I’ve spent the last month working to refine an idea to make a little coffin coin bank. It started out as a cardboard project that I wanted to make into a YouTube tutorial, but I quickly learned that cardboard is great for large cams and parts, but as they get smaller and smaller they get weaker and weaker too. I ended up resorting to wood for the majority of the mechanism, which required a bunch of tools that made it much less of a do it yourself style project.
I decided to go ahead and try making the entire thing out of 1/4 inch plywood. I thought maybe I could still make it into a set of plans for anyone with a CNC router or laser cutter. That decision led to a complete redesign of all of the parts and plans. The plywood I had was a scrap that my neighbor from the cabinet shop next door had given to me to play with and while it worked fantastic, I later found out that the plywood was $65-$95 a sheet.
I tried a few other less expensive plywood types and quickly found that most of them just fall apart or have voids, lots of filler that resists glue or stain, or a really thin outer sheet of nicer wood with thicker layers of soft ugly wood between them. I finally settled on an inexpensive plywood that is 3/16 of an inch thick (not quite 5mm) and has a really interesting stacked grain look to it. It’s not the greatest, but it doesn’t seem to have too many voids and it’s only $22-$28 per 4 foot x8 foot sheet.
I spent a couple of weeks tweaking and re-tweaking my design. I ended up re-sizing and changing the shape quite a few times. At one point I ended up cutting down the height by 1 inch so I could make it fit in my most common shipping box size and not have to buy all new shipping boxes just for this design. I must have designed about 3 dozen different cam mechanisms to grab the coin before I realized that I could use the bottom of the coffin as a way of pushing the arm up to open the lid and reach for the coin. That was the first big breakthrough. I also fought with the arm getting either stuck under the lower lid or flipping backwards and getting stuck facing the wrong way, which led me to add a lower piece to the arm making it more of a “U” shape so I could use the underside of the lower lid as a stop to keep the arm from flipping backwards.
Another addition was a ratchet mechanism to stop jams caused by turning the crank handle the wrong direction. That also took quite a bit of trial and error before I found a position that would use gravity to keep the pawl engaged on the ratchet so I wouldn’t have to add a metal spring or anything.
I’ve since further refined the design by moving the ratchet to the inside of the support wall (making more room for the hand) and putting a groove in the coin slot (which I turned into a cross shape) so that the hook could grab thin coins like dimes.
So the “final” design is plywood stained almost black with a water based stain and then finished in natural linseed oil finish.
I’m currently working on a file that may work as a laser cut file (I don’t yet have a laser cutter, so I need to find someone to help me test).
You can purchase my little coffin coin bank in my store up until mid October. I am taking preorders and have a limited supply already made. I don’t think I will make more than about 2 dozen this year because they take quite a bit of time to make and finish.