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!