Like a stome-polishing tumber…
Similar tumblers are also used for deburring small machined metal items, giving them smooth edges and a matt finish.
I’ve not tried it but one old dodge for keeping the surface of paint liquid is to float a disc of polythene sheet on it; though that won’t stop the paint from separating, of course.
…
Spent some hours today making a key.
Not any old key but the one that connects the off-side wheel of my steam-wagon to the axle. It’s about 1-1/2″ long on the key part, by 1/4″ wide.
I used one of my very old “full-size” text-books to find the proper proportions for a gib-head key.
To give the 1:100 taper, as well as plenty of material to hold, I scribed a line close to the end and another 300mm from that, on about fifteen inches of stock bar. Then clamped the bar to a angle plate on the milling-machine table, with the edge of a parallel under the 300mm line, and the origin line on 3mm drill shank on a second parallel: sine-bar principle.
To make it more fun the keyway in the axle (1″ dia stainless-steel) is accurate but that in the wheel hub less so and slightly over-width, necessitating a key with a rebated cross-section.
Then much of the evening carefully draw-filing the blade until it fitted as it should (ish!)
Finally stopped for tea at approaching 10pm with just the key to be severed from the stock and its head filed to shape.
I know what will happen now…. I will find the lost one this evening’s 5 hours’ efforts is to replace!