Monday, September 26, 2011

Card Scraper -- Thanks Jim!

     One of the items used by cabinet makers and furniture builders alike is the cabinet scraper.  What is it?, not much more than a piece of metal with a burnished edge that can be pulled or pushed along the face of the wood and make it incredibly smooth.  Works extremely well on wood with interlocked grain.  As a kid, I remember my uncle scraping the paint off of a piano using nothing more than pieces of glass.  Of course he allowed us kids to do it in an inconspicuous place and it worked.  When the glass no longer scraped off the finish we just got another piece of broken window glass -- hey, we are Dutch after all!
     What brings all of this about is that on the last day of class, one of the students asked me about using card scrapers and my luck with them.  I had to admit that lately I've struggled with it but had good success in the past and was somewhat puzzled.  That prompted me to re-visit the scraper and do some research.  There is a ton of it so let me summarize what I learned and what works.
     The first problem is that my one card scraper had been burnished so many times the edge was "work hardened" and no matter how I tried to burnish it, it wouldn't hold the hook that does the cutting.  More on that aspect of it later.  My first step was to use a single cut file in a holder and really work the edge down. The purpose of the holder is to keep it square to the blade.  It can be bought or you can cut a file sized groove in a block of wood and use that.  Probably removed at least an 1/8 of an inch or so.  In the picture below, you can barely see a holder I use.  It's in the vise, on the left side and is nothing more than a piece of wood, split 2/3 of the way that I insert the card scraper into.  It's then put in the vise and clamped in place.

Whoops, no steel safety toes!
     After filing, I marked the edge with a Sharpie and using a block of wood to keep it at 90 degrees, ran it over a 1000 grit water stone to burnish it.  I then laid it on its' side and did the same for the flat sides of the scraper.  The goal is to get two sides and one edge that is smooth and square.  The smoother the piece of steel is, the better your cut will be.
     Burnishers -- there are two in the picture.  The triangular one is an official, store bought version.  The other is a fuel pump push rod from a 1973 Capri  V-6 that I've had since replacing that car's fuel pump in '75 or so.  If I were going to buy one I'd definitely not get the triangular one, it tended to catch the edge when I used it.  There are round and oval ones available commercially that I'd buy instead.  Your first burnishing action is to lay the scraper flat, apply a drop of oil on the edge and run the burnisher along the flat, side edge 5-6 times.  The purpose is to "draw" the steel towards the outside.  Now it's time to put it back into the holder and burnish the edge to form the hook that will smooth your wood.
     In my frustration with not being able to get a hook anymore, I bought the black thing you see at the top of the board.  This works well, it's from Veritas and has a burnishing rod that you can adjust for any angle up to about 15 degrees.  The only problem is that it was difficult for me to start it right at the beginning of the scraper.  I found that I could get equally good results with it or the old push rod.  The triangular one -- not so much.  I think it's destined for E-bay!
     As I thought about it, the major problem I and probably others have when you burnish is knowing where the heck 10 degrees or so is!  Familiar angles like 90 or 45 we can get a pretty decent guess on but 10 degrees isn't that common.  What I did and it worked great for me was to take an angle checker (upper left of picture) and set it at 10 degrees.  I then had a visual to look at and match my hands angle to it and have success!  Three to five strokes is all it took to form a nice hook.
     In practice, you hold the scraper in both hands and flex the blade.  I find that I'm a puller but you can do either -- push or pull.  By adjusting your angle the scraper will take fine shavings off of the wood much like a plane will.  These are pretty aggressive with a 10 degree hook, lessening the angle to half of that should result in a lighter cut.  You should be able to put a hook on both sides of each edge including the short ends.  At this point I've only done one side.
     So, there you have it.  You can do lots of research on the web to find more details but this is one of those woodworking things that once you find what works for you ----- leave it alone!

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