Popular Woodworking Editors' Blog

I've been away from the blog for a while. It's been a busy few weeks with Thanksgiving, filling book orders and the main job, publishing a woodworking magazine. Since putting the February issue to bed, I put on my Woodworking Magazine hat and set to work investigating chisels for hollow-chisel mortising machines. I've always been geeky about sharpening things, not in the sense of polishing chisel backs to 32,000 grit, but having a good edge before going to work. Before using a router bit, I dress the edge with a diamond file, and I usually touch up the chisel before machine cutting mortises. Sharp is good, but with tooling used in a machine like a mortiser, you hit a point where your efforts meet with diminishing returns. Here is a procedure that will take less than 15 minutes and will give you cleaner, cooler cuts.

This is  a typical dull chisel. I found it in the cabinet in the base of our old mortiser, and don't know what brand it is, or how old it is. It wasn't completely trashed, but the end was discolored, and the grinding marks from the factory were still visible on the outer faces.

If you look at the pile of chips, you can see that they are fairly large, and some of them are scorched. There's is a lot of friction between the chips and the metal as they work their way up the flutes of the auger bit. The chips rubbing against each other can get hot enough to burn, and once that happens, the smoke and resins in the wood start to get sticky. You can also see the chips in the flutes of the bit. If you can keep things cool, they won't be there.

Here is a close look at the dull chisel, just about to undergo the first stage of the tune-up. The discoloration is mainly smoke damage, the chisel hasn't been overheated to the point where the metal loses its temper.

The sharpening cone came from Rockler as part of a 3-piece set that includes a coarse and fine diamond coated hone, and a handle to put them in for hand honing. The set costs a little over $20, and I think it's a good buy. The handle accepts hex-shanked screwdriver bits, and is comfortable to use for that purpose as well.

This is chucked in our drill press, set at it's lowest speed, with the chisel held in a drill-press vise. It doesn't take long to grind a good edge on the inside of the chisel. It takes me more time to get it locked in the chuck than to sharpen one chisel. All you need to do is bring it down until you raise a burr on the outside of the chisel.


The next step is to get rid of all the grinding marks on the outside of the chisel. I stick a piece of 150 grit sandpaper to thecast iron bed of one of the machines in the shop, and rub the faces of the chisel on it. I start with the clearance slot facing up and give each face the same number of strokes.

I do twenty-seven on each face because I like the number, but anywhere from 20-30 will do. The idea is to take an equal amount off of each side. Don't worry about making the chisel smaller than its nominal size. You may have to go around 2 or 3 times, but this is a once in a tool's lifetime operation.

After the sandpaper, switch to the finer cone at the drill press, and hit the inside again. Like the first round with the cone, you only need to grind for a couple seconds to raise a burr on the outside. Then work your way around the outside on a medium grit diamond (or any other) sharpening stone.

I tried seeing what going to a finer grit would do, but measurable improvements in the working of the chisel stopped about #1000 grit. You can keep going to finer grits if you want, but you'll only have a shinier chisel, not a better working one. My grandfather used to call that "polishing the polishing"


The last step is to file a notch on each of the inside corners with a triangular file. I wish I could take credit for thinking of this, but it is a feature found on some chisels. I first saw it on the premium chisel set from Lee Valley. Depending on the hardness of the chisel, this filing may take a while, but I think the results are worth it.

This provides some more clearance between the outside of the auger bit and the inside of the chisel. I also think it makes it easier to plunge the corners of the chisel into the wood to start the cut. The benefits of doing this aren't as great as the benefits of smoothing the outside of the chisel, but it doesn't hurt, and in some species of wood may really help.

Once you've taken a chisel through this procedure,  you shouldn't have to go through it again. You will need to dress the edges occassionally. This won't take more than a minute or two. Twirl the fine cone inside the end of the chisel by hand to raise a burr, then take a few strokes (I like 9 in this case) on each face with a sharpening stone.


Here's a picture of the sharpened chisel, along with the chips it made. The chips are a lot smaller, and the chisel is a little easier to plunge into the work. There isn't a tremendous difference in the amount of force you need to make the cut, but the bit and chisel will run considerably cooler.

Heat is the real enemy, and in addition to dressing the outside of the bit, the other important consideration is leaving a big enough gap between the bit and chisel. Most bit manufacturers and published advice suggest a gap that is way too small-a credit card or dime sized gap will likely smoke and burn. Set the gap a bit bigger, and you'll enjoy much better results.

Bob Lang

---

How do you accurately test a seven-piece professional set of Infinity router bits?

Let’s face it, you could spend months in the shop trying to accomplish such a feat by using them day in and day out while building several projects and studying their performance along the way.

I didn’t have that kind of time, so I applied some standard tests to check the precision of the manufacturing.

I used micrometers to check the various steps in the rabbet combination bit, to check the diameter of the bearing in relation to the cut on the flush trim bit and to the cut of the 3⁄4" pattern bit.

I moulded a piece of hardwood with the 1⁄2"-radius roundover bit in a hand-held router, and with the 1⁄2" cove bit in the router table in order to check for a matching fit and determine if they could be used for a drop-leaf profile. I found that they all worked superbly under shop conditions.

But the true test of a packaged set is: Are these bits the ones most often used in a professional woodworking shop or that most woodworkers would use in their shops? Or, did they select a few usable bits and finish out the set with less-than-desirable contents? No, this is a useful set.

Each of these bit profiles has been a workhorse in my  shop during the past 12 years. I’ve used them all and I find myself using at least one during each of my woodworking projects.

This is a nicely assembled selection of router bits for use in your shop and these bits also have 1⁄2" shanks for added strength and durability. The set is $149.90. For more information, call 877-872-2487 or visit infinitytools.com.

— Glen D. Huey