Week 3, CNC Cutting

Objectives


Group assignment: Do your lab’s safety training; Characterize your lasercutter’s focus, power, speed, rate, kerf, joint clearance and types.; Document your work to the group work page and reflect on your individual page what you learned.
Individual assignments: Design, lasercut, and document a parametric construction kit, accounting for the lasercutter kerf, which can be assembled in multiple ways.; Cut something on the vinyl cutter.

Group

Safety Training

David and I reviewed the policies and procedures for our lab and for the laser cutter specifically. We were breifed on the safety systems on the machine, how to turn it on, how to send a job, the importance of the exhaust fan, the location of the fire blanket near the machine, and shown the location of the nearest fire extinguisher.

Laser Characterization

We created a small part to characterize the laser kerf. I drew a small comb in SolidWorks that used a parametric design to take the material thickness as an input and then decrement the thickness of the comb gaps by a set distance.

Then we ran a couple of the parts on a piece of wood and checked the fit. It turned out that the gap that was 0.4mm smaller than the nominal thickness produced a nice snug fit that was still easy to assemble. This is what I used to take forward into my kit project.

Vinyl Cut Lens Hood Sticker

For the vinyl project I decided to make a decorative sticker for the lens hood of my camera. This allowed me to experiment with the workflow from SolidWorks to our Roland vinyl cutter.

Process

Creating the Flat pattern

I started by creating a flattened surface in SolidWorks. I had a surface model of the hood already. So I used the sheet metal tools to create a simple lofted "sheet metal" part that matched the surface. From there I was able to unfold the flat pattern and extract the perimetter.

Adding Text

I then brought a dxf file of the flat pattern into Illustrator. I added text and aligned it with a guide curve to make it centered on the art.

Cutting

I exported the .ai file and brough the geometry into Roland Cut Studio. After many attempts, I realized I had to downsave the file to Illustrator version 8 to get the geometry to load, but it was no problem after that. Then I fed a roll of white vinyl into the machine, setup the default parameters with 0 adjustment on the cutter and tried it. It ran fine and I was able to test the fit on the lens hood, which was quite good.

I then moved on to cut in a reflective piece of vinyl. I loaded the same program and ran the cut profile. I then weeded the letters and put some transfer tape over the artwork. I took the tranfer tape and vinyl pattern and carefully wrapped the lens hood to achieve the final product.

Files

Laser Cut Bokeh Filter Kit

For the parametric instruction kit I made a bokeh filter kit for my DSLR camera. Bokeh are the blurry out of focus areas in a photo that is shot with a narrow depth of field and help to make the subject stand out. Typically, point lights will render as circular or polygonal as they have to pass through the shape of the aperture. However, by adding a different shaped filter in front of the lens, new bokeh shapes can be realized.

Iterations

My camera currently has a fixed focal length 50mm lens that I like to use for portraits and general shooting. It also has a wide aperture setting that is perfect for creating good bokeh. So I decided to build off of this lens. I ended up doing 4 major iterations.

First Iteration

I started by adding a bulkhead to the back of the lens with a simple filter at the front with upper and lower cross braces. I added slits to the rear bulkhead in an attempt to help it conform perfectly to the lens. For the filter I chose a heart shape for testing.

There were a number of problems with the first design: Stretch was too fragile Bokeh hole was too big and was not showing the shape Thickness was wrong in some places

Second Iteration

I updated my CAD file to have fewere holes in the stretching section. I also lowered the diameter of the heart shape.

This change was better but still did not work perfectly. The filter hole was a good size and the heart shape started to show in the LEDs I was taking pictures of. However, I was still breaking the rear bulkhead. After measuring it I found that the diameter of the lens was wrong in my model.

Third Iteration

For this iteration I updated the diameter of the rear bulkhead and I made the interior point of the heart in the filter more pronounced. I also updated the geometery of the cross braces to be taller.

Despite the update to the rear bulkhead, it was still breaking and I decided to abandon this idea going forward. I also realized that even though the lens was fixed focal length, there was still about 8mm of telescoping that the lens did to focus the image. So, I realized that the filter piece needed to be able to move axially with the lens.

Fourth Iteration

I completely overhauled the design. I started by going to Home Depot and getting some new wood. The new wood was flatter that what I had been using and was 5mm thick instead of 4mm thick. Then I changed all of the CAD. I decided to keep the rear bulkhead, but to add another bulkhead to the front of the lens just in front of rotating focus ring. This would provide aligned slots that would locate the filter and allow it to slide.

I ran the first test and the parts fit together pretty well, though I did have to fine tune the diameter of the rear bulkhead to get a snug fit. The filter slid well in the 3 slots and the focus motor was able to drive the lens without any noticiable resistance.

I felt like I wanted the filter to stay on the front of the lens, so I attempted to add some wooden spring elements to help. However, after 3 interations they were too fragile and I decided to abandon the idea and leave the solid legs.

I made a few more small changes to the design. I added some cutouts to the rear bulkhead to allow it to stretch onto the lens. I also update the filter with longer legs and added the Fab Lab logo to see if it would work.

The updated filter worked really well and I took a few sample images to show the effect.

CAD Files

As per the assignment, the CAD file was built parametrically in SolidWorks. Global variables were setup for the thickness of the material and for the kerf allowance. In the sketches of the different parts, equations were used to define the gaps so that the pieces would fit together properly. This allowed the CAD to be rebuilt correctly when I updated the material thickness partway through the build.

CAD file for the bokeh filter