Metal Cutting and Post-Processing
For this assignment, I was tasked with cutting out two identical diamonds using a plasma cutter and applying various post-processing techniques learned in class.

1. Angle Grinding

• To remove the dross from the plasma cutting process, I used an angle grinder. Fortunately, there wasn’t much dross since I opted not to add any intricate designs to my diamonds, allowing me to focus on getting more creative with the post-processing techniques. I quickly completed the grinding using both the angle grinder and the magnetic grinding block.

2. Sandblasting

• After grinding, I moved on to sandblasting to remove any remaining impurities such as rust and to create a smooth surface for the next steps. This process took longer than anticipated, but with patience and periodic checks, I was finally satisfied with the appearance of my pieces.
  

3. White Spray Paint

• After sandblasting, I cleaned my pieces thoroughly in preparation for painting. I applied three coats of white spray paint to each side of the diamonds. I spent one day painting the top side, applying additional coats every twenty minutes, and repeated the process the following day for the bottom side.
  
  
• This part was actually a little tricky for me. The day that I decided to paint my pieces white was a very humid day and it was taking way longer than expected to dry and I ended up smudging one of the sides. To fix this I sanded it to make the surface even again, and reapplied a coat of spray paint to fix one of the sides.

4. Creating the Stencil

• While waiting for the paint to dry, I decided to create a spiral stencil. I found a suitable design online and converted it to an .svg file for the vinyl cutter. Although I only needed two stencils, I made two extras as backups. One of my stencils didn’t adhere properly, but thanks to the extra, I had a backup ready.
• Applying the stencil to both diamonds was challenging, especially since the design wasn’t symmetrical. I trimmed any excess parts to make handling easier before moving on to the next step.
  
• Removing each line of the stencil was very tedious but I was very careful and used tweezers from home so I could easier grab the stencil. The tweezer was also helpful when the stencil was snagging on itself at the very middle, because I could make sure the stencil remained where it was supposed to be instead of ripping away with the part of the stencil that needed to be removed.

5. Gold Spray Paint 

• Once the stencil was in place, I applied a single coat of gold spray paint. To ensure easy stencil removal, I didn’t wait the full 20 minutes for drying and carefully peeled it off while ensuring the surrounding paint wasn’t disturbed.
  

6. Matte Clear Coat (2 Coats)

• After removing both stencils and allowing the gold paint to dry, I applied two coats of matte clear coat. Having used this finish before, I preferred its texture and appearance over the glossy alternative. Since it was a hot and dry day, I waited about 10 minutes between coats. I was very pleased with the final result once the last coat dried.
  

7. Clean-up

• After completing the project, I ensured that all my work areas, including the loading dock and vinyl cutter station, were cleaned up and organized.
  

Cost Estimate

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Steel Sheet	$10.47 per 1 sq ft	HomeDepot.com	15 sq in	$ 1.09
	Vinyl Sticker	$ 5.99 per roll (576 sq in)	Joann.com	30 sq in	$ 0.31
	White Spray Paint ( 3 coats each side = 90 sq in)	$ 5.98 per can (Up to 12 sq ft)	HomeDepot.com	90 sq in	$ 0.31
	Gold Spray Paint (1 coat = 15 sq in)	$ 6.98 per can (Up to 12 sq ft)	HomeDepot.com	15 sq in	$ 0.06
	Matte Clear Coat ( 2 coats each side = 60 sq in)	$ 5.98 per can (Up to 12 sq ft)	HomeDepot.com	60 sq in	$ 0.21
Labor	Metal Shop Operator	$ 15.00 /hr	Ziprecruiter.com	1 hr	$ 15.00
	Prototyping Engineer (You!)	$ 12.00 /hr		2 hr	$ 24.00
Overhead	Facility Cost (Machine Time) ·        ½ hr sand blaster ·        10 min angle grinder ·        10 min plasma cutter ·        10 min vinyl cutter	$ 80.00 /hr	Practicalmachinist.com	1 hr	$ 80.00
	Quality Control	$ 24.00 hr	Ziprecruiter.com	1 hr	$ 24.00
Design	Engineering and Development	$ 30.00 /hr	Ziprecruiter.com	5 min	$ 2.50
	Iterations	–	–	1	–

 

Cost Analysis

Cost Per diamond: $ 28.48

• This cost is determined excluding overhead because if this item were to be mass produced the cost of overhead per item would be nearly negligible and in the real world this would only be a small additional fee. I also used my own labor costs which would make the item cost more since it most likely took me longer than someone who is highly experienced in this field, but my charge per hour would be cheaper since the quality probably wouldn’t be as good. If the cost were to be calculated for an experienced worker, it would be $ 19.48.

 

• For this assignment two diamonds were made therefore the total cost would be $ 56.96 (using my hourly rate). It is also important to note that I did not include the wait time for the paint to dry into the hourly rate because this time will likely be spent working on other items, or for me, doing other schoolwork.