DIY salt and pepper grinders from old doorknobs

What can you make with two old doorknobs? A good friend was getting married and I wanted to make a gift that meant something rather than one more thing they'd feel obliged to keep. The doorknobs came from the house he and his fiancée were renovating, so I turned them into a pair of handmade salt and pepper grinders. Every meal they cook together will use something made from their own home.

Fitting a grinder mechanism under a doorknob

The hardest part was the mechanism. Standard grinder kits use a threaded rod through the top to hold everything together, but I wanted the doorknob as the top with no hole through it. I found an alternative mechanism where a turned top piece interlocks with the drive shaft. The doorknobs also had a retaining clip that limited them to a quarter turn, so I cut it off with a Dremel cutting wheel and ground away a lip to separate the knob (catching my hand on a sharp edge along the way). I 3D-printed a square-to-pentagon adapter to couple the grinder's shaft into the knob's spindle hole. After a bit of fettling it slid on snugly.

Turning the grinder bodies

The bodies were turned on my entry-level lathe, which really wasn't designed for this. My skew chisel left a poor finish, so I sanded from 80 through to 600 grit. With no tailstock drill chuck, I bored the centre by hand with a spade bit (a Forstner overheated), widening and tapering the hole with a chisel so the next bit would self-centre. The drill actually cut better with the lathe stopped. On the second grinder the finish was even rougher, and I eventually found the cause: a completely worn pulley wheel vibrating the whole machine. A foil-tape fix didn't hold, and with the wedding deadline looming I just sanded my way through it. I also learned not to measure spinning wood with pointy vernier callipers. The last deep hole was drilled on the pillar drill, packing the piece up on blocks until it met the hole from below.

Finishing: sealer, friction polish and wax

For the finish: sanding sealer, knocked back with 1200 grit by hand along the grain, then friction polish. I put far too much friction polish on, got ugly streaks and had to sand back and start again, then did exactly the same on the second one. A paper towel worked better than a cloth. The brass knobs got a hot soapy scrub and polish to look new, and everything was finished with microcrystalline wax for a food-safe, water-resistant shine.