'무한상상실' [Muhansangsangsil] (literal translation: 'Infinite Imagination Lab'... ) is a common name for government-run makerspaces in South Korea. I used to work in the one at Gwacheon National Science Museum as a maker-in-residence.
The lab went through an expansion last spring as it gained more popularity, but it turned out that number of desks required for the new larger area was seriously underestimated.
And the problem was, the museum as a public institution has a strict regulation when acquiring fixed assets such as furniture and machinery. They can only be acquired within the certain period of the year.
In order to solve this issue as well as to polish up my CNC routing technique, I decided to develop a CNC millable table design.
The design requirements for the table were:
- The table must be made out of a single sheet of plywood.
- Be less creative in form, but the design should be durable and timeless.
- Hide joints (not to look like a CNC desk).
- Use various CNC woodworking techniques as an educational tutorial.
A single sheet 18mm thick 4' x 8' plywood was used as we had enough in stock already.
For each leg, two parts(outer / inner) are joined together with wood glue to increase stiffness. And then each two legs are joined together with a dovetail connector. This is to fit all the parts within a single plywood sheet.
- A 4' x 8' CNC router
- 6mm or 1/4 inch single flute end mill (preferably a compression bit)
- CAM software of your preference
- A sheet of 4'x8'x18mm plywood
- 6 x 30mm wooden dowel pins ---- 16
- M6 x 60mm connector bolts -------- 8
- M6 insert nuts -------------------------- 8
- wood glue
- woodworking clamps (more than 8)
- belt sander, electric sander, varnish... other usual woodworking stuffs
Step 1: Tool Path Generation & Milling
I tried to incorporate different 2.5D milling techniques so that the desk itself can be used as a tutorial for CNC woodworking.
- 0_Fixture_2mm (blue) : Engrave designated places for wood screws (to prevent end mill to cut screw heads)
- 1_Pocket_12mm (brown) : Designated places for dowel pins for the outer side of leg module. Bore only 2/3 (12mm) of the thickness to hide pin holes when seen from outside.
- 2_Through hole_19mm (black) : Dowel pin and bolt holes and for inner side of the leg module. You can do 15mm - 15mm boring on both(inner and outer) side of the legs to hide holes completely.
- 3_Through hole_19mm (green) : Round ones are for connector bolts which connect the leg module with horizontal beams.
- 4_Pocket (pink) : If you use connector bolts shorter than 40mm, you'll need to bore . For example, bore 10mm for 30mm bolts.
- 5_Pocket_15mm (purple) : Slots for insert nuts.
- 6_Pocket_12mm (red) : Slots for desk slap - frame connections
- 7_Cutting lines (black) : Profiling
- 6mm single flute down cut end mill
- Cutting depth 3mm
- Spindle Speed = 12,000 - 14,000 RPM
- Feed Rate = 3.0 inches per second
- Plunge Rate = 1.5 inches per second
Instead of generating tool paths by layers, I grouped tool paths by parts so that I could proceed to the next step (sanding, glueing) with completed parts.
Total cutting time takes less than two hours.
Step 2: Assembly 1: Legs
When the legs are done, I recommend to start working with them because it's the 12mm pocketing of desk slab (layer 6) that takes most of the time.
- Starting with sanding down prickly edges with belt sander.
- then place dowel pins to the holes
- Add enough wood glue. Evenly.
- Apply wood clamps at least 3 points for a single leg and wipe off excessive glue.
- Assemble two legs into one piece with dovetail connecter.
- Leave the clamped legs for several hours, preferably a night.
If you have enough clamps for both side (i.e. +20) you can get them all done together.
Step 3: Assembly 2 : Frame
Connect the assembled leg module and horizontal beam with connector bolts and insert nuts. Use impact driver to tightly fasten the joints.
When the frame is done, put table slab on the floor with the pockets facing above. then carefully align the joints to the corresponding pockets.
Normally few rubber mallet strikes would make the joints perfectly fit in to the pockets, but at times you might want to apply wood glue if connections are not too tight.
When finished, turn the table downside up. Now it's almost ready.
Step 4: Finishing & Painting
Since I had no prior experience with wood finishing and neither wanted to spend extra money, I stuck with what I already had.
- I used a electric sander with 400 grit sandpaper to smoothen the bare surface. Clear dust with compressed air.
- Then first coat the varnish evenly, but also thick enough and meticulously.
- Wait one or two hours and sand the surface lightly with the electric sander.
- Finish coat the varnish, give enough time to cure, sand the surface again.
You'll get smooth, pleasant surface after this,but I don't think its 100% hydrophobic.
I've went through 5 iterations with different people and the desk turned out to be a great educational tool for beginners.