Week 3 Computer-Controlled Cutting

This page documents the group assignment for week 03 of Högni and Jóhannes.

Vinyl cutting

In our FabLab we have the Roland CAMM-1 GX-24 Servo vinyl cutter. It can load up to 700 mm wide material, but the cutting area is 584 mm wide. The maximum cutting speed is up to 500 mm/s.

Safety Information

There is no big hazard associated with using the vinyl cutter, but of course the operator shouldn't touch any moving parts of the machine.

Basic Setup

A sheet of material is loaded by lifting the rollers up, inserting the sheet and clamping it down again. The rollers must clamp the sheet in the marked area and the sheet must cover the material end sensor.

Then you select the type of material (roll, piece) in the menu and the machine will measure the size of the workpiece and display it.

The knife must be adjusted according to the material loaded, so the cutting depth matches the thickness of the material to cut. The knife is adjusted by removing it from the holder and turning the adjustment screw and test the cutting depth on a piece of material. It should just cut through the material, but not protrude any further to avoid damage.

Cutting

The files for vinyl cutting are vector graphics saved as pdf file where the line width is 0.02mm.

We did the first trial with Jóhannes design file on green vinyl.

Vinyl Cutting Test

Laser cutting

In our FabLab we have the Epilog Mini 24 laser with 40W power. It's working area is roughly 600 mm x 400 mm and the height of the workpiece is limited to 140 mm.

It is an air-coolerd CO2 laser and we also have a rotational Y-axis addon.

Safety Information

We did the safety training in our lab. The guidelines are to never leave the machine while it is in use so that we are ready to turn it off when needed. It is not allowed to cut PVC, vinyl or nylon on the machine. When the machine is operating we have to make sure that the air compressor and the suction is turned on while the machine is running to prevent risk of fire.

Fab Lab Isafjordur has a Epilog Mini 24x12 cutter or 61x 30.5 cm. It is a class 2 laser product and there is fire risk involved in using it particularly if cutting acrylics. It is important to always stay near the unit when cutting to be ready to turn it off if something is catching on fire. When operating it it is important to turn on the air assist units there are two of them in Fab Lab isafjordur.

Basic Setup

We used the following student's page for reference Ahmed_Ibrahim

The procedure to cut is as follows. Select the material and place it in the cutter. To adjust the focus we use a magnetic clip that we hang on to the laser and then gradually move the laser unit until the clip barely touches the surface. Typically it will overshoot a little and then we move it back with one push of the button. Next step is to select the starting point so we press x/y disabled and then go and then we can manually move it to our desired starting point. We need to make sure the pointer is turned on to see where the starting point is. Then we his set home and are ready to cut. We load a pdf in the printer software, hit print and then once the job appears in the cutter we hit go and it starts cutting.
These are the attributes of the laser cutter that we need to characterize in this assignment and their definitions.

focus- The distance between the laser cutter and material to get the smallest focal point. Ahmed's lab has something called a focus coin which if we don't have it at our lab we should replicate. power- The wattage of the laser needed to cut different materials Speed- The speed of the laser needed to cut different materials

Power- The wattage (in percent) of the laser needed to cut different materials Speed- The speed (in percent) of the laser needed to cut different materials For mdf the speed/power/frequency combination is 5/100/5000 For plexiglass 5mm it is 5/100/5000 as well and for 3mm it is 7-9/100/5000 Kerf- Is the width of the cut and joint clearance- the tolerance of a joint needed for optimal fit. That is if I have a 5mm width "male" component should the "female" optimally be 4 4.5 4.6 etc for a good press-fit. We will review the test results below.

Power vs. Speed

We started with acrylic sheets of 3mm thickness and made a rastering and cutting test in some iterations.

Here is a picture of what we intended to cut. (original file from Ólöf, modified by Jóhannes)

Power Speed 1

We wanted to use color mapping to adjust speed and power for all the boxes and do rastering and cutting in one step. However we had to learn, that the colormapping function has a limit of 16 colors. We then defined the first 16 colors and discovered, that the other colors are then rastered with standard settings. We also realized that the speed for cutting needs to be much lower, so we cannot use the same settings for both operations
Then we reduced the number of boxes to 16 and adapted the color mapping and settings. However, because it is a lot of manual entering of numbers we made some mistake and had produced one more scrap piece.
Now we did want to get it right. We repeated the procedure from nr. 2 but with the right numbers entered and it finished nicely. Here is a screenshot of the file and the result.

Power Speed 2

Power Speed 2 result

Link to the cut file.

The results show cutting through the material starting from 40% Power or 10% Speed.

Kerf and clearance

Then it was time to make a kerf and clearance test. We used 7% speed and 100% power for cutting the acrylic sheets.

The test file Jóhannes made looks like this.

Kerf & Clearance 1

We measured the kerf gap which was 2,2 mm what results in a kerf of 0,22 mm.

Kerf measured

Then we realized, that the fit of the comb was way too loose. We measured the sheet and it was only 2,7 mm thick. That is of course fatal for fits that need an accuracy ogf 5/100 mm.

Now we reduced the the starting size and took into account the kerf and the below-spec sheet thickness.

This is the new file and the result:

Kerf & Clearance 2

The result shows a clearance of -0,05 mm resulting in a good tight fit.

As the MDF sheets we also wanted to test, have a measured thickness of 4,0 mm we reduced the comb dimensions for the 4 mm side less then on the 3 mm side.

Then we repeated the procedure with the MDF and got the following results:

Kerf: 0.205 Kerfimage