Chapin Tools

Block Planes

Stanley Planes USA, LLC

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Restoring Chisels, Turning Gouges and Other Edge Tools

  Chisel Backs - Flat at last by Scott Grandstaff  

Flat at Last, Flat at Last. Great Gawdamighty, Flat at Last...

I love chisels. Guess that doesn't surprise anyone here.  But... If you are like me you have absolutely had it with hand lapping out backs down to the bottom of the inevitable pits.

Oh sure it works. As you heave and grunt and vacuum and magnet off the dust and rub some more and change sandpaper with the lovely spray glue that always takes longer to stick than you had in mind and then the paper or cloth comes loose at the edges and curls and eventually you end up with a chisel or plane blade back that's -almost- flat but not quite after grueling hour after hour of, looking like Popeye the sailor before the end, work. Not to mention never quite square to the sides anymore.

I've been so desperate lately I've been looking at surface grinders.  Handy gizmos those surface grinders. FOR A THOUSAND DOLLARS (and those are the tiny ones) !!!! What are you, kidding?

Well, I tried the revolving platen approach. I built a heavy disk grinder gizmo. It's thick plate steel welded up and turned on a heavy tool room lathe and to this I mount rt angle grinder cloth sandpaper disks to. It's a great thing but I'm not. In other words I can't hold the chisel straight or steady enough with my hands to flatten a back with any degree of accuracy. I was planning another disk approach and even scored a jeweler's lapping plate and a heavy arbor to mount it on.

It's got good ball bearings. But I was still stuck with the prospect of trying to square up and hold the chisel somehow.

Well, to make matter even more pressing, today I got a new old chisel from Trevor. It's a killer. It's big and I mean big. For a 1/2" wide chisel it's got one of those full beer mug sockets and 7 glorious inches of deep thick mortising blade. Needed a little work though. Naturally. This one had probably been kicking around like so many others with nobody wanting to tackle the lapping.

I have a cross vise and was thinking of trying something with my drill press. I had in fact already tried a failed approach. I thought, how cool would it be to flip the table column on it's side and mount a regular grinding wheel in the chuck? This was a good idea except for the fact that the cross vise on the table wouldn't reach. Damn geometry. Drat, so close and yet so far.

Next I tried mounting a small flat end grinding wheel in the chuck and with the table in the regular position push the chisel mounted in the cross vise across it. This nearly worked but the center of the little wheel caused undue swirling and grabbing. But finally, tah dahhhhhhhh...

I mounted a small cup wheel in the chuck. With a cup wheel only the edge is cutting. Cranked the speed up to around the usual 3600 or so, got me an eye dropper and a coffee can of water. This is machinist work. You have to measure and tap the work piece and measure again etc. until you get it squared up and flat to the wheel before you start in. Once you have it, set it so it just doesn't cut. Then loosen the table platform and crank up the gear ever so slightly. If a crank revolution represents 360 degrees, you want about one degree maybe 2 but no more. This cuts slow.

You set it to grind just about 1/8" of chisel per pass. No more. Sure it takes time but hey, you were willing to rub your arms off for days straight 10 minutes ago before you started reading this weren't you?? Don't snivel!

You run it up and then down on the x axis at your tiny cut and then move it over another 1/8th inch on your y-axis and go again. When you've covered it all, release the table clamp and nudge it up a skosh more for the next go round. Don't forget to dribble on the water now and again. Don't want to overheat the work!!

Well, that's it. In less than an hour this honking big mortise chisel has a back flat enough it's whole length that I cannot measure any outage. Pitts are gone, the original slight bow along it's length is gone. It's flat and gleaming.

Really flat. Flat the whole length. Flat at last!

The setup

Cross vise and small depressed center grinding wheel in DP chuck.

Chisel mounted and taking a cut

Last cut

I want to stress that it's lightest possible cuts and plenty of water if you're doing a thin paring chisel or you'll cook it. The big thick mortise chisels aren't as fussy but still a light cut is all you're going to get away with. Remember I'm only cutting about near nothing deep and an 1/8" wide cut per pass.

I flopped the last one I did down on my sandpaper plate for a test and got even scratches stem to stern in one second's lapping time.  Ahhh, flat at last...

yours, Scott
March, 2006

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