Popular Woodworking 2000-06 № 115, страница 9

Ingenious Jigs

Very Scary Sharp

A sheet of sandpaper, a slab of marble, a simple jig and wow!

Some years ago, Steve Lamantia of Seattle, Wash., posted a long, rambling letter to the Internet news group rec.wood-working (better known as "Wreck Wood") entitled "The D&S Scary Sharp™ System." Once you waded through Steve's superlatives, exclamations and his stream of consciousness, his message boiled down to just this: You can put a very fine cutting edge on hand tools with sandpaper. That's right — sandpaper. (To read Steve's original message, check out www.shavings.net/ scary.htm#)

Other travelers through Wreck Wood spotted Steve's post, tried his methods and posted their own raves. The news spread, sandpaper stock soared, and the term "scary sharp" became part of the popular woodworking lexicon. All of which amused those who remember woodworking before there was so much virtual sawdust flying about.

About 40 years ago, I participated in a rite of manhood known as the Boy Scouts of America. There, in the old "Handbook for Boys," wedged between square knots and Morse code, is this advice: Sharpen your pocket knife with sandpaper.

Well, it was good advice then and better advice now. Continuing developments in abrasives make sandpaper an excellent sharpening material. In many ways, it's easier to use, less expensive to get started with and more versatile than traditional sharpening stones.

Sandpaper — It's Not Just for Sanding Anymore.

The most common abrasives in sandpaper are aluminum oxide and silicon carbide, both of which were originally intended to abrade steel. Their application to woodworking was an afterthought. Point of fact

Nick Engler is the author of over 50 books on woodworking and normally prefers Flintstone bandages. As soon as his cuts heal, he'll be back at work building airplanes — very old airplanes. He has just finished a 1902 Wright glider and has begun a replica of the 1905 Wright Flyer 3. You can see his handiwork on the web at www.first-to-fly.com.

— these are the very same abrasives in India stones, grinding wheels, ceramic stones, even Japanese waterstones. Sandpaper is just another form of the abrasive you may already use for sharpening.

The difference is that sandpaper comes in a much wider range of grits than stones and grinding wheels. Grits between 50# and 2,000# are readily available, and if you look around you can find sandpaper as coarse as 36# and as fine as 12,000#. It's this range that gives sandpaper the edge (pun intended) over other sharpening materials. Traditional stones start between 100# and 200#. The finest Arkansas stone is roughly equivalent to 900#, the finest ceramic and diamond stones are about 1,200#, and the finest waterstone, 8,000# in the Japanese grit system, is close to 2,000# in our American system.

Why is range important? Because proper sharpening technique requires that you hone with progressively finer grits, much like sanding a wooden surface. You can't put a super-keen, scary sharp edge on a tool with just one stone. Start with coarse abrasives to quickly condition the edge and repair any nicks. This leaves deep scratches in the steel and makes the edge jagged. The chisel is sharper than it was, but not sharp enough. You must continue sharpening with progressively finer abrasives. As you work your way up through the grits, the scratches grow smaller and the edge becomes keener.

Sandpaper not only extends the range from coarse to fine, it gives you more steps in between. If you've ever tried to jump from 80# sandpaper to 150# when sanding wood, you know how long it can take to work out the scratches left by the coarser grit. It takes less time and you get better results if you work your way up in increments. So it is with sharpening.

The Secret Formula

Stones have it all over sandpaper in one respect — they are rigid. To use sandpaper for sharpening, you must mount it to a

flat, rigid surface. Steve and those who came after him recommended H'-thick plate glass, but this isn't rigid enough. It will flex slightly if your workbench isn't dead flat or there is a bit of sawdust under one corner.

Instead, I use a marble slab to back up the sandpaper. (Talk about rigid!) You can purchase a precision-milled granite block known as a reference plate from a machinist's supplier, or you can take your straightedge to a cooking supply store and find a reasonably flat marble pastry stone (for rolling out pie dough) for a quarter of the cost. I have a 20"-square pastry stone that mounts eight different sandpaper grits — four on each side.

You can use ordinary sandpaper and stick it to the marble with a spray adhesive — this yields good results. However, I prefer self-adhesive 8"-diameter sanding discs. Because these are made for machine

10 Popular Woodworking June 2000