Written by Chris B
At first glance, this might seem like a pretty dumb idea— but hang with me, there’s method in the madness.
I’m always reaching for a sanding block and usually just grab the nearest bit of scrap wood and wrap some sandpaper around it. Then I got a shiny new six-inch (150mm) sander, leaving me with a pile of unused five- inch (125mm) sanding discs. Add to that my brand- new Genmitsu 4040 Pro Max CNC and a desire to learn Fusion 360, and… well, here we are. What better way to try my hand at 3D carving than by making something weirdly useful?
The Plan (Kind Of)
I wanted a nice, ergonomic hardwood sanding block— something that feels good in the hand and looks better than scrap pine. My Fusion 360 skills are still developing, though, so instead of drawing it digitally, I mocked it up physically.
First, I built a simple 6mm MDF shell shaped to fit one of those sticky sanding discs. I eased the bottom edges so the disc could wrap around smoothly. Then I filled it with Plasticine and shaped it by hand until it felt comfortable. I’m very left-handed, so this was a chance to make a tool that fit me perfectly — or at least as close as I could get before my patience ran out.
From Clay to CAD: The Magic of Photogrammetry
Organic modeling in Fusion 360 is hard, so I went the scan route. I built a basic turntable, covered it in black paper, and added some scale markers. Then I used photogrammetry — a fancy way of saying I took a ton of photos from different angles and let software (Metashape, in my case) stitch them into a 3D model.
Pro tip: Use manual camera settings, tripod, and good lighting. It takes trial and error, but the results are pretty cool.
The initial model came out okay, but the bottom was rough — I didn’t photograph underneath. I cleaned it up using MeshMixer (free and excellent), flattened the base, resized it, and smoothed out the surface to get rid of the clay imperfections.
Metashape - model created from turntable photos.
Meshmixer - fixed, cleaned and sized model.
Genmitsu 4040 Pro-Max to the Rescue
I exported the cleaned mesh as an STL and imported it into Fusion 360 (thank you, free hobbyist license!). I set up two toolpaths:
- Adaptive clearing with a 4mm compression end mill
- Parallel finishing with a 1mm tapered ball-end mill
I cut the stock from oak, mounted it using blue tape and superglue on a 6mm MDF sacrificial board (no way I’m damaging my new spoilboard), and got carving using only my phone and the Genmitsu app via the Wi-Fi module. Simple, clean, and dust-proof — perfect for a workshop environment.
I quickly learned that the dust shoe wasn’t super effective with steep angles and tight corners and could get in the way. Also, my conservative speeds (and tiny bit size) made the process slooow — especially the parallel pass, which took over four hours.
Disaster (and Recovery)
The first oak block was coming out beautifully... until I lost power. Luckily I had set my origin into memory using G28.1. I tried editing the GRBL code to restart mid-job — risky move. Unluckily, my G28.1 position I saved was completely wrong and was about 6mm below the spoil board – not sure how that happened. The bit plowed right through the workpiece. Lesson learned!
Take two: I switched to a block of iroko, re-ran the job from scratch, and the result was stunning. The finish straight off the 1mm ball-end bit was almost perfect — I could’ve left it raw, but gave it a quick sanding to remove leftover Plasticine texture and finished it with Rubio Monocoat (sample pack for the win!). Add a stick-on hook pad, and boom — custom sanding block, perfectly shaped for my hand.
What’s Next?
This was a surprisingly fun project that helped me dip into 3D scanning, mesh editing, and Fusion 360 CAM — all using my Genmitsu 4040 Pro Max. Next up, I’m thinking about adding the 4th axis and trying my hand at sculpting custom bow grips for archery.
Moral of the story? Even a "stupid" idea can turn into a great project when you’ve got the right tools — and a CNC router that makes it all possible.
