Tune Up an Old Chisel Fremont NE
North Bend, NE
Tune Up an Old Chisel
Tune Up an Old Chisel
Turn a Beater into a Razor-Sharp Tool
by Tom Caspar
One of my favorite tools is a legendary Stanley No. 50 chisel. Made in the 1920s, it had seen hard times. Restoring it was a labor of love, and well worth the effort. Its steel holds a long-lasting, super-sharp edge. No doubt you’ve got some beat-up chisels in your toolbox that could be revived, too.
I’ll take you through the complete process of restoring a chisel that’s in tough shape. These steps are equally useful for a new tool, fresh from the box. Please notice that I put equal emphasis on the chisel’s bevel and back. Both must be in perfect condition, for every sharp edge has two sides. Let’s begin with the back.
Evaluate the Back
Inspect the back by sanding with fine paper (Photo 1). Put 220-grit pressure-sensitive-adhesive (PSA) sandpaper on a flat surface, such as a granite surface plate, 1/4-in.-thick piece of glass, cast-iron tablesaw wing or jointer bed. Sand the back a few times using diagonal strokes. Sanding reveals low spots. With an old tool, you’ll probably find rust pits, large hollows or a dip at the leading end.
Flatten the Back
My chisel’s back looked so bad that I began flattening with 60-grit paper (Photo 2). If the inspection sanding indicates few low spots, begin with a finer grit. The point is to avoid making unnecessarily deep scratches. Machinists call this process lapping. For the coarse work, I use premium-grade sanding belts stretched tightly on a shop-made jig. They can be reused many times, unlike PSA paper. Lapping a back in poor condition may require many strokes, which is hard on your hands, so I often wear rubber-coated gardener’s gloves and take frequent breaks.
Photo 2: Flatten the back on sandpaper using heavy pressure and diagonal strokes. I prefer to work on a 6-in. x 48-in. sanding belt. It’s easy to reuse and lasts a long time. The belt is stretched taut on a shop-made jig (see “The Lapping Jig, below”).
The Lapping Jig
Opposed wedges tighten a sanding belt placed over this jig. Strike the wedges with a hammer to stretch the paper taut. This jig works for a belt of any size, though I prefer 6-in. x 48-in. belts for their huge surface area. Make the jig from three layers of 3/4-in. MDF glued together. To round the ends, make two 45-degree crosscuts first, and then sand in between them.
Continue sanding until you reach the bottom of the low spots. How far up the back must you go? Two to three inches are minimum, but I usually lap the whole back. (A totally flat back enables me to use guide blocks when I pare mortises, tenons and dovetails.) If 1/4 in. or less of the back’s leading end is lo...