Clean all the surfaces with a scraper, then sand the whole guitar with 120grit paper. Vacuumclean all surfaces and repeat sanding with 180grit paper until all the scratches of the previous paper are gone; then remove any dust that may still be there with a vacuum cleaner.
For rounding off the edges I used the 1/16” (1.5mm) Veritas cornering tool. This simple tool produces a nice and smooth corner radius when used with the grain.
I chose Danish Oil for finishing the guitar. Danish oil is an oil-varnish blend that is very easy to apply. It gives a nice, smooth finish with a satin sheen and sufficient protection against the wear a lap steel guitar is exposed to.
Apply Danish Oil liberally to all surfaces with a rag or brush. Wait for 5 minutes, then remove any surplus with a rag. No oil should remain on the surfaces. Leave the guitar to dry for at least eight hours.
Repeat the procedure of day one.
Apply a third coat of oil and rub the wet coat after 5 minutes with "000" or "0000"-steel wool. Rub with the grain, then wipe off any remaining oil. One more night of drying and you can start assembling and stringing up the guitar.
Please note that oily rags can be dangerous: when wet, they can self-ignite by spontaneous reaction with the surrounding air. Used rags must therefore not be left lying around in the workshop but should be stored in an airtight glass container while waiting for the individual coats to dry. When they are no longer needed, they are best hung on a line and left to dry completely in an outofdoors place before disposing of them.