We do this by adjusting the small metal piece near the laser, and ensuring that it provides a bit of a friction.
After importing our design to the computer in the lab, we open it in Illustrator. We then “print” it with “media size” set to “custom”. This opens the laser cutter interface. We place our design with the help of the camera. It is better to do the trial cuts in the bottom right, because that is the place where the machine is the least accurate. If our cut works there, it will work anywhere.
I chose the settings for “cardboard 3mm” and started cutting.
After cutting, I started assembling the pieces. There were some apparent issues.
The dimensions of the pieces were not what I wanted them to be. The notches on the first piece did not fit the second one. The screw holes were too big for the screws that I was using. The reason for these inconsistencies were two things. Firstly I did not measure the kerf correctly for cardboard, and secondly I imported the wrong size screw from McMaster Carr (M3 instead of M2).
For the phone holder piece, things were not looking well either. In addition to the dimensional errors, the structure of the piece was also not working. The middle piece was too short and caused imbalance. Although some of these structural issues were caused by the nature of cardboard, most were due to my measurement errors. I had to fix my design before moving onto plywood.
Before going back to CAD, I had to measure the kerf for plywood. I drew 10mm squares in Illustrator and imported them to the laser cut software. However, the laser cutter did not cut, it only burned the top of the wood.
I realized this was because I had not set the line width to “0.01mm” in Illustrator. I went back and did that, but the laser cutter did not cut again.
The power and speed settings looked fine, so I tried changing the location of the plywood to the upper left corner of the machine. This time it cut, but when I attempted to remove the piece, all the small squares fell into the laser cutter.
I realized why nobody else was using 10mm squares. I repeated the same steps with 20mm. It worked. For kerf measurement, I lined up the 5 pieces and measured with a caliper. I subtracted the real length (99mm) from the expected length (100mm), and divided the difference with 5. The kerf was 0.2mm for 3mm plywood.
I went back to Fusion 360 and fixed the previous issues. It was a fast process because I was working with parameters. I changed the hole sizes to accomodate for M2 screws and nuts, and made the middle piece longer. When exporting I entered the kerf as “0.2 mm”.
When I was cutting with cardboard, I realized an error about the order the machine was cutting the pieces. For pieces with holes inside it was cutting the contour first, which made the piece fall down. Then it was cutting the holes, resulting in inconsistencies. To prevent this, I gave a different color to the prioritized cuts in Illustrator.
This way, in the laser cutter software I made sure that the red lines would be cut first.
After cutting, I assembled the pieces. The dimensions were much more accurate than the first iteration with cardboard. Although some notches were too tight so I had to sand them down a bit. The screw holes were working fine, but they could have been a bit smaller for a tighter fit. For my next projects with the “screw reinforced joint” method, I will make the nut and screw holes tighter than they actually need to be.
All in all, I think the design works as intented in the second iteration. The hinge mechanism allows for the readjustment of the piece, although it can be more refined.
Since I was using parameters, it is also possible to change the size of the phone holder, depending on the phone, screws available, etc. Below, you can see the original design (left) and a modified version (right) for 4mm plywood, using longer and thicker M4 screws.
For the vinyl cutter, I decided to document the process of learning a new vinyl cutter model. I recently had the chance to use a Brother Scan n’ Cut SDX 1250. The nice thing about this machine is that it can also scan what you feed to it. Therefore, it can be used to cut already printed stickers or precisely place designs on leftover vinyl.
I had experience with the Roland GS2-24 vinyl cutter machines before, where you can directly feed the vinyl to the rollers. In the Brother machine, you have to stick the material you are going to cut to a special mat first. These cutting mats come in two varieties: low-adhesive and high-adhesive. There is a reference table on the manual to help you decide which mat is useful for which material. I first tried the high adhesive mat for the vinyl, but soon realized it was tearing the back of it. So, I switched to low adhesive.
After sticking the vinyl to the mat, I wanted to perform a test cut. First, I loaded the mat by placing it to the mouth of the rollers and pressing the “load” symbol button.
Next, I pressed the “Test” button and adjusted the settings. You can change the size and shape of the test cut.
By dragging on the screen, you can position the test cut on the mat.
Positioning test cut
After the adjustments are complete, make sure the set “Half cut” “ON”. This ensures that the machine will only cut through the top vinyl layer, and not the bottom adhesive layer.
Here is the result of the test cut. It is successfull, since I can easily peel off the vinyl from the adhesive backing paper. One good thing about this machine is that it automatically sets the pressure of the cut, so you don’t have to do as much back and forth as a Roland, during test cuts.
Now I wanted to try how to import my own designs to the machine. I used cuttle.xyz to create this simple design. I wanted to test how cuttle outputs different stroke and fill property svg’s, and how the Brother software will interpret them.
From left to right: fill and no stroke, no fill with hairline stroke, no fill with thicker stroke, no fill with thicker stroke + “flatten” modifier. The final one basically turns the stroke into a closed shape.
You don’t need to download any software, you can just import the svg’s to the machine through a USB, and do all the placing there. After importing my files, I decided to try the scan function. I press the middle button on the first image, and the machine scans the cutting mat.
Scanning
After scanning, we can now see that the vinyl is visible on the interface. We can easily place our design on top of it.
Howewer, I realized that it was actually larger than the vinyl piece I had. So, I went into edit mode and adjusted the size of the design.
In the beginning of this video, you can see how the machine adjusts the pressure automatically before cutting.
Cutting
After the cutting is completed, I took the vinyl and peeled off the part I was not going to use.
I cut the whole thing into individual pieces, and put adhesive tape of the front side.
I flipped the paper and applied pressure from the back, so the vinyl sticks to the adhesive tape. Then, I peel off the backing paper. Now only the vinyl stuck to the adhesive tape remains.
I finally place the sticker on a surface, apply pressure on the adhesive tape, and peel off.
Below are a compliation of all the other stickers I tried. I found the Brother SDX 1250 a very handy machine for a few reasons. Firstly, you don’t have to bother with downloading programs or add-ons to your computer, you can just work with svg exports. I found the editor built into the machine quite useful. Secondly, the scanning function makes things very easy when you are working with small pieces of vinyl. Finally, the auto pressure blade saves so much time when trying a new material.
However, I wish that there was a way to separate svg paths in the machine editor. Because if I need to get two designs in the same file closer to each other, I cannot do it in the machine.
