One of the fundamental design decisions that I faced was whether or not to keep the existing lid. If I kept it I would need to build a collar to go between it and the top edge of the freezer in order to give the necessary height for the two kegs that sit on the compressor hump and to provide a surface to mount the beer taps through. The other option is to discard the lid and make a new one from scratch, with the collar built into it and then insulate it up the best that I can (bearing in mind that the cold air sits in the bottom of a chest freezer, thereby making a perfect seal on the lid less critical than a front loading fridge).
I decided to go with the second option – to build a whole new lid (with built-in collar). I feel that building around the existing lid doesn’t really save any time or expense, and merely serves as a restriction. A scratch-built lid can be designed to more efficiently use space, and I think that I run a better chance of having my lid line up with the body of the freezer if I am controlling all the dimensions.
I waited until I had built the body skin all the way up to the top surface of trim pieces before embarking on the lid design. This meant that I could build directly to the final dimensions of the body and ensure that all my shut-lines would be even and symmetrical.
I elected to build a double-wall collar rather than a single-wall solid wood one. Although more complex in its construction it does have the advantage of better thermal insulation due to the pocket of dead air. I also wanted to use the existing door seal so any collar that I make would have to be very thick to be small enough on the inside to take the seal yet large enough on the outside to meet with the new body trim. A single-skin collar this thick would be enormously heavy to lift.
The most important surface on the lid is the bottom edge. This needs to be perfectly flat to permit the door seal to mate with the top surface of the freezer correctly. For this reason I decided to use a flat panel of 12mm particle board – it is manufactured flatter than anything I could create with planks. I only needed to cut one exterior edge with the circular saw and run around the inside with the jigsaw.
The sheet of particle board that I picked up from the hardware store was slightly too small in one dimension. So once I had formed the baseboard above, I then needed to cut it in half. While this may seem undesirable (and indeed it is!) it was far cheaper than going to the next size up (which would also have been challenging to fit in my car) and it allowed me a bit of wiggle room to adjust the length of the lid so that the gap with the freezer body back-to-front was the same as side-to-side.
I used lengths of pine to build up the sides – starting with simple butt joints for the interior walls and mitres on the front and sides of the exterior. The gap left by splitting the baseboard will be filled with some bits of scrap.
Seeing as the collar will be subject to heating and cooling, the next step before putting the lid on is to paint the insides to seal the wood against condensation and to fill any gaps.
Next to go on is the lid. Here I used 12mm plywood, again cut slightly large and then flush trimmed with the router. Again, gloss paint is used to seal all the wood that might be subject to condensation and then the existing door seal gets screwed in place. The top surface of the lid will probably need some insulation, but I’ll deal with that later.
And lastly, a little more trim goes on around the top edge to hide the nasty plywood end-grain and break up what would otherwise be a fairly featureless slab of plain wood.
Next steps – filling and sanding all gaps/nail holes, hinging the lid and building a mount for the drip tray.