On the original bar, the ball end strings are hooked in the slots and then stretch up across the cap of the pointed bridge.
A “C” model autoharp like this Oscar Schmidt has a 5/8″ x 9-1/4″ x 15/16″ pocket routed into the top at the anchor end for an extruded aluminium anchor bar. The bar is a combination bridge and the slots that hold the ball ends of the 36 strings. It merely sits in the pocket and is wedged tightly in place by the lateral string tension.
I think that the anchor bar is quite a clever design. It’s light in weight and does its job very well… except when it doesn’t. Sometimes it can creep up and even jump free of the pocket. That’s frightening when it happens but it can usually be re-seated, blocked, and screwed to the frame inside the pocket.
On a conventional installation, the Daigle fine tuners are screwed to the tail end of the autoharp. A wood knee rest will cover the base plate and screw heads.
The Daigle Flat Line Fine Tuners aren’t designed as a direct replacement for the OS anchor bar. In a conventional installation, the back plate hangs over the end of the autoharp and is firmly screwed to the frame. A flat, brass wire capped bridge rests just in front of the aluminium bar.
The precision base is screwed to the head of the Dremmel router. It makes it easier to guide the cutter and can be finely adjusted to control the depth of cut
To install the Daigle tuners in the OS I must widen the pocket so that the new bridge will be in the same position as the old. I use my Dremel router attached to a Stewart-MacDonald precision router base to widen the pocket from 5/8″ to 7/8″. First, I cut to the depth of the plywood top and then into the soft wood below as deep as the base will allow. For the last 1/4″ or so of depth, I remove the material freehand without the base.
A filler block is screwed to the front of the fine tuner bar to hold the assembly to the rear of the slot. The ends are painted black to make the maple less visible beneath the chrome cover.
Now, when the bar is positioned all of the way to the rear of the pocket, the flat, brass wire capped bridge will be in the same line as the original bridge. To fill the empty area of the pocket in front of the new bar, I cut a 3/4″ wide piece of maple and attach it to the bar with flathead wood screws.
The new fine tuners with the the block fit snuggly in the pocket. This assembly should work much the same as the old OS bar but I have concerns that it could fail. Since I cannot conceal retaining screws in the pocket, I am going to shim it tight and glue it. This raises a new concern. What if it’s necessary to remove the fine tuners for replacement or repair? Gluing doesn’t seem easily reversible. I’m spectulating that if anything happens to the fine tuners, say fracture or extreme wear, they will require a new replacement. In that case, the old is no longer useful and can be cut from the frame. That would be a “worst case” but I’m confident of the quality of the Daigle tuners and don’t expect them to fail unless the instrument is abused or dropped.