Close-up of cabinet being constructed

Practical project step 4: Building the cabinet

The initial prototypes had now been done, and designs adjusted as needed, so it was time to get building! The first thing to build was the wooden cabinet. That was the central piece of the project, and I needed it built so I could mount the other parts onto or inside it to get the dials working.

Laser cutting the plywood cabinet pieces

After doing the wood bending laser cut test, I hoped that cutting out the plywood pieces to make the cabinet wouldn’t be too tricky. I was wrong!

First, I bought a piece of 4mm plywood from the Uni supply shop – a piece big enough to cut the long side/top panel (800mm long, as calculated in Step 3). This was 995 x 600mm and cost $15, so my total spend was now $55. I already had some acrylic for the dial faces and pointers that I’d bought at Reverse Garbage Brisbane (see Step 2).

Oh no – bendy plywood!

warped plywood
Warped plywood can often be straightened out – click image for more info

Unfortunately, the piece of plywood I was given wasn’t very flat. I think it may have been the ‘bendy’ plywood type, not the straighter type I’d tested on, or it was just a bit warped. I didn’t know there were two separate types – that’s a learning point for next time (and I’ll ask to select the actual piece, so I can choose the flattest one).

I’m sure bendy plywood would be great for making furniture, but (as I discovered when it came to using it) it’s not so good for laying flat on the bed of a laser cutter! If I’d had time, I could have tried to straighten the ply a little, or swapped it for another piece if the Uni shop had been open (which it wasn’t, during an evening class).

Tactics to address plywood issues

To try to keep the plywood flat on the laser cutter, our lecturer Paul suggested I tape it at the edges, and he helped me weigh it down with a couple of reels of cable. He also suggested I adjust the order of cutting, so the smaller items in the centre (like the ‘eyes’ of the front cabinet) would be cut before the larger outside shapes. This was so that the piece of plywood didn’t drop away and result in inaccurate cuts or overheating (due to the head being a different distance from the material). To adjust the order of cutting I edited the artwork to use a different colour (blue) for the stroke outlines of the cuts to be done first, and adjusted the material settings in the Trotec set-up so that the blue lines were cut before the red ones.

Another tactic to cope with the bendy ply was to cut one piece at a time, rather than doing all the panels at once. This meant the laser cutter didn’t have to move over the whole sheet of ply, and we could weigh down the areas that were away from the area being cut, making sure the weights didn’t interfere with the path of the laser head. These tactics worked, but made the process a lot longer than it should have been.

Here is a video showing the long panel being laser cut. You can see the masking tape at the edges holding the plywood down.

 

Seeing the first finished cut piece – the long side/top panel – was quite exciting! Here it is…

photo of long panel
The long side/top panel, straight after laser cutting

However, the excitement soon turned to disappointment when I tried bending the piece. As you can see from the image below, the plywood piece broke at the edge of a bend, probably because the bend cuts were going against the grain. It was not possible to cut it the other way, because the material wasn’t wide enough.

laser cut plywood
Broken plywood piece

I decided to work with what I had, and make the side/top panel in two pieces joined at the top. I cut out the front and back panels, and plus some smaller pieces to be used as strengthening or joining panels inside the cabinet.

Laser cutting the acrylic dial covers

I then laser cut the acrylic covers (to look like glass and protect the dials). The video below shows the dial covers being cut. The laser cutter settings were not quite right, because it was flaming a little more than it should, leaving smoky marks on the acrylic. These marks are possible to remove with oil-based clean wipes (Paul suggests Tea Tree oil is the best!).

The design intention was for the acrylic covers to fit into the brass dial cases and be secured by the three brass screws that were already part of the cases. This proved difficult, because the dials were not exactly circular, and the screws were not equally spaced apart. This was complicated by the fact that the two dial cases were not the same size (they had originally been lamp bases, after all!) and the screws on one case were less accurately spaced than on the other. So despite measuring these as accurately as I could, it was difficult to get the slots exactly positioned.

Although I had prototyped the dial covers in cardboard during stage 3, cardboard is a more forgiving material than acrylic. The acrylic circles didn’t quite fit, the slots weren’t quite wide enough and they didn’t align exactly with the screws. After two attempts the slots in one of the circles still didn’t quite align.

On reflection, I decided on a different approach – to mount the acrylic circles on top of the cases and secure them with washers attached to the screws. This would have the extra advantage of allowing more clearance for the dial pointer needles. So I cut out two slightly bigger circles to match the diameter of the top of the dial cases. You can see how this looks in the final product shots.

Putting the panels together

Assembly time! I glued the joining strips to the front panel, then glued the curved side/top panels to those. For the back panel, I used some offcuts of wood I had laying around at home to create joining pieces that would allow the back to be screwed to the side and top panels.

When I first fitted the back panel on, there was a little too much flex in the side panels, so I decided to add a piece of wood inside to strengthen the whole cabinet. I also added a small piece of wood between that piece and the front panel, which would give the CD something to rest on when fed in through the front ‘mouth’ slot. This included some rubber stoppers to act as a back stop for the CD.

I treated all the panels with some wood stain we had left over from staining our fence. It’s quite a lovely finish, giving the cabinet an aged look to go with the brass dial cases, and bringing out the beauty in the laser cut bend patterns.

laser cut bend in wood
Close up of bend pattern after wood stain

Next > Practical project step 5: Finishing the cabinet


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