Think carefully, actually his lathe can be used for this purpose.
Set the center of the iron disc on the spindle of the lathe, and spin it quickly.
His tool is fixed on the rack, and each rotation of the disc will scrape off a portion of iron filings by the tool.
The lathe is driven by three strong men using foot pedals.
It takes about two days to process the cylindrical sides of more than forty discs.
An additional day is needed to grind the bottom flat.
At this point, they are still not up to standard and require manual further adjustment by him.
He will manually sand the sides rounder and the bottom flatter.
Why isn't the machining round and smooth enough?
Because the components of the instrument are numerous, all of which he chisels out by hand, making it easy to get stuck or not fit during assembly, he fine-tunes their shape, so the assembled instrument itself is not precise enough.
This manual polishing takes a very long time.
He doesn't mind spending extra time.
