Help bracing large frame.

[Fxguy]

I have a very large picture frame that’s made out of 1/2” mdf. It is made of three pieces that are 27 1/8” tall x 114 1/2” wide. The joints are biscuit jointed along the long edge, but when lifted they have a lot of give. I was thinking of bracing with some 1x3 down the length of the joint but don’t know if the vertical should be solid or the horizontal brace should be solid. Or if I should cross brace with 45’ angles. Any suggestions?

 

 

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[Barron]

I am having trouble understanding the problem. Is the frame a triangle? Or a rectangular  frame made with three 1/2” thick pieces laminated together to give 11/2” thick sides?  And when you say it has a lot of give, does that mean the joints are opening?

[JohnG]

Definitely need some pictures for clarification.

[Coop]

I would use something similar to these. It will brace all corners and not extend from the wall as much as you propose. Probably the largest you can find for a frame that size.

https://www.lowes.com/pd/National-Hardware-5-22-25-in-Steel-Zinc-Plated-Corner-Brace/1000390925?cm_mmc=shp-_-c-_-prd-_-hdw-_-google-_-lia-_-145-_-doorandhomehardware-_-1000390925-_-0&store_code=1053&placeholder=null&gclsrc=aw.ds&&gclid=CjwKCAiA1L_xBRA2EiwAgcLKAzcfZOnXpDP4gOYfpVxjv4pWD8svI2eTPfFZN3yTKjYu6IqietIGZhoCd2cQAvD_BwE

[wtnhighlander]

How does one cut 114 1/2" lengths from MDF that comes in 97" x 49" sheets?  Do you have a source of special material, or is that a typo?

[Fxguy]

Not a typo. I had to have my local wood shop special order 2 10’ pieces of mdf for it. The picture below shows 2 pieces on top of each other. The finished frame is three pieces, so two very long biscuit joints that run the horizontal length of the frame. This is all for a gigantic jigsaw puzzle, the lower half of which can be seen in the photo.

[Isaac]

I would go with some vertical material, regularly spaced. If I understand, you are trying to make a 7' x 10' panel. The problem is that it will be prone to breaking somewhere along the length. if you ever set this on a normal table, you will likely have several feet extending out without support, which can cause a lot of stress. You need more strength in that transverse direction. You could run a series of 7' strips, spaced at 12 or 24" on center, along the back. That would greatly increase the strength. It may also start to give you something to use to mount this thing, as the MDF may not be strong enough to hold fasteners for most conventional ways of hanging something very heavy like this. What do you have in mind? A French cleat?  

[Fxguy]

Ok, so more important to run the bracing perpendicular to the joint. Yeah, we had it laying flat on a table and I had 3  1x2 strips under it to help keep it solid. Hadn’t thought much about the logistics of hanging it other than the thing weighs a ton! I like the idea of a French cleat between the bracing strips. Should distribute the weight nicely and allow for multiple studs to hold it. 

[Isaac]

The French cleat would also serve to brace it in the short direction, which isn't a bad thing. 

[wtnhighlander]

Isaac is on the money. MDF in the dimensions given, has a high risk of breaking under that sort of load. If possible, I might even consider a torsion box of thin (1/4 or less) material as a backer.

[Barron]

Thanks for the clarification. Even a backer of 1/8” ply would give a lot of support. It would still flex, but wouldn’t break.