Sorry, this is going to be a picture dump.
So I was contacted by a guy with a problem. He bought a set of Jamo 7.6 floorstanders from a guy from somewhere, and the guy messed them up. He used the speakers on the plinths, but without the spikes installed. If I had to guess, this led to water getting caught under the plinths and it absolutely wrecked them. I agreed to replace them for him. We worked on a budget here, so keep that in mind.
Original plinths arrived, one being severely damaged, and the other being only a tiny bit better:
First things first. I decided to use MDF, as that's what the originals are made of and it's cheap. The original plinths were 25mm thick, and the MDF I got 16mm thick. I contemplated for a while on how to do this, and ended up just going with two sheets of MDF per plinth, making them 32mm thick overall, 7mm thicker than the originals. I figured thicker/heavier is better than thinner/lighter. So I got a piece, and traced out the only good edge left on the better one of the two plinths:
I then grabbed the jigsaw and cut them out roughly with the jigsaw, leaving a ~5mm or so edge on the lines I drew. In hindsight, I could have made this a smaller edge, but I worked on the safe end here.
Next up, I used a trick I learned off YouTube. I taped masking tape to the original plinth as well as one of the new rough cut pieces. I then used CA glue to glue them together, tape to tape, creating my own kind of super thing double sided tape:
This done, I clamped down the piece and found the threaded inserts for the spikes to be in the way. I removed them. More on this a bit later:
Then, router. On the highest speed with a flush-trim bit, bottom bearing, I used the only good edge on the plinth to recreate the exact shape on the new 16mm piece of MDF:
And done. Perfect!
While they were stuck together I used this opportunity to copy the drill holes from the original plinths onto the new ones. I used a small drill, running it in the middle of each hole into the new plinth:
Once done, I split them apart with a chisel. This was a lot harder than it looked on YT, actually, the tape sticks like mad if it's flush like that:
I then repeated this entire process once more to obtain 2 16mm copies of the plinth's shape. That was also the last time I used the originals for cutting the shapes. After having two exact plinth copies I glued the copies each to another rough cut piece, to obtain a 32mm thick plinth. I used a good quality waterproof wood glue and clamped them down. While in clamps, I turned my attention to the threaded inserts for the speaker spikes.
It was at this time that I realized these inserts aren't steel like they usually are - these are aluminium for some stupid reason (I mean, really). Turns out that the white residue as seen above wasn't just MDF resin or whatever, it's oxidized aluminium. So elbow grease was required. On the outside of the inserts they had a thin rubber coating that turned hard, brittle and in some of them, started chipping off. I removed this completely. I then used a small blade and scraped as much of the oxidized aluminium off them as I could. I couldn't get it all, so in the end to clean them up I dropped them in some sodium percabonate. It's a very cool, safe cleaner and it cleaned them up very well, removing oils and gunk and all kinds of crap:
After all this, the glue on the plinths have dried to the point where I could start working with them. I used the router again, running the flush trim bit on the copied side to cut the rough cut side to the same size. It worked beautifully.
Next, sealing. Considering we were working on a budget I didn't want to spend too much money, so I used the wood glue and water mix. I painted each plinth twice, making sure to get good soak on the edges. I then let them sit overnight to cure:
Next day the wood glue was nice and hard, and it was time for drilling and sanding. I measured the holes in the original plinths and on the holes used to mount them to the speakers I worked in the extra 7mm and extended the countersink on those holes to the extra depth to ensure the screws still grab the same depth. It worked perfectly:
Then it was time for sanding. MDF being fairly smooth already, I didn't go through many grits and just did a quick 120, followed by a 180 grit sand. The edges took quite a bit of sanding, and here I realized I probably should have spent a bit more time on the edges. It would have taken more time and money though and the budget was kept in mind, so I left it as is.
After the light sanding, it was time for a base coat. I used some acrylic resin spray paint I had here as the base layer. It creates a film-like surface and I figured it would hide most imperfections in the MDF, specially on the edges. It worked to some extent:
