Overview

For this assignment, we used a computer numerical control (CNC) system to machine two pieces of wood into different shapes.

 

File Preparation

I started by going to TheNounProject.com to look for a .svg file that spoke to me. At this point in the semester, I was surprised that I hadn’t used my cat Tripper as inspiration for an assignment yet.

I looked up various cat images, then picked a particularly mischievous looking one to use. I picked Cat by Kim Sun Young from The Noun Project (CC BY 3.0).

I downloaded Carbide Create to my laptop, then imported my .svg file. I followed the directions in the assignment to scale the image to about 3” x 3”, create my pocket and contour cuts, and add tabs. I initially wanted to make the eyes and mouth raised, leaving a pocket around them.

However, due to the minimum size of the machine bit being 1/8”, I could not get that level of detail between the small features. Instead, the eyes were a pocket cut, and the mouth, being quite small, was a contour cut with no offset. I added three 0.1” x 0.1” tabs to keep my piece in place once the contour cut was completed. Once the simulation looked good, I loaded the file onto the CNC mill.

CNC Machining

The machine is used was the Carbide 3D Nomad 3 Desktop CNC Mill. I secured a piece of plywood onto the platform with double sided tape, then placed my 3.5” x 5.5” wood block on top, tightening the screws to ensure it wouldn’t move around. When working with wood, I like emphasizing look of the wood’s natural grain, so I placed the side with more striations on top. After attaching the probe piece, running the probing program, and removing the probe, I ran the loaded file. The total milling time was about 13 minutes. I repeated the process with my second block of wood to get two cats.

Post-Processing and Finishing

There were quite a few splinters and some remnants of the tabs after I popped my cats out of their blocks. I sanded these off with 80 grit sandpaper, then smoothed the surface, sides, and small features with 220 then 400 grit sandpaper.

To preserve the natural appearance of the wood while protecting the surface (and also adding a nice orange-y scent), I used beeswax and orange oil.

I worked it in, let it sit for 20 minutes, then wiped off the excess. The final pieces are in the featured image!

Cost Model

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Pine Board (1x6x12”)	$21.28 /6 sqft	Home Depot	0.29 sqft	$6.21
	Assorted Grit Sandpaper	$7.99 /36 sheets	Amazon	3 Sheets	$0.67
	Beeswax and Orange Oil	$9.98 /bottle	Home Depot	1 Bottle	$9.98
Labor	Prototyping Engineer	$36 /hr	ZipRecruiter	1 Hour	$36.00
	Wood Worker	$21 /hr	ZipRecruiter	½ Hour	$10.50
Overhead	Makerspace Access	$40 /month	The Maker Barn	1 Day	$40.00
Total					$103.36

 

Files from The Noun Project are free with attribution, but you could choose to purchase a royalty-free commercial license instead. Carbide Create software is also free to download. For the wood board, I couldn’t find any online that were the same dimensions as the wood I used, so I did the cost estimation by cutting 3.5” x 6” pieces instead. I included the cost of the whole bottle of beeswax because I couldn’t estimate how much I used, but it was probably less than 1/10 of the bottle. I chose to not include a CNC operator in the labor charge and instead just count one hour of the prototyping engineer’s time because I was able to prepare the file from the .svg, load it into the CNC mill, and get my two machined cats all in less than an hour (this was during the tutorial). I did add half an hour of wood worker time for the waxing process due to the waiting, even though that was only maybe five minutes of active work. The Maker Barn (that I often reference in these) has a CNC router. I included the cost for the whole month despite only needing one day because that’s how monthly memberships work. As always, labor and overhead were the most expensive with materials only costing $16.68 (probably much less if I measured the beeswax).