BTW, I know someone who makes blade guards out of leather. Cuts a piece, folds it, then adds rivets and/or tinglets, along with elastic pieces to bind it to the blades. I had a pair for 2 or 3 years. Surprisingly durable, yet you can walk on them, if the leather is tough.
The 3D printers I have watched can be off by a mm or two. Maybe in part because they were made by other 3D printers that were off by a mm or two, but the whole plastic melting and fusing thing looks pretty iffy and hard to control. The plastic they use doesn't look all that strong either. (There are expensive 3D printers that use other materials, like metal and fiberglass, and maybe some have better accuracy, but I haven't seen them.)
I suspect the computer controlled (CNC) routers have better accuracy. One of my childhood friends recently made a guitar that way.
Anyway, boots! Just because I've thought a lot about making my own, even experimented a little. Maybe the only way to make boots that fit perfectly is to build them around your feet.
But not something a 3D printer would be up to producing, in accuracy, or in materials.
Some custom shoes are made by using a laser profiling scanner, having a podiatrist to adjust the profile for desired corrections, and using something akin to a CNC router to build a custom last, around which the boots can be formed. I corresponded with one lady who had custom skates made that way, but the boot maker didn't know much about skates, and didn't make them stiff enough.
People have 3D printed kayaks, but it seems like a clumsy way to make them. But Chesapeake Lightcraft, a major wooden boat kit builder, uses CNC technology to cut out the parts for their kits.
Nonetheless - it also immediately occurred to me, upon seeing a 3D printer, that one ought to be able to use a 3D printer to create integrated circuits. Amorphous semiconductor rather than crystalline, not very small scale gates, and toxic dopants are probably an insoluble problem, but what a way to design a cool electronics kit. I picture using an inkjet printer with special ink cartridges.
I think that Jackson and Paramount use CNC laser cutters to make their blades. I was told by someone who uses one that it could probably also be done using high pressure water cutting equipment. The investment in either would be pretty high. The hardest part might be tempering the blade, and re-hardening the edge. Metallurgy is a black art, and apparently requires a lot of knowledge, as well as expensive equipment. I wouldn't know where to begin.
I wonder how hard it is to do computer guided sewing - could you gals make a skating dress that way? I've seen computer controlled fabric cutters in a store... If it could be automated enough, I can picture some ice princesses making a new outfit for every skate.
Maybe some custom dressmakers already do that?