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Purfling after closing the box


Roland

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Here is a quote of Wolfjk from Thorbjörn's thread:

Hi David,

According some experts Stradivari Done the purfling after closing the box, so finishing the final arching and fluting - and thicknessing round the fluting had to be done without access to the inside. So it is probable that he did prick the outside, especially round and near the fluting.

I've been thinking about this for some time now and there is one thing that I find a bit strange: The purfling of the front extends slightly under the fingerboard. This can be seen in various undisturbed violins, for example in Michael's latest blog (thanks Michael for these great pics!), the Messiah, the Chardon del Gesu and several Stainer instruments. It is very likely that the old makers nailed the neck to the ribs before gluing the plates to the ribs. Otherwise nailing would have been fairly difficult :) Therefore, the neck would have constrained the marking of the purfling channel. Certainly, the button does the same and you can easily extend the lines from the purfling marker with a knife under the finger board. However, it would be far easier to purfle the plates before gluing them to the ribs, wouldn't it? The old makers surely worked as efficiently as possible. So what's the advantage of purfling the plates after gluing them to the ribs??

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So what's the advantage of purfling the plates after gluing them to the ribs??

In part, to more easily establish a perfectly even overhang on th edgework. The Cremonese method of fixing the neck to the rib garland before glueing on the plates could also require slight adjustments to make sure the neck was straight down the middle of the top when the plates were glued on. This could introduce slight deformation of the mold outline, which was less troublesome if one simply trimmed the edge to fit and then purfled.

Not that it means a thing, but I purfle after the box is glued up and its very easy.

Best regards,

E

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Hi Michael:

Roger Hargrave, at figure 30 of this article http://www.roger-hargrave.de/PDF/Book/Chap...he_Back_PRN.pdf illustrates the movement of the ribs that could occur in the process of rendering the neck straight.

Also, if the cremonese shops made multiple rib garlands well in advance of their attachment to any plates, the potential for deformation of the garland from an ideal mold shape increases with time, all of which from a practical working perspective could recommend the scribing and installing of the purfling after...

Best regards,

E

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After making a garland, it seems sensible to make a back.

Better keep the garlands on the forms while scribing outline onto back.

So in order to make say 10 instruments, you need ten forms.

I have 14 violin forms.

One exception I find is when making alterations to a form, by eye.

When doing this I keep the garland on the form & draw around the garland onto the back, then remove the garland, stretch it by length or wdith, or both, making note of the symetries in relation to the pre-drawn marks, clamp it to the back, and scribe the new outline.....easier than using 10 forms and much more fun.

As far as mould / form material goes, I found that MDF board (high density particle board) is best for forms, since it is a uniform thickness, and very easy to work. The absence of real wood grain renders it easier to maintain and finish. A few coats of oil varnish and it's fine. Perhaps not as pretty as figured walnut, but much cheaper and it'll certainly outlive me.

I made one of my Cello forms with it, giving extra thickness at the block areas, the form weighs in at 9kg which is still managable.

Here are some recent photos :

http://www.flickr.com/photos/benconover/se...342873175/show/

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"After making a garland, it seems sensible to make a back.

Better keep the garlands on the forms while scribing outline onto back."

I was interested in Roger Hargrave's Figure 31 in the same article I've linked to above.

Studying it, would it not appear that scribing the outline of the back from the ribs would in fact be problematic while still on the mold?

If the rib structure was deformed to ensure the neck was straight as illustrated, the mold, if still on, would just get in the way?

E

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Therefore, the neck would have constrained the marking of the purfling channel.

Hi Roland,

I've been wrestling with this issue for a while. It's not the purfling channel that's a problem, it's the arching. If you leave a flat all around the edge, as Hargrave suggests, then you have a flat area under the fingerboard. You can see in Michael's blog and the other references that the arching is very fluid and consistent under the fingerboard. It doesn't look like it has been worked after the fact.

There are two ways to accomplish this; one is to carve the recurve under the fingerboard before gluing the neck. The second is to carve the recurve all around, cut the channel, insert the purfling and scrape the purfling and edge until it looks clean and the insturment sounds good :)

Robert Bein suggested that this is how it was done (in private conversation) and I scoffed at the time, now I'm tending to agree with him.

Oded

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Robert Bein suggested that this is how it was done (in private conversation) and I scoffed at the time, now I'm tending to agree with him.

The problem with Robert's observation is that he concluded this from noticing that the purfling had light and dark spots on it where dirt had built up in low spots representing low areas in the purfling and the wood around it. His idea was based on his conclusion that in hammering or pushing the purfling in, it and the wood next to it had been driven below the level of the surrounding wood, which was then not subsequently scraped enough to bring the resulting dents up to level.

I made him point out these spots precisely to me one day on a real violin, and I noticed, but he did not, that every dark spot that he pointed out corresponded with a change in the curl figure on the wood--he was seeing differential scraping depths because of changing grain direction. Robert, who essentially had a very poor understanding of tool use from the violin maker's perspective, scoffed at this (as he had a habit of doing with anyone who disagreed with him on anything.) Subsequently, I observed the same thing on many, many instruments.

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I have 14 violin forms.

When this discussion came up several years ago, I pointed out that all we seem to have from Stradivari is one form for each model, and that within what appears to be the Cremonese method of work, it would have been likely that they made many ribsets, removed them from the one form, hung them up on the wall (for instance) and then used them later. This would have permitted them to distort, and could account for the many differences in outline. Also, I pointed out a very simple method (the corners rest on a circle drawn from the midpoint of the length; the diameter of the circle is, conveniently, very close to the stop length. This does not assure symmetry since the corners can be up or down the circle, but it seems to work for many non-symmetrical Cremonese violins) for quickly aligning floppy ribs on wood for outlining which would preserve the asymmetry, while permitting precise dimensions to be obtained. Now, though it never occurred to me before, it makes perfect sense that plates could have been completely finished off the ribs, referencing from two scratch lines--one around the rib, for realignment, another for filing the margin, just as modern makers do.

As for RH's idea that aligning the neck resulted in the mis-shaping, I discovered making baroque violins that it's very easy to set the neck straight, and to achieve the amount of distortion seen in Strad outlines from straightening the neck, you'd have to be very incompetent, and possibly blind, as well.

I'm not proposing any alternative model for how the Cremonese worked--I'm only saying that the usually assumptions don't seem to based on the necessities of construction, nor on archaeological evidence, so they're resting on rather thin support.

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Now, though it never occurred to me before, it makes perfect sense that plates could have been completely finished off the ribs, referencing from two scratch lines--one around the rib, for realignment, another for filing the margin, just as modern makers do.

That still leaves the pesky pins at the ends where the purling bisects them to explain.

Oded

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Thanks for all the answers!

Ernie / actonern, I read Roger Hargrave's article again (it's definitely worth reading again :) ) and it seems that in his opinion, the outline of the plates was finalised before the plates were glued to the ribs. Refering to the last paragraph on page 33:

Having finalized the outline of the back, he took a

knife and cut a chamfer on the underside of the edge.

This feature can be found on almost all Cremonese

instruments, and the absence of any cuts running

into the ribs themselves suggests that the chamfer

was made before the back was attached to the ribs.

Wouldn't it make sense to purfle the plates then, too?

Moreover, the neck would render the box quite unhandy - imagine purfling a cello with the neck in place :)

(Ernie, I assume that you attach the neck after the purfling is glued in, don't you?)

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That still leaves the pesky pins at the ends where the purling bisects them to explain.

Oded

Yes, it surely does.

An additional data point: I think many people have failed to observe that a rather well-known late del Gesu has purfling which deviates from a consistent distance from the edge by nearly two mm, if I am remembering the numbers correctly. This happens slowly, so it's not readily noticed--I didn't until I had to take drawings and measurements from it to send to someone who was making a copy. This suggests that the purfling was done with the plates off, the violin glued up, and then the margin refiled to match the ribs. I'm not suggesting this was done all the time; only that whoever did it this one time (I would maintain that it's a Katarina) botched it miserably. I've always felt I couldn't have been the only one to notice this, but I've never seen it mentioned anywhere. I measured the distance at the time with an optical measuring microscope, but it was possible to see once you saw it once.

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I made him point out these spots precisely to me one day on a real violin, and I noticed, but he did not, that every dark spot that he pointed out corresponded with a change in the curl figure on the wood--he was seeing differential scraping depths because of changing grain direction. Robert, who essentially had a very poor understanding of tool use from the violin maker's perspective, scoffed at this (as he had a habit of doing with anyone who disagreed with him on anything.) Subsequently, I observed the same thing on many, many instruments.

Bob Bein's other argument was to cite the decorate instruments where scraping the edge away was not a good option.

~OK

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Even with a cello? (I'm just curious, not sceptical :) )

I have not made a baroque cello, but I doubt that the principle is much different. You have to remember that cello ribs are far from flimsy. I can see how it would be cumbersome, but not dangerous. At any rate, violin makers aren't, as a rule, hamfisted creatures.

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That still leaves the pesky pins at the ends where the purling bisects them to explain.

Oded

I don't understand why purfling through the pins is definitive evidence that the plates were glued on before purfling. What is to keep one from drilling alignment pin holes in the plates, carving the plates, gluing in alignment pins, then purfling (right through the pins) then gluing the plate to the garland, using pins protruding from the bottom of the plates for alignment?

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Any defects in this reasoning???

The neck/garland assembly was clamped to a newly planed back as illustrated in Hargrave's illustration 31 reference earlier.

When satisfied that the neck was straight and the ribs where the maker wanted them, while so clamped, 2 lines were scribed, establishing both the overhang and the inner rib line.

Then the back was removed, the plate cut out, finished, including the inner chamfer, and permanently glued to the ribs. A newly planed top was similarly provisionally clamped to the ribs, 2 scribe lines similarly traced, but this time there was no need to be concerned with neck straightness since the back was already glued on and looking after that.

The top was then unclamped from the ribs, similarly finished, glued to the ribs, and the purfling installed.

Perhaps the makers left less of a flat area on the plates around the edges than Sacconi or others suppose. The plate can be worked very close to final arch profile and then purfled and scraped clean. That would explain how there is an even and flowing arch under the fingerboard even if the plates were purfled after.

The split pins are also easier to explain this way.

E

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What you suggest is obviously not impossible, it's just more convoluted and doesn't fit as well.

Why go to the trouble of splitting the pin in the first place? Also purfling the plates off the garland with a couple of pins sticking out the bottom isn't very convenient.

Oded

Why indeed? It certainly is more convoluted to have to precisely locate the pinhole so that the purfling will pass through it :) The pins sticking out the bottom would be a convenient way to hold the plate fixed to the bench.

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