torstai 18. maaliskuuta 2010

Cutting the lute rose


Pictures to be added later.

The lute rose, or rosette, is a feature that can be seen on, I'd say, all lutes ever built. You can judge the skill and dedication of the maker by inspecting the rose. Cheap student lutes often come with a simplified design for a rose, due to the gain in production efficiency achieved by ignoring the rose. Still, it is rare to see a student lute with just a black hole where the rose should be. Of course, some makers do cut a decent rose even on their student grade instruments.

In this post, I present one method of cutting the lute rose, and making and sharpening the tools necessary for the process.

Let's assume a standard rose, pierced directly on the soundboard of a lute. Other renaissance and baroque instruments sometimes have elaborate layered roses that are cut from different woods and parchment, but this is rarely seen on lutes. However, the same methods still apply to the cutting of wood. The deep, white, multilayered parchment roses of baroque guitars are a whole other thing, requiring a different set of specific cutters for each shape that the maker wishes to cut - and that's all I know about them, so I don't want to advice on that.

The wood of the top (or if making a layered rose, the layers of wood) should be close, but not below 1 mm in thickness - that is, thinner than the soundboard around it. This can be achieved by taping a round piece of card under the exact spot where the rose will be, and then planing just the rose area, and checking for the correct thickness frantically.

The design for the rose should then be printed out on regular paper, or drawn on paper, and then glued with watered down animal hide glue (or regular paper glue, but it is easier to remove the paper with heat and water if you use hide glue). To glue the pattern on exactly the right spot, you'll need a tiny hole in the exact center of the paper. If the design has a hole in the center, you can make a tiny hole through the soundboard too, to make the alignment easier. Mark the center point on the soundboard with pencil or a tiny hole, and glue the design down, aligning it so that it is symmetrical to the central seam of the soundboard. Then glue a circular piece of thick artist grade water colour paper on the underside of the lute, some 7 mm larger all around the design, centered exactly underneath the rose. Here, the tiny hole comes in handy, as you can be fairly sure that it is accurate. Let dry completely, with perhaps a weight on to keep the papers from curling and lifting up.

Now it would be time to make the tools. The following are quite sufficient for lute rosettes. On the left is a regular hobby knife with a regular blade attached. The other blades are chisel-type blades that are made of used or broken blades. The group of three are slightly curved and the two on the right have a straight edge. These chisel blades are used for removing the areas that will be missing in the finished rose, and the regular blade is used for any finishing touches as well as for carving the v-grooves on the design.

[Picture of tools]

A metal file or some sort of electronic sander, of any kind really,  greatly speeds the process of shaping the chisels, but it can of course be done by hand with sandpaper. It helps if you can securely hold the blade when you shape and sharpen it, and the obvious method is to use the hobby knife for holding the blade. I recommend reading ahead to figure out the way they are used, which then should guide you to make correctly shaped blades: the point that cuts need to be under the force you apply to the chisel. So, that's the first step. Then the blades need to be tapered to a really fine point. Make a taper from about 6mm from the edge towards the edge. I recommend 120-200 grit sandpaper for this. The blade should taper from o.5 mm, or whatever the blade happens to be originally, to 0.1 mm. And then, the 0.1 mm edge needs to be sharpened just like a chisel. The design is a bit of a compromise between a thin blade, a blade that can actually withstand pushing through wood, and a blade that is sharp enough not to just push the wood. 

[pics of blades]

Instructions on sharpening: A blade is not sharp enough for serious woodwork unless you can shave the hair on your arm with it. That is a test I use every time I sharpen a tool, be it a chisel, knife or a plane. I will present the easiest way to achieve such an edge. You need 400 and 1000 grit sandpapers for this. First, you create the edge with 400 grit paper by rubbing the chisel on the paper, holding the chisel blade in an about 45 degree angle, until you see the blade edge making a burr on the other side. This burr then needs to be removed. You now move to 1000 grit sandpaper to remove it, by holding the flat side of the chisel absolutely flat on the paper and rubbing. Then you turn again to the 45 degree side, and rub that side again holding the blade in the correct angle all the time, on the 1000 grit paper.  Once again, remove the burr as above, and it should be ready. To test this, hold the blade against a hair to see if the hair is cut easily by the blade. If not, you must attempt the 1000 grit paper again. The chisel blade must also be polished with 1000grit on both sides for at least the length that goes into the wood, to make the pushing and pulling of the blade easier. Here is a picture that hopefully makes this clearer. Included is the instructions for sharpening the regular knife blade.

[kaavakuva]

The difficulties of working with spruce, the usual material for lute soundboards, is that is has an alternating hardness. This is caused by the way trees grow in temperate zones, fast during summer and slow during winter. The winter grain is the hard, darker lines you see running from the neck end towards the bridge end of the lute. Now, when you cut with the tiny chisels, the harder wood will resist the blade more than the soft wood. Sometimes you will be cutting with the blade in exactly the same direction as the grain of the wood, and then the harder lines may push your blade where you perhaps don't want it.

The difficulties of spruce don't end here. When you cut perpendicular to the grain, a dull blade will cut the darker wood relatively well, but tear little pieces of the soft wood. In such detailed work, those will look ugly. Also if the blade is dull, the hard wood can bend the thin edge of the blade to a shape that you cannot work with, and the blade then needs to be shaped and sharpened again. What do we learn from this? Sharpen your tools well and often and you will have more fun.

Cutting the rose

If this is your first time, practice on a piece of wood that is similar to the one of your soundboard, such as an off-cut of it, until you feel confident enough to move on to the actual rose. In case of emergency, such as if you have failed in your attempt on the rose on the soundboard, it is possible to cut the rose off and glue in a new one made of the same material. It can even be made so that people will never notice it's not the same piece of wood! But to save you that hassle, I recommend practicing on something else first.

A word about the different kinds of chisel blades you might want to make. These vary depending on what kind of cuts your pattern needs. If there are only straight lines, you will only need straight edged chisels, but cutting a floral design is made faster with curved blades. The width of the blades of course determines how many times you have to push through the wood for a given length of line in the design. It is a good idea to make blades that are exactly the correct width for your design.

So, you should have a pattern glued on and a piece of thick paper on the other side. You will also need a surface you can work on that will not break your blades. A hobby cutting mat is perfect. Begin with the chisel blade, and start from the middle of the design. The 45 degree side of the blade should always point towards the areas that you want to remove.

The blade must go absolutely vertically through the three layers, paper, wood and paper. To achieve this, you may need to slightly change the angle of your tool - here, experience will teach you better than I. So, how to determine the angle: push vertically, and don't pull the blade out immediately. Instead relax your grip of the knife and see if the knife wants to correct its position to match the angle in which the blade is lodged in the wood. Change your angle of cutting until you get the blade to go through completely vertically. The correct angle also depends on whether you are cutting with the grain or against the grain.

You will easily learn to hear how far you have pushed the blade. It makes a distinct sound when it cuts the water colour paper. The idea is to use as few cuts as possible (less work but also better results), so change blades according to what part of the design you are cutting. 

Resist the temptation to pop out the pieces you have already cut, because they support the design when you make more cuts. The chisel blade is after all a wedge that will drive the wood on its sides away.

When done with the cutting, the paper can be removed by either sanding the rose area with 400 grit sand paper or, if you used hide glue, you can use a slightly moist towel and an iron (you know, the kind that is used for removing wrinkles from clothing) , but be careful because too much moisture will make the soundboard bend into unusable shapes. The paper on the backside is left on to help keep the rose together.

And then you remove the little pieces that you have cut.

Cutting the v-grooves and finishing

Sharpen your hobby knife.

All (in my experience) single layer rose patterns have an over-under pattern to them. That is, if you follow one element throughout the design, it will go first under, then over, then under then other elements and so on, as if it were a string in a piece of cloth. This is of course an illusion, since it is just a piece of wood. But to achieve the illusion, we cut off wood so that the elements appear to go over and under each other. You start somewhere, take a crossroad and choose which element is on top. Then, cut straight cuts on both sides of the top element to about ½ depth of the wood. Now cut out the under element on both sides so that the blade is in a low angle. See picture. Mind the grain of the wood, and choose the way you approach the cut (from left or from right?).

[side view of a crossroad]

Remember, over-under-over-under. Where an element "terminates" it usually goes under, and then you may have a situation where you have two unders one after the other, but rest assured, there probably is no way to make all designs completely over-under. Do the whole rose like this.

The v-grooves of this design are cut with the knife blade. Here it becomes important to understand what wood grain is and means. Think of wood as a bundle of dry spaghetti that you hold in your hand. If you push a kitchen knife from the end towards your fist, it is easy, but if you try to change direction, the spaghettis will resist. When you push across the spaghettis, they bend and separate. Wood is similar, and the dark-soft variations of spruce show very clearly which direction the grain runs in. So, the reason why we need to care about the grain is because it affects what directions you can make cuts in. Also, when a tool is not sharp enough, it pushes wood grain aside instead of cutting it, creating rugged surfaces. Here is a picture where I try to illustrate the directions for cutting, as words seem to fail me.

[pic]

You can use a ruler to guide your blade in a straight line and a 45 degree angle to create the v-grooves. I usually do it freehand, and the ruler can't of course be used when cutting the curved elements of a design. If the design is floral, the leaves and flowers are also cut with the knife. Aim for clean cuts. Roses look best with sharp edges and clear surfaces, so sand paper shouldn't be used. Also refrain from trying to round the v-grooves or any edges with the knife. The beauty of the rose is in how it reflects light, and crisp edges are the most effective.

[picture that nicely illustrates this...]


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