The easiest way to make the cheiroballistra case is to attach the pieces to a central core. Thus there are five parts in total:
- The core
- Projecting block: below the core, braced against the little ladder
- Top block: above the core, meets the end of the female dovetail halves
- One half of female dovetail
- One half of female dovetail
This article describes one way to make the case. Here I've used high-quality pine that weighs about 0.6g/cm^3. My first case was made of birch, which worked well, but was rather heavy. In retrospect using some other lightwood than pine would have made more sense: pine is quite prone to splitting, which complicates things. In particular attaching T-clamps proved to be difficult.
The core, projecting block and top block Edit
The process for making these parts is simple. Just take pieces of plank that is close to the desired dimensions, then plane it to correct dimensions. Alternatively you can use a circular saw to cut the planks to correct size. If you do so, take care to plane the planks smooth. Cut each part to correct length and slightly sound the corners. The end result should look like this:
The projecting block shown against the core:
The top block shown against the core:
The end of the core:
Note how the growth rings in the core and the two blocks point to opposing directions; this is done to help prevent wood's natural tendency to warp when its moisture content changes. In addition, the inside of the tree is pointing up in the core: if core manages to warp, the concavity formed by the two female dovetails will open up, not close down, which would prevent slider movement.
Once all the pieces are ready, they are glued together. Here a straight piece of wood is used to help align the projecting block:
A liberal amount of glue is applied to both the core and the projecting block:
Finally the pieces are tightened with several clamps. Take care to prevent the projecting block from moving and rotating. The easiest way to do this is to nail the projecting block in place with a few small nails, and only after that apply pressure with the clamps:
If the location of the nails matches that of the wooden dowels (see below), no trace of the nails will remain in the finished piece.
Once the glue joint has dried, mark the places of the wooden dowels to the underside of the projecting block. Here I've placed two dowels side-by-side near the front end of the block, against the little ladder:
Drill holes to the the marked places. The holes should house the dowels very snugly:
The dowels should preferably be of hardwood (here probably beech). They should be slightly longer than absolutely necessary - any projecting parts will be sawn and sanded flat.
Use a wooden mallet to force the dovels into the holes:
Once the dowels have been beaten as far as they go, remove the excess glue:
Let the glue joints dry, then saw away the projecting parts of the dowels and sand the underside of the projecting block smooth:
The top block is glued in place in the exact same way as the projecting block, but the wooden dowels can be omitted, because the top block is not under significant stress.: