Dennis J

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About Dennis J

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    Adelaide, South Australia
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    Anything and everything.

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  1. What I'm saying applies to new instruments, or at least test fitting a neck minus the fingerboard. That is to line up a centre line on the neck gluing surface with the centre join of the top plate. That can easily be done with a straight piece of aluminium shaped to do the job.
  2. If the neck mortise is tight enough it comes down to a matter of checking that it is aligned with the centreline of the body. Using plate edges seems an unreliable way of doing this to me.
  3. With pins through the top's glue line into the centre of the end blocks the glue line itself can be used to check the neck's alignment while adjusting its angle.
  4. I'm genuinely curious about whether distortion or sinking in front of the bridge is a common thing, especially in recently made instruments. I've come across tone wood that has very low density/weight which I would not use. I think that sinking between the fs is probably a combination of bridge pressure and longitudinal compression or bending. So keeping thickness there is important. But I think the best way to limit bending would be to make the back thick and strong enough to do so.
  5. I think that most or all of the bending/distortion/failure would be confined to the waist area because it is the weakest part of the box. A violin body is not like an archery bow where bending mostly takes place at the ends of the bow's limbs. It's just the opposite. After all we know how a steel tube flattens and spreads at its centre when bent. I think any noticeable sort of distortion/sinking is not desirable in a violin. But just how common is it? If it is a problem the solutions are fairly obvious.
  6. I know there are plenty of examples of obvious distortion like sunken areas in front of the bridge in older instruments, but is it seen much in more recently made ones?
  7. Whether by intention or not I suspect many violin top arches peak forward of the actual centre of the body. For the upper bout part of the long arch to have a shorter radius of curvature than the lower part the best arrangement is to have the highest point forward of the centre.
  8. I do. But I didn't need scans to tell me that. However I believe that a violin should be made in such a way to keep that bending to a minimum. It's tempting to compare the violin under string tension to an archery bow. But it doesn't behave that way because most of the bending takes place at its centre.
  9. That's the sort of constructive insight this discussion needs. Probably why some makers in the past have done it.
  10. I think it is just a question of how the violin body bends and what that may mean as far as distortion is concerned. If the back is sufficiently thick/strong enough the reference point can be taken as the location of the back where the soundpost rests. If the central back area is not strong enough to resist downward pressure of the bridge without bending then things change. I see some makers are graduating the back in that location as little as 4.5 mm. I thought about 6 mm was accepted as necessary. As far as I can see a bit of intuition and common sense is the best way of looking at
  11. It may just be semantics, but I agree that the soundpost is a stationary element around which the violin bends. It is not pushed down by bridge force. That means that the end blocks will rise upward and rotate towards the centre. I've looked at Reguz's violin geometry and it doesn't conform with mine as far as arching is concerned. One thing I did take away from his work is the importance of the Double String Length Lines.
  12. The exaggerated deformed shape shown in fig. 6.12 shows the back long arch stretched out and downward by sound post force. The trouble with that scenario is that the maple backs of violins are made much thicker in that central area to prevent that happening. And the extra thickness is mainly achieved by having a flatter floor inside the back.
  13. Looks like progress at last. Violins do bend under string pressure.
  14. I've done a lot of experiments along those lines using carbon fibre. It very efficiently transmits distorting pressure. But violin tops are not the same. Pushing down on the central area of a violin top will depress an area around that pressure point. The force distorts the surface in all directions, not longitudinally as you seem to suggest.
  15. Instruments that bend a lot under string pressure are the ones that distort the most. They bend at or around the base of the sound post. Downward pressure from the bridge holds the central area in place or depresses it a bit. In this scenario it is is possible to assume the sides of the arching in the central area would bulge outward under compression while the central area is held in place by downward bridge force, or even sink further. So nearly all distorting forces play out in that central area.