VIBROPHONE BUILD EXPERIENCES
CHRIS BURNE. UK
1. RESONATOR TUBES.
I could not find external cemented caps of the type available in Aus. Aluminium tubing seemed more attractive and at a cost of £33 only, turned out cheaper than UK plastic end caps & tube. I made discs from 3mm sheet and fitted them inside the cut tubes with Silicone. I cut the tubes to your dimensions plus 3mm for the caps and two washers. These were placed under the caps whilst setting. The tubes were positioned vertically on the floor and the caps tapped down with a stick. After setting, I ran an extra sealing fillet of silicone under the caps. The tubes were then tuned to your instructions, but trimming from the tops. In the event of errors, the discs could be removed easily and re-set on one washer.
2. THE BARS.
The Video was an essential guide. After my first couple of bars I used an Angle Grinder to speed up metal removal for rough tuning. I purchased a Korg DT-4 Chromatic tuner and a Chop saw for the work. I drilled the bars using the small vice shown below. I positioned the bars using the small set-square against the line across the bars. To avoid drill slipping, I found it essential to centre-punch both sides of the bars and start drill at 3mm on the more acute angled holes. To avoid string chaffing etc. I also cleaned up the hole entries manually, with a large drill bit.
3. THE FRAME.
I used Obeche for the frame. It is cheap, light weight, stable and easy to machine.
Note the bench drill, the vice (great for drilling bars), vernier calliper, centre scribe (for accurately drilling the 10mm holes in two stages, in the resonator tubes) and a hardwood jig that I made to press (in a bench vice) the butterfly discs around a piece of the stainless steel shaft rod locating in a drilled 'U' shaped groove in the wood.
5. THE DAMPER BAR.
I adopted your design in supplement 2 but would have been better off using drilled rod with nuts on the bottom instead of the eyebolt. That would have allowed me to change the spring if required. As I found my spring to be too light to dampen the lower notes, I was able to insert a wooden spacer under the spring. I drilled a spring seating recess in the top of this spacer with a slot to pass the eyebolt. I used a 5mm thick 'Leatherette' backed synthetic felt fabric for both layers on the damper bar, fixed with contact adhesive. Only time will tell!
6. RESONATOR ASSEMBLY.
Using Aluminium tubes I was able to match their O/D exactly to the bars. The riveting process could be undertaken by clamping the aluminium beams either side of the positioned and marked tube then lifting the beams and propping both ends on timbers across the A frames. This avoids having to remove the assembly each time. To keep the beams spaced correctly, I taped a small piece of the smallest tube between the beams at the top end. This procedure puts less strain on the rivet joints.
7. DRIVE PULLEY.
After cutting a circular blank to my chosen pulley O/D out of 'Tufnel', using my pillar drill, I drilled a centre hole for my shaft and Araldited the shaft in position. When set, I spun the pulley in the pillar drill and was able to cut the cord groove with a round (chainsaw) file. I'm sure that any hardwood would be OK.
I found four S.Steel, hex head woodscrews which proved ideal for the string ends as they are not threaded where the strings contact, avoiding chaffing.
My wife suggested the Jacobean Oak finish. A stained varnish is better than using wood-stain as the wood stains do not stain the timber.