Tip #19
Sharpening Woodworking Tools (continued)
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Pg.1-5, Pg. 6-10, Pg 11-15, Pg. 16-20, Pg. 21-25

Sharpening Mortising Bits

Along with the chisels, the bits must be periodically sharpened. They can be honed with contoured slips when only slightly dull, but must be filed and then honed after they become extremely dull. Clean the bit thoroughly before attempting to file or hone it.

Figure 24-53. Construction details of a filing block for filing and honing mortising bits.

Filing Mortising Bits
Before the bits can be filed you must make a filing block that fits in a vise (Figure 24-53). Use drill bits, not mortising bits, to drill the holes in the filing block. Mortising bits flair out at the tip and will drill an oversized hole.

Attach the filing block to the inside of the vise jaws with double-sided tape. Close the vise to within 1/16". Slide the mortising bit in the proper hole with the cutting flutes of the bit parallel to the vise jaws and no more than 1/4" above the top of the wooden blocks. Close the vise to clamp the bit in position (Figure 24-54).

Figure 24-54. Position the mortising bit in the filing block and close the vise.

Use a small square or rectangular fine single or double cut file to sharpen the cutting edges of the mortising bit. Filing should take only a couple of strokes. Start with the inside surface of the two side cutters. Follow the “factory ground” angle on the inside of the bit.

File from the back of the cutting edge to the front on one of the side cutters. Count your strokes and repeat the same number of strokes on the inside surface of the other side cutter (Figure 24-55).

Figure 24-55. File from the back of the cutting edge to the from on the side cutters.

Figure 24-56. File the bottom relief angles from back to front.

In a similar manner, hold the file on the "factory ground" bevel forming the bottom relief angle of the bit and file this surface. Count the strokes and repeat the same number of strokes on the other bottom relief angle (Figure 24-56).

The final filing steps are performed on the front of the cutting edge. This will remove the burrs created by the previous filing steps. Hold the file almost vertical against the front cutting bevel and push the file down along the bevel (Figure 24-57). Count the strokes and repeat the same number of strokes on the other front cutting bevel.

Figure 24-57.File vertically to sharpen the front cutting bevel.

Honing Mortising Bits
In most cases the use of a fine enough file will sharpen the bit sufficiently. If there is a burr on the cutting edge, or tearing of the wood fibers during use, honing of the bit's cutting edge will be necessary.

Use a fine contoured slip stone. A triangular or a teardrop shape works well. These are usually oil stones, rubber bonded abrasives, or diamond hones. All work equally well.

Figure 24-58. Hone only the inside edges of the two side cutters.

Hone only the inside edges of the two side cutters (Figure 24-58) and the two front cutting bevels (Figure 24-59). Do not attempt to hone the bottom relief angle on the bottom of the bit. Honing is done in the same manner as filing. Remember to count your strokes and hone each surface equally.

Figure 24-59. Hone the two front cutting bevels.

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