n-Hedral – Behind the Scenes, Part 3: CNC Routing

June 4, 2014 CNC
If you haven’t checked out my Masters Project, n-Hedral: Customizable Furniture System, please do so here!

 The main structure of the n-Hedral Furniture System is made from CNC routed panels.  For a commercialized product, fabrication would be done with pre-finished panels like, phenolic faced plywood, to reduce finishing time and simplify manufacturing.  While this would be great if I had a source for purchasing them, and some extra time to do some test cutting and dial in the correct speeds, I wasn’t able to do this for this project.

So, for my display model, I chose to use Baltic Birch plywood to provide a simple, light aesthetic.  From a few tips on CNC forums, I decided it would be a good idea to pre-coat the plywood with a sanding sealer.  The purpose of a sanding sealer is to put a coat of finish on the wood that sands easier than the final finish, so finishing time is minimized.  For me, this seemed to make sense, as I was cutting two full sheets of plywood and would have to sand around 100 individual parts.  From additional reading, I found that applying finish prior to CNC cutting actually aids in reducing tear out from the endmill.  So, I started by first giving the plywood a good sanding with 150 grit, and then a good, thick coat of Minwax Water-Based Sanding Sealer.

  • Sanding down the bare wood.

With the sealer dried, it was time to cut.  It turned out that the sanding sealer did the trick.  Instead of outright chipping, the sealed wood just had a bit of feathering, which could then be easily sanded off later.

  • CNC cutting at Philadelphia University

To keep the pieces from moving once they were cut, tabs were left to keep them attached to the sheet.  These tabs needed to be cut and removed, and then each part was sanded smooth by hand.

  • Cutting out the pieces with a keyhole saw.

After smooth sanding the raw wood, the parts were then coated with two coats of brush on water-based polyurethane.  They were then sanded down using 220 grit, and sprayed with Minwax Polycrilic.  At my local hardware store, I picked up some 3M Sandblaster sandpaper, to try it out, and I’d like to report that it really does work.  Compared with conventional 220 grit sandpaper, this stuff was much more durable, and clogged up much less frequently.  It is a bit more expensive, but totally worth the money.  I usually wouldn’t take the time to talk about the products I use, but this stuff really works.

  • Brushing on the 1st coat of water-based polyurethane.

What isn’t shown is that I also used a wipe-on polyurethane on the edges after sanding, but before spraying.  Spraying the parts only really covers the flat sides, so I needed a way to coat the ply-edges without creating streaks or blobs.  So, I used a rag to rub waterbased Minwax Polyurethane on the edges.  Here is the full finishing process listed out:

  1. Brush-on Minwax Water-Based Sanding Sealer onto raw wood
  2. CNC routing
  3. Cut tabs to free parts and clean up edges with standard 60 grit sandpaper
  4. Sand with generic 150 grit sandpaper on all surfaces
  5. Brush-on 2 coats water-based polyurethane
  6. Sand with 220 grit “3M Sandlaster” sand paper
  7. Rub on 2 coats of water-based polyurethane to ply-edges with a rag
  8. Lightly sand faces to remove any excess rubbed poly
  9. Spray with 2 coats of Minwax Polycrilic

Now, as I said above, this whole process would have been simplified in an industrial setting.  But for this prototype, this was the cheapest, most time efficient method I could come up with.  Here are the finished parts ready for assembly:

Click here for the next installment of n-Hedral, Behind the Scenes!

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