Thread: Lapping chisel faces with a hand drill

I've been following the thread on using electrons to flatten the backs on very pitted or bellied blades.

This is of particular interest to me, as I've no machinery of any kind in my shed (except a hand drill), and decided to enter the woodworking hobby by purchasing a few huge buckets of rust, in particular, a collection of Titan chisels. (I've mostly bought aftermarket blades for my planes).

I've found that the problem with old chisels and irons is that they seem to have been repeatedly lapped on oilstones or some other sharpening medium that's well out of flat, with the result that they develop a large "belly". Those I've found that show very little use, with complete blade length, generally don't have this problem, tending to be concave, suggesting that they weren't manufactured out of flat.

One in particular, a fine 1 1/4" Titan registered firmer specimen, I put in the too hard basket. It had a SERIOUS belly, and that's an awful lot of hard steel to remove. I have named him Bob the Crash Test Chisel and conducted all sorts of horrible experiments upon him, including using a homemade MDF-and-sandpaper-flattening-wheel thing, and (when I was feeling particularly vengeful) opening paint tins with him, used him to defrost the freezer, and used him to perform various tests on my grinding wheels. I have included a picture of Bob in this debilitated state, but didn't take a photograph of the extent of the convexity, unfortunately.

Then, however, I read Garrett Hack's "The Handplane Book", in which he suggests that plane irons can sometimes be flattened with the assistance of a small grinder wheel in the chuck of a normal hand drill, providing a sort of Japanese-style hollow back.

So, out comes Bob.

First, I ground the bevel back about 1/8" to get rid of the worst of the dubbing. This took a fair while on a hand-cranked grinder, but still much easier than lapping it out.

Next, I purchased a grinding wheel for the drill from eBay, for $15. I clamped Bob to a sawbench, donned safety goggles and then had at him for a while, testing every now and then on the waterstones to see how far the scratch pattern was from approaching the edge.

Initially I used the grinder to produce regular "furrows" in the steel. Later, I realised that a better result can be had by attempting to spread a relatively even surface using quick, even strokes. It isn't at all difficult. I've included a picture of the chisel at this stage.

Every now and then, I would use the Sigma #120 waterstone (the "Black Beast"), applying lots of bodyweight pressure with a cork sanding block as a handgrip. It wasn't really necessary to completely remove all of the drill marks this early, but I did so anyway to ensure I hadn't gone too deep. It didn't take very long. This stone is (by far) the quickest way to lap metal via hand-power I know, and I've also tried other waterstones, abrasive papers, SiC on glass, diamond paste and diamond stones. I realise I've already banged on about this stone at length, but still - it's remarkable, albeit a little finicky. In the photographs you'll notice my Extra-Course DMT diamond bench stone lying around looking embarrassed (it's become nothing more than a very expensive way of flattening my King waterstones); there's just no comparison in cutting speed.

After doing this a few times - a little more confidently each time - I reached the point where the Sigma stone produced scratches right at the cutting edge. I then stopped using the drill and used the Sigma for about 300 strokes, briefly unclogging the stone every 50 strokes or so with course SiC grit on glass. The grit must be course, else it will have the opposite of the desired effect and clog the pores rather than open them. Pressure should be very light. It doesn't really matter how much water or grit you use, but a small pinch is adequate.

Once I was very sure that I had a consistent scratch pattern all across the cutting edge, or very close, and could no longer see any grinding marks from the drill, I moved to the Sigma #400 ceramic, for around 150 strokes. This turned out to be the perfect tool for the job; it was course enough to remove the (very nasty) scratches left behind by the #120, especially when used with pressure, but left a nice enough finish to spare the altogether less effectual King #1000 a lot of work. Nonetheless, the #1000 could also have been put to the same job with a little more patience.

The result is a nice, flat, not entirely polished bevel. (Why not polished? Story for another day).

This drill / Black Beast trick worked great. It cut down on my lapping time enormously (although I still estimate this took well over an hour). I hope that I can further reduce my lapping time in future by working more aggressively with the drill before touching up on the stones - I discovered that there's really nothing you can do with the drill that the stones can't remove in quite short order, short of trying to bore straight through the blade.

The only thing I would do differently is avoid the edges of the chisel with the grinder - as you can see in the photo, I allowed enthusiasm to overtake me and ground right to the edges, predictably dubbing them. Happily, nothing the Sigma couldn't fix.

What do you guys think? Admittedly, I wouldn't try this on your brand new Harold & Saxons or anything. Nonetheless, given the costs involved ($15 for the grinder, $27 for the Black Beast, plus postage) I don't know any cheaper or more effective way of rehabbing chisels.