Now is a good time to remove the ribs from the mould. For that, refer to the Finishing the rib structure chapter.

Chamfering the underside

Before gluing the back plate to the ribs, you should create a chamfer on the bottom side (the first of a series, which will make the edges of the plate round). It goes all the way around the plate, except for the button. The same chamfer will later be done on the front. See Fig. 1. for illustration.

1. Using a suitable file, create the chamfer at about half the distance from the edge to the ribs' outline.
   
   

Clamping the back to the ribs

The back is clamped to the ribs prior to gluing. Self made spool clamps can be used, see the Tools section.

1. Fasten the back plate to the ribs using locating pins.
   
2. While carefully aligning the ribs to the outline marked on the plate, start adding clamps, making sure you are not over-tightening them. See Fig. 2. for placement. The top and bottom blocks are clamped with the use of C-clamps. Put some soft-wood padding between the clamp and the back plate to avoid damaging the plate.
   
3. Remove the locating pins.
   
   

Gluing

1. Prepare medium thickness glue and have a pitcher of hot water, a parting knife and a brush at hand. Put the knife and the brush in the hot water.
   
2. At one corner, remove a few clamps which will allow you to pull the ribs away and insert the knife with the glue.
   
3. Take the knife out of the water and dip it in the glue.
   
4. Insert the knife in the joint, spread the joint if necessary with your fingers and make sure enough glue gets applied.
   
5. Put the knife back in the hot water and remove excess glue with your damp brush.
   
6. Check that the alignment is right and re-clamp quickly.
   
7. Repeat with the other corners.
   
8. Go over the bouts, including the top and bottom block.
   
9. Let dry thoroughly.
   
   

The endpin hole

1. Mark the position of the endpin hole, on the centerline, just 1 mm bellow the horizontal center of the ribs, see Fig. 3.
   
2. Mount the back on the plate holder you used to carve the inside of the plates.
   
3. Drill the hole using a 6 mm drill bit making sure you are drilling at right angles to both the horizontal and vertical plane of the body of the instrument. Be careful not to split the wood especially at the end of the drilling.