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6. 3D Scanning and printing

I’m really proud of my accomplishment this week, at least the 3d printing and modeling part. I’m very sad with the 3D scanner because it was super glitchy and low res. Anyways, I 3D printed a plastic part that hooks around an alligator clip to help kids use them. The tiny metal ends of the alligator clip make it hard for young students to use them. This allowed my 2 year hold to work the alligator clip without my assistance.

I designed the model in SOLIDWORKS as two pieces with .3mm clearance at the hinge. I combined the two parts into an assembly and exported the assembly as an SLT model. Once taken off the printer bed the two parts hinge perfectly allowing you to insert the alligator clip. This design would be impossible to create with a subtractive mill because of the hinge.

Files

Alligator Clip Assembly (SOLIDWORKS) (.STL)

Part 1 (SOLIDWORKS) | (.STL)

Part 2 (SOLIDWORKS) | (.STL)

Assem2 by bcrichardson on Sketchfab

The goal of week 6 is to print a calibration model to test the design rules of Fab Lab Houston’s 3D printer. Then, design and 3D print an object that could not be made subtractively and 3D scan an object.

3D Print Calibration Model

There are a ton of premade models to test 3D printers. I used this model because it has extreme overhangs and a variety of wall thicknesses.

The first print started off a little rough because the printer bed was not perfectly leveled. Several of the layers didn’t stick to the bed or other traces.

Once the bed was leveled the calibration model printed very well. The most extreme overhang suffered from some slumping but none of the print failed. Also, to save time the model was shrunk by 50% to save printing time. It took 2 hours to print.

Lessons Learned

The calibration tool was really helpful for several reasons.

  • Always level the bed (or at least check the level) and not assume it is. Fab Lab Houston is a public Fab Lab and people don’t always leave the tools in the same shape as when they found them.
  • The forms that are printed are not exactly the same size (0.2 - 1% difference) as when designed due to material shrinkage. This article by 3D hubs helped my understand. Not I can use the circles printed to adjust the design based on the material.
  • The Ultimaker does a really great job with overhangs as long as they are gradual, like the arch. Behind the arch is a 90 degree overhang that didn’t print. With drastic overhangs like these I will use supports.

3D Scanning

For my first attempt 3d scanning I used the 3D Systems Sense 2 . Due to previous experience building a scanner using multiple cameras and a turn table, I thought I would set this test up the same way. I used a kitchen lazy susan as my turn table and attempted to scan an alligator clip.

I quickly discovered two things.

  1. The Sense 2 scanner needs to move around the object with the object stationary.
  2. The alligator clips are too small to scan. The scanner could read the cup fine but couldn’t detect the alligator clip.

When I moved the cup(mount) and alligator clip around on the lazy susan with the scanner stationary the model was generated from only one angle.

Designing Functional Hinge with SOLIDWORKS

Design Challenges

  • I had to guess what tolerance would allow the printer to print the model as two seperate/interlocking pieces that still hinge. The correct clearance was .3mm.

  • I needed to design it to the hing could connect but the model could lay flat. This proved to be the hardest thing. I initially designed th file with a hinge that protruded perpendicularly from base of each part but then when I went to assemble them the parts jammed against each other unless the part was holded. To solve this problem I designed the hinge so each part’s hinge extended at an angle.

Design Approach

I used a bottom up approch to designing the alligator clip holder. I actually hot glued popsicle sticks to an alligator clip to see the angle of the clip and the pivot point.

With the measurements taken from the rough prototype and the alligator clip I modeled both sides of the holder in SOLIDWORKS, like described in week 3 of Fab Academy - Computer Aided Design

Once both parts were modeled I combined them in an assembly and cut away meterial so the pieces combined would lay flat and be .3mm apart.

Once the design seemed good I went to save the model and realized that SOLIDWORKS saves assemblies as seperate STL file. After some research I learned that there is an option under EXPORT OPTIONS to “Save all components of an assembly in a single file”. Once that box was checked I had the file to load into Cura to 3D print.

I used the default settings for the Ultimaker. These are the same settings I used in the test above. The file printed in under 1 hour.