Make a Scraper Shave
Tuesday 24 August 2010
David Barron fits a wide and useful blade to his narrow-bodied scraper shave
In days gone by the scraper shave was a common sight in the toolbox. It is such a simple tool to make from readily available parts that most of the second-hand versions I have seen are user made. It is effectively a cabinet scraper held in a similar fashion to a spokeshave and used to remove tearout and tool marks prior to final sanding.
The narrow sole provides control while also allowing it to be used on concave, convex as well as flat surfaces. They are very useful for chair making and I know longbow makers use them too.
As with many other old hand tools there has been a mini resurgence amongst finer tool companies, Veritas, Woodjoy and Kunst Griff among those now offering them.
They have tended to use narrow blades in keeping with the typical width of shaving taken which is logical. However, a much wider blade offers a much more useable blade area and takes very little extra time to sharpen. Also the wider blade can be set for different depths of cut along the blade, which can be utilised without making any blade adjustment.
It is probably for these practical reasons that all the old scraper shaves I have seen have wider blades fitted. With this in mind I decided to use a blade 70mm wide, with a height of 50mm to allow for plenty of re-sharpening.
I opted for Japanese scraper steel, hardened to Rockwell 54 because this is much harder than the Rockwell 40 normally used for cabinet scrapers. This was purchased in 500mm lengths from Dick Fine Tools in Germany and even with the very poor exchange rate it worked out to cost only about six pounds, or 60p per blade.
The shave body needed to be made from as durable and hard-wearing a wood as possible. The choice of Macassar ebony Diospyros celebica was ideal and it also helped to give some weight to a very light tool. Rosewood Dalbergia spp and boxwood Buxus sempervirens were common in days gone by, sometimes reinforced with brass inserts. Incidentally I am not a fan of adding brass soles to tools as although it reduces wear it also adds plenty of undesirable friction in use.
The Macassar ebony I used had numerous little cracks and splits due to poor storage at some time in its life. This made it ideal for cutting up into small lengths and I was able to work round the cracks with relatively little wastage. There was a certain amount of lighter coloured sapwood that was just as hard as the heartwood that is typical of exotic woods. I always try to include sound sapwood as it gives a nice contrast particularly in African blackwood Dalbergia melanoxylon and cocobolo Dalbergia retusa.
The blanks are cut and planed up to 300mm long x 20mm high with a width of 29mm reducing to 27mm after the bandsaw cut.
Just as with my planes, I drill the necessary holes before cutting the blank in half which ensures the two halves match up perfectly when they are screwed back together again.
The first hole is 10mm wide and 4mm deep to recess the machine screw head and this is cut with a Forstner bit. The next hole is done with a 4mm lip and spur bit, utilising the centre hole left by the tip of the Forstner to keep the hole centred. This 4mm hole is drilled deep into the blank but stops short of going through the other side.
After marking the blank with a carpenters triangle, to avoid head scratching later, the blank is cut lengthways in half on the bandsaw. The bandsaw marks are cleaned up with a high-angled plane or scraper. Sandpaper can be used although it would have to be glued to a flat surface and great care taken to avoid rounding over the edges of the two pieces.
Blade recess and escapement
The next stage is to cut a shallow recess to take the blade and this is done carefully on the router table. The blade is only 0.7mm thick and the recess needs to be slightly less than this in order for the front section to hold the blade firm. The router marks are cleaned up with a fine file taking care to keep things flat and avoid rounding the edges.
The front section needs an escapement to be created for the shavings to exit and again this is done on the router table utilising a crosscut sled to achieve the 70 degree angle. Care must be taken not to encroach on the base part as this would unduly widen the mouth. The escapement is cut 14mm narrower than the blade in order for the blade to be held tightly on each side.
The corners of the blade are ground off to avoid taking shavings on the sides that would clog up the shave. The resulting effective blade width is 56mm.
Tapping and drilling for screws
The 4mm hole in the rear section is tapped to take a 5mm machine screw, taking great care to keep the tap at 90 degrees to the stock in both directions. The 4mm holes in the front section are then drilled out to 5mm using an engineers-style drill bit that will self centre in the 4mm hole if you proceed slowly
I used 16mm stainless steel pan-head screws which give a nice firm hold and will not rust from any moisture in the wood. The corners of the square blank are rounded over on the router table, two passes being taken to avoid the small blank being grabbed by the cutter. This was followed by a curved-edge scraper and sandpaper to leave smooth curves.
The blank was then buffed on a buffing wheel using blue compound. This produced a nice hard sheen, working with the natural oils in this dense timber, and required no further finishing.
Shaping and honing blade
Producing clean cuts in the Japanese steel required some experimentation. It was too hard to cut on the bandsaw and a hacksaw would have been slow and left a ragged edge.
After scoring the blade with the edge of a triangular file, fix it in an engineers vice with the score line flush with the top of the jaws. My first attempt was to bend the steel and although this worked, eventually, it left rounded edges. I found it much more successful and faster to hit the blade hard with a heavy engineers hammer as close to the vice top as possible. This produced a clean break with little or no rounding to the edge. This work went quickly and I soon had 10 50mm-high blades ready for shaping with a disc sander.
Using a disc sander, shape the blades, rounding over the top corners and chamfering the bottom corners to prevent shaving traps at each side. Care is needed not to burn or blue the steel as this will draw the temper, making the blade softer
After rounding the edges on both sides to give a friendly feel, use the grinder, with a rest for accuracy, to form a 45-degree cutting edge. This is a quick job, the blade being only 0.7mm thick
Transfer the blade to an Eclipse honing guide which is just wide enough to accommodate the 70mm blade.
I used a Digibox to find the 45-degree angle which is then worked with 800-grit and 8000-grit water stones to a nice flat polish, leaving a small burr on the back side. The back of the blade is then worked through the stones to remove all the grinding marks as well as the small burr.
With polished edges on both the bevel and the back it is time to turn the working burr. This is done over the edge of the bench using a burnisher, working from the 45 degree bevel with firm pressure up to about 60 degrees. Do not turn the burr too far as it will not cut.
A fine burr should result. This can be detected with a fingernail. If it does not come first time or there are any gaps just go back and burnish the burr from 45 degrees again.
Setting for a cut
With the blade inserted in the body and the screws tightened the scraper shave can now be set for a cut.
It is better to insert the blade just short of the sole and tap the top and sides until the correct protrusion is achieved. If all has gone well the shave should take whispery shavings and leave an almost polished surface.
This is a very useful little tool that is much faster and more pleasant to use than sandpaper.