Adding strength to a frame/

[johnnymachin]

Hello,I need a few ideas on strengthening a fairly large frame.
I've just framed an old map for a commercial job(130w x 70h cm). It's going to have springlock security fixings(hang plates at the top,lockable bridge at the bottom).
Because of the moulding chosen and the width,it just doesn't feel quite as solid as I'd like.
Does anyone have any ideas for adding strength to the back of the frame?
Any ideas much appreciated.

Cheers,Johnny.

[GeoSpectrum]

Something like this might do. http://www.screwfix.com/p/angle-plates- ... 1914888464

[Abacus]

I usually put a baton across the back half way along the long edge secured with mirror plates or t plates, this stops the longs from Bowing.

[GeoSpectrum]

Same here. I use pine painted or stained to match.

[prospero]

I've sometimes used strips of MDF screwed to the frame. They make it surprisingly rigid.

Angle plates are a good idea, but I would use 3" ones on a frame that size. A handy tip is to place the plates on a piece of wood - face side down - and give them a wack with a ball-headed hammer on the corner. This will bend them slightly and make it so that when the screws are tightened they will apply a tiny bit of force to grip the front of the join together.

[IFGL]

I have also used strips of mdf in the past, these days I just use the whole sheet and cut it 5 mm shorter than the external size of your frame , just screw into place, use whatever thickness you think will give you the right balance, but even a 3 mm sheet will add a good amount of rigidity. ( tip was from Pete bingham a few years back )

[prospero]

I've used the method of fixing the backing board to the frame in the past. Mostly for shallow rebate reasons rather than strength. Never done it on on anything large.

One snag: If the board expands it will either bow out or break the frame corners, depending on which is the stronger. Sealing the board with PVA will help prevent this.

[johnnymachin]

Thanks for the tips everyone. The strips of MDF seem to have sorted it out.