What’s your trick for burning lines cleanly on a slope? I’ve done it many times, but it’s sometimes a hassle with a wire. I know a lot of folks use mica or similar with good success.
Ha, sometimes, for me at least, it's IMPOSSIBLE with a wire!
The method I use is actually pretty simple. Basically, cut a little "v" ledge on the slope and friction burn the bottom of the "v". Then cut away the ledge. Rinse and repeat as desired.
I didn't take these two photos to accompany the diagram below, but they should give the idea.
I made the diagram below a long time ago. I should improve it some day, but it would be better to write a short document and include consistent photos of the process and result.
For orientation, the sketches are a cross section view of one half of a little finger top from the turners point of view, as it is held in the lathe (the way I make them).
The gradual concave slope to be enhanced is on the upper side of the finger top, toward the handle to the left (the side shown in the lower photo above), with the contact point of the finger top to the right in the diagram. This method works on even very steep slopes.
The
top sketch: suppose we want to end up with two friction burned lines on the smooth concave slope, represented by the black dots.
The
thick brown lines are the intended final surface. The
thin horizontal lines represent the grain of the wood.
For A, B, and C, the
green lines represent wood to be cut away.
The simple process, as mentioned above: cut a series of ledges to catch the wire for burning.
When starting on the sloped surface where I want the lines, I might leave a millimeter or two of extra wood on purpose, but in reality I don't bother, usually just shape the sloped surface then cut away a bit more where needed.
The green line in
sketch A shows the wood surface before burning any lines.
As in
sketch B, I make a shallow cut down to where I want the first burned line, leaving a little v-shaped "ledge" to catch the wire. Hold the wire against the wood and make the first burn. (Best to burn fairly deep.)
Then repeat, as in
sketch C, cutting away the extra wood below the first burned line, careful to leave the surface flush with the first cut. Burn that line (again, fairly deep). Then continue the cut to the end.
I try to make very smooth cuts requiring only 600 grit or finer sanding so the burned depressions aren't sanded away. Burning a little extra deep helps here! If my cuts aren't quite smooth enough to suit me, before sanding I might twist the spindle gouge a bit and use the lower wing to
very lightly shear scrape the slope.
I think I've put as many as five burned lines down a 1" surface, but one or two is easier!
BTW, I had discussions a few years ago with some who seemed to scoff at this method and said they could do the same thing a lot easier with formica or something else, sharpened and pushed into the spinning wood. However, at least in my experiments, that doesn't always make clean, very fine lines. For many fine-grained woods, the method I use usually leaves smooth, clean black lines burnished and almost polished by the wire.
Notes about friction burning: Most people know these things but for those who haven't tried it, a some points.
- To avoid possible serious injury, NEVER hold the wire directly with the fingers. Especially, don't wrap it around fingers you want to keep uninjured. I use wires about 10" long or so. Twist the ends of the wire securely around two short pieces of wood. (I like to turn nice little handles, just because)
- Another, lesser, hazard: the wire can get VERY hot. However, a thin wire cools in a few seconds.
- The wire: I prefer to use solid steel wire. Long ago I found some very thin galvanized lockout-tagout steel wires commonly used in industry. These are perfect. Some people use copper wire, but copper thin enough to suit me is not as strong as steel. Some say they have used braided wire but that's also pretty thick - ok, of course, if you want thick burned accents. To easily hold a braided wire, it might be best to pass it through some holes in the sticks, maybe tie knots in the ends. I've never tried stranded wire but can't imagine it better than what I use.
- When burning, use a high very high lathe speed, the smaller the diameter, the higher the speed. Wrap the wire about 1/2 way around the diameter to put it in contact with as much wood as possible. (I wouldn't even think about wrapping it more than 1/2 way around.) I've never had a wire get caught in a groove but be prepared to quickly let go of the two sticks.
- After a wire is used a bit, it can easily get "polished" too smooth, making it hard to get enough friction for it to get hot. To fix that, I use a piece of coarse sandpaper, maybe 220 grit, to roughen up the surface.
- It sometimes takes a fair amount of force to get a good burn. Be aware that after some use, the wire can get weak, especially after using it repeatedly on small diameters. It will eventually break. Please don't fall into the spinning wood or chuck!
- Some wood species are difficult or impossible to friction burn. For example, some exotics, especially lignum vitae, are naturally so full of oils or waxy lubricant I can't get enough friction for the wire to get hot. In cases where I really wanted black lines in wood I couldn't friction burn, I've cut small v-grooves in the wood with, say, a skew or point tool, then after applying a grain sealer and/or finish, fill in the grooves with a dark grain filler, then use a piece of paper towel to remove the excess. I use an ancient can of dark walnut filler for this.
That's all I can think of at the moment...
JKJ
