Violin Forum/Message Board

[Jack London]

I have been looking at a lot of pictures to get the idea of what good purfling miters look like at the corners, but I can never get a result that is pleasing to me. I have read other threads about gluing them in, but I have not found a thread about how to actually cut them so they line up so sweetly. I was wondering if some of the experienced makers out there had any advice, or even better, a few pictures. Still staying within this thread, how much of the way the miters join up cleanly is due to the way the purfling arches around the corner to form the miter? I have wondered if the way purfling goes a little off to the side of a corner is due as much to the way it moves around the curve of the corner as it is to an aesthetic choice--if the beauty of the line results naturally form the arc it has to take. I really admire makers out there, a couple of whom are on this forum, who make purfling flow so smoothly through the miter and into the bee sting.

[Andres Sender]

I may not be understanding you right, but if we're talking about lining up the blacks, that comes from creating a miter shape that curves in such a way that (speaking only of the black elements now) the side that wants to be too long is shortened (more concave), and the side that wants to be too short is lengthened (more convex), so they end at the same place.

Is that the issue you're focused on?

[Jack London]

If I were more computer literate, I would post some pics and diagrams, but I am not. So I guess we are on the same page. But what i am wondering is (other than lots of practice, which I am doing and not getting very far from the original disappointments) if perhaps someone could post a diagram that would illustrate how you cut the purfling to get get all elements, black and white, to line up and flow as seemingly single unit into the corner. Some possible points to discuss: What do you look for? How do you line up the purfling? what are you looking at and for when you draw in how you want the purfling to lay as it moves around the corner and into its point? how do you cut the miter? I realize this might be something that is best demonstrated, but I thought I would just ask and see what happens. Thank you for your help in advance.

[David Tseng]

First, you cut the miter of the C-bout purfling; the inner black should fit the inner corner of the groove. The longer outer black for the bee-sting is from the upper/lower bout purfling.

[Andres Sender]

No time to make drawings but for the sake of having something to talk about here's a Strad corner (the "Harrison" at the NMM):

(Don't be too depressed, it's probably got filler helping shape the point I expect)

[Michael Darnton]

A couple of points about Andres' photo:



First, you may see that the upper bout purfling black is the one that makes the beesting, what little of it there is, in this corner. The beesting is not two pieces, both extending to the end. This piece goes in first, because it's thin and fragile and has to reach out farther into the corner, and the inner bout "clamps" the joint closed by being forced into place after and against the outer piece. I would say that about the last mm of the point is upper bout purfling, alone (that would be everything between the two small and conveniently placed vertical dashes formed by dirty wood pores in the photo)

Amati corners have less beesting, and are generally more open (wider) at the tip, less compressed and "pointy" than a Strad. Here's an Amati corner, for comparison--you can see that he brings both purflings out to the tip, and doesn't bring the c-bout purfling lower and closer to the edge as it reaches the tip, resulting in no beesting, and a less pointy purfling tip that's more centered in the end of the corner. When you compare the two photos, you can probably see that the Strad's inner bout purfling's lower black line comes up to it's joint with the upper bout's outer black at a blunter angle that doesn't allow for the lower one to stretch all the way out to the corner--it more runs into the upper purfling from the bottom rather than curving around to blend with it. To see this clearly you really need to flip back and forth between the two corners, because this is a relatively tiny difference that make a lot of difference in the shapes of the two corners' tips.



Below, I've magnified Andres' picture and added some marks. The clamping of the mortise is forced by cutting the c-bout purfling section a bit too long to fit in the c-bout--about 1-2mm too long works about right. If you strike a line down the center of the joint, from the tip of the maple at the back of the purfling joint down to the tip, you'll see that the inner bout purfling has pushed the joint off center, up and to the right in the photo.

A couple of tips to getting a good joint: the length of the first cut end (the outer bout piece) has to stretch exactly from the place where the two purflings meet at the top left (the upper green dot in my photo) to the tip (the other green dot). Put this piece into place, and the bevel section should fit perfectly in the space allotted for it between those two points. Also, when purfling gets forced along the outer curve, the bevel should end up straight (more later). Next, the inner piece's bevel is shorter (it only reaches to the blue circle, which marks the extent of that piece of outer black--before I put the circle on you could see that). When it's jammed in, hard, the back (the beginning of the bevel's cut at the first green dot) should stop right at the back of the space it has to fit, right at the green dot. If the inside of the joint is in the right place, and the angle of the cut is just reasonable--not even perfect--everything else falls into place.

Both cuts should be slightly concave--when the purfling bends around the corner contour, the outside's curving will straighten the concave bevel inside of the joint out to a straight line. The part with the beesting is cut in two blending bevels, one curved cut down through the inner black and the white, and then a slightly different cut out through the outer black for the beesting. You can do this in one long sweeping cut that gets slightly flatter as it approaches the tip.




The gluing order for this is to place all of the purflings in place, then lift out the c-bout, drip glue in everywhere except within 3/4 inch of the corners, set the corners back in tightly, and dry at this point, and then push the center back in partially, getting it started in the groove sort of all at once, and press it down into place into the bottom of the groove. Squeezing the purfling down in the center of the c-bout first drives the glue outwards under the purfling, and it jets up and out around the purfling at the corner, finally. Next, lift the outer bouts out, but NOT the corners--hold them down in place. Fill the groove with glue, push the purfling in, and then stroke it down moving towards the corners. Again, this pushes glue underneath and out to the corners, and it spurts up to the surface there. The corners get glued without ever having been lifted out. This prevents you having to manage fragile wet corners in areas which are swelling shut from being wet--you get the original dry fit, and the wood swells closed around that, making everything tight.

While you're looking at the photo, notice the c-bout cut coming into the corner. Almost contained within the area of my circle it's flat (the flat extends a bit beyond the circle on the right), and there's a little point in the c-bout groove's line just inside the left edge of the circle where it meets the smoothly flowing line from the c-bout. This is because when you make the initial cut for the beesting, it's from the upper bout, a single cut that goes about 1+mm beyond the natural junction point of the inner and outer lines. To open the cut up enough for the tapered black to fit, he took one straight little cut to open up the tip and lengthen the tip junction just a bit beyond the natural junction. That's what makes the junction so long and elegant, just a bit more than the natural cuts would dictate. Strads consistently have that little flat cut and the tiny bump that results just behind it, but in later ones, he blends this better than in this earlier example, which is the Harrison, from 1693.

While you're looking at that, look at Andres' longer view and see that the c-bout purfling diverges from a constant distance from the edge, moving closer to the edge starting right at that little cut. While you're looking, see the little marking cut that goes beyond the beesting, indicating that the beesting is formed as a continuation of the outer bout's line, not the c-bout. It's hard to see, especially on a slightly worn corner, but Stradivari usually starts pulling in the outer bouts' purfling from the edge just before the joint. On this one, probably because the corner is so small (small for a Strad), he doesn't diverge at all. On cellos the divergence is quite large. Different makers started that at different points--Andrea Amati started where the concave curve in the outline for the corner starts, and subsequent generations moved the diversion farther and farther down towards the joint.

I don't usually do other things this way, but when I'm making this joint I always look at the dry fit with a magnifying loupe to really see what's going on and make sure I can't make it better. Make sure you don't undercut both bevels so that the top part you can see looks good, but as you go farther down the joint opens up.

While you're noticing things, notice that the outer and inner cuts of the groove are curved right out to the tip. A common amateur mistake is to straighten out the outer line into the tip. Not making a concave outer purfling bevel can also make this happen by forcing the outer line of the purfling straight. On the c-bout purfling you can get away with less concavity in the bevel cut because the bevel joint there is short, but it still needs to be cut a bit concave for things to come together well.

Here--I've run a quick, exaggerated, sketch to show what the initial Strad corner marking cuts might have looked like, before he cut the groove:

[Jack London]

Wow, Michael, I cant say enough about how much that helps. The pictures and your verbal explanation really illustrate a lot. Thank you-- I am sure that took a lot of time.

[Jack London]

I'm sorry-- I did not mean to exclude the others who have taken the time to comment here from my thank you-- so thanks! (Sometimes I just get so excited....)

[M.Lange]

Yes, thank you very much for that great explanation of the purfling corner work!
The most detailed and comprehensive, I've ever seen. It's a pleasure to learn from you.

Matthias

[actonern]

Michael thank you so much!

This tutorial is going in the binder for sure...

Ernie

[Joseph Leahy]

Just wanted to add my thanks here Michael. I'll be keeping this for future reference. Its very generous of you to share these details.

[Chris Knowlton]

Very nicely explained Michael. I too added this to my reference file. Thank you.

Chris
_________________
I make sawdust mostly

[jethro]

Thanks Michael !
If my printer worked I'd print that for sure!

I will have to seclude myself in a quiet place for about 45 minuites
and focus to understand your deep and thourough explanation !

I just can tell my corners don't look like that yet !

Very subtile curves but it seems even the slightest variation ruins
the beautifull gracefull lines, like changing Marilyn Monroe's shape !

T

[mikemolnar]

In My Humble Opinion (IMHO) Darnton does some of the best corners. He has shown good examples and explanations here and on Maestronet.

He really knows what he is talking about.

Andres, thank you for that great photo.

Mike

[DonLeister]

Glad you brought this up again Michael M. That is a wonderful description of doing purfling miters, thanks Michael D. !

So Jack, have you had a chance to put any of this into practice? I know it can be a while from the point of seeing to doing.

I was at Michael's workshop, or I should say Jim Brown's workshop last year, and Michael helped me with my purfling miters, and I have just in the past month gotten back to doing purfling.

Michael is an excellent teacher and he has a sharp eye and mind.
After seeing my plates I had brought, to work on arching, he walked by and said, something like ' I think the reason your miters are that way is because the purfling is too close to the edge and when they get to the corner they (the corners) are too Strad like , or too square , and would work if the corner were longer, or better if the purfling were further away from the edge.
I had unwittingly moved the purfling closer to the edge a few 10ths of a mm on this batch of instruments just thinking it would look a little different. Not that my corners are that great, but I had noticed that this batch was having some difficulty in the miter department!

I have had a chance to do six plates recently, and i'm trying out Michael D's way which is working well, although I still am not terribly fussy about miters, I tend to like to go on autopilot.
What I enjoy is doing F holes.

These things happen so quick, it's over before you know what happened!