Friday, April 10, 2015

Progress on the Second Bass Horn for the Sound Transformer

The first two sides are trapezoids because they do not need curved sides.  After the opposing trapezoids are fitted and fastened, the second pair of sides needs to have the edges machined into the curve to match the bent trapezoids.  A compass is handy to scribe the edge of the panel after it has been positioned parallel with the planes of the plywood flanges.  In the following photo, some material has already been machined from the throat end of the work piece.

Second Bass Horn - Fitting A Side Panel - A
Second Bass Horn - Fitting A Side Panel - A
Second Bass Horn - Fitting A Side Panel - B
Second Bass Horn - Fitting A Side Panel - B

Second Bass Horn - Fitting A Side Panel - C
Second Bass Horn - Fitting A Side Panel - C
The tools needed for this are a scroll saw and a small block plane.

Scroll Saw and Block Plane for Fitting Bass Horn Side Panel
Scroll Saw and Block Plane for Fitting Bass Horn Side Panel
You can use the first one as a template to mark the second for cutting.  If you make it a little bigger than the first one, you can shave it down fairly quickly for a custom fit.  After you mark for the second side, you can fasten the first one into the horn.

Fastening the Third Side into the Bass Horn
Fastening the Third Side into the Bass Horn
Here is the Bass Horn with all four sides attached.


Second Bass Horn With All Four Sides Attached
Second Bass Horn With All Four Sides Attached

Second Bass Horn With All Four Sides Attached
Second Bass Horn With All Four Sides Attached
To stiffen the panel edge, the cleats are necessary especially to hold the corners in place


Second Bass Horn With All Four Sides Attached And Cleats
Second Bass Horn With All Four Sides Attached And Cleats
With the panel edges secured, you can now apply adhesive to the panel corner joints.  I removed the white finish along the landing for the glue joint with coarse emery cloth.  Then I applied a bead of vinyl-based adhesive to all four joints.


Second Bass Horn - Adhesive Applied to Corner
Second Bass Horn - Adhesive Applied to Corner

Second Bass Horn - Adhesive Applied to Corner
Second Bass Horn - Adhesive Applied to Corner
I used a vinyl-based adhesive instead of PL-200 to give the joints a little flexibility for when the wood shrinks or swells with moisture content.  On the first horn, I found hairline cracks adjacent to some glue joints.  Apparently, this happened because the PL-200 is quite inflexible after it sets.  To fix the cracked glue joints, I applied a second bead of the vinyl-based glue over it.  So far, cracks have not reappeared in the first Bass Horn.

Tomorrow, I will cleat the side edges at the smaller end of the Second Bass Horn.

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