Making Window Sash

One of the common uses to which moulding planes were put was in making window sash. The picture above is of some sash I made myself, using some of the tools illustrated in this article.

A traditional window is composed of an upper and lower sash, the outer one running in a track toward the outside of the building and the lower in a track toward the inside. When the window is closed the outer sash is all the way up and the inner all the way down. In expensive windows the outer sash was counterweighted by cords attached to weights that hung inside the hollow sides of the window casing, making it easy to raise and lower the upper sash as well as the lower, or inner sash, for better circulation of air. Sadly in many of these windows the cord has broken and the weight has fallen, and the upper sash is now fixed permanently in position.

Making a traditional window then involves making the casing that will hold the sash as well as the two sash that will run in it.

The moulding planes that were used in making window sash in the Victorian period in Central Canada seem to have been of the two piece variety, in which what were effectively a moulding plane and a rabbet plane ganged together to cut in one pass both the rabbet where the glass would be set and the moulding that were go to the inside of the window .

These two-piece planes were joined by screws that allowed the plane to be slightly adjustable to the thickness of the stock.

The window sash was essentially an open wooden lattice frame with wide stiles and rails (the outer frame) and narrow inner bars, all connected with mortise and tenon joints. The stiles and rails are moulded on the inward facing edges to form a rabbet for the glass to the outside of the room, and a decorative moulding to the inside of the room. The narrow bars to the interior of the sash are moulded on both edges.

Here is a sketch of a sash if it was made without moulding the components:

Now this simple version of a framed lattice would not work as a window because there is no rabbeting of the frame members to receive the glass. The decorative moulding on the inner side of the window is not essential to the function of the window, but it is nearly universal, and since our sash planes are two piece, it will be cut anyway and so has to be accomodated.

Therefore in laying out the mortise and tenon joints we have to assume that the "shoulder" of the joint will lie further into the stock than in the simplistic unmoulded example. The length of sash bar between tenons will have to be longer then in the simple model.

In other words in laying out your framed lattice you pretend that the quarter round moulding of the sash doesn't exist, and cut the morises and tenons as if the moulding will not be there. Then to assemble the sash properly you have make some kind of accommodation for the quarter round moulding at the shoulder of the tenon.

In general it is best to lay out and cut the joinery first, and then do the moulding. Laying out and cutting mortises and tenons on moulded stock is not impossible, but difficult and prone to error. The following illustration compares the unmoulded and moulded versions of a sahs bar: