This is a fairly easy way to make covers for guitar or other instrument pickups. I sometimes have a phase of winding my own pickups but they can end up in different shapes and sizes that require a cover I can't buy off-the-shelf , so I spend ages searching for something I can use.
This method uses a cheap source of foam , insulation board , although you could buy modelling foam quite cheaply in small blocks , and epoxy resin. Not everybody will have that to hand , but I would imagine you could get away with using araldite or other two-tube epoxy. The only drawback with that is it tends to not harden off sufficiently for sanding , so thin layers carefully applied would probably be the way to go.
It's a project that requires a bit of time , waiting for each layer of epoxy to dry before going on to the next , but you end up with a thin, strong and magnetically transparent pickup cover that just fits!
You'll need :
Foam board or block
Epoxy resin. (There are other kinds of moulding resin etc available, I have not tried them but they might well work. Having something that goes hard enough to sand is a big plus .)
Epoxy filler. Car-body "Easysand" type for repairing holes.
Sandpaper , medium/fine.
Craft knife/ Stanley knife
Cardboard and knife or scissors.
Filer powder , colloidal silica or household filler.
Step 1: Get Your Foam.
A piece of scrap insulation foam board , cuts very easily to a slightly oversize cube for the cover you want to make.
Step 2: Start to Shape
Foam shapes very easily with sandpaper and a craft knife. It's easy to oversand , go slowly until you have a feel for it. I use a board with a piece of sandpaper glued to it so I could get flat sides easily. Wear a mask , the dust is not nice , and keep a hoover close by for frequent clean-ups unless you want to live with foam bits all over the house.
Step 3: Resin
I use West System Epoxy with a Fast Hardener. This isn't super fast , especially when the ambient temperature isn't very high, it takes about twenty minutes to start to gel. It is very runny before that , so I ended up wetting the shaped block with resin then waiting for it to start to thicken up before adding more. It will sit on the top in a good thickness but still run down the sides.
Step 4: Drips
You'll get drips , they are unavoidable . They will need trimming and sanding. The epoxy will go through a phase of being cuttable with a knife before it fully hardens , it's just that it is quite fragile then and easily damaged , I waited until the second coat of resin was hard and sanded it then.
Step 5: Second Coat
I stuck a small cube of foam to the bottom of the model so it could stand and drip as it dried. Once dry it has quite a hard surface but is still delicate. Now another coat of resin is applied and left to dry.
Step 6: Sand Bottom Flat
Sand the bottom flat . (After you've taken the supporting block off) You can start to clean the rest up but it's still very thin , so best leave any heavy shaping and flattening until the end. It's very easy to sand through the corners if you aren't careful . It's OK , it can be fixed later , but you don't want to be making it too weak.
Step 7: Knife the Foam
Use a new blade , very sharp. I cut just inside the sides of the cover , and then made several cuts along and across the foam.The foam chunks will pop out with a bit of leverage.
Step 8: Scrape It Out.
I used the blunt end of a hacksaw blade to scrape the rest of the foam out. Keep going at it , gently because it is still pretty thin especially the sides and corners.
Step 9: Cardboard Reinforcement
I used strips of thin but stiff card to reinforce the sides and give them a flat surface. You could use other things , carbon fibre or other specialist material or thin veneer wood. Fabric type material would be harder to keep flat and precise at the edges. I glued it in place with another coat of resin. Then I added a third coat over the cardboard with some filler added to the resin to make it thick enough to sit in place and not run down the sides. I used silica filler powder made for the job , but ordinary plaster type filler powder will work.
Step 10: Finish Sanding.
This is a picture from an earlier stage but it's the same process , trimming lumps and scraping down with the knife blade , and sanding flat while trying not to oversand the corners. A spray of water can help the sanding go smoothly .Repairs are easily made with epoxy filler if necessary. Here I made one with a curved top and one flat.
Step 11: Paint
And add the finishing touches. the resin is quite translucent , still pretty thin , so I painted the inside black so interior parts wouldn't show through. I tried using glitter and acrylic paint , sort of worked out . Then I used a clear cellulose spray and waved the covers around while they were drying so it didn't run down the sides and pool . They are not perfect , I'm not a great cosmetic finisher.