Fixing a Broken Button with a Clavette


Adding a clavette to a neck reset to fix a broken button is an efficient way to fix a broken button. This article will outline how to pick and orient the wood for a clavette, how to fit and glue the clavette, and how to reglue the button.

Required Tools

  • Lamp
  • Pencil
  • Razor edge straight edge
  • Rulers
  • Block plane
  • Upper block closing clamp
  • Small chisel (2.75 mm wide) with a 15 degree bevel on the sides
  • Cyanoacrylate 
  • Strong hide glue
  • Upper block closing clamp
  • Various knives
  • Japanese pull saw with a small kerf
  • English dovetail saw with a small kerf

Why use a clavette?

The button is a weak point on every instrument. It doesn’t take much force for a button to break. A clavette is a good alternative to reinforcing the button with a patch. It is less invasive because the top of the instrument is not being removed, the upper block is not being removed, the ribs are not being altered, and original wood is not being removed from the back to create a patch. The clavette is a strong reliable repair.

Step 1:

The first step before beginning the repair is to document as much of the neck set as possible. Since the neck has fallen out of the mortice, many numbers will be off. Getting any information will be very helpful when it comes time to reset the neck. Taking many pictures of the instrument before any work has been done is also advisable.

Saw out the neck. There is no need to saw off the button area, since the player did that for you. Instead, use water on paper towel squares to slowly remove the button form the beck heel. This must be done with care, especially if it is a joined button. Take the time to diligently remove the button rather than creating more work by breaking the button.

After the button is removed from the neck, set the neck aside and clean up the mortice. You don’t need to be too thorough just remove big chunks of glue and make the area where the clavette will be free of debris.

Fit the Button

This is the time to make sure the button will fit. Check the fit in the same way you would level a crack. Make sure the button is level in relation to the back and that it fits into place well. If it does not fit, make the appropriate changes to get it to fit. This can mean coaxing maple fibers back into place or removing some wood to get the button to lie level. Maple is a tricky material due to the way the grain grows. Sometimes to get the button to blend with the back is to remove some of those  nuisance fibers.  

Excavate the clavette mortice

Now it’s time to make the mortice for the clavette. The mortice needs to be an even height and depth. The height is determined by the thickness of the chisel used. Try and use the smallest chisel possible. For this clavette a 2.5 mm chisel with the sides beveled at 15 degree was used. 

The depth of the clavette mortice is determined by the purfling on the instrument as well as the depth of the upper block. The mortice needs to be deeper than the purfling, but not extend all the way through the block. To check the block depth, send a skinny stick through the end button of the instrument until it hits the upper block, then make a pencil mark on the stick. Take the stick out of the instrument and line the pencil mark with the end button and see where the stick ends in relation to the upper block. This is a rough estimate of the block depth. A hacklinger gauge may also be used but if the block is too thick it will not register.

Now that the depth and width of the mortice has been discussed, it’s time to cut the mortice. Score a line at the height of the mortice and then using the 2.5mm chisel, start excavating to the desired depth. Do not worry about extending the mortice all the way to the walls of the neck mortice, but instead keep the walls at 90 degrees until the mortice depth is achieved (photo 2 below).

When the desired depth of the mortice is achieved, now extend the sides to the wall of neck mortice. This where having the bevel on the sides of the chisel is handy. Having the clavette fit at a dovetail makes the neck set and neck shaping much easier later on.

Making the Clavette:

The clavette needs to be apparent to future restorers. This is done via the orientation of the medulary rays (ray fleck) in relation to the neck heel. The ray fleck and grain of the clavette must be perpendicular to the ray fleck and grain of the neck heel and parallel the grain and ray fleck of the back. THIS IS VERY IMPORTANT! The grain of the clavette is oriented differently than the neck heel so it will be apparent to a professional if, for some reason the neck needs to be taken out in the future. If a neck is broken out without taking into account the clavette a great deal of damage can be done to the instrument. 

Pick out the wood. Matching the flame of the back is nice, but not necessary. The wood for the clavette should be something relatively straight grained and mild flamed; a stable piece of wood.

Clavette Diagram 1

Clavette Orientation

Fitting the Clavette:

Using a sharp block plane; plane the clavette until it is just proud of the height of the clavette mortice. Then bring in the sides of the clavette to match the angles of the mortice. This is all done with a plane, no scrapers or files.

While making the clavette mortice a uniform dimension is optimal, the upper portion of the clevette mortice usually becomes slightly bigger than the bottom. This is fine. When the clavette is getting close to dimension of the mortice, the fitting process can begin. Keep planing until the clavette fits snug in the mortice. Do not force it. If the fit is too tight it could split the block. When the clavette fits, it should have a snug contact with the mortice walls, there should not be rock in any direction, and it should be able to be inserted and removed without to much effort.

Glue in the Clavette:

Use fresh strong glue, with a relatively low viscosity. If the glue is too viscous it will stop the clavette from reaching the bottom of the mortice. Clamp lightly with an upper block clamp. Let the clavette dry for a 3-5 hours.

Clevatte glued into the mortice

Fit and Glue the Button

Since the button has already been pre- fit to the back, this step should not be too difficult. Keep the clavette piece long to act as a platform to glue the button. Glue a square piece of maple to the end of the clavette with a dot of cyanoacrylate. Make two wedges that fit between the button and the maple barrier (these will act as clamps for the button). Check the fit of the button one last time.The button should fit into place on the back, the cracks should all be level and the button should lie flat along the clavette.  If it does not fit well, make necessary adjustments. When everything fits, dry clamp the clavette using the wedges. Check the setup. Perform a couple dry runs of the gluing process. When confident that the gluing will be a success, glue the button to the clavette and the back. To do this apply glue to the button, put it in place and clamp using the two wedges.Do not force the wedges too tight, tis can distort the button and result in an uneven crack area. 

Let the glue set up overnight. Carefully saw away the excess clavette material, leaving enough wood to fit the neck heel. Begin the neck setting process. If wondering how Triangle Strings does a neck set, check out our three part series on the procedure.

The Final Product

When the neck has been reset, everything should be elegantly blended. The claveete should be noticeable but not an eyesore. You can see in the pictures below the grain orientation of the clavette opposing that of the neck heel. Viewed from the back, the button is even with the body of the instrument. The crack can still be seen which is another signal for future restorers that the button has been broken and to pay heed if the neck needs to be removed again.

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