By Ron Geppert
Someone else may have already discovered this trick but it’s been so useful to me that I felt it’s worth passing along.
Holding a washer in a lathe is not a problem when enlarging the ID, but holding it to reduce the OD can be a challenge without a wide assortment of expandable arbors in stock. I’ve found that a flathead bolt works great as an arbor and will cover a wide range of ID sizes.
The photo should illustrate how it works. You will often need additional smaller washers so the nut will press against the washer to be turned without bottoming out its threads. The taper on the head of the bolt does a good job of centering the washer when the nut is tightened.
To use, chuck the threaded shaft of the bolt in the lathe and the washer is ready to be turned down, using light cuts of course. The 5/16″ flathead bolt in the photo has a head diameter of 5/8″, which will hold and center washers to just over 1/2″ ID.