4. Computer controlled cutting¶
This week we worked on characterising our laser cutters. We looked at the following topics:
- Focus
- Power
- Speed
- Kerf
- Joint Types & Clearance
Focus¶
When you first turn on a laser the first step is to focus the laser on the top surface of the material you are planning to cut or engrave. Here are images showing the positioning of the focus tools.
Speedy 300:
Rayjet:
There are cases where you would offset the focus point in the print settings.
Material Thickness¶
With the focussing tool you end up focusing on the top surface of the material.
On the whole this is fine, however if the material is getting quite thick, 6-10mm, you can adjust the focus so that it is in the center of the material. This allows for a deeper cut as the laser loses power as it loses focus.
You can see the offset focus collum in the material settings.
It can help with reducing the slat you can sometimes see on thick laser cuts. Most noticible in foams. This is because when it is focussed in the center you can lower the power of the laser meaning it will take away less material my accident.
Engrave Speed¶
It is also useful to reduce engrave times. You can print the image with a dither pattern then unfocus the laser slightly so that the dither is blurred, fills in nay gaps and it looks normal again.
Power & Speed¶
You can adjust the power from 1-100% to vary the intensity of the laser beam. - Lower power - Shallower cut & lighter engrave - Higher power - Deaper cut & darker engrave
You can adjust the speed from 1-100% to vary the speed at which the laser head moves. - Lower velocity - Deaper cut & darker engrave - Higher velocity - Shallower cut & lighter engrave
We created a grid which demonstrates you can edit either values and achieve similar results.
For example:
High power + High velocity = Low power + Low velocity
In genral you want to keep the velocity as high as possible so that jobs are fast to complete.
Kerf¶
Kerf is the material removed where the laser beam passes. This means a piece that was designed with perfect joints would end up being loose.
I designed a test piece in fusion360 which featured slots that varied in size so we could test how much we need to account for to remove the effect of the kerf.
File Download
I then cut it on the Rayjet 50. Here is the result:
We determined the kerf of our lasers was 0.1mm.
Joint Types and Clearance¶
As lasers are two dimenti0nal machines you need to build in joints in order to create a 3D object. There are many ways to join parts together.
Niel shared with the class a image of a few different joint types.
I then redesigned these in fusion360 so that I could adjust material thicknesses and kerf amounts.
Joints Download
My first versions did not work properly as I had added twice as much kerf than needed on most sides. When the laser goes past a edge it takes off half the kurf of the laser as only one side of the laser is cutting into the actual piece, the other side is cutting into waste most of the time.
Second attempt¶
Second attampt was more sucessful. Six out of the eight worked.
Pressfit and Chamfer¶
They are both quite similar. Both over lap to form the joint. The chamfer just allows for easier connecting as the slope guides the two pieces together.
Snap¶
The snap joint is an example where the second attempt didnt work. I susspect this is more of an issue with the material choice. The MDF 6mm is not very flexable so even with small bump sizes it didnt bend enough to go through the hole.
This is a theme for nearly all the flex joints.
Snap-fit¶
This joint had even less chance of working as the wall on either side of the opening is too wide.
Max’s attempt at snap fit joints were more successful.
For his individual project he designed a construction kit that relied on them.
Flexture¶
As the walls were thinner it allowed for more flex. This was the only one that worked out of my flexture joints.
Pinned¶
This joint slid well together then could be fastened together with a diagonal pin. I quite liked how this joint looked. May attempt to use again the the future.
Wedge¶
The parts slid together then gets fastened by a wedge.
I can see how this would be useful for 90 degree joints.
Finger Joints¶
This was the main confusion for the kerf but the second attempt was better with the fingers laying flush.
90 degree angle.
Flat.