Chris Pye Slipstones
Monday 11 August 2008
Russell Parry tests the 12mm Norton signature series woodcarvers slipstones
Do you use slipstones when sharpening your gouges, and if so are you happy with the ones you have? I would guess that most readers will answer "no" to both of these questions, so let's look a little closer at why the highly regarded British carver and teacher Chris Pye, has collaborated with Norton Pike in the USA to make these stones available.
First let's be clear what we are talking about. A slipstone is a small, shaped stone, designed to be used on the inside of the gouge. For most gouges the stone is an arc of the same radius, or slightly smaller than the gouge. A slipstone that is a little too small in diameter for the gouge can be manoeuvred around, whereas one that is too large can never reach the bottom of the curve. Slipstones for V-tools are different. They come to a sharp edge which fits into the V of the tool.
Who needs inside bevels?Most carvers these days apply a bevel to the outside only of the edge. This is how (nearly all) tools are supplied, and when I began carving, I distinctly remember being told by more than one experienced carver that tampering with the perfect inner surface was a "no-no"; the sign of an amateur.
So much for dogma! Small inside bevels were widely used at one time, and many professionals still sharpen this way, Chris Pye for one. The main advantage is felt when the gouge is used upside down; the inside bevel gives a surface on which the tool can be 'rocked' slightly in the same way the main bevel does when the tool is used the usual way up. It is mainly by pivoting on the bevel that we make the gouge surface again from the bottom of its cut. In theory, the inside bevel should help us cut a smoother upward path when used inverted. Since mainly shallow gouges are used both ways up, it is these which might benefit most from the inner bevel.
V-tools, old gouges and pattern makersRegular gouges aside, there are other instances in which a slipstone is near essential. I have found that with V-tools, a slipstone run along the inside angle improves things enormously. A pity this test did not include the V-tool slips which are also available.
Pitting of the inner surface on old gouges can render them useless with a single bevel. By adding a small inner bevel, the pitted surface is avoided.
Finally, good quality patternmakers' gouges (main bevel inside) are often cheaply available second-hand. If you wish to use them - there can be reasons other than economy - you will need a range of good slipstones, fine and coarse.
Inside knowledgeA little while ago, I was delighted to receive an Ashley Iles No.2 1/2, 19mm (3/4in) as a present. I was intrigued to find this gouge had a small inside bevel (and almost as small an outside bevel). Since it worked extremely well, I left well alone, and two years later it still has the inside bevel (and a much longer outside one). It has become a real 'workhorse' and performs extremely well upside down. But of course, I had never used it without the inner bevel, so it was time for a little experiment with my new stones.
Let's get startedThe sample I received was the 12mm Woodcarver's set, consisting of two stones 12mm (1/2in) thick and a leaflet. There was also a DVD by Chris Pye that describes the use of these slip stones, but is not in the set itself.
The stones are identical in shape and size: one coarse carborundum, the other a beautiful fine, translucent Arkansas. Each of the four edges is a different radius, from just off-flat to about No.7. These should cover all gouges which we should ever want to use upside down.
Spare the gouge, spoil the reviewI decided to 'sacrifice' a greatly loved Ashley Iles No.3, 9mm (11/32in) to the spirit of experimentation. It was one of my first dozen gouges and is much used both ways up.
The DVD suggests the gouge should be held firmly in one hand and the slipstone rubbed along the canal at an angle of 5-10 degrees with the other hand. I briefly tried other methods, but settled for the original approach. I used a generous squirt of 3-in-1 oil as a lubricant on both stones.
The carborundum cut very quickly and within five minutes I had my bevel, of about the angle suggested and 1-2mm (3/64-5/64in) in length. The stone was a loose fit in this gouge, which meant working different areas of the blade as I went along and looking to see that the bevel was even across the width of the blade, a little lighter towards the corners. Sounds trickier than it actually was.
With the Arkansas, the fine honing took a little longer, perhaps ten minutes. After that I 'stropped' outside and (very gently) in, with my usual soft mop and green soap, running on a grinder.
VerdictUsing the re-shaped gouge canal-up on a scrap of lime, I could honestly detect no difference; the inside bevel had no ill effect on the feel of the tool. Upside down was more interesting. Taking a scoop out of the edge, it seemed rather smoother pulling up out of the scoop than it had without the inner bevel. It is, of course, a very personal thing, but I think I will be experimenting a little further with this form of sharpening, at least for some of my shallower gouges.
The slipstones were certainly efficient, and with very little else on the market that will work in the same way, I think it is likely I will use the Chris Pye Signature Series. At around £50 per set, I will probably stick with the 12mm stones, only buying one of the other widths if I really feel I need it. That said, I believe penny-pinching on sharpening is a false economy; better to spend money on good sharpening aids than buy more blunt gouges.