Sharpening Carbide Inserts
Silicone carbide inserts that are flat across the top can be sharpened with a diamond impregnated credit card sharpener.
Silicon carbide sandpaper can also be used to sharpen the inserts on a flat surface like a table saw top. Use 220 or 320 for a coarse sharpening, 600 to 1000 for a fine finish.
Place the insert upside down with a small spot of light oil or water. Rub in a figure eight pattern a number of times, and then rotate the insert 90 degrees and repeat the figure eight pattern for the same number of times. Two more times and you are done and have a sharp carbide bit.