The bucker di Grassi recommends has a metal ring nailed onto it in order to capture and break blades. There is no illustration, but I imagine it to be something like this reproduction by Museum Replicas.
As I don’t want to actually break a blade, the design I’m working on will use a wooded ring instead of raised posts. Here you can see the nearly completed bucker. It just needs the be planished and riveted together.
The flaws in the steel ring are the result of some mistakes setting up the plasma cutter. It was done in four parts to reduce the amount of steel needed.
Here is the rough cut disc and wood ring. I used a plasma cutting for the disc, but with practice that can be cut out using a Beverly sheer (or the cheap Harbor freight knockoff). For the ring I used a CNC router.
Next up is the steel ring. That bead you see around the edge is called dross. If you setup the plasma cutter correctly you can knock it off by tapping it with a chipping hammer. Do it wrong and you’ll spend all afternoon trying to remove it with a grinder.
Once you have each part cleaned up, mark and drill the holes in the steel ring. Then transfer those holes to the wooden ring and drill it as well. Make sure to mark where each ring goes.
For the disc, you’ll want to clamp the wooded ring in place before you start marking holes. Since a pen can’t fit in the hole, a transfer punch is essential.
After cleaning up the holes, bolt everything together in order to check the fit.
Flip it over and mark where you want the boss. Also mark and drill the handle holes now, otherwise it will be a pain in the ass later.
A stump can be hollowed to an appropriate shape, but I prefer using a swage block from Iron Mountain Forge. I’ve been having good luck using a combination of their shallow and deep 4” ladle. (A ladle swage block is circular, a spoon is oval or egg shaped.)
As I said in the introduction, the next step is planishing. This will not only smooth out many of the imperfections, it also hardens the metal somewhat.
Historically they would have used a water-powered trip hammer or the labor of several apprentices. As I have neither, I’m going to borrow one of these:
It can’t get the corner between the boss and face, but in a few minutes it can do what would take me hours if not days.