Bracing a Large Frame

[prospero]

One way which I have used in certain situations is to fix internal steel brackets on the inside on the frame.
Not really helpful in this case as you don't really have enough meat to screw into. Also you would have to rout a
shallow channel on the inside of the rebate to swallow the thickness of the bracket - reducing the meat even further.

The subframe is much easier. The way of attaching it depends mostly on how it sits in the outer frame. If it's well below the
back of the outer you can use bent mirror plates. Lion do some very handy thin bendy ones. These also allow a bit of 'give' to allow
for and expansion/contraction between frame and subframe. If it is flush or protrudes slightly from the outer fixing screws at an angle
is the way. You can get pocket screw jigs for this or just eyeball it. A jig will make life easier.

The Wessex subframe moulding is cunningly shaped to make screwing simple.

[Jamesnkr]

Mark's point about the screws not doing you any good is a very good point. However, you could fix this by sending them in the opposite direction. Countersink a hole for the screwhead on the outside of the frame, send the screws through from the outside to the subframe. Fill and finish in the usual way.
Yet another reason for hand finishing...

[prospero]

That's great James until you want to take the thing apart.

[Jamesnkr]

Prospero, that's almost certainly somebody else's problem, and they will thank you for the hours they can charge for it.

[markw]

After you have hand finished and totally disguised where the screws are - pity the poor sod who just cant get the frame apart. Possibly more amusing is when it comes back to you and you cant remember where you put the screws.... maybe a note on the subframe indicating where they are?

[Jamesnkr]

Don't forget we're starting from a position where a frame has been made and it doesn't work. So either we start from scratch with some new moulding, or we come up with an engineering solution.

[prospero]

If you are in a position where you can only get a screw penetration of maybe 6mm the solution is to use fatter screws
and put more in. And don't over tighten them.

Remember, the outer frame is not under stress. It only serves to cover the edge and hold the glass in place.
The hangings should be on the subframe.