Brass & Onyx Ring
A Max Westerman Project | Exploring the limits of machining
For ShopCraft, a theatre class dedicated to manufacturing props, costumes, scenery, & structures, I decided to make a brass ring for my prop. It was sort of a two-birds, one-stone situation - create a prop for the class project and learn valuable machining lessons.
Video Game Model
Resulting Solidworks Model
The entire model had to be remade using Solidworks. The model from the game has very few polygons and would be incredibly uncomfortable, requiring an altered band. While seemingly simple, this required some advanced modeling tools.
Planning & Theory
Given my school's machine shop only has a 3-axis CNC and not a 5-axis, great care was required for the planning behind machining this part. Due to its noncircular nature, it could not be placed in a lathe and thus the outline of the ring had to be created in another way. The final design included material on the edges of the ring to clamp. If these pieces were not there the ring would not be affixed to the bed of the CNC and fly off due to the cutting bit.
Resulting CNC Plan
The side profile of the ring was CnC'd out, flipped, then the other side profile was cut. This resulted in the required geometry on the sides but did not include any inlays where the onyx would sit.
Thus overhangs were planned into the design to level the ring out so the gem pocket could be milled out.
The drillbit was at the forefront of the design process. There are curves in the clamping attachments to allow for greater bit freedom, and hard pocket corners were avoided as they would cause rounding. Once the ring was machined, the clamping attachments had to be removed with a hacksaw and ground down with a vertical belt grinder. A dremmel was placed in a vice with a polishing compound and the ring was buffed.
In the game, the ring is inlaid with onyx, and due to onyx's low cost, availability, hardness, and resistance to cleavage, it was also used in the real ring. I bought a pyramid of onyx for ~20$ on Amazon and CnC'd the pyramid into a pillar, with the head of the pillar cut into the shape of the main gemstone. Then, using a belt grinder and files, the onyx was cut to size. It was then epoxied into the ring and clamped.
The onyx was very small compared to other items made in the machine shop and due to the danger of dropping the onyx into the belt grinder, a large portion of the material had to be removed by hand.
Theory Turned Practice
Machining the Brass
Before embarking on this project I did not have a good grasp on the limitations of the CNC machine. Given my work on machining parts for the Jet Engine Project, I knew that there would have to be clamp geometry and clearance for the endmill, but not more than that.
The initial design with the diamond shape backing for the gem inset had to be scrapped as the CNC doesn't like 3D geometry like that. The chamfers also had to be meticulously honed in by Justin, the Machinist here at DU. I had thought I could send in a SolidWorks file and the program would figure out how to machine it - in reality, it had to all be hand programmed. I believe this will be absolutely key for my work as a mechanical engineer in the future - a small design change on the part of the engineer with the machinist in mind could save tons of time.
The first operation was machining down the side profile of the ring, beveling the inside and outside of the ring, then creating the chamfers on the gem inset in the center. This took ~3 hours with the programming and Justin, with his endless kindness, stayed an extra two hours after closing to help me get this project done on time. The next day the opposite side was machined, removing the base plate seen here.
Second Face Machined
The piece was then machined further down, accidentally forgetting to make the overhangs to center the gem for the inset. Luckily, the inset can be created by just clamping the ring itself, so the overhangs were not required.
Final Rough Copy
The remaining brass blocks on either side of the ring were machined down and then cut off with a small bone saw. Seen on the right is one of the blocks after being cut off.
Polishing the Ring
The large tabs on each side of the ring were ground down using a Dremel tool in a vise, then a more aggressive round-over for the interior and exterior diameters was created. These left gouges in the surface of the ring so it was polished on a polishing wheel using red compound.
The onyx & inlay has not been completed yet.