PROJECT: Slab-built Bookcase

PROJECT: Slab-built Bookcase

River tables and live-edged furniture are immensely popular, but I’ve been thinking about other interesting ways to use a slab in a more non-traditional way. Slabs can offer spectacular grain patterns and more character than you’ll often find on typical dimension lumber, because they’re frequently sourced from trees that aren’t part of forests that are periodically logged.

Since this sturdy bookcase has fairly simply styling, I thought resawing a unique slab might provide a chance to spice up the design with thicker components, showier grain and distressed figure. So I went to a local sawmill and selected a slab of red elm — it’s a species you won’t find at many lumberyards. I think its strong grain pattern, natural defects and warm color look great. The large box joints on the corners of the carcass complement the bookcase’s black, stocky base to give the project a contemporary look. Here’s a design that should work well with many home decors.

Selecting the Slab

When I had my piece of red elm picked out, I made sure to take note of its moisture content. Material around 12 percent or less moisture content is ideal for furniture building, and mine was dry enough for immediate use. The slab I bought was 7 ft long and about 14″ wide. I checked for any embedded metal objects with a metal detector and then rough-cut the plank into three sections that were about 26″ long.

Rockler slab flattening router jig
Rockler’s Benchtop Slab Flattening Jig features a reinforced plastic router carriage with ergonomic handles that slides along pairs of aluminum cross rails. A clear acrylic baseplate (not shown) attaches to the router carriage and is predrilled to fit a variety of mid-sized routers. Used in tandem with a spoilboard surfacing router bit, such as the one shown at left (sold separately), this setup and your router will make quick work of many smaller slab-flattening tasks.

I sized my pieces, in part, to fit into Rockler’s soon-to-be-released Benchtop Slab Flattening Jig. It fits workpieces up to 18″ wide, 28″ long and 1-3/4″ thick. My slab was about 2-3/8″ thick and had a slight crown to it, but that was no problem for this slab-flattening system. One of the unique features of this aluminum-railed jig is that it can be shimmed up to any height to match the thickness of the slab for surfacing. I raised the jig by inserting strips of 3/4″ MDF under its rails on top of the jig’s MDF substrate.

Flattening Both Sides

Creating risers for slab flattening jig
While this Slab Flattening Jig is intended for slabs up to 1-3/4″ thick, it can be raised higher with spacers for thicker slabs, as the author did here.

When preparing a slab for flattening, it’s important to stabilize and secure it to the jig’s MDF or plywood substrate so it can’t shift. I used a combination of shims and blocking, hot-glued to the substrate and the slab sections, to lock things down.

Prepping slab for smoothing process
Be sure to shim and secure the slab so it won’t shift during routing.

With a 1-1/2″-diameter carbide-insert spoil bit installed in my mid-size router, and the router mounted to the jig’s reinforced plastic router sled, I was able to easily remove the rough surface of the wood and eliminate the cupping/crowning. The process to flatten a slab in this jig is simple: Slide the router carriage back and forth on the jig’s aluminum rails, taking off about 1/8″ of material or less of thickness at a time.

Running router over wood surface with flattening jig
With the router set to remove about 1/8″ of material thickness, flattening a slab involves sliding the router carriage back and forth slowly in side-by-side passes from one end of the slab to the other.

After one side is flat, you could flip the slab over and repeat the flattening process to create a second smooth face. That might be really helpful if you don’t own a planer. But since I do, I ran the slab sections through my planer at this point with the flattened faces down to reduce their thickness to 2-3/16″. This way, I could resaw them to achieve the 1″ stock thickness I needed plus account for the material lost to the blade kerf and a bit of cleanup.

Checking flatness of wood slab surface
Once you’ve completed the process, you will be left with a dead-flat surface.

Once the faces of my slabs were flat, smooth and parallel to each other, it was time to work on their live edges. At the table saw, I used Rockler’s Straight-Line Rip Hold-Down Clamps attached to a plywood sled to rip one irregular edge off of each slab. I cut the opposite edges off using the rip fence, leaving each piece about 1/2″ wider than the Material List dimensions. I squared up their ends at the miter saw and kept them a tad overly long.

On to Resawing, Gap-filling

Prepping resaw cut of thick slab on table saw
Starting an ambitious resaw cut at the table saw is one way to reduce the amount of material that a modestly powered band saw must then cut through. Square both workpiece edges first.

It’s sometimes easier with modestly powered band saws to first begin a resaw cut at the table saw, making a deep cut into both edges. That’s what I did here, which reduced what would be left for the band saw to finish up.

Finishing resaw cut with band saw
Even though the rip fence on this Laguna band saw isn’t in view (the tall workpiece obscures it), it’s supporting the opposite face of the slab section to help guide the cut along the line the author marked on top of the workpiece. A tall featherboard presses the slab against the fence to also help keep the cut on track.

After making the table saw cuts along the slab’s centerlines, I took them over to the band saw and split them the rest of the way, turning three thicker pieces into six thinner ones.

Tools for smoothing rough cut lumber
Once a resaw cut is completed, the roughsawn faces can then be smoothed in a surface planer. If you don’t own one, however, a belt sander or bench plane can do the job by hand, too.

I cleaned up the six sawn faces with one more pass through my planer, which brought them all to 1″ thickness. But you could use the flattening jig instead, or even a belt sander or a bench plane. It’s up to you. The important thing is, make sure the stock thickness for the bookcase’s top, bottom and sides match.

Setting dado blade cutting depth
The author set the height of his 3/4″-wide dado blade just slightly above the 1″ thick bookcase stock so the box joint pins would be cut a tad proud.

One of the reasons I selected this slab was because of the unique cracks and voids in it. I filled those defects with a black tinted epoxy designed for this application.

Adding spacers before making dado cuts
A second wood key served as a spacer for indexing the box joint jig’s fixed key the correct distance away from the blade during setup.

After a few hours of curing, the epoxy was ready to sand flat, which I did with my random orbit sander. Then I trimmed the bookcase’s top, bottom and sides to final size.

Cutting Box Joints

Making initial box joint cuts for assembling bookshelf
A pair of slot cuts, made by flipping the bookcase top and bottom panels edge for-edge and fitting them over the jig key create the irregular box joint pattern.

This bookcase features an irregular box joint pattern on the corners to add some visual interest as well as strength, since the project has no back panel. I cut my box joints using the old tried-and-true shop made “miter gauge” jig. It consists of a piece of 3/4″ plywood attached to my miter gauge’s fence with a 3/4″ x 1″ wooden key installed in a notch in its bottom edge. I chose a piece of plywood measuring roughly 12″ x 16″ for the jig fence — it was large enough to provide plenty of vertical and horizontal support for these large bookcase components, particularly when two of them need to be standing side by side on the jig for cutting the box joints. With a 3/4″-wide dado stack installed in the table saw, I set the height a hair above 1″, so the pins of the joints would extend just a bit past the workpiece faces when assembled. (I think it’s easier to level those flush than have the pins come up short and need to plane the whole faces of the parts instead.)

Box joint cuts with marked up lumber
Then these panels act as indexes for setting up the first slot cuts along the edges of the side panels.

I cut a 3/4″ slot through the edge of the jig’s fence, about halfway along its length, for the wooden key. Then I made up a piece of 3/4″ x 1″ key stock about 4″ long. I cut it in half and installed one piece in the jig’s notch so it was flush to the back face of the fence and projected outward.

Masking tape drawn out to lay out box joint cuts
Two more slot cuts create the outer pairs of pins that fit in the top and bottom panel slots. The inner slot cut being made here also defines one inside edge of the 3″-wide center slot. Masking tape helped the author keep this tricky pattern clear.

To prepare the box joint jig, set the second key against the first key on its left side (looking down from above) to act as a spacer, and place the jig fence against the miter gauge fence with the miter gauge in your saw’s left miter slot. Slide the fence assembly over so the spacer key touches the right side of the dado blade. Holding it carefully in this position, fasten the miter gauge to the box joint jig with several screws driven through both fences. Then remove the spacer key and cut a second notch through the jig fence. The distance between the jig’s key and the blade must match the width of the blade precisely, or the joints will be difficult to assemble. Accurate setup is really crucial here!

Making second set of box joint cuts
After making the necessary slot cuts on one side of the bookcase side pieces, flip them over, edge-for-edge, to repeat the three cuts in from the opposite edge.

I used masking tape to lay out my box joint pattern on each of the bookcase’s top, bottom and side workpieces to help avoid confusion — no room for mistakes here on one-of-a-kind lumber! The tape layouts are merely visual guides, not exact templates for cutting.

Cutting out middle box joint pins
Then remove the last of the inner waste in side-by-side passes to complete the wide center slot.

As you can see in the Box Joint Layout Drawing, the 3/4″-wide pins are spaced between 3/4″-wide slots, and there’s a 3″-wide “pin” in the middle of the pattern on the bookcase top and bottom panels. I cut the joints on the ends of the top and bottom panels first, indexing each slot cut by fitting it over the jig’s key. Notice that you cut two slots in from each edge of these parts to form two thin pins. What’s left in the middle is the wider pin. Once the top and bottom panels are cut, use them to index the first slot cuts on the edges of the bookcase sides. It’s typical box-joint cutting procedure. Finish cutting the wider center slots by removing the waste in several passes.

Assembly Time!

Test fitting bookcase joinery
If you do a careful job of setting up the box joint jig initially, these joints should slip together without needing to be pounded home or showing extra gaps. However, if this is your first attempt at making box joints, be sure to test your jig setup and the entire cutting sequence on scrap stock first.

With the tricky step now behind you, dry-fit the corner joints to make sure they slip together — if you made the jig correctly and worked carefully, they will!

Clamping up parts of bookshelf
Assemble the bookcase’s carcass with glue and plenty of clamps so the joints close fully.

Then I disassembled the carcass, gave all four parts a finish-sanding up to 220-grit and brought them together one last time with glue and clamps. When the glue dried, I flattened the protruding pins with 60-grit abrasive in my random orbit sander, then finish-sanded those areas again.

Sanding down joints after assembly
Flatten the protruding pins of all four joints with a sharp hand plane or with 60-grit sandpaper in a random orbit sander. Work up through the grits from there to 220. To avoid scratches, don’t skip grits.

I wanted the bookcase shelf to be adjustable, so it was time to pull out my Rockler shelf pin jig and drill/driver to bore the 1/4″ shelf pin holes. Make sure all the rows of holes you drill align with one another so the shelf will sit evenly.

Drilling out pin locations for installing shelves
Bore two rows of shelf pin holes into the inside face of each bookcase side. A shelf pin drilling jig like this makes the task easy. Masking tape can help avoid accidentally drilling too many holes.

The base’s legs and short and long stretchers are simply 1-1/2″ x 1-1/2″ stock joined with pocket screws and glue. Since I would be painting the base, I just milled down economical 8/4 poplar for these parts. Once you’ve got the components cut to size and shape, fasten pairs of legs to each short stretcher with glue and pocket screws, orienting the pocket holes so they’re inside the base where they won’t be seen.

Assembling base for bookshelf
Poplar is a sturdy paint-grade hardwood for this bookcase’s base. Assemble the legs and stretchers with glue and pairs of pocket screws at each joint. Orient the screw pockets to hide them.

Then join these base end subassemblies to the long stretchers, again hiding the pocket holes on the back sides of the parts. When the glue dried, I sanded the base and brushed on two coats of General Finishes Lamp Black Milk Paint to wrap up its construction.

Finishing Up

Attaching base to bookcase carcass
Paint the base and apply a topcoat to the carcass and shelf before attaching the base to the carcass with 2″ screws driven into countersunk holes.

This bookcase will receive lots of use in my busy home, so I opted to finish the carcass and shelf with a hard wax oil. It’s easy to apply by hand, and it buffs beautifully to a soft luster. It’s also easy to repair down the road by simply wiping more finish on again.

Once the paint and finish thoroughly dried, I bored 1/4″-deep countersunk holes into the bottom of the base stretchers, centered the base on the bookcase’s bottom panel and fastened the components together with 2″ wood screws.

Now grab some metal shelf pins and install the shelf at a height that works for you. I hope you’ll enjoy this rugged and attractive bookcase as much as I do!

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