This weeks assignment was to CNC an object out of a piece of wood. I found an image of Kirby on the web and converted it to an svg file. I then used Adobe Illustrator to refill and reconnect some gaps that were left after the conversion.

I measured the piece of wood I would cutting from using a ruler (for height and width) and calipers (for thickness). Using Carbide Create on the computer attached to the Nomad machine, I set the dimension of the base and imported the SVG file. I set a pocket with different depths for each of the internal sections of the image. The depths in order of shallow to deep, and grouped together for same depths were: {pupils, front foot, lower eye}, central body, {back foot, back hand}. Then a contour cut was set to cut around the image.

I used two pieces of double-sided tape to stick the wood onto the cutting platform, then set the zero.

Now that everything was set up, it was time to run the CNC. However, during the contour cut the wood block came off and the mill cut into the body of the Kirby. So I would have to try again.

I also noticed that the 1/8″ mill bit was too large for some of the finer parts of the image, like around the cheeks and eyes. So I edited the pocket cuts to use a 1/16″ bit instead, while the contour cut would still be 1/8″ since the 1/16″ bit was not long enough to cut through the whole wood block. I also covered the bottom of the wood block with double-sided tape and was extra careful in cleaning off the adhesive surfaces on the wood block and the cutting platform.

I changed the mill bit out for a 1/16″, re-zeroed the machine, and tried again. The pockets turned out very good with the 1/16″ and wasn’t much slower than using the 1/8″. Once the pockets were cut, I switched to the 1/8″ bit and began the contour cuts. However, like last time the wood came off the platform during the contour cut, creating holes in the piece again.

Taking this opportunity, I decided to improve on the design of my CNC cut. I removed the glare marks on the Kirby’s feet to simplify the svg (since I didn’t really like how they looked on the CNC anyway) and closed up the left cheek which had a hole in the shape. I also decided not to cut out the pupils of the eyes, I felt this looked better than the shape that resulted when trying to cut them out. I also grouped all the pockets with the same depths into one command each in Carbide Create to simplify and speed up the CNC process. The depths were: 1.27 mm (front), 2.54 mm (middle), 4.31 mm (back). I also let the feet and back arm be cut with the 1/8″ bit as the smaller bit did not affect the quality of those cuts and using the 1/8″ would be a little faster.

After remeasuring a new block of wood, I again covered the bottom with double-sided tape. I also wrapped masking tape around the block to give it additional holding strength to ensure it did not come off again.

This finally worked and the CNC was able to complete the cut. Though parts of the contour did not cut through all the way to the bottom. This was because I had averaged the thickness of the wood after measuring it in several places. By averaging it, I accidentally ensured that it would not cut through the parts of the wood that were thicker (though it would reduce the possible damage to the cutting platform). The uncut parts were very thin and easy to take off, leaving me with the final non-post-processed object. I then sanded the object with 180-grit and then 220-grit sandpaper.

I would repeat this process for the second copy of the object. This time I tried using the Shapeoko device (as the Nomad was being used at this point). It was basically the same, but instead of tape I used clamps, wore safety glasses, and used a shrapnel shield in front of the piece. Unfortunately, on my first attempt the 1/16″ bit snapped as soon as it touched the wood. I was able to complete the cut after replacing it.

Having not learned, I had a similar problem in that the contour cut did not penetrate all the way through. This one was a little more pronounced and I had to cut the object out. Then I used a rasp, then a file, then the sandpaper to smooth it out.

For post processing, it felt wrong to paint it anything but pink, which we did not have. So at first I thought of just applying gloss to make it shiny. However, the gloss actually ended up making no visual difference to the objects. So I sanded the gloss down and decided to apply wood stain to the objects instead. I applied the wood stain and then removed it according to the instructions on the tin, and then sanded the object down with 280-grit sandpaper to remove any remaining stickiness.

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Whitewood Board (1”x4”)	$1.11 /ft	Homedepot.com	1.3 ft	$1.44
	Double-sided tape	$0.07 /ft	Xfasten.com	3.9 ft	$0.27
	Masking Tape	$0.03 /ft	Uline.com	1 ft	$0.03
	Clear Gloss Spray Paint	$6.48 /can	Homedepot.com	1/10 can	$0.65
	Walnut Wood Stain	$20.99 /qt	Mcguckin.com	1/15 qt	$1.40
Labor	CNC Operator	$18.75 /hr	Talent.com	1.2 hrs	$22.50
	Prototyping Engineer (You!)	$39 /hr	Salary.com	0.33 hr	$13.00
Overhead	Facility Cost (Machine Time) – CNC	$20 /hr	At-machining.com	1.2 hr	$24.00
	Quality Control	$20.93 /hr	Indeed.com	0.5 hr	$10.46
Design	Engineering and Development		Covered in Prototyping Engineer		$0
	Iterations		Covered in quantities of above cost types	3	$0
Misc.	Waste and Scrap		Covered in total materials quantities (equivalent of 2 iterations)

Total Cost: $73.75