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.
Day one:
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.
Day two:
Repeat the procedure of day one.
Day three:
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.
Safety measure
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.