Columbia no. 15 soundbox: spare parts and rebuild tutorial?

[Phono48]

The nut is obviously original, as the diagram also shows one. We live and learn!

Barry

[Marco Gilardetti]

I'm proud to say that the soundbox rehaul and diaphragm replacement has been a success. The replacement diaphragm sounds all right, and cleaning and re-lubricating the ball bearings also improved the sound greatly. The spheres cleaned very nicely, and showed no trace of rust or corrosion.

I was quite impressed by the fact that the ball berings need indeed to be tightened to sound well over loud passages. Very similar adjustable ball bearings are used in bycicles, but you definitely want to leave some slight backlash there. Not with the needlebar: the slightest backlash gives an audible noise.

Many thanks once again to all those who contributed with a hint or a link to my questions!

[Marco Gilardetti]

As a side note, the "nut needlebar" type of soundbox has also a completely different arm lock-up attachment. It is secured in position by means of a screw that fits into a conical notch in this case, while more commonly it has a twist-and-lock bayonet mount. The throat of the soundbox is also narrower than that of the more common bayonet-mount type.

I ignore if these differences are typical of "nut-type" versus "screw-type", or if they're due to differences in the machine on which the respective soundboxes are mounted. For example, a different throat gauge was perhaps adopted by calculus to better suit an internal arm/horn of a specific gauge/length/mouth.

In any case, the engravings on the soundbox' back are also different (more ornate in the "nut needlebar" type).

[dado]

i dont wont to open new topics....does anebody knows diametar of diaphragme used in this soundbox.... is it 54 mm??
tnx