StewMac tools            

Cello body joint for guitar

Please put your pickup/wiring discussions in the Electronics section; and put discussions about repair issues, including fixing errors in new instruments, in the Repairs section.

Cello body joint for guitar

Postby Brian Evans » Mon May 29, 2017 3:43 pm

It seems there are several people building instruments with the "cello" style of rim joint. No binding, slight overhang, decorative purfling on the top. The oft-quoted advantage is take-apart-ability, you can split the joint more deftly, I presume because there is no binding. It seems to me the joint might also be stronger and stiffer, since any binding channel is really cutting into the joint, sometimes exposing the kerfing or lining. If you do a wide purfling, the top gets thinned down right over the joint as well. I've always looked at those points with doubt, wondering why, aside from bling factor, you would weaken such a critical area. I suppose the binding and purfling itself adds back significant strength as it replaces the wood of the top and side.

So - what is the thought about the cello type joint? Stronger? Stiffer? Not? Doesn't matter? I do think a significant downside is damage to the rim edge, which binding was presumably invented to protect against. Any ideas about this?

Brian
Brian Evans
 
Posts: 529
Joined: Sat Aug 30, 2014 8:26 am
Location: Tatamagouche, Nova Scotia

Re: Cello body joint for guitar

Postby Barry Daniels » Mon May 29, 2017 3:49 pm

People don't hold cellos in their lap. The overhanging edge cutting into your legs and arm would be the major downside.
MIMF Staff
Barry Daniels
 
Posts: 1734
Joined: Thu Jan 05, 2012 10:58 am
Location: Houston, Texas

Re: Cello body joint for guitar

Postby Brian Evans » Mon May 29, 2017 4:43 pm

I really tend to agree. I wonder if a mid-way point is a no-binding flush joint, but that doesn't seem right. I've done a no-binding top before and it is standing up just fine, yet extremely plain visually.
Brian Evans
 
Posts: 529
Joined: Sat Aug 30, 2014 8:26 am
Location: Tatamagouche, Nova Scotia

Re: Cello body joint for guitar

Postby Beate Ritzert » Mon May 29, 2017 7:37 pm

The main advantage of the overhang is the larger tolerance against opening the instrument for repair. And in the baroque period it was probably also a decorative component.

BTW: a cello also ha contact with the body, and the overhanging edge may well cut into the legs. Especially when the 17th century playing techniques are considered.

And the Viola da Gamba? Sometimes it has overhanging edges, more often the top and the bottom are flush with the rims (but there is a purfling).

The purfling does not weaken the top resp bottom very much if at all: it is filled, traditionally with wood of contrasting color, and that gives the plate back its stiffness. Moreover it protects the plate from cracking in very much the same way as the rosette around the sound hole of a classical guitar does - and that is actually its main purpose.

A personal note on the skin contact of overhanging edges: it is more the two sharp edges that cut noticeably into the skin. According to experience with my violin... a carefully rounded edge of a plate with the typical thickness of an archtop or cello top is pretty smooth at least not "sharper" than the usually pretty sharp edges of guitrs with a binding.
User avatar
Beate Ritzert
 
Posts: 413
Joined: Thu Aug 02, 2012 8:20 am
Location: Germany

Re: Cello body joint for guitar

Postby Alan Carruth » Tue May 30, 2017 1:35 pm

"The purfling does not weaken the top resp bottom very much if at all: it is filled, traditionally with wood of contrasting color, and that gives the plate back its stiffness. "

Actually, the purfling on a violin or 'cello does loosen the edge up to some degree, and can also weaken it. Generally it's considered an acoustic benefit.

Violins and 'cellos use solid liners that are rather narrow as compared with what we use on guitars. On the violin it's typically about 1.5mm wide on the top edge, and my table of Holy Numbers' derived from Mittenwald gives the thickness for 'cellos at 2.5mm. The purfling, which is about 1.2mm wide, is set into a groove that is centered over the glue line between the liner and the rib. On a violin the edge is 3mm thick or so at that point, and the purfling goes halfway down, so there's only 1.5mm of wood under the purfling. German practice is to compress the purfling before gluing it in, so that the swelling of the wood when the glue hits it will make it tight in the groove: it has to be hammered in. Italian practice is to make it loose in the groove, but not sloppy.

Fred Saunders noticed in his early research that there was often a crack in the finish over the inside edge of the purfling. It's also often said that if the purfling comes out and needs to be re-glued that can hurt the sound. He took a little sqw in something like a Dremel tool and made a groove around the edge of one of the disposable violas that Carleen made for him, which had no purfling, and the sound improved. Computer models have shown that the edge of the violin is neither 'hinged' nor 'fixed', but somewhere in between. That's what the purfling does.

On the violin it's the end button that keeps the neck from folding up. With the purfling cut nearly through the back across it, there's not much wood to take that load. End buttons break off pretty regularly, and you can't get away with just gluing them back on. Instead you have to remove the back, and make a counterpart to match the contour of the area above the neck block. The back is then carved away from the inside in a cylindrical manner, as wide as the neck block and almost through at the center line, tapering to nothing at the edges parallel to the center line of the fiddle. A block of maple is chalk fitted carefully, glued in, and trimmed down to level the inside surface of the edge. This patch extends out as far a the heel of the neck, and the end button is taken down from behind and glued back on. When the back is remounted all you see of the repair is the new wood along the edge, and that gets touched up. Often they will put horse shoe shaped cap of ebony around the end of the button that is mitered in to a point at the purfling edge.

I have used this sort of joint on archtop guitars often. I just do the standard edge, mitering the binding and purfling in at the top end in the way that's often done on Classical guitars that are built on a Solera, where the heel cap is also an extension of the back. They often cut the binding and purfling all the way in to the center seam on those, but I just make a short miter so as not to cut away the end button of the back. This has worked well for the most part.

In one case I did get one destroyed by UPS. The guitar in the case and shipping box was dropped on the tail end, and the whiplash popped the neck up. There was a break across the heel cap at the body end which, in the absence of the purfling cut, was jagged. Since I had no wood to make another back I eventually just did a quick and dirty fix with a large screw and sold it to a student for next to nothing. Of course, in the eyes of the shipper, the guitar was 'improperly packed'; if it had not been it would not have broken, right?

More recently I've been using my usual single tapered mortise and tenon, with the bottom surface if the tenon under cut and carefully fitted to lock into the lower end of the mortise. So far, so good...
Alan Carruth
 
Posts: 746
Joined: Sun Jan 15, 2012 1:11 pm

Re: Cello body joint for guitar

Postby Beate Ritzert » Tue May 30, 2017 4:40 pm

In other words: the purfling channel of the violins has a similar function as the recurve, hasn't it?
User avatar
Beate Ritzert
 
Posts: 413
Joined: Thu Aug 02, 2012 8:20 am
Location: Germany

Re: Cello body joint for guitar

Postby Alan Carruth » Wed May 31, 2017 1:20 pm

I'd say similar in general, but maybe on a different scale? Keep in mind that the recurve can add stiffness as well as reducing it, depending on how the plate is bending. Also, a wide and deep recurve on an archtop guitar seems to me to be asking for trouble. I've seen a number of older gutiars with bor4ad recurves where the top has sunken in to the point where the bridge adjusters are maxed out trying to maintain a workable action height. It's not so much of a problem on violins, as the sound post helps keep the top from collapsing.
Alan Carruth
 
Posts: 746
Joined: Sun Jan 15, 2012 1:11 pm


Return to Archtop Guitars and Bass Guitars

Who is online

Users browsing this forum: No registered users and 1 guest

Your purchase from these sites helps support the MIMForum, but only if you start at the links below!!!
Amazon music     Amazon books     Amazon tools     Rockler tools     Office Depot    

The MIMF is a member-supported forum, please consider supporting us with a donation, thanks!
 • Book store • Tool store • Links •