Design
The design for the Scotch and Yoke is based on this depiction of the machine
This design uses two sheets of acrylic, one as a baseplate for the mechanism to lay on top of, and a second to cut the moving pieces out of.
Here are the DXF files for the baseplate and the moving part cutouts
The first part of the design started with creating the border dimensions for the acrylic sheets (12 inches x 24 inches)
The next part is to create the circle that will act as the rotary motion out of the baseplate. This circle will also have etches around it for tabs to hold it in place for rotary motion. It will also have a circle cut out of it for a pillar to be inserted, connecting the rotary circle and the mechanism that moves from that motion.
The rest of the baseplate was then made. A cut-out to connect the mechanism’s bar to the baseplate is created and two points are put in to hold it straight. There are also circles etched in the corners for posts to hold up the baseplate.
For the moving part, first, the cutout was made for the end of it. It was originally drawn out as a box.
Next, the ends are rounded in the following process:
First, a three-line tangent circle is created
Then, all of the unnecessary parts are trimmed out
The final part of the design includes creating various-sized circle cut-outs for the different parts of the baseplate and moving parts of the mechanism. It also includes creating the bar for the mechanism
There were a few minor errors in this iteration that were fixed, namely, there were two more circles that needed to be made, as shown below
These are the final 2D designs for the acrylic Scotch and Yoke:
Putting It Together
Here are pictures of the final cuts from the acrylic:
Here is a picture of the final assembled mechanism
Final Movement and Design
Finally, here is a video of the fully assembled acrylic Scotch and Yoke in action. While, in theory, this design works, there is a lot of friction in the moving circle piece, making it very choppy. In addition to this, one of the small circles meant to be assembled and placed in the mechanism’s bar fell through the laser cutter, making it impossible to create two anchor points to straighten the mechanism’s movement. I did create a lot more later on and assembled them together for the anchor points, making the full mechanism.
Dr. Haden Feedback
On Monday, October 9th, 2023, Dr. Haden was given a demonstration of my Scotch and Yoke Machine and gave the following feedback
- Size: The scale of my prototype is too large and wastes too much material – need to make it smaller for future iterations
- Friction: The friction that occurs with the circular motion can be reduced through the use of a center pivot instead of an inlaid mount
Design 2.0
Here are the DXF files for the new and improved Scotch and Yoke
First, I needed to create the border to know how big the acrylic sheet is
For this design, instead of a circle, I switched the moving part to be a center pivot. This center pivot would have a free-spinning bearing for someone to hold and crank the mechanism, and there is another bearing that goes through a backplate for centering and having somewhere to pivot. Here is the design for the center pivot plus all other circles that needed to create the bearings (with measurements)
Please note: anything that is an orange dotted line gets etched instead of cut
Up next is the baseplate. To do this, I created a circle 11 inches in diameter and squared it off at the bottom. I also created guidelines for the eventual bottom placeholders that will keep the Scotch in place.
I finished the baseplate by adding text to it and creating the markings needed for the top placeholders
Here are the measurements for the arrows
Here are the measurements for the placeholders that will go on the baseplate
Next, I had to create stands for the baseplate, make two of these – one for each side. I created them with an angle to have the entire mechanism tilt back, making it easier to stand
Next, I created the Scotch
After that, I drew arrows on the bars of the Scotch to show the movement of the mechanism
I also made two more parts for the guide brackets for the Scotch
Cutting and Assembly
I used Ruby to send over and laser-cut the acrylic sheets
I got excited and put together the center pivot here
Here is a picture of all the pieces cut out and assembled (View The 3D Printed Handle to find out what the yellow part is
Here is a video of the mechanism working (Please note, I did not have time to attach the stands for the baseplate, so someone is holding up the mechanism!)