Introduction: Footstool With Hidden Sliding Storage Compartment

About: My passion for making has blossomed and expanded since its inception. The ability to realize my imagination and work as a part of a group is the most empowering and satisfying thing I’ve done, and I’ve made i…
Welcome to my footstool instructable!  I hope you're in for the long haul, because this thing took some work!  I compiled my process through photos and text (edited several times) into what's hopefully a solid jumping-off point for your own adventure into small-scale furniture making.

The steps here are the ones I took, and certainly not the only ones possible, and I've done my best to break each step up into a brief version for those of you with woodworking experience, and a longer section explaining the step more in depth..  I had a great furniture-maker helping me out, and that was perhaps the best part of this project, the learning of new things and honing of my skills through someone who really knows what they're talking about.  Above all, I would recommend finding someone like this and getting them somehow to help you through the project.  It'll do wonders.

Now, that said, I also should disclaim myself from liability and say that I have no safety instructions in here, and nothing about how to operate or use machinery properly or safely.  That's your job as a user of a shop's equipment and the manager/monitor's job of the place while you're there.  So take a few minutes to learn the stuff if you haven't already.

Alright, alright, onto the project.

For this project, I used:

Materials
• wood (I used 6 2x4s @ 24in each)
• wood for the legs (4 pieces)
• wood glue
• plywood (seat)
• dowel (pegs)
• scraps
• upholstery cushion
• fabric
• staples (for staplegun)
• oils, waxes, finishing materials
• rags

Tools/facilities
• Jointer
• planer
• tablesaw
• bandsaw
• lathe
• router
• chop saw
• chisel mortiser
• chisels, mallet
• drawknife
• combination square
• marking gauge, pencils
• measuring tape
• clamps
• staple gun

And I'll throw in an outline of the process for reference:

1 - Mill yer wood!
2 - Laminate yer boards
- stick them together and glue 'em up
3 - Make the inner dovetail box
4 - Turn an' shape yer legs

5 - Outer box and leg joinery
6 - The seat
7 - Inner box movement
8 - Sanding & glue-up
9 - Upholstering


And now, ifyou're ready, let's get started...

Step 1: Boxes: Milling

Alright, so you've decided to soldier into hand-crafting furniture.  Awesome!  Let's prep the stuff we've got to work with.

I used leftovers from other projects for this thing: 2x4s from a friend's giant mustache bench and some cheap mahogany from my folding silverware set last year, as well as some scrap plywood and other stuff for later on.  That said, the principles apply to whatever you're using.

First of all, have a plan.  Duh, right?  Mine involved mainly sketching how the inner box would move and be hidden.  This initial drawing stage is key, and I had to revert back to it a few times when I came to something I hadn't thought of already.  So come up with a plan, draw it from all angles, make sure you know all about each part of what you're doing.  Mentally going through the entire construction process can be very helpful as well.

Onto the Instructable!

First things first: square boards!  2x4s of my length (just under 2 feet) probably won't warp too much, but better safe than sorry.  So place your pieces on a flat surface and poke its opposing corners, seeing if it rocks at all.  If it does, flip it over and try the other side.  Whichever rocks less or not at all is what you'll run against the jointer.

If you do know...

Joint a face and a side, plane the other face just until it's flat, and table-saw off the remaining face (you can use whatever is available to you, if you don't have access to the tools mentioned).  Mark a center point on an edge of each squared 2x4 and rip them on a bandsaw.  Plane those cut faces afterward to re-square all your boards.  Don't worry about the ends yet, we're cutting these all to size later anyway, so they'll get taken care of.

Done?  Boom, you've jumped through the photos and are ready for step 2!

If you don't know...

Head over to your jointer, turn on any dust collection system there is, and making sure it's up against the fence at all times, push the board through the jointer blades and check its bottom for flatness.  Depending on your warp you might need to do this a few more times.  Mine varied.

Next, put that jointed face up against the fence and even out one edge of each board.  Do that with all of your pieces (6 in my case).

Place all boards jointed-face-down and plane the opposite faces until there's no old wood showing.  It's a good idea whenever using a thickness planer to set the planer's height, send all the boards through, and then change the height.  That way everything is decreased in size evenly, and when one thing is correct, the rest will be too.  Waay less headache than trying to match each one individually.

Once they're planed, head over to a tablesaw to cut off the last untouched edge (a bandsaw with a wide blade would work, you might just want to plane all those edges together afterward to make sure they're even.  Keep as much width as possible, just slicing off the very edges of each board.

Mark the center of each board along an edge, line that mark up with a wide bandsaw blade and pull the fence right up against the board.  These boards are getting harder to hold through a blade, and bandsaw accidents can be scaary, so use push sticks to keep the board up against the fence and push it through the blade.  Do that with all the boards and plane all of the bandsawn faces, in sequence like before, to keep everything even.

Alright, onto step 2, where we'll line them up so they look purty, glue 'em together and clean 'em up into the boards we'll use for the rest of the project!

Step 2: Boxes: Laminating & Prep

Now, we've got 12 boards ready to be glued together.  Line up all your boards into panels, I had enough for 3 boards per panel, in whatever way you want.  Since you ripped them, you can book-match them, or make random looking panels.  I had some color differences that I stuck between the top and bottom book-matched boards and it came out pretty nicely.

If you know...
Glue your boards into panels, clamping everywhere necessary, wiping away as much glue as possible, and let dry overnight.  Scrape away as much glue residue as necessary, plane all boards to desired thickness (mine was 1/2"), and cut to length.  If you're following my plan, two should be longer than the other two.  I didn't provide measurements, because my footstool was specific to the chair it was going with, and I think it's valuable to plan out much of your own process as well.  Once you're glued and scraped and cut, head to step 3.

If you don't know...

Once your boards are arranged, you're ready for glue-up.  Since everything's square, your sides should all fit together flush and even.  My thicknesses weren't even, so I only clamped horizontally.  Usually, you can put more cauls (those 2x4s between the boards and clamps, to keep the clamps from marring the wood) on the tops and bottoms of your panels and clamp those too and everything should dry flat and even.

When gluing, set up and even dry-clamp everything to make sure the process will work as expected.  This case is pretty simple, but especially when doing complex glue-ups (like the final glue-up) it's great to take it slow and carefully to end up with a true and solid piece.

Once you're ready, brush glue onto the full edge of each board being put together (both edges of each connection).  I brushed the two edge pieces first, then the center piece on both edges, slid everything into place by hand and then tightened the clamps down.  Make sure all gaps between the pieces seal up, and remember: glue squeezing out isn't a bad thing; it means that seal is happening.

Have some wet paper towels or rags on hand to wipe all of that away.  If everything doesn't come off, no worries, we're going to clean these up once they're dry anyway.  If your board surfaces are even, put some cauls on the top and bottom of your panels and clamp those down too.

Once all your panels are glued and looking good, let them dry overnight.

Come back the next day, remove (and clean, if necessary) all of the clamps, and check out your panels.  Pretty cool, huh?  From six 2x4s to four panels, ready for a little piece of furniture.  Makes the mind wander, doesn't it?

For any dried glue on the surfaces, take a scraper and scrape off as much as possible.  Don't worry about removing a little bit of wood as well, since we're going to plane the boards after this step anyway.  Don't use a chisel or run these through the planer before cleaning off dry glue; those are for removing wood, and it will dull the blades very quickly.

Once the panels are well cleaned, set your desired thickness on a combination square and check your boards each time them come out of the planer to see how much more you'll need to take off.  Once everything is even and you're at your thickness, you're good.

Cut away both ends before you move on; the ends probably won't be flush, and 2x4 ends are pretty rough anyway.

Figure out how long each board has to be and mark them, using a square to mark your cuts.  Cut all four boards to length.  In my example, I cut all of the boards so I ended up with 4 shorter boards and 4 longer boards, two of those being even longer than the other two, since my stool is more rectangular than square.  Keep to your plan, if the boards seem small, remember you're fitting them into legs, so the stool will be a good size when everything is assembled.

Once you're ready, head on to step 3.

Step 3: Inner Box Joinery

Alright, you've got 8 boards now.  4 of those are for your outer box to be joined with the legs and contain everything.  Set those aside.  We're going to deal with the smaller ones for now.

These are for the sliding storage box inside the footstool.  Since there's downward pressure on this piece of the project, we're going to join these pieces together using dovetail joints.  Working like this with pine or a similar softwood is pretty difficult, as it really loves to split and break and isn't at all like chiseling a hardwood.

I didn't sand these pieces after the joinery was done, and once a box is together it's hard to get in there and sand it.  Since this is one of the main parts of the project that'll be interacted with, go ahead and sand those panels before you glue them together.

If you know...
Figure out your layout, mark and cut your boards, and chisel out the joints.  Apparently it's recommended with softwoods to keep the joints pretty steep, which I was told later by a friend.

Test-fit the pieces together and see how it looks.  I didn't keep this part of the project square, which didn't end up a problem, but was oversight and should be avoided.  If they fit well, make some cauls that push the correct parts of the joints and glue 'em together.  Measure your diagonals (corner to corner) to make sure they stay equal, ensuring a square box.  Once it's dry, scrape and sand off any dried glue.

If you don't know...
This is pretty simple.  A dovetail joint is a joint that can only be pulled apart outward, not in the direction in which any force on it will usually be pulling.  Therefore, we'll have the tails shooting upward, caught in their pockets, keeping them from falling out.  Obviously it'll all be glued, so there's really no cause for concern anyway, but it's cool to craft nonetheless :).

So, figure out which boards you want connecting where, keeping in mind about 2 inches will be hidden by the outer box when this one hangs out of it, so the top one doesn't need to be pretty.  If you have an ugly panel, maybe use it there to keep it hidden.  Once you're happy, I'd recommend marking and cutting out the pockets first (the top and bottom panels), because they're easier to scribe onto the other pieces.  But either way is fine.  3-4 joints on each panel is very adequate.

Mark on the end of the board, and on either side, down as far as the thickness of the board it's connecting to. [image 2]

Saw down your lines, keeping as straight as possible.  Then clamp the piece down onto a scrap piece of wood (so you don't ruin your work surface) and using a chisel and mallet, chisel out the area where the dovetail will sit. [images 3-5]

It's a good idea to chisel out half the pocket, then flip the board over and chisel out the other half from there [image 5].  You might even stay a bit away from your line to get the bulk of the material out, and then clean it up more carefully afterward.

Once that board is done, put its end onto its mating end in an L shape [image 9].  Keep all edges flush, and mark with a sharp pencil where they connect.  Mark all the way around again, to the thickness of your boards.

Put the new board in a vise and cut on the inside of each of those lines (the lines are just outside of where the joint needs to be.  If your cuts are too small, you've got something to shave away at until it fits).  It might help to clamp the piece at an angle and cut vertically rather than cutting at an angle.

Chisel like before: half on one side, half on the other.  There are router jigs for this, but it's good to know the hand tool method.  Besides, it's easier to do at home.

Once you've got a rough version, check the fit and see where it needs work [image 10].  Be gentle, take off little bits at a time, and take your time.  These joints will be seen.

Once everything fits, sand the things evenly until you're happy with their smoothness.

Cut some cauls from scraps that will clamp the piece only in the areas that will push the box together [image 13].  A straight caul will only push the pieces together until the edge is flush.  Your joints might be able to be tighter than that, so take the time to get it clamped and glued snugly.

Once those are ready, do a dry run to make sure everything will work.  Measure one diagonal once it's clamped and compare it to the other diagonal and see if they match.  If not, you can angle the clamps a tiny bit to compensate and make sure the box glues up square.  Get someone to help with this if you need it.  Glue-ups can be stressful, and help is awesome.

If it works, brush glue into the pockets of the top and bottom panels, and the cheeks of the joints wherever things will be coming together.  My documentation of this part isn't the best, but hopefully it's clear enough.  If not, find someone knowledgeable who can help you.

Coat a corner and fit it together.  What might help is dry fitting 3 panels, coating the other with glue and fitting it into the other 3, clamping everything square and waiting about 20 minutes while the glue sets.  Then take the other end apart, coat that in glue and fit that together, clamping everything, making sure it's square, and leaving it to dry after that.  It gives you less headache, and makes sure you don't rush through and miss something (like gluing the cheeks on half the box, like I did) or forget to square up the box before it dries (like I did).

Leave it overnight and come back the next day.  Or take a break.  Or, continue to the next step and work on another part of the project :).

Step 4: Legs: Turning & Shaping

If you know...
If you know how to use a lathe, and have experience, and a design for your legs, go for it!  One of the tough parts to make these legs was getting the right angle from where the joinery would happen into the curves of the turned portion of the leg.  I ended up using a skew to alternately sever the fibers at that point and clear the material on the turned side away so I could get the tool in closer.  Basically we've got a rectangle-gone-cylinder in one place, with no gradual change of form, so that method seemed to work the best.

Unfortunately, the tool caught a few edges and ended up splitting out a large chunk of one of the corners, so I adjusted my design to include some hand-shaping of those corners after they'd been turned.  I'm pretty happy with the results, and have been itching to do more hand-shaping ever since.

If you don't know...
Start with square lumber.  Square your leg material like in Step 1 and make sure it's as thick as you want the rectangle bits to be (where the outer box sides will join).  After that, it's helpful to have a plan, even a profile of the leg design on a piece of scrap that you cut out on a bandsaw.  You can trace this onto your turned pieces, hold it up to them and see where things might not be matching quite yet, and use it for general reference.

What helped me a ton, especially since turning a pretty new to me, was getting my excitement out on a few test pieces.  I got to test out my design on some scrap wood, and play with adding other details or simplifying the design to see what would look best.  It's a great exercise and great practice.

Lastly, even if you're somewhat familiar with this, get someone to help you.  I'm lucky to have access to a shop with managers who do this stuff regularly, and my key helper is a furniture-maker by trade, and she spouted advice whenever I had any questions.  Biggest lesson of the project: get a great helper and you'll learn a ton more than any Instructable can teach you.  I'm not going over lathe workings or procedures, partly because I just learned them myself, so a knowledgeable manager/monitor/helper is invaluable here.

Now.... essentially what you do is the following:

Square your lumber, get a design idea and do some test pieces on scrap wood.  Different woods turn differently, so use extra of your leg material if possible.

Once you've got a good test piece, mount one of your actual leg pieces on the lathe.  Turning takes time, and patience, and is more like sculpting than the rest of the project.  So take your time; it took me two sessions over two days to get all four legs done, and they're not perfect.  You'll speed up once you get the hang of it, but it's most important to be slow, careful, and get what you want.  You're sculpting, so have fun.

Matching the design on all four pieces was easiest when I set a bunch of calipers to all of the varying thicknesses on my first piece and matched each successive one to those from then on.  They didn't come out perfect, but I'm pretty satisfied with my first set of matching pieces. :)

One of my legs chipped badly, so I had to add some hand-shaping to the plan [image 11].  I sketched the designs on my broken piece first, making sure they would take away the chipped area, and traced that onto the other pieces.  Just using some clamps and cauls, a drawknife and a chisel, I was able to rough out and then smooth out the shapes I wanted.  I had to be careful, though, not to take away too much flat material on the sides where the outer box sides would join into the legs.  I also decided to chamfer and round out the tops of the legs, a little with a chisel, and smoothing later with lots of sandpaper.

Once you're happy with those (don't worry about sanding them just yet, although I did sand the turned parts on the lathe when I was done), grab your outer box panels and head to the next step...

Step 5: Outer Box-to-Leg Joinery

Alright, so if you've got your outer box panels cut to length, cool.  If not, figure out how long they need to be to fit around the inner box leaving room for it to move around, and remember to account for their tenons going into the legs.  This was really tricky for me, but eventually I figured it this way:

Length: (Inner box outer length) + 1/4" + (3/4" for tenons) = final length for 2 pieces.
This length put the legs past the ends of the inner box by 1/8" on either end, so the width measurements aren't as key.
Width: (Inner box width) + (3/4" for tenons).  This was more or less my final dimension.  I thought about it so much I'm still confused about how I ended up where I did, but basically you add 1/8" on either end to get the legs out of the way of the inner box, and 1/8" on either side to give the inner box room to slide and its pegs room to fit into the outer box groove.

Note:If anyone has a good method for calculating this, that would be immensely appreciated.  I've done two projects now where I've thoroughly confused myself trying to figure out the dimensions of something like this and I can't imagine it's that complicated for people more in the know that I.
 
If you know...
Figure your tenon dimensions, mark them and cut them on a bandsaw.  Rout a shoulder onto the tenons (mine were 3/8" so mine was 1/16", respectively).  Mark a center line on the legs where the panels should join into them.  Using that as reference, trace your tenons onto the legs, keeping the tops of both flush with a square or rested on a table, and use a chisel mortiser or a drill press/chisel combination to make the holes.  Clean 'em up with a narrow chisel and test fit after every few adjustments.  Ba-BAM!  Movin' right along...

If you don't know...
I like to cut my tenons first and mark them directly onto their mating pieces to get the most accurate and tight-fitting joints.  So once you've cut your panels, mark where you want your tenons to be (remember to mark the depth on both faces) and head over to the bandsaw.  I was worried my thin panels might be weak, so I kept two really big tenons right through the glue joints on each one.

Usually you should stagger your tenons so they don't come in at the same places in the leg.  Taking out that much material in almost the same place can make the leg pretty weak.  And, if they're not overlapping, they can be longer and go deeper into the leg, making a stronger piece.  This is going to be a footstool though, and doesn't need huge amounts of strength.

Once those are cut, head to the router and set it to take off about 1/16" of material where the tenons are.  This is going to make a shoulder so when the tenons are fully inserted in the legs, you won't see the joints in the final piece.

Now let's bring 'em together.  Mark your panels and legs so you know what panel goes into what leg, and to make sure you're always test-fitting the right panel in the right leg.  If you try a wrong one once and work for that one, the mortise won't fit either tenon correctly and could be wobbly or weak.  So mark them a, b, c, d, or something, right on the pieces themselves.

Hold your panels and legs together, keeping their top ends/edges flush with a square, and the tenons centered on the legs, and mark where the tenons hit the leg [image 7].  These will be your mortises.  I used a chisel mortiser for this, but a drill press and chisel would be fine.  Put tape on the bit at 3/8" so you don't go too deep into the leg, and make sure your mortise marks are dark enough to see in the thick of things.  I almost drilled an extra 1/4" below where one of my tenons stopped before I realized I'd gone past my line.

Drill out as much material within the lines of your marks as possible; if you don't have a drill bit the size of your tenon, use one slightly smaller.  Better for the mortises to be too small than too big.

Once the roughing out is done, take a skinny chisel (mine was 1/8") and clean out all the mortises.  Scrape away at the bottoms, make sure the edges are clean and relatively even, but keep your lines!  The lines from your mortises are on the outside of the mortises, so you don't want to chisel those out until something doesn't fit.  If you do, they'll probably be too loose.

Test-fit [image 15] once you've cleaned out each mortise and see what needs work.  You shouldn't have to jam the panels into place, but they shouldn't move once they're in there.  They should fit snugly all the way around; ideally you won't have any gaps between the mortise edges and the tenons.  Simple wood glue isn't gap-filling, so you want the two pieces to be right up against each other for a strong bond when everything is glued together later.

Once everything fits nicely, let's make that inner box fit and slide...

Step 6: Making the Seat

The seat should be a pretty loose fit, but for more accurate results than mine you can do it after glue-up.  Basically it should have a lip, so its top outer dimensions are flush with the frame of the seat, but the groove in the seat bottom gives room for the upholstery fabric to be folded under and stapled.

Most of the seat gets hidden, so you could use anything as long as it's strong enough.  Mine scrap plywood was about 3/4" thick, and I took about half that out with the router around the edges, so the load-bearing areas are about 1/4"-3/8" thick.  With the size of the piece and loads this will most likely be bearing, I'd say that's fine.

If you know...
Cut your seat to size and rout along the edge, giving a good inch for clearance for the upholstery fabric.  Rout away where the legs sit, if your design is like mine, giving extra room there as well.

If you don't know...
Put the stool upside-down on top of your piece [image 2], and mark around the outside edges of the stool and cut that to size.  I cut my at 45 degree angles so they'll only cover up half of the legs.  I didn't want to hide the legs once the cushion was on the seat, so that overlap will give the seat support, plus a frame for the cushion and fabric.

Next, take your seat panel to the router and set it up so you're taking about a full inch off all four edges of your board.  That ended up not even being enough for mine, so depending on the thickness of your fabric, you may want a larger groove.  The fabric needs room to wrap under and let the seat still fit in place.

Take off more around the corners where the legs are, since they protrude into the inside of the box [images 3, 8].  I was pretty rough with this process, as it doesn't have to be super accurate (except the outer dimensions), and won't ever be seen when the piece is finished.  I did sand and oil it, however, to keep it smoothish and somewhat sealed.

Step 7: Inner Box Movement

So you've got a box with legs and everything is great.  Cool.  We're makin' strides...

Now, the inner box needs to have its rightful place in this little piece of furniture.  To do this is pretty simple, but slightly delicate.  We have to get some dowel, drill holes that size in the top of the inner box, and cut pieces of dowel to sit in those holes.  Next, we'll rout a pathway along the inside of the outer box sides for that dowel to slide through.  Lastly, we'll drill and chisel two holes in the bottom of the outer box sides for the two stop pegs to sit in that keep the inner box in place when we want it to stay hidden.  Let's get to it.

If you know...
Find the center of two opposing box panels, mark it, and mark a path down each one with the dowel on those center lines.  It should come through the top and stop 2-2.5 inches from the bottom.  Drill holes the width of your dowel through the top of your inner box so that it sits in the center of the outer box when suspended in the top of it.  Design and make some pegs, trace their ends onto the panels, drill holes for them and clean up the holes with a chisel, squaring them if necessary.  Glue the pegs into the box and move on to the next step.

If you don't know...
First, find your dowel.  You need that first to know how wide your inner box holes and outer box groove should be.  There was a scrap dowel in my school's shop that I found so I used that.  Unfortunately it was a strange diameter (something like 1 35/64" I think), which meant I had to run two slightly offset passes with the router and manually make the hole in the inner box bigger.  Not so pretty.  Use standard-dimension dowel, something you have a drill bit for.

Before drilling holes, I made the seat, put the stool upside down on that with the inner box inside, and marked its bottom edges to figure out where the stop peg holes should be.  I'd recommend doing that.

Once you've got the dowel, mark the center of your outer box panels.  It needs to stop roughly 2 inches from the bottom edge of the panel so there's wood to support the box when it drops, as well as room for the hole for the stop pegs to fit in [image 9].  Line that up on the router and clamp some scrap butting up against its edge to be a stop.  This will stop your panel when you're running it through the router and keep you from accidentally running the groove through the whole piece, as well as help you lift the panel off the router when you've reached the end of the cut.  You should go through the top of the panel, however, to allow the removal of the inner box if necessary, for waxing the groove in the future, or other maintenance.

Because my panel was only 1/2" thick, my groove was only 1/8" deep.  It could have probably been deeper, but I didn't want to weaken those 2x4s.  Depending on your materials and amount of weight on the inner box, you might choose something different.  Run your two panels, ends against the fence, through the router (set the bit height and depth first!) to make the groove.  It's not really necessary, but I squared out the end of the grooves with a chisel [image 9].

Once the grooves are cut, go ahead and make your stop pegs [images 4-8].  I used some scrap mahogany for these, quickly bandsawing out their shape and refining it on a spindle sander.  Use whatever resources you have, and have fun with these.  Like the legs, it's an opportunity to make something unique to the project.  I rushed this phase, because I wanted to get the project done (it was for my roommate's birthday and I was already late).

Trace the pegs onto the panels about 1/2"-1" below the grooves, 1-2" above the bottom edges.  Drill holes and finish them out with a chisel, to whatever your peg shapes are [images 6-8].  Make sure they stick out a ways into what will be the inside of the stool, they need to support the inner box and its weight to be functional.

I was super tempted to figure out how the inner box would slide right away, but the whole game changes once the outer box is glued up, so don't worry about it just yet.  I cut some dowel to rough length, and glued it in, clamping flat scrap to the inside of the box and clamping the dowels into that, keeping them flush with the inside and hopefully the outside, and ideally parallel to each other. [images

Now, onto sanding...

Step 8: Sanding & Glue-Up

WEAR A DUST MASK!!  I inhaled so much dust that day I was coughing for the rest of the day.  Not fun.  And not good for you.  So wear something that helps ya breathe.

If you know...
Sand until you're satisfied, using blocks for flat areas and hands for rounded areas.  Sand turned portions on the lathe.  Some sort of power sander would be ideal for the panels, like an orbital sander where you can change the sandpaper pads.  Next is glue-up.

I glued up one end at a time and let that dry, then did the sides.  Mostly because of time constraints, but this allowed me to be careful, thorough, and calmer than I might have been if I'd tried the whole thing at once.  I have a more detailed breakdown below but essentially I assembled it all, glued up an end (not to the sides, mind you) and clamped it all square for about 20 minutes.  Then I did the same with the other end.  The next day I did the same with the sides, making sure the box was square each time with two piece of wood overlapping to check my diagonals.  It worked out great, I had very little squeeze-out, and all the joints closed up nice and tight.

If you don't know...
Basically we want the whole thing clean, smooth and user-friendly before it gets glued.  Sanding thoroughly after gluing is tough and annoying.  I sanded my panels with an orbital sander, using 80 grit and 120 on the insides, and then 80, 120, 180, and 240 on the outsides.  Then I hand-sanded the inner box and the legs up to 240 as well.

As far as sanding goes, I've seen woodworking where only the visible stuff gets finished.  The undersides or backs of things are left pretty much untouched.  And why not?  Nobody's going to stick their head up inside this thing and feel how smooth it is, so why worry about it?  I just smoothed out the grooves for the inner box pegs and focused on the visible parts.

The legs were interesting.  I used a sanding block for the rectangular parts, and to help round out all the hard/sharp edges of things, but I had to just use my hand on the shaped parts.  I'd already sanded the turned sections when the pieces were on the lathe, which made those portions much easier.

Once everything was sanded, I wiped it all down, sometimes it's a good idea to use a damp (damp! not wet) paper towel or rag or something to pick up all the dust of your pieces and your workspace.  Next step is gluing, and we don't want any weirdness or interference.

For glue-up, I learned some tricks this time.  As before, though perhaps more importantly given this is the final piece, do a dry run.  Or two.  Make sure all your clamps are sized correctly, make sure when everything is clamped it can stay square and stable.  It's nice when things with legs sitting on the ground don't rock when you bump into them :P.  Make sure the space is clean and organized, and that you've run through the process of glue-up in your mind.  Having a helper would be awesome.

We decided gluing up all the joints in one go was a lot to do.  You've gotta coat the mortises, tenons and cheeks with glue, fit them together, fit the rest of the box together, clamp everything, and adjust the clamps to pull it into square if necessary.  Doing that for 16 mortise-and-tenons was a daunting to tackle all at once.

So we tackled one end at a time.  Assemble the whole thing except for one end, so you've got everything fitting together except two legs and a short panel.  Pour some glue onto a scrap of wood or something and brush glue onto the cheeks of the two legs' mortises (only where the end panel will be fitting!) and the cheeks of all the short panels' tenons.  You should not be putting glue on any part of the longer sides, or the mortises they fit into.

Fit the two legs and the end panel together snugly, and then fit that end onto the rest of the assembly.  Clamp everything down, and use a measuring tape or two overlapping sticks to measure your diagonals and make sure they're equal.  If they're not, angle the clamps so they pull the box into square.  Do this quickly so the glue sets when things are in the right position.  Have damp paper towels or rags handy to clean up any glue drips or seepage.  That stuff is super tough to clean off afterward.

Leave it about 20 minutes to set up, then go ahead and disassemble the clamps and do the same with the other end.  Coat all the end piece cheeks with new glue, fit them together, and re-fit them onto the side pieces, clamping everything together and checking for square.  Leave this assembly overnight and come back the next day to do the sides.  You can do the same with the sides (one at a time) or all at once, depending on your comfort level and how much time you have.  Make sure things are square so they sit right when the piece is done, wipe off any extra glue with damp paper towels or rags and give it time to dry.

Step 9: Finishing

You're almost there!

After glue-up, take the clamps off, and check it out.  Your new footstool is super close to being done!  Now, if you haven't already, cut some dowel to rough length and glue it into the holes in the inner box (glue-up photos in Step 7).  Set some stops on the inside of those holes, put glue around the edge of the dowel where it'll sit in the box side and put the pegs in place, clamping them against the stops so they're flush with the inside face.  Wipe up any glue squeeze out/drips and leave for a good 3 hours to set.  (Note: if you don't have access to a sander, cut your lengths pretty close.  I got mine pretty close and then sanded them until they fit just right.)

While that's setting, inspect your footstool.  If there's any glue squeeze out around the legs, try sanding with the grain on the panels away from the legs, or with the grain on the legs.  Put some paper or thin wood scrap against the perpendicular surface to project it from scratches.  After wiping away any squeeze out during glue-up, there shouldn't be much to clean.  I was pretty skimpy with my clean-up, but I got most of it with the rags when it was still wet.

Once you're happy with it, bring it into a ventilated area and prep for finishing.  I just used some denatured alcohol to clean the wood and then put 3 coats of Watco Danish Oil on the piece over a few days.  Wearing rubber gloves, and using rags (got 4-5 rags out of a pair of ratty boxer shorts), just wipe on the finish.  Read the label of whatever you're using and follow its directions.

One of my legs was really fuzzy, and I ended up wet-sanding that a bit.  I rubbed oil onto it, sanded with 240 grit, and oiling again.  I also waxed the ends of the legs, the grooves on the inside of the outer box and the pegs on the inner box, which made its movement waay smoother.

Set all parts up on scrap to keep them elevated, and be sure to coat the surfaces with two good coats of oil.  I did a third coat out of habit, but it's not necessary with Watco's Danish oil, as it doesn't really build up a sheen like waxes might.  I was also more careful and thorough about my visible surfaces than the non-visible ones, similar to the sanding process.

Whatever you're finishing with, make sure it's even, clean and you like the results.  Sometimes people thin finishes with denatured alcohol, or mix their own finishes.  It's worth researching pieces you like of whatever wood you're using to get an idea of how you'd like to finish your new footstool.  For me, all of this is experimenting and skill-building, and I wanted this done and give-able to my roommate, so I just did what I knew.

Apologies for the lack of photos for this step; most of my finishing trips were between other things, so I was usually in and out.

Step 10: Upholstering

I am no upholsterer.  In fact, after this project I need to do some research.  In reality, the groove in the seat simply wasn't big enough, and I'm sure if I'd taken that down a little bit more things would all sit just right.  But my roommate is happy and I'm content to move on, lesson learned.

Briefly outlined, I put the seat panel onto a chunk of upholstery cushion and outlined it, keeping its corners so they'd poof out a bit over the edges of the wood panel.  I tried using a knife to cut this but scissors did a much better job.

Then I squashed the thing down onto the fabric, pulled the fabric over it and stapled it in place on both long sides.  This squished the cushion, making it firmer and giving it a nice rounded profile.  Next I cut away at the ends so what folded up was thin enough to hopefully not get in the way of the groove and its placement, and stapled all of that in place.

Et, voila!  Finale.
Congratulations!  I'm pretty proud of this as a project, and very excited to have a new piece of furniture in the house, and to be able to share its process - and hopefully some inspiration - with you readers.

Best of luck, and as always, any advice/suggestions/iedas are more than welcome.  I look forward to seeing what you create!  Be safe, and have fun :).