A platform for gluing a broken button

A method that takes the guesswork and uncertainty out of this challenging repair job

BY GREG SAPP Luthier based in Batavia, IL, US

Any form of damage to the area where the neck joins the body is a critical issue for all violin-family instruments. When repairing this damage, in addition to the structural integrity of the neck joint, there are numerous geometric constraints regarding the neck length and its projection. For the purposes of this article, I will only be discussing the actual reattachment of a broken button. My example will be on a violin, but the following procedures can easily be applied to the viola, cello or bass.

The button is the semi-circular tab at the top of the back. Structurally, its job is to provide a stable gluing surface that binds together the end of the top-block and the heel of the neck. Artistically, the button also allows the maker to express his or her artistic flair, in conjunction with the f-holes and the scroll. These three features often influence the opinion of the world’s greatest experts when they are tasked with identifying the maker of a particular violin. Therefore, the originality and integrity of the existing button should be maintained as much as possible.

These challenging types of repair are what get my jig-making juices flowing, so I set out to design and make a universal platform specifically for the controlled reattachment of a broken button. I refused to accept the advice from a few of my mentors when they said: ‘Well, sometimes you just apply the glue and hold the parts together with your hands and hope for the best! Isn’t that why God gave you two hands?’

The button-gluing platform assembled

ALL PHOTOS GREG SAPP

1 My ‘button-gluing platform’ is made mainly from aluminium. It comprises:

• arectangular base

• three vertical clamping standards

• an adjustable gluing platform with a raised ridge at the far end

• aplywood counterform and a tapered wedge for applying the clamping pressure

The only prerequisite for using the platform is that the top plate must be removed, and the topblock must still be in place.

The button separated from the violin

2 A broken button can be the result of weak glue,material defect or degradation, or poorly executed joinery. More often than not, though, blunt force trauma can take the greatest toll on an instrument, sometimes causing the wood to fracture and splinter, making for a more complex and costly repair. From a repairer’s perspective, a button broken in this manner elevates the repair to the highest level of complexity.

First I take off the fingerboard, then remove the neck from the body. If the button is still attached to the lower heel of the neck, I will carefully separate it as well. Then I remove the top plate from the ribs. All parts are cleaned and examined for any further damage. Usually, by this stage I am reminded why a broken button can be such a difficult feature to reattach to the back. In its normal state, it just hangs out there as a fragile appendage to the back, and in most cases, no more than 1.5mm of wood is bridging the button and the back.

This might also be the stage when most luthiers realise there is no logical approach to reattaching the button with any control and assurance using any of the available traditional luthier clamps. The flowing three-dimensional organic shape of the violin will defy the chance of a predictable outcome. It’s a well-known fact that once the glue is applied, all bets are off.

3a The violin clamped in the jig

3b Adjusting the levelling screw

3 After everything has been prepared (3a), I slide the platform down over the top-block assembly and lightly push the clamping pad against the top-block by tightening the thumb screw (3b). I adjust the position of the ribs so that its alignment to the platform is as parallel as possible, and then tighten the thumb screw just a little more. I use the four levelling screws at the bottom of the platform between it and the base for adjusting its final position, so it is in exactly the same plane as the back. Now I check that all the components are secure.

The button in position

4I position the button in its place against the back of the violin, ensuring it is aligned correctly. If need be, I repeat the previous step until I am satisfied with how it registers with the back.

I typically make a large generic batch of counterforms on my CNC router. So at this point, I use a round file or sanding stick to adjust the shape of the counterform to maximise its contact with the button.

5a The counterform and tapered wedge in place

5b

5 I make sure that when the tapered wedge is slid into position between the back edge of the counterform and the raised ridge of the platform, there is a clean line of contact between them. Once the fit of everything is confirmed, the process of gluing the button is quite simple and accurate. Using the platform in this manner has removed the guesswork and allows me to have the utmost confidence that the button reattachment will be successful.

The platform modified for cello buttons

6 I designed the platform to be easily configured for use on a cello button repair. I simply remove the violin vertical standards and install the taller cello standards to the base. Then the platform is stacked on top of the cello riser box, which allows for the higher rib height of the cello. The gluing platform assembly is just as fully adjustable in either configuration and can be used for violin, viola or cello button attachments.