In this assignment, we were challenged to create an original, reproducible part that fits in the geometry of a rhombus with side lengths 2.9 inches and amplitude 2.5 inches. The trick? We had to use the plasma cutter to cut the initial shape.

I chose to start my project with a zigzag pattern with 5 strokes. To create this pattern, I had to create a vector file which accounted for the material loss and the imprecision of the plasma cutter which would be addressed in post-processing. These considerations led me to the this design.

 

This part was designed with even spacing between the ‘zigs’ as well as consistent ‘zig’ size. After a long search for a material which was 1/4″ thick which could handle the precision of this cut, I resolved to produce my final part on 1/32″ plate steel. For the machine settings on the plasma cutter, I used a feedrate of 130in/minute at 30Amps.

 

 

 

Immediately the after, I removed the slag by bracing the design with a clamp and chipping it away with a chisel and hammer. This method was very effective at quickly removing pieces without damaging the part.

 

I then sandblasted the part to better see the physical discrepancies between the pieces. This allowed me to see the variation in the parts very precisely, and I was able to process the parts so well that they became very close to identical.

 

The angle grinder allowed me to round all of the exterior edges very quickly and remove a significant amount of material very quickly. This step allowed me to follow-up with the file and have significantly less material to remove by hand.

 

 

But, with that said, it still took approximately 2 hours to file the parts down to the point that they were essentially identical to the eye. Filing in-between the zigs became incredibly challenging due to the limited number of files that had coarse edges at such a thin size. Eventually, the pieces overlapped quite nicely.

 

I felt that my part was ready for finishing, so I took my piece outside where I covered it with a few layers of clear-coat spray paint. And at first, I thought I had finished. Over time, however, I began to see that the clear-coat had not protected the part from oxidation and rust the way I thought it would.

So, I decided to re-sandblast the part and try powder-coating. Unfortunately, powder coating does not effectively remove the base layer of a powder coat, and in an attempt to remove that layer using the belt sander in the machine shop, one of the diamonds slipped out of my hand and was completely destroyed.  So, I refabricated a new pair using the same steps as before and sandblasted it correctly. Recreating the piece (particularly the filing) took a long time, but I was very happy with the final product which has done a good job of maintaining its luster.

When evaluating the cost, I feel that it is unfair to charge for the time I lost due to mistakes made on my part. But, overall, this is a more time-heavy project and the nature of the work reflects my how I valued my time when I was completing each step.

Evaluating the cost:

• Design Cost
  • File preparation beginning with adobe and going all the way through generating the G-Code took me approximately 2.5 hours to prepare due to small changes made in the machining software to accommodate a more precise cut. I also had an issue with endpoints being incorrectly aligned which significantly delayed the amount of time I spent on this.
    • I would charge $20 for this out of frustration that the part isn’t being made on a WaterJet.
  • Access to Fondren Library for a Rice Alumnus is $75/year. Fondren Library has computers with the most up-to-date Adobe Creative Cloud Software.
    • I would argue that this assignment would constitute another 1/52 of the Fondren Library cost as the file creation a period of one week for me.
  • Post-processing using the various techniques explained above consumed a total of 7 (6 more for the first attempt) hours due to the material strength of steel and the lack of use of a more appropriate tool to do the fabrication (*cough* *the WaterJet* *cough*).
    • I would charge a total of $60 for the time I spent doing this, because as frustrating and slow-paced as this step can be, it is also peaceful.
• Consumable Cost
  • 12″x12″x1/32″ steel sheet = $15
    • This is an appropriate size sheet to do this part fabrication on a plasma cutter’
  • Powder for Powder Coating = $12
    • This is for an 8oz canister, and one successful coat would likely use up about 1/10 of this material.
• Machine Time
  • Access to a Plasma Cutter, an angle grinder, chisel, hammer, clamps, files, and a Powder Coater
    • Machine time including file processing with the plasma cutter was approximately 30min. Everything else typically is expected and priced as part of the machine time when outsourcing to a machining company
    • This would cost approximately $7.50 per part for the plasma cut and another $15 tool rental for the additional needs.
    • The powder coater would incur an additional $10 rental due to the necessary support machinery of an air compressor and an oven.

Total Expense: $131 (Including the first attempt: $235)