Cabinet Scrapers

[Robert W.Hohf]

A cabinet scraper is the most difficult tool in the shop to sharpen with any 
consistency.  It takes considerable effort to develop the technique, but, once 
you get it, you will not regret the time.  I don't use full size, rectangular cabinet 
scrapers, but have made a set of smaller scrapers with the various flats, 
angles, and curves necessary to get into the nooks and crannys of pianos.   I 
recommend using Sandvik scraper material since it seems to hold an edge the 
longest.  It is important to remember that, on all edges, it is the "wire edge" 
which actually does the cutting.  Scrapers are no different.  The wire edge is a 
microscopic burr which forms on the edge of steel when it is worked.  The 
direction the wire edge is pointing, degree it is polished, and its size determine 
how the edge will cut, and how long the edge will last.  This is true of scrapers:  
how you sharpen it will determine what it will scrape, and how fast it will get 
dull.  The angle you burnish the wire edge will determine the angle to hold the 
scraper at when scraping.  Holding a scraper an too low an angle for the edge 
will "roll" the edge and ruin it in one pass.

Here is how I sharpen scrapers:

	1.  The scrapers I use are relatively small so I put the file on the bench 
and file all edges of the scraper by hand.  This produces a large, rough wire 
edge on both sides of the scraper.  Even with burnishing, this edge will cut 
poorly and dull quickly.
	2.  Rub the same edges you filed on an 800 grit waterstone until the 
scoring from the file is gone.  Feeling the small surface of the scraper edge flat 
on the stone is one of the tricks you need to develop to do this effectively.  Not 
having the small surface flat on the stone will remove the wire edge from one 
side.  
	3.  Rub the same edges on a 6000 grit waterstone until the narrow 
edges of the scraper are nicely polished.  
	4.  Put the scraper flat on the 6000 grit stone, turn the wire edges 
perpendicular to their original direction and polish the underside.  "Turning" the 
wire edge wrong here can ruin the edge.  The first pass must be "away" from 
the edge.  Once it is turned, polishing can be done with back-and-forth or 
circular motion.
	5.  The wire edge is now very small, very sharp, and perpendicular to 
the direction you want it.  Burnishing must be done with very hard, very smooth 
steel.  Most screwdrivers, etc, are neither hard nor smooth enough.  I use a 
Kunz triangular burnisher (Woodcraft Supply) with all machining marks 
removed, and polished on waterstones.  With the burnisher "roll" the wire edge 
back over with several passes.  This takes practice.  

A four-sided scraper can be sharpened with 8 usable edges.  Curved edges 
scrape finish better than flat.  One of the beautiful things about a scraper with 
small, very sharp wire edges is that it will remove finish from spruce without 
cutting or tearing the wood.  I can scrape an entire, medium sized (old) 
soundboard in about 40 minutes, without having to resharpen the scraper.  New 
plastic finishes are more difficult.  Before gluing maple,  I always scrape the 
surface with a flat scraper to remove any machining irregularities.  This leaves 
the surface flat and glassy smooth.

If you have never used a scraper that is this sharp, I highly recommend  that 
you spend the time to develop the technique.  You will not believe what can be 
done with them.

Bob Hohf
Wisconsin