Use and sharpening of card & cabinet scrapers.

 I have a Stanley number 80 cabinet scraper that I picked up second-hand that I have been using for some time to smooth surfaces that the plane finds difficult where there is "tear-out" of the fibres. An example is the hazel mirror frame that I recently finished.  More recently with some time on my hands I looked at the sharpening methods on the internet and also the use of card scrapers in general. One thing to recall is that the term "scraper" is a misnomer as these scrapers are designed to cut the wood fibres and not produce a lot of sawdust as sand paper does. 

Card scrapers have been brought to my attention whilst in Spain and visiting one of the Chinese supershops that sell about everything including tools. I found these scrapers that looked ripe for modification for use as wood card scrapers and making burr edges using traditional methods.

Possible card scrapers in a pack for 1.50 Euro. These are made for KMT tools and distributed in Spain. There are four in the pack of different widths, 10.5, 9, 7 and 4 cm with a plastic handles at the top as shown. They are 0.2 mm thick.

Cabinet scrapers and card scrapers are different and need a different method of sharpening and preparation. The cabinet scraper is mounted in a tool or jig that sets the blade at an angle to the wood scraped and the blade is thicker and bevelled to 45 degrees with a burr on the end. In comparison a card scraper is not mounted but held in the hand to "scrape" the wood. The working end of the scraper is sharpened to 90 degrees and a burr drawn from the surface that does the fibre cutting.

Cabinet Scraper

Basically the scraper consists of a rectangular steel plate that has two long sides ground to an angle of 45 degrees and then honed to something like 1200 grit, much like sharpening a chisel (although these a normally about 30 degrees).  I normally do this free-hand with a diamond stone (as the main filing has already been done). However I noted that Paul Sellers on one of his videos mounts the blade in a wooden block (he uses a block 3/4 inch thick and 2 3/4 inch by 9 inches) at an angle of 45 degrees with another small block underneath screwed to rotate and keep the blade from moving whilst filing and honing. The blade is put in the block with about 1 mm protruding up, fixed in position and then the block clamped into a vice. If needed the edge can then be filed diagonally across the blade ("through filed") and when there is a good bevel, the file direction is changed and the file is drawn horizontally  across the edge (i.e. file at right angles to the edge). The next stage is to use finer grits up to 1200 grit, and then remove the blade and remove the burr on the flat faces so that a nice clean sharp cutting edge is obtained on both long edges.

The next stage is seen to be crucial to creating a working edge to the blade. In principle this involves "bending" the sharp edge of the blade to form a burr that acts as the cutter when in use. To do this a tool called a "burnisher" is needed. This is any hard steel surface such as an older chisel but you can purchase burnishers for this purpose. Burnishing is basically pushing the hardened steel along the cutting edge of the blade, starting at 45 degrees to consolidate it. The blade can be mounted in a vice, the burnisher wetted with oil (some descriptions of this method talk about "kissing" the burnisher, so I guess wetting the burnisher also works!) and then pushing the burnisher along the blade starting at 45 degrees but gradually turning the edge to about 70 up to near 90 degrees. The pressure on the burnisher should not be accessive as this can be counter productive. In fact it should be no more than you'd use to push a traffic light crossing (if that helps; practice makes perfect?). You should be able to feel the turned edge or see it when magnified. 

When the blade next needs preparing, it may be possible to just repeat the burnishing stage. The next step is to mount the blade by putting a piece of A4 paper under the front of the cabinet scraper (the curved edge is the front) on a flat surface and then dropping the blade into place with the bevel pointing to the rear of the scraper. On the Number 80, the rounded edge is the front of the scraper so that it is pushed in the opposite direction to a plane as the bevelled surface does not cut but the burr formed at the tip does the work.  Then squeeze the blade in the scraper and tighten a little whilst squeezing. The wing-nut in the centre of the blade can then be tightened a little before trying the scraper. After that is is a matter of adjusting the wing-nut to get the required action. You should get shavings of wood or curls and not a lot of sawdust. I have found is useful to finish a surface after planing particularly where there are changes in the grain, knots or other features in the wood that make planing difficult  even with the sharpest blade and finest adjustment. Sometimes it also helps so go across the grain but again it comes down to reading the grain in the particular wood and how the surface is reacting to the scraper. Also I have found it useful in green wood working when working with wood with lots of growth "character",  e.g wood ripped from a smaller trunk where there has been spiral or twisted growth or lots of side branches. Some work can be done when still green but I have had more success after the wood has dried indoors for a couple of months or more, planed and is ready for finishing.

Card Scraper.

The preparation of the cutting edge is in many ways similar to the procedure described above for the cabinet scraper. The main difference is that the edges of the scraper are firstly flat, i.e. there is no cutting edge just a perfect box section with edges at 90 degrees. A wooden holder (this time 2 inches thick, 3 inches deep and 6 inches long) can also aid in the procedure but this time the blade is held perfectly vertical just above the wooden surface. The blade is inserted along the centre line, i.e 1 inch from the edges). The square edge is filed etc to produce a smooth surface with 1200 grit finish, the card removed and burrs on the flat surface removed so that a perfectly square edge is produced to a smoothness of 1200 grit or better. At this stage it is a good idea to remove the sharp corners of the card to prevent scratches on the wood when in use. 

The next job is to produce the working burr on both long edges of the card. The method here is a little different according to who you follow. Paul Sellers does it by oiling the burnisher, mounting the card in the block and pulling the burnisher over the surface at the same angle it was filed, i.e 90 degrees to the card. Then the burr is removed again on a flat diamond stone (or similar). Then the card is again mounted in the wooden former so edge protrudes by 1/8 inch. Starting with the burnisher level, itis passed long the face and then gradually the burnisher is lowered until is finally hits the wooden edge of the block. Again light pressure is needed with something like 8 to 10 passes at each stage (but I expect experience will aid in this). This geometry (1 inch width and 1/8 inch protrusion gives an angle of 7 degrees but anywhere between 5 and 10 degrees is said to be good.

The scraper is used almost vertically with fingers around the side and thumbs pressing the card in the centre to produce a curved edge. If the holding angle to the wood is too perpendicular, the scraper will slide over the surface without cutting. If the angle is too low, the cut will be too aggressive so it is a matter of feeling the action and making sure that you get "curls" of wood rather than a lot of sawdust.

Card scraper holder made of beech. The block is 2 inches wide with the card clamped in the centre. To produce the burr, the burnisher (in photo on the right) is drawn across the top of the card with it protruding 1/8 inch with the burnisher touching the edge of the block.

This shows the peelings from using the card scrapers. These are curls of wood and not saw dust.

The scrapers worked well in shaping the lampstands (see other post) after they had dried. A spokeshave was used to shape the stands but left some marks particularly near knots that needed smoothing to get a good finish. Using a card reduced the amount of sanding needed. It was also easy to see how the grain changed around knots etc and reverse the direction that the card was moved (as both edges of the card had a working burr).

Here are some examples of the use of a scraper when used to prepare the final surface of a hazel lampstand. The "peeling" edge of the scraper seemed to last a long time on hazel and ash.

Hazel lampstand after spokeshave and before using scraper.

Surface of hazel after using card scraper.