Thread: Arched door jambs

Must be getting old - I can't visualise what your describing, any chance of a sketch to give us a clue - please!

Personally I'd go for either a simple butt joint or possibly a small rebate.

The standard method is to use a simple butt-joint with the tops of the vertical jambs cut at an angle to accommodate the arch's curve as closely as possible. The arched section is fitted first, spanning the full width of the opening and being tacked to the frame at several locations along it's length.

The vertical jambs are then cut to size and fitted.

Trying to do a mitred joint is finicky, time consuming and often goes wrong. Especially considering that after the architraves are fitted, you see very little of it... and that you need to get it right the first time, unless you have a whole slew of extra wood and time on your hands.

I like the idea of a rebated joint - as I imagine anyone who enjoys woodwork would do - but, like the mitred joint, it'd be fiddly to get right.

There's really no physical need for structural strength at that joint; like your architraves, it's basically just trim.

Even if you're hanging doors, it's only a case of firmly affixing the vertical jambs to the frame. Any load transferred through that joint to the upper section means you're doing it wrong!

we have rebated a strip into the two sections and glued on bench before installing with tempoary ply nailed to hold it together while installing

How about rosettes at the junctions? Square blocks with turned patterns, similar to those shown here: Grizzly.com

Turn your own, or use a dedicated cutter for uniformity. They're often used at head/jamb intersections to eliminate fiddly miters. Similar to crown molding, they hide misfits of underlying material. Make an eyesore into a feature.

Cheers,
Joe

Originally Posted by Hesk

Can anyone tell me which is the best way to join a arched top jamb to the vertical section of the jamb. I have 4 archways that I'm installing jambs and architraves around. I am laminating the arch and am wondering which is the best way to connect it to the straight jamb. I have three options a butt joint, rabbit joint or a mitre. A 45 deg mitre will be ok for the architraves, I'm not sure about the jambs. Any suggestion and tips would be appreciated.

Hi Hesk
you've prompted me to pull out a copy of George Collings' Circular Work in Carpentry and Joinery. If the vertical posts are wide enough (say >120mm) then cut a double tennon on their ends and fit into a mortice cut in the end of the curved section. (if the verticals are not that wide use a single tenon) Draw the joint together with a handrail (or barrel) bolt from the unseeen side of the joint.

Importantly, the spring line (the line where the vertical post joins the arch) should be horizontal

I rember working on a very old Government building many years ago and all the heads were joined to the stiles with finger joints. The must have had plenty of time when the building was first built about 1900 I would think.
Rowley.

I woiuld go for a tongue and groove. Cut a groove in both peices and glue with a loose tongue.

Originally Posted by Ken-67

I woiuld go for a tongue and groove. Cut a groove in both peices and glue with a loose tongue.

Originally Posted by Rowley

I rember working on a very old Government building many years ago and all the heads were joined to the stiles with finger joints. The must have had plenty of time when the building was first built about 1900 I would think.
Rowley.

there's two main issues with curved transoms
1) aligning the pieces so that there's a smooth transition from the vertical style to the curving arch. If the opening has a fan light, the bottom rail (?) of the fan light conceals this transition making life much easier. Without a fan light care is needed to get everything aligned, hence the M&T

2) closing the joint. with a square opening you can wdege the styles off the sub floor so that the joint is tight, but if you do this on a curved opening you risk pushing the styles off vertical.
the traditional way to close the joint is to use a pair of alignment splines and a loose hammer head tenon tightened with wedges. Though Collings suggests that the wedges can dry and fall out so a hand rail bolt is superior