Introduction

We (Paul Glenski and Jake Sperry) decided to create 8 pawns for our midterm project. We first made our design on TinkerCAD using a Super Mario 1up Mushroom file from Thingiverse made by limeworks and a cylindrical pedestal we designed ourselves. We used our TinkerCAD file to create a preliminary 3D print using a Prusa_I3_Mk3 printer. As we liked the resultant 3D print, we then sliced the design in half using Fusion360, and sent both files to be further edited in SolidWorks.

Solidworks and 3D Printing

In Solidworks, we created two files, one of the front half of our design that would be 3D printed, and one of the back half of our design that would be CNC machined. On SolidWorks our main focus was adding a base to each of the halves of our design in addition to adding pegs and holes, which would eventually be used to easily put our two molds together. We made sure the base and peg holes were the same dimension for both files. The base was about 65cm long and 60cm wide, with a height of 10cm. The peg holes and pegs had a radius and height of 2.5cm. We also decided to not add an additional part at the bottom of our design, as we thought we could use the base of our pedestal as our pouring hole for when we were casting our pawn pieces. We then downloaded both Solidworks parts as STL files, one being moved on to Fusion360 (see below) to prepare for CNC machining, and the front half file being added as a file on 3DprinterOS.

We used the Prusa_I3_Mk3 printers to 3D print our design. Our first 3D print of the positive of the front half of our design looked pretty good except the eyes on the mushroom were not visible as the layer height was not small enough. We then adjusted the layer height from 0.15 to 0.07. We did not use any supports or build plate adhesions as the base of our print was just a rectangular prism. While the print did take twice as long, the second time around the eyes were visible, and the entire 3D printed piece looked very nice.

Combining an estimated 1.5 hours working on the SolidWorks CAD and 15 minutes preparing and slicing the 3D printed file, the total time spent creating the 3D printed positive was 1.75 hours.

Fusion 360 and CNC Machining

In order to CNC our pawn, we first had to convert the CAD of the pawn into a gcode suitable for the OEDK’s Carvey. However, since we had already saved the pawn as two separate halves and the piece did not contain complex geometries, we were able to bypass Autodesk Meshmixer and proceed directly to Adobe’s Fusion 360. After importing the pawn’s .STL file, scaling and setting the correct origin of the part, converting the part into a meshbody, and converting that mesh into a BRep solid part, we were able to use the CAM tools of Fusion 360 to define the wood our part was to be carved in (~2x~4x~6 inches), determine the CNC process our part was to undergo, and export the setup using a downloaded gcode compiler specifically made for the OEDK’s Carvey CNC Machine. In all, it took around 20 tries before we created a viable gcode file for the CNC Machine as we did not properly define the setup’s origin among other minor things. However, we eventually succeeded and went on to repeat the process by exporting another gcode setup with different settings that made up a finer, final cut for our part. Finally, with both operations correctly configured into respective gcode files, both files were uploaded to Easel and the CNC mold for our project was cut.

The first attempt of our CNC cut was not fully completed as we ran out of time. However, even though it was incomplete, the first attempt rough cut looked quite good, so we didn’t change any setting or adjust our gcode before our second attempt.

As the cut was not complete but still used most of the first piece of plywood, we decided to cut again and use a new piece of wood for our second attempt. We decided against using a fan attached to our drillbit as everytime the fan was present, the drillbit would collide with the L clamp while the machine was calibrating. So, we decided to vacuum every 5-10 minutes to remove all of the sawdust the machine produced. It should be noted that the fine cut of our part had to be stopped midway through as the drillbit became lodged in a hole of the wood. We originally thought the small hold would not have an effect on our cut but we incorrectly judged the length of the hole. However, after reflecting upon the results of the finer cut, we decided that there was not a noticeable difference between the rough and fine cuts of our part and we therefore decided to keep the part with its fine cut only part way finished.

Combining an estimated 3 hours spent preparing the files for the CNC machine with the 3 hours it took to prepare the Carvey and carve both cuts, the total time spent creating the CNC part of our project was 6 hours.

Molding and Casting

With both positive halves of our mold either machined or printed, we used liquid silicon to form the two negative halves that would go on to actually cast our pawns. However, in order to make these silicone molds deep enough to completely submerge our pawn, we had to increase the height of positive molds by adding cardboard to their edges. With this done, we mixed 100 grams of the 2 liquid silicone components in a 1:1 ratio and poured 50 grams of the mixture onto the positive molds, which cured after a 5-6 hours.

After removing the silicone negative mold halves, we were finally ready to cast the pawns. Using cardboard behind each mold half for support and three rubber bands to hold the halves together, we mixed 15 mL of each of the 2 liquid plastic components in a 1:1 ratio and poured the mixture into the cavity formed by our silicone molds. We determined the estimated total volume of our piece was around 30mL by using playdough to fill our molds.

After about an hour had passed on our first cast we grew concerned about our liquid plastic as it had failed to completely harden in that time, and we knew that it should have only taken 15-30 minutes for it to harden. To remedy this, we focused on mixing the liquid plastic components more vigorously for over a minute, making sure the liquid was quite warm/hot before stopping mixing, which solved the problem. Every cast after that hardening within 15 minutes of pouring. One problem we had with casting was that the CNC half and 3D printed half was not perfectly aligned and the seam was very visible. We believe this problem occurred because our original CAD file did not have the mushroom centered on the pedestal. We attempted to fix this problem by visually making sure the pieces were aligned as best as possible before pouring. Our later casts definitely show this effort as their seams are not as visible and the two halves seem to line up well.

For many of our casts, we attempted to add color and designs. Some examples are having a different color for the base and for the mushroom, pouring two different colors in at the same time, and only adding colored dye after mixing the liquid plastic components to attempt adding a swirl of color.

13 pawns were made in total (12 completed with 1 failure). Combining the 30 minutes we spent pouring the silicone molds, the hour spent pouring the failed plastic pawn, and 4 hours for pouring the 12 successful pawns at 15-30 minutes per pour, the total time attributed to molding/casting was 4.5 hours.

Conclusion

In conclusion we are really happy with how our pawn pieces turned out. Some things we are proud of about our project is our 3D printed positive, our ability to keep working through problems with making the gcode in Fusion360, using the Carvey, and making casts, and our final casted pieces and their colorful designs. If we were to do this project again, some things we would change would be making sure to center our mushroom on the pedestal in our CAD file, attempting different fine cuts to see if any would make our CNC half look better, and sanding our final casts so they all were the same height and the seams were all aligned.

Cost Analysis

3D printing: 1 print of full design using 16.49g of PLA for $0.33. 2 print of positive front half of design using 20.62g of PLA for $0.41. Total cost of 3D printing is $1.15.

Wood: 2 pieces of 2x4x6 inches at $1.48 for a 2x4x24 piece yields ~ $0.74
Silicone: 2 halves * 50 ml per halve * 160$/gal ~ $1.60
Plastic: 13 paws * 30mL per pawn * 70$/gal ~ $2.73
Cardboard: Minimal Cost
Popsicle Sticks: Minimal Cost
Paper Cups: Minimal Cost
Dye: 3 bottles at $2 per bottle for a total cost of $6.

Labor: 3.5 hrs (1.75hrs per person) for 3D printing and CAD + 12 hrs (6 hrs per person) for CNC + 5.5 per person for molding and casting, at $10 an hour makes a total labor cost of $210.

OEDK Access and Resources: Free

Total Cost is $222.23.