Sunday, January 27, 2013

Chisel Sharp



I discovered I needed my chisel for a woodworking project.  I’m taking a course in hand-cut dovetails.  I need a special saw, which I have courtesy of my grandfather.  The chisel I have courtesy of myself.


I bought it maybe 30-35 years ago.  It’s a Stanley 5/8 inch wood chisel made in the US.  The steel?  Beats me.  I bought it at a time when Stanley stood for quality and that was enough for me.


I took it once to a community theater when I did technical theatre.  We were building a set with lots of doors, so that mean lots of passage sets (aka doorknobs and locks).  I looked up and found a co-volunteer using my chisel to hammer small nails out of wood.  


I’d like to say that he was able to use his hands after a few years to therapy but I’d never hurt anyone that bad over tools.  Fortunately I put a halt to his activity before too much damage had occurred.  I just took it home and kept the damaged edge as a reminder never to lend any tool I cared about. 


Now it was time to rehabilitate that tool.  So I got out my stones.


Just in case you don’t know, most wood chisels are sharpened on only one side.  Hence the term, chisel-grind.  The flat edge lets you cut straight through the wood, while the beveled edge clears the wood away from the cut.  If you sharpened both sides, yes it would be sharper, but it would drift away from the cut line.


I have a nice Norton combination coarse/fine stone I bought years ago.  It’s 11.5 inches long and 2.5 inches wide and I really like that size.  It’s hard to get the right angle for each stroke, but once you get it, 11 inches gives you a lot of sharpening distance.


I oiled it up and started on the coarse side, but it wasn’t taking the metal off as fast as I wanted.  So I switched to my little DMT combo diamond stone.  These stones use water as a lubricant so it’s easy to clean up and store.  I bought the DMT so I could touch up an axe or knife blade in the field.  The coarse diamond worked great, but the relatively small size made the job tedious.  I also thought the ratio of diamond material to open polymer made the effective sharpening area significantly small and reduced the metal removal efficiency.

My selection of sharpening stones
On the left the Norton combination stone; the red is the fine grit. The EZE Lap, and the right is my diamond DMT Combo.
I pulled out my EZE Lap, a six inch long fine diamond stone.  That really took the edge down.  Before long I had worked out all the edge damage and had a nice wire edge. 

Now it was back to the Norton stone.  I continued on the coarse side, which made finer marks than the fine diamond EZE Lap.  I guess it makes sense.  The coarse stone is less abrasive than the fine diamond.


I first flat polished the wire edge away on the back of the chisel and did a second uniform one across the chisel’s edge and moved to the other side of the Norton stone, the fine side.  ("Come to the fine side Luke!  I am your father…") Again I removed the wire edge and repeated the sharpening until I had a third wire edge.  I carefully polished the back of the chisel and was finished.

Almost a perfect job, the right edge isn't perfect, but it's very good
It's a pretty good edge, but the right tip isn't perfect.  I suspect its part of the way I put pressure on the chisel during sharpening.

Did I get it sharp?  I think so.  I shaved a few curls from a block of yew wood I had in the basement and was very happy with its action.


Sharpened chisel shaves yew wood
I shaved a few small shavings with my chisel.  I wanted to see how thin I could make them and how much effort it took.

Could I get it sharper?  Maybe.  Depends on the steel.  I could have gone to an ultra fine polish and left the face mirror shiny.  But would the edge hold up?  Steel for chisels is selected for impact and bending properties not necessarily hardness or even edge retention . Some woods are so hard the best you can do is to slowly remove a 32nd inch thick shaving at a time.  Most woodworkers would rather have to resharpen more often than break a chisel.


I’m happy with the way this sharpening project turned out.  I got a uniform edge at about 25 degrees, with a straight, sharp cutting edge.  

In the spirit of complete honesty I used a little wheeled gismo that holds the chisel at a constant angle.  I don’t have any idea where I bought it, but for sharpening a chisel or wood plane blade, it’s the bomb!!!

2 comments:

derrick38 said...

I have the same problems when sharpening chisels. Very difficult to get the edge a true 90 degrees from the sides. Got one that I think a co-worker used as a screwdriver--pretty sure it'll need the intervention of a belt sander to erase the damage.

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