Computer Numerical Control (CNC) has always been both a fascination and a mystery for me before my studies as a mechanical engineering student. This is my first time doing woodworking with parameters set in the software to complete CNC work. Most importantly, this is a rewarding experience for me to make two identical wood kittens of mine in CNC.

HOW THE REPLICA OF MY TWO KITTENS, pOKI & wHISKI, WERE BORN

1. FIND THE CAT OBJECT ON THE NOUN PROJECT WEBSITE

I found the cat object in SVG format on the Noun Project website. I am envisioning to have two identical pieces cut in CNC to represent my two kittens adopted this June. If I am doing a great job of setting up parameters in the CNC, I should be able to recreate each of them in the form of silhouettes perfectly since they are a bonding pair. Trust me, they look almost the same in a way, lol.

2. process the cat svg file in carbide create

First, load the cat SVG file acquired from Noun Project into Carbide Create software.

Second, go to Job Setup to change the wood stock size to 5.5″ (X), 3.426″ (Y), and 0.75″ (Z: thickness).

Third, scale the cat size to 3.548″ x 3.0″ to fit the size of the wood stock (5.5″ x 3.426″).

Fourth, a 0.125″ offset vector was added to the inside of the cat’s outer perimeter to make space for the pocket cut.

Fifth, 3 tabs were added to prevent the cat piece from flying around after the outermost contour cut was complete. The tabs were added to where the icon has a cross in a square.

3. create toolpath in carbide create

For the replica of my two kittens, I opted for a simplistic design to have one pocket toolpath inside the 0.125″ offset vector and one contour toolpath to cut out the cat’s silhouette.

First, the CNC will do a pocket cut for a max depth of 0.125″ for an estimated time of 4 minutes.

Second, the 13-minute contour cut was set to achieve a max depth of 0.75″ (stock thickness) to make sure only where the tabs were present were uncut by the bit.

Note: pocket cuts (internal geometry) must be done before the contour cuts (external) by using drag-and-drop operations in the toolpath menu

Simulations are a valuable tool for checking CNC operations before the real CNC run.

4. secure wood piece in shapeoko pro & Nomad 3

I made sure nothing was in the way of the toolpath when I was securing the wood and the bottom left corner was free to home the machine.

For Shapeoko Pro, I positioned the clamps to have free space on the left available to cut.

For Nomad 3, the wood piece was secured using the vise on the moving platform.

Note: make sure to have a sacrificial wood beneath the intended cut wood piece to prevent accidental damage to the machine

5. use homing device to probe in carbide motion

First, I loaded my .c2d file made with Carbide Create software in Carbide Motion software. I placed the homing device on the bottom left of the wood piece.

For Nomad 3, I taped the homing device down using painter’s tape since the vice will move during the probe process.

For Shapeoko Pro, there was no need to use painter’s tape to secure the homing device to the wood piece as the platform would remain stationary during the probe process.

I jogged the tool above the homing device hole and lowered the bit into the hole. Before starting the Probe feature, I made sure to attach the magnetic knob to the top of the spindle.

6. start the cnc run to cut out my kittens

Make sure to remove the homing device before starting the CNC cut. In total, the pocket and contour cut took 13 minutes for each cat wood piece.

7. remove wood piece from wood stock using orbital sander

Clamps were used to secure the wood piece to the workbench on the OEDK’s loading deck. The paper towel was used as a buffer between the workbench and the wood piece to prevent the wood piece from rubbing against the dirty workbench.

I used an orbital sander with a 120-grit sandpaper disc to remove the three tabs originally meant to retain the wood piece from flying off during the contour cut.

Occasionally, I flipped the wood piece to sand down the wood chips generated from the not-so-wise use of upcut bit.

8. finer hand sanding for better surface finish

After using the orbital sander to remove visible artifacts from the CNC cutting and milling, finer hand sandings were used to achieve a better surface finish. I used 180-, 280-, and 400-grit sand papers sequentially to get the desirable finish before the final finish using beeswax.

9. used compressed air and damp paper towel to remove wood dust

First, I used compressed air in the woodshop to remove residual wood dust resulting from sanding. Second, I used a damp paper towel to wipe off the remaining wood dust.

10. applied beeswax for surface finish

I opted for beeswax to complete the final surface finish in order to achieve a natural finish while highlighting its grain like the strips in my cute kittens.

11. more sanding to smooth out the surface

After allowing the beeswax to sit and penetrate overnight, I came back to OEDK, only finding the grain appeared more pronounced. I suspected the appearance of wood grain on the surface resulted from the added moisture during the paper towel wipe-off. I redid the fine sanding sequentially using 180-, 280-, and 400-grit sandpaper.

12. clean up the workplace

I made sure to use the vacuum to clean up wood chips in the CNC machine and wood dust from extensive sanding during post-processing. The cleaniness of the workplace is the collective responsibility of everyone who is using the space as our privilege.

reflection after completion

I enjoyed the process of pre-processing the vector file in Carbide Create and CNC machining in Carbide Motion. More importantly, I am better equipped with the skills of post-processing to remove the manufacturing artifacts throughout the semester. In the future, I would love to learn the nitty gritty of CNC metal as it is an essential skillset to complete my prototyping arsenal.

Two takeaways for future woodworking using CNC

1. Use a downcut bit instead of upcut one to achieve a cleaner cut on the wood surface after CNC
2. Refrain from using a damp paper towel to wipe off sand dust. The absorption of moisture can cause raised wood grain, which requires more sanding afterwards

mANUFACTURING COST analysis

The overall cost of manufacturing my two bonding pair of kittens in CNC is $ 128. Unsurprisingly, the biggest part of the manufacturing cost came from labor, overhead, and design, which accounts for almost 96% of the total cost. In the future, if the manufacturing method of CNC is chosen, we need to justify the choice to offset the greatest upfront cost compared to other manufacturing methods.

Cost Type	Cost	Price	Source	Quantity	Total
Materials	Unfinished Natural Poplar Wood Board (0.75″ x 5.5″ x 72″)	$38.26	homedepot.com	9.52% board	$3.64
	5″ Sanding Disc	$16.99	amazon.com	1.37% pack	$0.34
	Fine 180-Grit Sheet Sandpaper	$6.68	homedepot.com	5.5% pack	$0.37
	280-Grit Sandpaper Sheet	$6.99	amazon.com	1.67% pack	$0.12
	400-Grit Sandpaper Sheet	$11.29	amazon.com	1.67% pack	$0.19
	Feed-n-Wax Wood Polish & Conditioner	$11.99	howardproducts.com	5% bottle	$0.59
Labor	CNC Operator	$23/hr	ZipRecruiter.com	0.5 hr	$ 11.5
	Prototyping Engineer (You!)	$25/hr	Indeed.com (Engineering Intern)	1 hr	$ 25
Overhead	Facility Cost	$100/hr	deburringtechnologies.com	0.5 hr	$50
	Quality Control	$22.5/hr	Glassdoor.com (Quality Assurance Inspector)	0.5 hr	$11.3
Design	Engineering and Development	$25/hr	Indeed.com (Engineering Intern)	1 hr	$25
Total					$128