Here's the second part of our
two-part series on sharpening chisels. Last week, we ground the bevel of the
chisel using a bench grinder. That gave us a hollow ground bevel -- the bevel
reflects curve of the grinding wheel. This week we'll work on the cutting edge.
After grinding the bevel, you're ready to move from the grinding wheel to the
stone. To hone a tool that's been hollow ground, I use a 1,000-grit waterstone.
I like to use waterstones because they cut very fast. The 1,000-grit waterstone
(a "medium" grit stone) will hone the cutting edge to a mirror
finish.
When you've finished grinding the bevel, you'll notice that the grinding wheel
raised a burr along the back of the cutting edge. So the first step is to
remove that burr. To do this, hone the back of the last inch of the chisel flat
on the sharpening stone.
After removing the burr, you're ready for the final step: honing the cutting
edge. But why hone it? After all, you've probably got a really sharp edge
already. The answer lies in what makes an edge last a long time.
If you take a close look, after grinding the bevel, you can see marks left by
the wheel. Magnified, they look like deep grooves. These create a ragged
cutting edge that feels sharp. But it doesn't stay sharp because the points on
that ragged edge break off easily. The more they break, the more ragged the
edge becomes, making it duller faster -- a sort of snowball effect.
To make a long-lasting edge, you'll need to remove that ragged edge. The
smoother you get the cutting edge, the longer the edge will stay sharp.
To hone the cutting edge, hold the hollow ground bevel against the waterstone
so both the front and back edges of the bevel touch the stone. Then gently push
the bevel over the stone. You can push from end to end or make little arcs.
Just do what is easiest for you to keep both the front and back edges of the
bevel on the stone.
How long do you hone? Well, not long. Just until the grinding wheel marks along
the cutting edge disappear. Then check for a burr on the back of the cutting
edge. When you feel a burr along the whole cutting edge, hone off the burr
(like you did with the burr created by the grinding wheel), and your chisel is
ready to use.
One of the really nice things about this technique is that touching-up the edge
after use is really quick. This is because you don't need to re-grind the
bevel, just re-hone the edge. You should be able to touch-up the edge several
times before you need to re-grind a new bevel.
Go to Tip #57 |
