Carpentry and Woodworking - Using MDF for Bookcases

Application is a bookcase with 1/2" (maybe 3/4") sides. Inside width will be about 30", depth will be about 10". Floor mounting, with bottom shelf, two inner shelves, and a top. I'm leaning toward 5/8 or 3/4 for everything, but it's so heavy and I tend to overengineer everything - any ideas here?

Shelves would slide into dados (for practical experience with the table saw). Alternatively, shelves would rest on wooden or metal dowels poked into holes I would predrill into the sides (for more flexibility later on.

I don't want the shelves to sag after loading them with books.

I don't have a lot of money for this first-time project, so hardwood is out of the question. I was thinking about either MDF or plywood.

1. Which would be better for the sides shelves?

2. I can buy a cheap ($35) dado at Lowes for my table saw. If I make grooves to hold the shelves, how deep and how wide can I make grooves in MDF that would support the shelves?

3. Is MDF easily "dado-able"??

4. How deep and wide for the grooves if I use plywood?

5. How thick MDF or plywood should I use?

6. If I use dowels (or those little plastic or metal shelf mounts that twist into holes), how deep should the holes be?

Sorry for so many questions, hope somebody can give me a bit of help or comments, ideas...

You would definately need to go with 3/4 MDF and yes, it will weigh a ton when you are done. MDF is very heavy. 30" wide shelves will eventually sag under their own weight, let alone the weight of anything you put on them. So you will want to glue and nail faces onto the front of the shelves, and maybe even the backs.

To allow for future positioning of shelving, you will often see the sides predrilled with shelf pin holes. In fact, you can buy melamine that already has the holes in it. I use a Veritas shelf hole drilling jig.

MDF dados very well, but it's also hard on blades. You'll have no problem with it, but if you were doing it 365 days a year, your blades would get dull in a hurry.

If you are buying an adjustable wobble dado blade, you will want to test the fit on a scrap before cutting all your dados. You want it to be snug, but not so snug that you have to club the piece in order to get it to fit. And not so loose that you can feel play. Your dado should be between 1/4" and 3/8" deep when using 3/4 MDF. MDF will split when nailed through the endgrain, so keep that in mind if you nail anywhere.

For the shelf pins, there are several sizes to choose from, but generally the holes should be no more than 3/8" deep. You would want a stop collar and a brad point drill bit to drill those holes.

I second what XSleeper said, and add that cutting MDF makes an enormous amount of dust. So take appropriate precautions for your respiratory system.

Thanks for your reply.

I forgot about nailing through the endgrain. I'm beginning to believe that making it with plywood (one good side) might be a bit better for me at this point.

What thickness plywood would work (you mentioned 3/4" for MDF) for the sides and for the shelves?

The dado set I was looking at was not the wobble style, rather two outside pieces and a variety of inner diggers.

Thanks again for your help, also to the other gentleman who mentioned dust. That's definitely another disadvantage of MDF.

I'd still suggest going with 3/4" AC ply throughout.

Not sure I understand - your first reply to me didn't mention anything about plywood, just MDF, but your 2nd reply said, "I'd still go with 3/4" plywood." Did you mean MDF?

>>I'm beginning to believe that making it with plywood (one good side) might be a bit better for me at this point.
>>What thickness plywood would work (you mentioned 3/4" for MDF) for the sides and for the shelves?

Your last reply asked one question, quoted above. In answer to that, I would recommend that you stick with something 3/4" thick. Plywood, if that is what you decide to use. MDF if you go that route. I would not use any material that is smaller than that.

Home Depot sells a 3/4" poplar ply that I have had much success with, working on cabinets and other applications. Very easy to work with, and is a nice finished product.