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Friday, June 19, 2015

Sharpening: Chisels and Gouges IV

V Gouges

There are two main ways I have seen V gouges sharpened, and both of them begin the same. First, where each of the intersecting faces is treated as a skew chisel, and the point where they meet is naturally kept sharp by nature of careful holding of a constant angle while sharpening. Second, after the two edges are sharp, the point between them rounded very slightly as though an extremely small round gouge so there is less of an intense line left by the meeting of the two faces. I personally do the first, leaving the point as sharp as possible, but that is because I use it solely for defining crisp lines, whereas I have a small gouge for the latter.

In a previous post, I mentioned how I use files on my harder chisels to manipulate the burr. Here, I will demonstrate that method. Unlike with the round gouges, I cannot use the corner of the stone on a V gouge because the angle is less than 90 degrees.

First, however, I begin sharpening as I did with a straight/skew chisel. Here, it is more important to keep an even lateral pressure on the cutting edge so each pair of points is not swept out from the centre. 

One trick to getting these sharp (for me) is to sharpen both bevels evenly. That is, not creating an excessive burr on one edge while the other is just barely beginning to form. For one, it will make removing the burr easier, and for another it is more effective at carving when the two edges are in plane with one another. 

Due to the hardness of the chisel, these needle files do not do much to the edge, but are fantastic at rolling the burr back to the outside of the bevel. I use a triangular file for the V gouge, and a double half-round for the round gouges. Here, the angle of the file is just slightly smaller than the angle of the V, so I can reach all the way into the corner. A few light pulls away from the edge is all it takes, and feeling for the burr on the inside with a finger tells you if it is enough. Once it is back to the outside, take a single perpendicular stroke across the stone with the bevel flat against it. This shears off the burr. I tend to go in a motion that has the corner of the V on the leading edge so any flashing that may be left over is on the outside edges which I hardly ever use.

Once you are through all the stones, it's once again onto the strop. Here, pull instead of push, trying not to pull up on the handle through the stroke. Medium pressure and about 25~30 repetitions, periodically checking for a burr, and that's it.

As with the round gouges, for the inner surface, I use the corner. Because the inside of the leather is spongy, it conforms to the tight angle. 

After stropping, check for sharpness, returning as necessary to the highest grit stone that can reasonably handle honing the edge to its sharp state.

Tuesday, June 16, 2015

Sharpening: Chisels and Gouges III

Gouges (Outer Bevel)

Sharpening gouges has been one of the more daunting tasks for me over the years, especially without special jigs that allow for a consistent bevel across the entirety of the curve, and without rounding the sharp corners at either end.

Whether for bowl, spindle, fishtail, spoon, or any other sort of outer bevel gouge, this will all be the same. However for inner bevel gouges, I have no experience, and they seem (to me) to be much more difficult to sharpen by hand and without speciality equipment.

With a bit of practise and a few tricks, I have found a method that works well for me, although there are a few things that will make this easier.

These chisels, as mentioned previously, are exceptionally hard. Softer chisels will still benefit from this method, although require a little more care in dealing with the burr. That being said, the hardness makes this both easy and difficult for different reasons. For the worse, they tend to chip very easily, the gouges more than straight and skew chisels. Because of this, the sharpening may take a far longer amount of time as it is necessary to take the entire edge back to the deepest chip. One of the benefits (other than having longer edge retention) is that I am able to use a needle file to push the burr back to the outside of the edge without it cutting into the edge itself, and thus defeating my efforts.

Unlike straight and skew chisels, I do not move the edge perpendicular to the stone. Instead, I slide it in line with the edge.

To begin, I place the length of the chisel flat against the stone. Since a gouge does not have a large surface to contact at once (only a single tangential line perpendicular to the edge), it is more difficult to perfectly match the angle.

On one corner of the gouge, lift up until the edge just touches the stone. It is important to have a little of the gouge body on the stone too, or else you will develop rounded corners (like I have gradually done to this one). Sharp corners are not strictly necessary, but they make it easier to develop crisp lines with the gouge.

Holding this angle constant, roll to the same position on the other corner of the chisel as you sharpen it across the length of the stone. To maximize the effectiveness of each stroke, I roll the gouge opposite the direction of my hands (if it were a wheel that rolls freely as you move your hands to the other end of the stone, turn the chisel the other direction).

After reaching the end of the stone each time and return to the other side, I check the angle of the edge again to make sure I am not creating a steeper bevel or needlessly polishing the back side without touching the edge.

Throughout the process, a burr will begin to form on the inside of the gouge, and obviously a flat surface cannot remove it. I will demonstrate using a needle file when sharpening a V gouge in a later post. For wider gouges, however, the corner of the stone can be used (assuming it is not a diamond plate which does not have consistent grit on the sides). Ideally, a slipstone that is the same or slightly smaller radius of the gouge should be used, but I do not have any, so this is what I do.

Holding one corner of the gouge barely over the face of the stone as shown above. With a very slight pressure (little more than the weight of the chisel), drag it to the other end while rotating the gouge sweep so the opposite corner then contacts the side of the stone. At this point, try to have the chisel as parallel to the stone corner as possible to mitigate the creation of a microbevel.

One or two passes at each grit should be all that is necessary to remove the burr. By sharpening parallel to the edge, a smaller burr is formed than how I perpendicularly sharpened straight chisels previously.

After moving from the lowest to highest grit stones, I turn to the strop. Instead of using the same hand motion, I pull the gouge backwards over the surface, rolling from corner to corner.

As with the stone, I remove the burr the same way, using the edge of the strop to reach the inner radius in its entirety.

That's all. The gouge should be nice and sharp, and if not, return to the highest grit reasonable by the extent of dullness.

Sunday, June 14, 2015

Sharpening: Chisels and Gouges II

Chisels Part II

With long blade chisels out of the way, I thought I'd also take a look at small chisels (palm chisels, micro chisels, etc.) that are more commonly used for detail carving. Because of the length, they will not fit in a jig, and they really do not need one. That is to say, jigs in general are not necessary, but here they are highly impractical.

First step, as always is preparing your stones, whatever sort they may be. My water stones do not need to be soaked, so running them under the tap for a few seconds is sufficient.

The chisels that I will be sharpening in the next three posts are significantly harder (65 Rc) than normal chisels, which is both an advantage and a drawback. While they hold an edge far longer, they also chip very easily. As a result, I need to make use of the very coarse stone to bring the edge back into a line. From there, it is the same grit progression as I would use on an already shaped edge.

For these smaller chisels, I set a lower angle on the bevel, in this case around 20 degrees. I would prefer around 25, but from the manufacturer they came lower, and I have taken it up only to 20. This in part is a cause of the fragility and tendency to chip, so for such hardness I will be taking it up another 5 degrees over time. 

Once you have a feel for the angle on your chisel, try and keep your arms/hands as locked in place as possible to minimize any rolling of the flat edge. 

When I sharpen, I take the chisel to stone at a slight skew angle, applying downward force on the forward stroke (as though 'carving' the stone) and relieve force on the pull stroke. 

Assuming you have already surfaced the back when the chisels were new (shown in Chisels Part I), the only time you need to touch the back to the stone is when you begin to feel a burr rolling over thee edge. On the lower grit stones, I often do not do this at all, and on the highest only one or two quick passes to remove it. Holding the back flat against the stone, again at a slight skew angle. I prefer to push rather than pull, as this mitigates the chance of rolling the burr back to the other side, but it is just personal preference.

After the final stone I turn to the leather strop. Treating it just as the final stone, I polish first polish the bevel, then the back with one quick pass flat against the surface.

For a final stage, I take the edge and (left to right in the above picture) slide it across a corner on the piece of wood holding my strop. A very slight pressure is all it takes to remove that remaining minuscule burr.

Although this is something that should be done throughout the process, I periodically check to ensure that the bevel is square to the blade of the chisel. For a straight chisel, that is. For a skew, this obviously doesn't matter. It should be noted that I treat skew chisels exactly the same way as straight, only that the edge is at an angle to the length of the chisel. 

With these low temper chisels it takes a little longer, as the rough stones need more work to repair chips and the higher stones do not cut as quickly, so it takes between 5 and 10 minutes depending on the extent of the damage. If I am simply honing them back to a sharp edge, it will take a fraction of that.