Week 3: Characterize the lasercutter (group assignment)

This week we followed the computer cutting class (see video here)

This group assignment was about characterize our lasercutters in the lab.

We documented our group assignment in this common GitLab issue: https://gitlab.fabcloud.org/Computer_Controlled_Cutting/Group_Assignment/issues/2. Content is copied here below for those who do not have access.

There are two laser cutting machines that can be used at the moment at FabLab BCN.

A Trotec a Speedy 100 and Speedy 400.
The small one (100) that handles pieces with maximum size of 60x30cm, the big one (400) can go up to 100x60cm

IMG_Trotec_100_Machine_Small

IMG_Trotec_400_Machine_Big

How to use a laser cutter

There are some preparation steps to do for using the machines:

  1. Choose and measure your printing material and cut it manually to fit machines if needed;
  2. Check under honeycomb for material leftovers. If so, clean them otherwise they might catch fire;
  3. Remember to turn on vacuum system (ask instructor to do so), so that fumes get expelled outside;
  4. Turn on machine and place your material on the honeycomb surface making sure it’s as flat as possible. If not you can tru masking tape or cut the piece in smaller parts;
  5. Focus the laser. We are using a manual measurement tool/guide and move up the plate until the guide falls.
  6. Move machine laser manually (using the touchpad) to a “0-0” origin point on your material;
  7. Close the lid;

IMG_Trotec_Control_Pad

At this point we are ready to set up our job on the computer

  1. Import your files from the shared Iaac Cloud drive;
  2. With Rhino setup the printing window so that it contains your drawing and print your design;
  3. At this point the Trotec Job control windows will open;
  4. Connect to the laser machine () to find your laser origin and place your desing under it;
  5. From “setting” adjust the laser power/speed/frequency for each color that you’re printing. Also select either “cut” or “raster” (this is good for engraving);
  6. From the menu select the option “optimize vector order” to optimize/reduce the path that the laser will follow. This can save a lot of time for big pieces;
  7. Print you job! And check that the cutter is executing it properly.

Cutting

We started using some plywood because we thought it might be more relevant for our group projects than cardboard.

When we started our exercise we didn’t have a clear strategy about how to do it. We had issues importing one of the templates and we moved to the piece that could help us evaluate the kerf.

Our first try went on :fire: ! So we had to stop the machine.

Initially we used the “kerf” desing but was taking to much time.
We learned that it is important to have a very simple design and try variations of power, speed, and pulse rate.
Also it is important to have a clear strategy to explore the values (see the example below).

IMG-Lasercut-characterise-strategy

On the Trotec 400 we found that the optimal values for a 3mm plywood is the following

Power Speed PPI/Hz
80 1.7 1000

With these setting the kerf measured was: 0.15mm

IMG-Kerftest-for-plywood-trotec400

We also found that is important to keep at hand few sample test files in Rhino:
Prepare and improve few sample for testing every new materials and every laser cutter condition!
Because our lab is using Rhino to connect to the laser cutters it is useful to have those files ready in Rhino format.

At the end of the session I ended up creating some following sample files that could be reused for this.

Screenshot-Rhino-simple-test

Download simple test source file (.3dm)

Screenshot-Rhino-kerf-test

Download kerf test source file (.3dm)

Based on the Laser cutting materiale template by Noloxs but just converted for Rhino format.

Download rastering and hinges test source file (.3dm)

note: See the other assignments for week 3

Engraving

On the next day we wanted to try engraving to print images as different shades of colour.

The important difference is to select Engrave in the material settings panel of the cutter Job Control tool.

I created a sample file with different colour to try different power / frequency settings. In the example below we set a base line for black; changed power along red-blue-green; changed frequency along magenta-cyan-yellow.

After different trials we saw confusing results (eg. 800hz is darker than 600hz, but ) realised that the different colours were translated during the printing step in shades of gray, and after this the different material-color setting were ignored.

Screenshot-Rhino-simple-raster-test

IMG-Simple-engraving-test

We found optimal setting for “Red” colour

Power Speed PPI/Hz
100 100 1000

Which translates more or less to the following setting for “Black” colour

Power Speed PPI/Hz
70 100 1000

Finally we the setting aboce we tried to print a bitmap image IMG-Image-Engraving-test

Happy Cutting! :wave: