One of my favorite things to do with old worn burs is to use nitric
acid to sharpen them! I use an etching solution of approximately 20%
nitric acid to water and dip the cutting head of the bur for about 10
to 20 seconds. When I first read about this process, I kind of
laughed thinking that it might shrink the bur in size but probably
not sharpen it much. Months later I had to pave’ set about 200
matched stones into a leopard broach and didnB9t have the right size
bur. Luckily I remembered the nitric acid trick and decided to give
it a try. It worked great, it shrank the bur in size and to my
amazement it was as sharp as new. The 20% etching solution works
at room temperature for tungsten burs but if you’re going to use it
on high speed burs you have to heat the solution a little to get the
same cutting action.
I believe the process works because the teeth on a bur are slanted
with one side of the angle slanted more than the other. Since
nitric acid mainly etches straight into the metal and doesnB9t
undercut, itB9s the long side of the tooth on the outside edge that
gets removed , shrinking the bur in siz e and removing the worn edge.
Here’s how I’d do it, first use an ultrasonic or steamer to make
sure the bur is clean. Wear safety glasses and obey the rules of
working with acids. Dip the cutting head of the bur into the solution
of nitric acid for about 10 to 20 seconds then neutralize in baking
soda and water. You can repeat the process if the first etching
didnB9t do the trick. Use a ultrasonic one more time to removes any
scale that might be left from the process. Oil th e bur before using.
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