Plywood selection

[Eric Bong]

I'm getting ready to build a fairly large built in entertainment center and I would like to use straight grained oak plywood. Unfortunately, the only riftsawn/quartersawn "plywood" that I've been able to find locally is MDF core. This makes me nervous as I've never used MDF as a structural element. I'm assuming that it would be ok for all the vertical sections of my cabinets. The horizontal surfaces(like the cabinet top that holds the 100 lb TV) concern me the most. I'm also assuming that biscut joinery is completely out of the question. Any thoughts? I have attached a pic of my 2D plan (sorry just starting to learn SU)

http://i244.photobucket.com/albums/gg12/ernmere/Home%20Improvement/EntertainmentCenter3.jpg

[Ed Peters]

You could always double up the underside with a less expensive piece of plywood as it appears that it would be concealed by your face frame. Honestly though, the spans that I am seeing do not appear to be candidates for bowing.

Ed

[Eric Bong]

Other than sag, is there anything else that I should be concerned about using MDF core vs plywood core?

[Howard Acheson]

Here are some things to consider.

First, MDF is just fine for cabinetry but it is not as rigid as solid wood. I recommend you sign on to Woodnet and plug in the species, dimensions and weight to determine how much sag will be created by the TV.

http://www.woodbin.com/calcs/sagulator.htm

I suspect you will have to create some additonal support structure to hold the TV where the weight is concentrated in the center. Another step you should take is to make up your support shelf and raise it up on either end with 2x4 strips at each end. Then put the TV (or equivalent weight) on the shelf and measure the deflection. Remember, that constant weight will cause deflection to increase over time.

A second point is that biscuit joinery was developed in Europe to assemble carcass made from composition materials like particle board and MDF. It's the preferred jointery technique for MDF. In the shop I was involved with we used biscuits all the time for carcass and cabinetry.

The third point is that MDF is going to be very heavy. I would suggest you go to a specialty wood supplier and order some plywood that meets your needs.

[Steve Jenkins]

I don't see any problem with using mdf with your design. As for the weight of the tv it looks like you have a partition on each end and two in the middle to support the shelf. Shouldn't have any problem with sagging. Biscuits are great for carcass joinery.

[Jim Becker]

You can also put the screen on a wall mount that is secured to the back of the construction for a much better shadow line since you eliminate the stand. Even if the back is the MDF core, you can put some solid plywood behind it to add additional support for the fasteners of the mount.

I have a friend who builds cabinetry almost exclusively with MDF core material...and has for years.