Not having adequate luggage can add stress when travelling. By adding wheels to your hardside luggage you'll save time and money. While wheeled luggage is the norm these days, a new set of luggage can run in the hundreds of dollars. If your old, hardside luggage is still in pretty good shape, why not retrofit it with a few castors and save some cash?
Cut a metal plate slightly smaller than the bottom side of your luggage. Take a castor, place it on the metal plate and use a felt-tipped marker to place marks on the metal for where to drill the holes. Place additional marks on the edges; you can drill four extra holes here, one in each corner, for extra stability.
Drill holes on your marks. The hole you drill should be the same size as the bolts you have. If you drill the hole too big they will not fit. Start off drilling the hole smaller, and gradually get bigger; this way you can watch the hole enlarge to ensure it's not too big.
Place marks on your luggage with a felt marker to show where you want the metal plate to line up on the bottom of your luggage. Place grommets over the marks that you drew for the holes. The grommets will add extra stability for your bolts. Use a hole puncher to punch holes in the marked spaces on your luggage, place a grommet on the other side, and hammer the two pieces of the grommet together.
Line up the wheels over the holes you made and bolt them; repeat for each set of wheels.