Expert: Jamie Yocono - 12/2/2009

Question
Jamie,

I am building an approximately 10'w x 4'h bookcase, using solid oak 1x12 boards.  I am building it in 2 halves, each about 62"w x 49"h.  I plan the 2 units to sit side-by-side, atop a concrete-block lower-half-wall, and fastened against the 2x6 studs in the upper-half-wall behind the bookcase (this is an outside wall).

I am building each of the 2 sections with 4 verticals (i.e. divided into 3 vertical spaces, each about 19" wide).  I have cut cross-wise, 3/4"w x 1/4" deep dadoes in the top and bottom horizontal boards, and I am fastening the verticals into those dadoes, using screws and glue.  I built a jig, leveled, squared, and temporarily glued to my basement concrete floor, for holding the sections square after I assemble them with glue and screws.

I routed 1/4" deep by 3/8" wide rabbets into the back edges of all the horizontal and vertical boards, so that after assembly, each open space would accept a 19"w x 47.5"h x 3/4"t oak plywood backer board, to be fastened with glue and screws.  I used 3/4" plywood for extra strength in fastening to the wall studs.  In retrospect, 1/2" plywood probably would have been sufficient, and I also probably should have made the rabbets wider, to accept more of the thickness of the plywood, but this should probably work.

Finally, on all applicable sides of each vertical board, I have routed vertical dados, front and back, to accept metal shelf standards that will be flush with the board surface, and allow for adjustable shelves.  I have also bought 1x12 oak for the shelves (to be cut 3/8" narrower, because of the backer boards in the 3/8" rabbets at the back of the bookcase).  

I have three questions:

Q1) For assembling the vertical and horizontal boards, I am using #10, 2-1/2" long "self-drilling" stainless steel screws with square-bit screw heads.  Even though they are "self-drilling", I am pre-drilling the screw holes using a 9/64" twist drill, which appears to be larger in diameter than the screw shank, so that the threads should bite the wood without the screw shank binding.  However a few of the screws have still twisted off in the hard oak.  I tried bar-soap to lubricate the screws, and that helped, but it's still easy to twist a screw off, or strip the square head out.  Are there cabinet screws for use with hardwoods, which are heat-treated to prevent twisting?  Do you have any other recommendations?

Q2) I am assembling the horizontals and verticals for the 2nd section, and the verticals appear to have cupped enough that I cannot get them into the dadoes in the horizontal boards by hand.  I tried making a contraption using blocks of wood and clamps, to temporarily "un-cup" the end of a vertical board, and allow me to insert it into its dado.  I have not gotten it to work yet, but I was using workbench clamps, and I may have to buy smaller clamps.  In any case, do you know any tricks that are less clumsy, and less time-consuming, for temporarily "un-cupping" the ends of the vertical boards, so I can get them into the dadoes?

Q3) The cupping I mentioned above is also occurring with some of the shelf boards.  This will almost certainly make the boards not sit properly in the adjustable shelf brackets.  I could perhaps be convinced otherwise, but at this point I don't think I want to mess with plywood shelves and the attendant veneer gluing that would be required on the edges.  I am thinking of a couple other options:

A) My first choice would be to not use oak for the shelves, but instead try to find a strong polymer material (3/4" thick, black Corian would be ideal, if it were available) that I could use for the shelves.  Is there such a material that isn't exorbitantly expensive?

B) My second choice was to get some polished brass (or aluminum) angle, cut to the same length as the shelves' width, and screwing the small angles to the ends of the shelves, to remove the cupping and allow them to sit squarely on the adjustable brackets.  However this is probably very time-consuming, not to mention expensive (brass angle is not cheap).

Can you comment, especially on A) above, and/or make better suggestions for correcting the shelf cupping?

Thank you for any help you can offer.  I hope answers to these questions are helpful to others, and I think they should help if I endeavor any future projects like this one.

Bob


Answer
Bob,

Let me answer your questions as you asked them, and then I'll go into a couple of other things.

Q1) I buy all my screws from MeFeeleys, I use square head screws, too. Here's a link: http://www.mcfeelys.com  They have a page where you can search for screws by different applications. There is a place on their site where you can search for the correct fastener to use. Better yet, I suggest you call their tech support department and ask them what screws they would recommend.

I used to break screws fairly frequently, but have found that a combination of several things have made that a problem in my past. Proper pre-drilling, lube, good screws, and an impact driver all combine to make breakage a thing of my past. I think breaking a screw is a matter of developing a good "touch" with your driver. If you're heavy-handed, you'll break the screws, regardless of how good of a screw you're using. So try to develop a better technique when sinking a screw. Not to be harsh, but I think the problem might be your technique, not the screw.

Q2)Clamps should totally allow you to pull the vertical boards flat and screw your components together. I couldn't really figure out if the gap (when screwing each side together) was on the two outside edges, or in the middle. But either way, you should be able to use a couple of long bar clamps across the width of the piece to pull it flat. Install the screws, and then re-clamp and draw the other edges up.

Q3) I'm going to roll all of these questions into one answer. The problem is using wide solid wood boards. Even though you have a board that's 12" wide, that doesn't mean you should use it. Solid wood cups, and to minimize that movement, you need to rip it into strips, and flip every other board, so that the annual rings are oriented opposite of each other. I would rip a 12" wide board into three pieces, and flip the center rip over (end for end) so that you keep the grain all running in the same orientation. If you look at the very end of the board, you would see that annual rings are in the same direction on the two outside pieces, and opposite that direction on the middle board. So... (for example) - up, down, up.  This will minimize cupping.

The brass or aluminum angles are a bad attempt at correcting this problem. Once again, if you rip the wood and reglue it in the proper orientation, you should
eliminate most of the cupping. The only problem is that when you rip and re-glue these boards, you'll have to plane them. Which will make then thinner. Bad idea for a shelf. I suggest you put a piece of wood (vertically) on the front and back edge of your shelves. A 1x2 would work fine, and will stiffen up that board so it won't sag. When you install your shelving verticals in the sides, make sure you locate them so that they don't interfere with the vertical pieces.

This bookcase has some material problems, in the wood and the screws. But I think the bigger issue is a matter of design and technique. Using solid wood components presents a big problem, as you've discovered. Cupping is a problem, but so will seasonal movement, meaning that those boards will shrink and swell with humidity changes. I think plywood would have been a better material to use for the carcass, and solid wood for the shelves. As far as dealing with the plywood edges, more woodworkers are using solid wood edging rather than veneer tape. It's durable, and much easier to use, since it can take a bit of sanding.

Finally, the metal adjustable brackets are a little old fashioned for a piece like this. Maybe old fashioned isn't the word I want. Crude? Old technology. More cabinetmakers are simply drilling holes into their cabinet uprights and using shelf pins to support the shelves. In fact, if you drill your holes carefully, you can go completely through the interior vertical dividers, so that you're drilling the holes for the the shelves on both sides of that support. Here's the exact device I use - it's expensive, but it works like a charm: http://www.veritastools.com/Products/Page.aspx?p=163

Cupping problems are mostly from solid wood. That's why plywood is a good choice. Don't be a wood snob, cabinet grade plywood is a perfectly good material to use. And it solves so many problems.

Here is a good site for calculating shelf thickness: http://www.woodbin.com/calcs/sagulator.htm

Hope this helps, write back if you have more questions, or if you want to expound of something that I've written.


Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV
www.wooditis.com
My woodworking blog: www.wooditis.blogspot.com