Chisels, plane blades and other edged tools need regular TLC to keep them functioning properly. Mine were getting blunt and I'd misplaced my oilstone, so I decided to make a powered sharpening system using parts hacked from a broken breadmaker. I also used a busted toaster oven to get a glass baseplate for creating the final edge, and a ruined briefcase to make a leather strop.
Step 1: Repurposing and Sharpening Philosophy
We've now had 7(!) breadmakers (3 different brands; 4 were replaced under warranty) fail from metal fatigue on the paddle driver. It seems it is not in the manufacturers' best interests to make this part strong enough to survive more than a few hundred kneadings. So, as a result, I had a broken breadmaker handy, and this one had some interesting parts - a beefy motor, a massive gear and a thick circular glass viewing window. I figured I could salvage it to make a rotating sandpaper disc to do the heavy work on my tools before doing some quick establishment of the final edge with some finer grade of sandpaper by hand. Basically, the breadmaker would be hacked to mimic WorkSharp's $250 power sharpening system... for $0.
It is important to find an effective method of sharpening that works for you. For example, I long ago gave up trying to get kitchen knives conventionally sharp, because I found that a cheap crossed carbide sharpener gives my knives wicked micro serrations that are super-effective slicers of everything from fresh baked bread to soft tomatoes. However, wood is a lot harder than food (at least it should be...), so you need a better way of getting a good lasting edge.
Step 2: Dismantle Breadmaker
Pretty straightforward - remove all the screws and you should be able to extract the innards fairly easily. You need to keep the round glass window, motor, power cord, capacitor, and gearing system. Recycle the rest.
The breadmaker I used was this Black & Decker one, which I don't think is manufactured any more. There do seem to be newer ones with round windows though, from Hamilton Beach and Oster. Keep an eye out for them at yard sales and the like.
Step 3: Make Platter
You will need a circular platter to mount the round of glass on. I cut mine out of 15 mm plywood using my router table; I just clamped a piece of wood with a nail in it at the right distance from the outside of the bit, raised the router into the work piece a few mm, rotated 360 degrees, and repeated until I had a nice circle. I chamfered the edge then screwed the large gear onto the plywood circle through the plastic arms. This necessitated drilling a hole through the steel mounting plate.
Step 4: Add Glass
To allow removal of the glass for easy replacement of the sandpaper, I used adhesive velcro to join the two discs, and glued a 120 grit round of sandpaper on the glass.
Step 5: Build Housing
I needed a way to mount the sharpening system, so I built a plywood box out of offcuts to keep the gears and motor out of harm's way. There is nothing fancy about the box - it is just two frames, one inside the other to provide a ledge for the metal frame to be secured to. The pictures show how it was built. I haven't specified measurements because I didn't take any myself - I just marked against the metal frame. The box was assembled using wood glue and a nailgun, my favorite method for quick builds. The top and bottom are 6 mm plywood, screwed in place for easy removal in case of maintenance issues. Note the cross piece with slots cut for the belt to protect the motor from dust.
Step 6: Add Switch
Caution: electricity is potentially dangerous. If you are in any doubt about a task involving wiring, consult a professional electrician.
I also added a large switch to the side (a regular wall switch from my box of electronics). All the wiring was done with pigtails and wire nuts, and was not complicated (just pop the switch in line with the line coming from the wall). The disc doesn't spin all that fast (about 200 rpm, based on inspection of video - it takes about 7 frames at 24 fps to describe one full rotation), but that's OK - remember that this process works just fine by hand, and you don't want the tool getting too hot anyway. The commercial one spins at ~600 rpm.
Step 7: Magnetic Sweeper Arm
I screwed a hinge from my bits box so that it hangs over the disc, and added a large rare earth magnet to it. This sweeps up the metal powder you make during the sharpening process. It generates a surprising amount and fast, and you will have to take the magnet off periodically to clean off the metal dust.
Step 8: Finishing Plate
The powered platter does a decent job of restoring the bevel on a tool that has been damaged or nicked, but it won't get the tool really sharp. For that, a nice cheap simple approach is the scary scarp method; basically, using sandpaper of increasing grit counts glued to plate glass. I didn't have any plate glass handy, so I removed the glass door from a broken toaster oven, scraped off all the glue and scorch marks, and gave it a good clean. The dimensions of the plate are 290×133 mm. It's only about 4 mm thick, but I figured that given it was designed to handle large thermal fluctuations it ought be reasonably tough. Any sort of glass is probably fine for this purpose, the bigger and thicker the better. I like mine because none of the edges are sharp - they've all been neatly beveled and polished.
I don't actually bother gluing the sandpaper to the glass, because I use a jig that allows me to sharpen one-handed while I secure the paper with the other hand. It means I only need one piece of glass and can use whatever grit paper I like. See later for how I go about it. The approach I've used is a simplified version of Brent Beach's method. I highly recommend his site for anyone interested in getting things seriously sharp. The high-end micro-abrasives he uses are available here. I've not used them myself, but will be picking some up at some stage if I ever feel the need to start shaving with my woodshop tools...
Step 9: Strop
A strop is just a piece of leather that burnishes the blade by removal of the minuscule strands of metal left over after creating and breaking off the burr. I made mine by gluing a piece of leather, shiny side up, to an offcut board 370×75×18 mm. If you're using the aforementioned microabrasives, stropping will not help.
Step 10: Build a Sharpening Jig
If you're an experienced sharpener you can get a good edge by hand. I'm not, so I rely on a jig - it makes the whole process vastly easier. You can buy such jigs, but they can be pricy (>$50 for this one, though there are inexpensive ones available too), so I made mine for $0 with two pieces of wood that trap the blade with a couple of flat head screws. These are easy to make, hold the blade very firmly with only light tightening, and you can size them according to the size of your chisel/plane blade. The one shown is made of two pieces of wood (53×18×38 mm and 53×18×6 mm) and two pocket hole screws.
Step 11: Sharpening
The powered platter does most of the donkey work. Sand the back until it is nice and flat and scratched all over. Then put the blade in the jig, setting it so the bevel is flush to the sandpaper. Just make sure that you're making one facet, not several, and that the end of the chisel stays perpendicular. This step is more of a rough grind to restore the primary bevel and remove any chips; all the real sharpening gets done on the plate glass.
Step 12: Scary Sharpening
Put your plate glass on a thin (~6 mm) sheet of material. You want to raise it slightly because that will make it easy to create the microbevel you need for a really sharp edge. Now set your jig up so the bevel is flat to the 150 grit sandpaper when the jig is resting on your workbench. Tighten the screws, then sand the bevel until it is flat and smooth all over. I usually then swap the sandpaper for 320 grit, remove the scratches, then swap again for 600 grit to make it shiny.
Remove the plywood under the plate glass and sand again with 600 grit paper until a microbevel appears along the full width of the blade. THIS DOES NOT TAKE LONG, so don't overdo it. Removing the plywood changes the angle of sanding just enough to create a microbevel. I have some 1200 grit paper with which I like to create final bevels on both sides of the blade.
I find that at this point I have a really good edge, but I drag both sides of the blade along the strop anyway - it removes any stray bits of metal and leaves the blade silky smooth. You can shave fine hair and sever end grain fibers without any crushing with this edge. That makes it roughly as sharp as a new Exacto knife blade.
Step 13: I've an Ax to Grind...
The sharpener is good for things other than chisels and plane blades, of course. My ax had a rather dinged edge so I spent a happy 10 minutes lightly sanding out the nicks. The system is nice and quiet; the cutting action is not aggressive and does not get the blade hot. The photos shows how much metal dust was generated during the sharpening process. All sharpening here was done by eye (no jig) and the edge created was deliberately kept quite blunt for longevity. An ax doesn't need to be especially sharp for splitting firewood.