Sharpening can very easily become an end in itself, so it's worth remembering that for a busy cabinet maker it's a task that is often repeated many times a day - so it makes sense to spend as little time as possible fiddling around with grindstones, whetstones, honing guides, multiple stones and whatnot. At least, that was Mr. Ford's policy, but he was a dour practical man, for whom the romance of woodworking had probably vanished long ago in his youth. Nonetheless he was a good teacher, who (rare gift) was happy to let his students continue headlong into disaster: "Learning the hard way", he would have called it, but the lessons stayed learnt.
(One of our batch of would-be bench joiners, a cockney ex-serviceman - Kenny? - was at one point engaged in making a fairly simple four panel stile-and-rail door, with all mouldings stuck and coped by hand. It gave him a lot of trouble, but at the end of the week he finally got it all glued up, wedged through-tenons and all. He summoned Mr. Ford to approve it as done. Mr. F. had been keeping an eye on progress (of course), and came across. "Not bad", he said, "but how are you going to put the panels in?". Then Mr. F. handed him a cross-cut saw and told him to put the bits of his panel-less door in the firewood box when he'd done.)
Anyway, I thought I'd try to follow the progress of a much mistreated Salt Spring Island Middle School chisel through a basic reconditioning process. Tom McKeachie, who seems to have taken the shop refurbishment under his wing, brought me a plastic tray with 25 assorted cabinet-makers' chisels; they looked neglected and abused: nicks, burns, short bevels, angled edges, ground back bevels, rust spots. Normal for the situation:
Not a sharp edge amongst 'em.
The first job is to grind out all nicks, chips, dubbed corners etc. (As well as any malignly added back bevels). The goal is to grind the damaged edge away quickly, with a true, sharp, coarse grinding wheel, or as above with a disc (80 grit). The coarse grit removes metal quickly without generating excessive heat. Note that this step is only necessary if the cutting edge is in need of reshaping or repair. Otherwise skip to the bench grinder set-up, adjust the jig angle to the existing primary bevel, and grind until the secondary bevel has been reduced to a narrow parallel strip.
Check for square, and cool if necessary in water:
When it's done, you should have a square, straight flat on the end of chisel, at ninety degrees to the blade surface, which will show up bright in an overhead light when looked at from directly above:
As you can see, a fair amount of metal has been removed.
The next stage is to grind a new primary bevel. This bevel is almost invariably 25 degrees. It does not form the cutting edge (this is provided at a later stage with the whetstone), and as above it can be made with a clean coarse stone on a simple rotary bench grinder.
This is not as easy as it sounds, as there are a couple of problems to solve: first, how are we to establish a 25o grinding angle, and second, how are we going to maintain that angle during the removal of a fair amount of metal?
The tool rests provided with most grinders are barely adequate for this task, and should be removed. I use instead a method commonly used for lathe tools, which is equally useful for joiner's tools:
Fasten a board to your bench under the grinding wheel. Make provision for an adjustable stop where the heel of the chisel handle can rest. Place the chisel with its handle against the stop, and the bevel on the stone. Clearly this will maintain a constant grinding angle. First problem solved. Next - how can the correct angle be found? (This angle depends of course on the position of the adjustable stop, which will vary according to the overall length of the tool.
A crude (but effective) jig is all that is needed. Two points of the jig rest on the curved surface of the wheel, and a projecting flat section fits against the chisel blade. Move the stop so that everything is simultaneously in contact (with the wheel, the chisel and the stop) and tighten the stop adjustment. (In this case a clamp. More sophisticated methods will occur to the ingeniously minded) This simple jig can be used to find the correct grinding angle for any tool length.
How to get the jig angle correct in the first place? Find a correctly ground chisel, place the bevel firmly against the wheel with the heel touching the board. Slide the stop up to the chisel heel and secure. Then place the jig on the wheel with the two points touching, and mark the flat cut on the face of the jig using the chisel as a guide. Then saw away the waste, leaving the correctly angled projection as shown.
Before grinding, remove the rag on the square-ground edge with the blade held firmly flat on the whetstone:
Finally, briskly grind the new primary bevel. Keep the edge cool by dipping in water as needed - although with a clean coarse stone not much heat will be generated. (Only light pressure on the tool is required, and the edge should be kept in constant side to side motion while grinding).
Since there is no fine edge (having been ground away) the tool will not be particularly susceptible to burning. Watch the bright metal edge constantly, removing the tool from the grinder and holding it so that the square-ground edge catches the light. When the new (correct) bevel reaches this edge, it (the flat edge) will quickly become narrower as the newly ground bevel approaches the flat back of the blade. The trick (and it's not hard) is to keep this bright "flat" parallel as the newly ground bevel slowly approaches the back of the chisel. Equally important is to ensure that you stop grinding before an actual sharp edge is formed. Here some judgment must be used as to when to stop grinding. Much better too early than too late. (You run the risk of burning the tool if the edge is too fine, as well as losing the straightness and squareness of the edge.)
The next instalment will deal with the honing of the secondary ("micro") bevel.