Building a Bookshelf...

Hi all...
I am going to build a bookshelf out of 3/4" MDF. I am not a wood worker by any means, but this seems relatively easy. It will be approx 3' x 3' with three shelves.
I plan in screwing it together (as opposed to nailing and glueing).
My question is two fold. 1) Would 1 1/2" wood screws be adequate? 2) Should I use glue anyways with the screws.
Thanks
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I wouldn't rely on the screws alone - they are not meant to take a shear (sideways) load and MDF is pretty flaky when it comes to holding a screw. If you can, get some 1/4" dowel rod and use that along with glue and screws. Also, pre-drill the screw holes with a drill bit several sizes smaller than the screw OD or you'll possibly end up splitting the MDF apart. 1 1/2" long screws should be fine.
If you want to use the dowels to carry the actual load, cut the dowel into 1" lengths, drill 1/4" holes in the ends of the shelves and into the mating sides about 1/2" deep. Use wood glue in the dowel holes to help hold it all together. Then the screws' only job will be to hold the joints together, the dowels and the glue will do the real job of supporting the weight on the shelf.
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I would recommend going to a local lumber yard and having them cut the pieces from a piece of 4x8 3/4" plywood. You should draw how you want it cut to use the wood effectively and minimize the number of cuts since they often charge by the cut. For example you could have them cut it into 4 pieces about 1 foot wide by 8 feet long, then cut these the right length for the shelves and sides. Screw together with 2 1/2 inch deck screws. If it wobbles too much side to side then add some corner braces.
MDF will sag with time and does not hold screws well. There are some nice plywoods with veneered surfaces you might consider. You can buy rolls of the same wood to glue to the front surfaces if you want to make it look classier.

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Skip the MDF. It is good for things like speaker cabinets, but not for a weight bearing structure. It has too much flex. Plywood or regular lumber is much better. I'd use both glue and screws, or, use glue and dowel instead of screws.
There are ways of stiffening a structure such as a long shelf. If you we to cut a strip of wood (or plywood) and attach it 90 degrees to the shelf, glue and screw it, you will have much more strength.
Can be oriented either way |___________
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Jonny wrote:

It sounds like you just want butt joints. Forget the MDF. If you put any weight on those shelves the whole thing will collapse. You need 3/4" plywood or real wood. If you want something you can take apart (assume so by your insistence on screws), you need supports 3/4 x 3/4" strips under each shelf end. Directly screwing through the side and into the shelf will not be satisfactory (that means it will eventually collapse).
Answer to you questions, make the screws long enough that they are 3 times as long as the first board they go through. Glue on butt joints won't do much good. So, no, you don't need glue, you need supports under the shelves.
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George E. Cawthon wrote:

I would add a 1 x 2 support under the shelves and there are screws specifically for particle board (coarser thread)
Depending on the finish desired you can use the finished melamine shelving to build the thing. If you get a piece with predrilled holes for shelf supports the whole thing is a preety quick job.
I would not use 3/4" for the shelves. I would use 1/2" and add a support of solid timber.
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I guess I failed to mention that within each shelf there will be horizontal divider/support. 2 on the top, 1 in the middle and then 2 more on the bottom. I am assuming that will be more then enough to take the load and I shouldn't need to use the 3/4" strips under each end.
I don't plan on taking it apart, I just thought that screws would be better then nails. Is it recommended that I use the dowels to carry the load, now that everyone knows there will be additional support :-)
Thanks to all who replied.

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George E. Cawthon wrote:

Nobody seems to have mentioned the most important part of shelves -- the Back. The back keeps the shelves square and serves as triangular bracing. (It always amazes me that people seem to have forgotten about triangular braces and think that strong joints will somehow make up for it!)
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Good point. I like to use a 1/4" plywood sheet for the back and it makes it very rigid. If the shelves are not movable/adjustable, you can screw or nail the back to the shelves to add some support against sagging.
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