Glass Rebates, Mouldings, Mitres, and Assembly

Glass rebates

The glass sits in a rebate on the outside of each member. On Norwegian museum planes the glass rebate is about 9 by 6 mm, roughly 3/8 by 1/4 inch ¹. Cut it on the stiles and rails with a plough or rebate plane, working from the outside face.

Bars need a rebate on both sides. Heiberg and Renmælmo describe two ways: plough both rebates at once, leaving a thick tongue about 14 mm wide in the middle, or rebate one side at a time with a rebate plane ¹. Either way, hold the bar in a sticking board, a board with a groove that grips the bar, so the plane can run its full length.

Mould the profile

The room side of every member gets a moulding. The Trondheim profile, from the edge in, is a narrow fillet, a quarter-round ovolo, another narrow fillet, and a concave quarter-round cove ¹. On the bars the two quarter-rounds meet in a single half-round bead, so the bars are slightly narrower than the rails; the rail profile depth equals half the bar width, about 1/2 inch ¹.

At home you have three routes:

1. A sash plane that cuts the profile, from an antique dealer or a modern maker.
2. Hollows and rounds: a round plane cuts the cove, a hollow cuts the ovolo, and a rebate or shoulder plane cleans the fillets.
3. A scratch stock: a profile filed into a scrap of saw blade, held in a wooden stock and scraped along the edge. Slower, but it works on small parts.

Mould with each piece held in the sticking board, so the plane’s own body acts as the depth stop ¹.

Mitre the moulding

Where a bar meets a rail, or two bars cross, the mouldings must meet. British and American joiners usually cope them, scribing one profile over the other. Norwegian joiners normally mitre them instead ¹:

1. Cut back the moulding on the joint area of the rail to the depth of the profile, leaving the shoulder flat.
2. Mitre the moulding on both pieces at 45 degrees where they meet.

A Norwegian mitre chisel (gjæringsjern) or a wooden mitre template guides the 45-degree cut ¹; a paring chisel against a 45-degree guide block works too. A bar cut 45 degrees on both sides to a point gets its inner length automatically, and its outer length is that plus the rebate depth ¹.

Assemble

1. Dry-fit the whole sash. Check that the faces are flush, the mitres close, and the diagonals are equal.
2. Decide on glue. The pegs alone hold the joints, and a pegged mortise-and-tenon sash comes apart easily for repair ².
3. Drill through each corner and drive two square pegs, about 8 mm, from the inside face ¹. Square pegs driven into round holes bite at their corners.
4. Plane the faces flush, then bevel the closing edge of the stile about 8 to 10 degrees, as on the Stiftsgården sashes, so it opens and closes freely ¹.

Try it

Mould one length of scrap with your chosen method before touching the real bars. Mitre two pieces of it together. A tight mitre in the moulding is the detail that makes a sash look right.