Unfasten any metal hardware from the bed frame using a screwdriver and set the hardware aside. Take the frame apart with the screwdriver and pliers.
Carry the disassembled bed frame to a well ventilated area that is not dusty. Dust is an enemy of varnish and will stick to the finish when drying.
Sand the bed frame using 180-grit sandpaper to get rid of splinters, then smooth it with 320-grit sandpaper.
Blow off the sawdust from sanding with compressed air. Make several passes over the bed frame to ensure all the sawdust has been blown off.
Apply a coat of oil-alkyd varnish using a paintbrush, going with the wood grain on the bed frame. Let it dry between six and eight hours.
Gently sand the first coat of varnish with 400-grit sandpaper, then blow off the dust with compressed air. Apply a second coat of varnish, let dry and sand lightly once more with 800-grit sandpaper to finish.
Carry the piece back into the bedroom and reassemble the frame with a screwdriver and pliers, then reattach any hardware.