Bearings are a fundamental component of any device that moves. Your STEM students learn about the forces of friction and how to reduce them by designing and building their own mouse trap cars and robots. Reducing friction in these and other projects is made easier if you can have students design and manufacture mounts for ball bearings using the desktop CNC tools available to them. The freedom to customize with these tools means that you can design around harvested parts you may get for free. For example in my classroom, we have a large supply of old ball bearings from printers, fishing reels, and various broken down machinery. Since many students are familiar with bearing in skateboards, they will be delighted to see that these same bearings can be used for a variety of other purposes. Often students will bring in their old skateboard bearings when they decide to upgrade to a newer set.
In this particular application we will be using small bearings from an old fishing reel, in 3 x 10 x4 mm size, perfect for our 3mm axle harvested from a broken printer.
This pillow bearing design allows for the axle to ride on the bearings, and has a built- in spacer machined in to the bearing mount. That allows the bearings to snap into place on both sides of the mount without the need to worry about keeping them from shifting about. Choose your favorite CAD program to have students design a similar to fit their project parameters.
Bearing Mount With Built-in spacer
For machining the part we will import our .igs file into SprutCAM.
Locate the Z axis at the spot shown for easiest machining. Sew the faces together first.
Transforming the Z
Create a box around your part based on the size of your stock. This is found in the machining tab using the ‘add primitive’ button. You can use a face mill or fly cutter in advance for approximate Z dimensions.
We have added .25 inches to the x+/- as well as the y+ axes in this example. Including an extra .001 inch on the -Z to allow for better part control is a common practice in our lab.
Adding Stock Around Part
For our first operation we will drill a .125 in hole completely through the piece. This gives us an extra .1mm to ensure the axle is riding on the outer bearings and not the built-in spacer.
Hole for the axle
Next we want to create pocket for the 3x10x4mm bearing. The pocketing operation will be used at a depth of 11/64 inches. Normally we don’t like to mix and match Imperial and metric units, but it is a small inconvenience that is made worthwhile by using harvested ball bearings.
Pocket For Bearing
A 2D contour operation will be used to outline the pillow bearing. Select the outer edges, and leave .01 in for part control. We will use the .5 inch endmill here to make quick work of metal removal.
However the .5 inch endmill will not remove the inside corners so we add a second 2D contour finishing operation with a .125 endmill. This finishes the outer perimeter of the part.
Finishing With 1/8 End Mill
Students may forget that they still need to complete the other side of the bearing mount. They will need to flip the part and re-create the first pocketing operation. This basically involves setting a new coordinate system in SprutCAM after flipping it over, and adding the same pocketing operation as before. For further details, see Tormach’s video tutorial on flipping a part in one operation. Finally, the block mounting holes will need to be drilled in one final flip.
Mounting Holes After Part Flip
Mount and Bearings
You will want to use collars on the ends of the axle to keep it in place.
Let’s consider the power of activities such as this in the classroom. As teachers, we are well aware of the tremendous level of engagement and demonstration of learning that we observe. We watch our students in amazement as they argue for their designs using simulation data, using sophisticated CAD software like it was just another app on their phone. They consider scientific laws when determining the needs of their projects, and often quote Newton or Boyle. Complex geometric relationship are manipulated on the computer screen as they optimize material choice and cost requirements.
The strength of these STEM activities for education reinforce our mission that it is through teaching advanced manufacturing in schools that students can learn so much science, technology engineering, and math on a meaningful level. You can and should take the time to document these accomplishments in terms of the latest educational performance standards.
The three dimensions of Science Framework are well-represented here . Taking an idea from investigation of a problem to CAD design, then optimizing it through simulation is true Engineering Practice. Crosscutting Concepts and Disciplinary Core Ideas in the Physical Sciences and Engineering are demonstrated in multiple ways. Students can also meet certain Common Core Math and Language Arts standards depending upon how these lessons and activities are structured.
Taking advantage of long-term, high-level collaborative projects with proper assessment can bring your STEM program to the next level without extra work. Good teachers who have been doing these sorts of hands-on activities for years have always had their students demonstrate mastery of performance expectations. With a bit of adjustment here and there, your curriculum will have a fresh face that showcases the power of design and manufacturing as a great way to bring your students to the forefront of 21st century job skills.
Author: Al Chirinian