Monday, June 30, 2008

Sharpening a Dovetail Plane

Abe Lincoln once said "Give me six hours to chop down a tree and I will spend the first four sharpening the axe."

Well, I spent 6. 5 hours on Saturday fiddling around with the blades on the dovetail plane and got pretty good, but not perfect, results. The blades were easy—too easy—to sharpen. Too easy, because I realized they had not been heat treated. That's fine if you're working with pine, but to plane curly cherry meant having to resharpen blades that were being nicked by the hard wood and which dulled quickly.

Rather than take the time to heat treat the irons in order to produce a clean dovetail—I'm terrified of propane torches and need to spend several days working up my nerve to use them—I forged ahead with planing them, and resolved to make scratch stock to clean up the tearout.

To sharpen the plane blades, the backs first needed to be flattened. I used drywall screen sitting atop a sheet of glass, but you can also use a sheet of coarse sandpaper clamped to a known flat surface, like a cast iron table saw or jointer bed. From there, I polished the back on 1,000 grit and then 8,000 grit waterstones. A veritas gauge helped maintain the bevel angle while sharpening it on the 1,000 grit stone, followed by the 8,000 grit stone.

Sharpening the side bevel was a little trickier. It was rounded over, so I first flattened it with a file and then used 1,000 and 8,000 grit slipstones to polish the bevel.

Scratch stock is very easy to make. The trick is to make sure you polish both sides of the metal as well as the edges. You want very square edges. I rough-shaped the profile with a hacksaw, used a grinder to finalize the shape, flattened the edges with a file, and used an 8,000 grit waterstone to polish all edges. It only took about a half hour to make, whereas, had I elected to heat treat the blades.....well, let's just say, this being two days later, I'd still be trying to bolster my courage.


Anonymous said...

Regarding heat-treating the blade... you don't *have* to do it yourself. Every reasonably-sized city has a heat-treat operation nearby, and they're open 24 hours per day, because it's not economically feasible to shut the ovens off and heat them back up again. If you walk in and ask nicely (and if you know what kind of metal the irons are) then they'll toss them in with the next batch of that kind of metal (and thickness) that's being done to the kind of hardness that you're after. This way the blade is hardened right through, guaranteed to the hardness that you want.
It's a thought, anyway.


Kari Hultman said...

Thank you, Metalworker Mike! That's a great idea. I will definitely look into that. : )

Anonymous said...


What is the metal you started with for the scratch stock? Card scraper? Great post, I am intrigued by the dovetail plane. I'll keep an eye out at the next flea market.


Kari Hultman said...

Shannon, that is a piece of old bandsaw blade. I've made other profiles in it, as you can see. No need to just use one edge of it.

Jan Michael Hedlund said...

from 800 to 8000 grit isnt that a to big jump?

Kari Hultman said...

Jan Michael, that was supposed to be 1,000 and 8,000 (I just changed it). It's not too big a jump in my opinion. It's the way I was taught to sharpen by David Finck who was taught to sharpen by James Krenov. However, a lot of people add a 4,000 grit stone in between. I've never had any trouble skipping the 4,000 grit.