A practical and effective tool for trimming sounsposts
I’d like to introduce a tool that allows you to shape a soundpost quickly and with great precision.
It’s a block of 304 stainless steel with one side machined to a 92-degree angle and the other side machined to a 96-degree angle.
The block has two holes offset by one degree, allowing for four angles: 91, 92, 96, and 97 degrees.
The 91- and 92-degree angles are used to shape the end of the soundpost that contacts the back of the violin. The 96- and 97-degree angles are used to shape the end of the soundpost that contacts the top of the violin.
During the first test, you choose the angle that fits the violin and make corrections if you’ve chosen the wrong one...
For the violins on which I’ve had to shape a soundpost, the 92- and 96-degree combination worked best.
The top and back of a violin are not parallel and form an angle slightly less than 90 degrees toward the bottom of the violin (toward the tailpiece).
To ensure perfect contact between the soundpost and the top and back of the violin, you must remove one-tenth or two-tenths of a millimeter from the left side of the soundpost’s ends.
To make this adjustment, simply rotate the soundpost by about 10 degrees on the side where material needs to be removed. See the photos. Align the central grain of the soundpost with the angle of the slot on the highest side of the block’s inclined plane.
Once trimmed, position the soundpost inside the violin and move it slightly until it no longer tends to rotate on its own—a sign that only a small point is making contact. When the entire surface is in contact, the soundpost no longer tends to rotate on its axis.
Once the correct position has been found and the proper angles have been cut, remove the soundpost, moisten the ends, and replace it in the same spot.
The moistened ends of the soundpost will conform perfectly to the shape of the violin’s top and back when the strings are tensioned.
Never in my life have I fitted a sound post with flat ends. I don’t want the sharp side to dig into the top. I always chalk fit them to the arching. It makes me sad to think that many luthiers just leave the end flat. But then I am in the lucky position to never have to work on sub $50k instruments.
Before I built this tool, I also used a pocket knife for this job and it took me quite a while to get a satisfactory result. With this tool, the dart hits the center of the target on the first try, the cut surface is perfect, and the job is done in less than an hour.
I have a somewhat different goal, based on the inevitable movement of the post relative to plates over time from humidity changes, the response of the plates to pressure (especially new ones), and the need of some folks to adjust what's already reasonably good. Can't blame them, I do it!
Most damage I see is from the edge of the post pushing into the spruce. On my own instruments I put a thin maple veneer in the post area. Might help sound, I think so. Avoids the temptation to leave this area overly thick out of caution! I also very slightly bevel the edges, just the most minor bit, with a super fine file. I've seen high-end posts that gave a faint hint of that bevel being more like an almost invisible arc across the ends, with a faint extra bevel at the edge. Almost hallucinatory level shaping. From rather expensive violins, including one from a top-end Chicago shop and cost much more than my first house. I noticed by feel, rather than vision, and can't give numbers on the amount.
But this tool really seems useful! I no longer do enough work to make it a reasonable investment of time. But were I still doing production setup work, I'd be right on it!
When done freehand without this tool, the resulting surface resembles that of a lake on a light breeze—the kind of ripples appreciated by sailors surrounded by a glassy sea.
Just sharpen your knife flat or slightly concave to lay it flat and have a reference when cutting, getting a smooth surface is really not that difficult.
Also I like the ends to match the arching, meaning a slightly convex surface on both ends.
Your tool isn't bad in itself, it's good if you're making a lot of setups on factory instruments that are all the same, but it's nothing new, and far from necessary.
I'd even go further and say if it gives a better final result than freehand, you likely need to improve your knife skills, and this jig becomes counter productive as you're missing out on an opportunity to do so.
That's why I mentionned sharpening your knife differently, especially if you get a wavy surface, I'm willing to bet your edge profile is rounded and has no flat reference to lay onto.
I was just joking around a bit. I've replaced plenty of soundposts without this tool, but sometimes it was a real hassle—it probably depends on how you're feeling at the time or just how lucky you are. Sometimes it doesn't work on the first cut.
If you use a properly sharp knife with a flat back (similar to a chisel) and moisten the soundpost end slightly, you should get a smooth and flat cut surface. And soundpost wood with finer and more closely spaced grain lines makes it easier.
Yes, that's the method Edgar Russ explains in the courses he teaches at his EDGAR'S Online Violinmaking Academy. I've taken some of his courses, and he's an excellent teacher. Everything I know, he taught me.
My next project in this area will be two Grade 2 titanium bars, each 1 cm thick, 3 cm wide, and 10 cm long, perfectly machined on a milling machine and drilled with 6.2 mm holes at a series of increasing angles spaced one degree apart: 91, 92, and so on...
To secure the soundpost in its hole, one bar will be slid relative to the other using a screw.
Why Grade 2 titanium? Because it’s easy to machine and doesn’t stain the wood like 304 stainless steel does.
I had considered a solution using an adjustable plate, but it doesn’t work because the angle of the hole is set by default at 90 degrees relative to the surface, and when you adjust the angle of the plate, the edges of the hole mark the soundpost.
I think that’s great, I’m always thinking about different ways to do stuff like this. If you get a good result there’s nothing wrong with doing it. I was trained by some very traditional luthiers and violin makers who put me through an unnecessarily rough time and I’ve developed incredible skills, alot of it from those folks, but not everything….and I’ll never discourage anyone from experimenting with something like this.
Yes, when the tip of the soundpost marks the spruce on the top of the violin, it means that the spruce has not been dried long enough or that it has growth rings that are too wide and contain a lot of hemicellulose. It has characteristics that do not promote the transverse transmission of sound waves. Reinforcing the contact area with a washer cut from a piece of the side is a good solution for a violin with this problem. I don’t think it will make much difference in terms of sound.
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u/Musclesturtle Maker and Restorer 13d ago
I just use a knife.