Monthly Archive for May, 2011

Shop Knife 4: Hafting

Published on May 30, 2011 in Tool making. Closed Tags: .

 

The blade, nicely polished

Well, my daughter’s wedding is over, so there should be a little more time for writing now.

The previous posts took you through turning an industrial bandsaw blade segment into the blade of a shop knife. Here you see it after the polishing steps.

Now for the final procedure—”hafting”, or attaching an handle.

We have to overcome a technical issue in hafting the blade. There are no holes in it to secure the blade to the handle, and the blade is hardened steel. You can’t drill through it with normal twist drills. Here are a couple alternatives. You can drill with a diamond drill, which is harder than the steel. Those are expensive. Or you can soften part of the blade and then drill through. I chose the latter approach.

 

The rivet hole area is spot annealed, then drilled through.

I had a 1/4″ solid carbide router bit, too dull to use. I chucked it in the drill press with the shaft side down, clamped the knife blank securely on an insulating surface, then brought the spinning rod down against the blank. In only a moment, the spot under the rod heated to several hundred degrees and the tempering colors began to radiate out, indicating that the spot had been softened. This process is called “spot annealing”. I let it air cool for a few minutes, then sharpened a 1/8″ drill bit and drilled easily through the annealed spot.

 

All the pieces, ready to assemble

I sawed a scrap of live oak firewood into two pieces to make the matching sides of the handle. I hand-planed the interior surfaces so they’d glue together without gaps, then used a straight bit in my router table to cut a pocket for the blade into one of the two handle sides. After that, I laid the blade in its final position in the pocket and drilled through the hole in the blade, making a hole in the handle side. I attached the two handle sides together with double-stick tape and drilled back through the same hole, now from the outside, to make a matching hole in the second handle side. Then I cut the outside of the handle blanks to shape while they were taped together. Finally, I cut a rivet from a length of 1/8″ brass rod. You see all the parts, ready to assemble, in the photo.

 

The finished shop knife

At last, it was time to put it all together. I glued the two sides of the handle together with yellow glue, then epoxied the blade and rivet into place. I then shaped the outside of the handle with rasps, files, and sandpaper until it felt comfortable and the rivet was perfectly flush with the surface on each side. Then I sharpened the blade.

The result is a knife that has served me well for general shop use. Since then, I’ve made a couple others from the same bandsaw stock, shaping the blades for various special purposes. I would up with free knives that exactly met my needs, and kept a little steel out of the landfill or recycling bin.

Shop knife 3: Polishing

Published on May 20, 2011 in Tool making. Closed Tags: , .

It’s been hard to find time to post recently. I just returned from a business trip, and my daughter’s getting married Sunday, so we’ve all been pretty busy. I’ll try to do better next week.

Start the finishing with sandpaper, just like with wood.

I finished the last post talking about shaping the blade. Now it’s time to make it pretty.

Think of polishing as extreme sanding. Each stage removes the scratches from the preceding stage. When the width of the scratches which remain is smaller than the wavelengths of visible light, the surface reflects like a mirror. It’s completely polished. Since I’d already wire-brushed the surface, I started with #P400 wet-or-dry paper and a little water lubricant, and sanded until I saw an even scratch pattern. Same with #P600.

Emery compound on a sisal wheel cuts fast

At this point I switched to buffing wheels and compounds, holding the blade in vise grips against the wheel. I use a Grizzly Knife Belt Sander for this work, mounting various 8″ wheels on the left arbor as needed. In this case, I started with a sisal wheel and black emery compound. (There’s an excellent set of instructions for polishing with wheels at Caswell Plating.) Sisal is a hard, naturally abrasive fiber that cuts fast in wheel form, and is a good applicator for coarse cutting compounds such as emery. It removes all the sanding scratches quickly, leaving a smooth surface. When applying these compounds, use just a little compound and use it often. Don’t apply so much you build up a residue of compound on the blade.

Next step is “white diamond” buffing compound on a spiral-sewn cotton wheel. The cotton wheel is softer than sisal, while the spiral sewing gives it considerable rigidity for fast cutting. It’s important to dedicate a buffing wheel to each compound. Don’t try to clean off coarse compound and then do fine polishing with the same wheel.

I finished up with green, chromium oxide polishing compound on a soft cotton buff. This yields the final, mirror-like surface. Next, fitting the handle.

Shop knife 2: shaping the blade

Published on May 11, 2011 in Tool making. Closed Tags: .

breaking the blade out of the stock

Previously, I showed how to score along the outline of the blade with an abrasive cut-off wheel, chewing away the metal to weaken it. Bandsaw blade stock is fairly brittle, so it will snap where you create a “stress concentrator” such as a deep scratch. Now, clamp the blank in a metalworking vise with the score line just above the jaws and tap it with a hammer. (Remember your safety glasses!) The waste should snap off cleanly. If it doesn’t, grab the waste in a pair of ViseGrips and bend it back and forth a little until it breaks looks. This is a lot faster than trying to grind the whole blade out of the blank.

Blade blank, ready for shaping.

Now take the blade to your grinder and smooth all the edges, bringing the outline to it’s final shape and removing all the burrs before one hooks into your hand.

Once I’ve ground the blank to final shape, I grip it in ViseGrips and use a rotary wire brush to develop an even scratch pattern across the whole surface, removing any blemishes.

Wire brushing the blank in preparation for polishing.

Wire wheels sometimes throw bristles, so it’s good to stand out of the line of fire. And be sure to present your blade to the receding side of the wheel, as in the photo at left. If you feed it into the top of the wheel, the wheel might grab the blade and throw it at you.

The next step is to polish the steel.(You need to get the surface looking the way you want it to before starting sharpening, since polishing later can take off the sharp edge.) There’s no magic to polishing. It’s very like sanding in that you start with an abrasive coarse enough to remove the worst scratches in the surface, then go finer and finer. But instead of stopping at #180 as you might with wood, you go all the way to chromium oxide (green) honing compound for a mirror finish.

Next: the polishing steps.

Making a shop knife

Published on May 7, 2011 in Tools. Closed Tags: , .

Shop-made knife

The question came up recently in a class, “how do you make a shop knife?”.

Now maybe you’re thinking “The real question is, WHY would I make a shop knife!”, but sometimes you can’t find what you need on a store shelf. Maybe you want a special size, shape, or handle. Shop knives are easy to make from scrap (read, “free”) materials, and you can make them just the way you want. This next series of posts shows how.

By the way, you’ve perhaps noticed that I haven’t posted in a while. I’m helping build a new company, and that’s taking most waking hours. I’ve hardly had time to get into the shop recently.

I make shop knives from pieces of worn out 1″ industrial bandsaw blade. Any metal supplier that cuts metal will throw these out regularly, and you can sometimes have a lifetime supply for the asking. For the knife in the picture, I began with about a 4″ piece.

Length of bandsaw blade with knife blade marked.

Now bandsaw blade stock is difficult to shear. It’s hard and somewhat brittle. But it’s easy to break into the right shape. I just put a length in a metal vise with the “cut” line right at the top of the jaws, then pull the piece over a bit and whack it right above the jaws with a hammer. (Remember your safety glasses!) It snaps cleanly at the jaw line.

Grinding away the metal before snapping it

In the photo above, I’ve cleaned the bandsaw blade stock and painted it with Dykem, a shellac-based machinist’s dye available from Amazon.  Then I scratched the outline of the blade I want to make. Next I put a little cutoff wheel into a die grinder (a big, strong rotary tool), and ran it along the scratched outline, abrading away most of the metal there.

Next, shaping the blade.