Leg placement on L-Shaped Desk

Question

I am building an L shaped office desk from white oak or hickory boards joined together. The top will be assembled from joining multiple boards together with adhesive and sanding them down to make 2 large individual boards (25x50 and 25x60).

I'm in the military, and as such I move a lot, so I'd like the desk to be fairly disassemble-able. I figured I would use metal threaded inserts for the wood to be able to easily unscrew the pieces.

I'm looking for recommendations on supporting the tabletop effectively with a minimal apron. (there will constantly be about 50-75 lbs on the side with two legs)

I'm pretty new to making something of this size, but I have done smaller projects in the past, some ideas I have are:

An apron across the edges (undesireable, but if it's the only way) (green) A recessed apron connecting the quad legs together, maybe 5 inches into the table (blue) An additional 'leg' support going diagonally at the joined boards

Answer 1

Although at 3/4" thick solid-wood panels made from strong hardwoods such as white oak or hickory are plenty stiff, there's a fair bit of unsupported span on designs like this so some minor tweaks would be beneficial IMO.

When there's too much unsupported material on L-shaped desks even gentle pressure from leaning on the surface in the key working zone at or near the inside corner adds a lot of strain and I've had a look at a few commercial desks with no front support which did sag. The dip is usually not excessive, not enough to cause structural concerns certainly, but still is more than I'd find acceptable in normal use.

And it is important to build for the what-if scenario, like if someone were to sit on the desk right in the middle; it's designing for this sort of occurrence that makes additional support highly desirable to semi-essential.

So for this reason I think

• one or more diagonal supports coming up from the rear legs;

or

• a supporting 'batten' spanning the gap between rear legs;

are important additions.

Diagonal support
Diagonal supports don't have to extend too close to the front edge, where they might interfere with sitting, and to save on hardwood these could just be triangles of plywood. Any such support would be invisible when working at the desk but could be seen from further back, so if the aesthetics are important then I think solid-wood struts win over plywood triangles here.

Batten
But a batten board joining the outsides of the rear legs, acting as a beam of sorts, could provide nearly equivalent support and would be completely hidden from view. The more you move the legs out from the corner as you suggest in the Comments the further forward this board is positioned and the more support it adds, but, the longer it needs to be naturally.

Here again this could be made from plywood rather than solid wood (e.g. two strips of 3/4" laminated together, edge-up) so it won't add a lot to the cost. I'm assuming material being bought for this project specifically, rather than scraps of wood/ply¹ being used up.

Outside legs
If you want to keep the current outside leg positions because you think this looks best then don't change this part of the design, but if you're not wedded to them being where they are in the image I wanted to suggest you move them inboard of the ends.

The accomplishes 2 1/2 things:

• It great reduces the unsupported spans.
• It makes the table easier to hold on to when moving fully assembled.
• I think it looks better, but obviously this is a YMMV kind of thing :-)

So I think this will remove any need of aprons, reduce build time and material costs.

Desktop joint
I go back and forth about which I prefer for these purely in terms of looks, but once you have to factor in wood movement things get more complicated. I am fond of the look of a 45° join in work surfaces and L-shaped desks with chipboard/particleboard but they're problematic if you're dealing with solid wood².

Also something that might not be immediately evident, there's the potential for far more wasted wood with a 45° joint — the shorter panel which currently can be made with all boards a smidge over the final 50" length would have to include at least one board a little over 75" long.

So the joint as pictured might seem totally the way to go, but this is a cross-grain situation.....

Remember, to allow for movement: the longer panel has to be able to move away from this joint (expand to the left in the image) OR to push and pull the shorter panel with it as it expands and contracts during seasonal changes in humidity, while still allowing the shorter panel to be free to expand and contract forward from its back edge.

---

¹ If you'd prefer to use solid wood but have no single board long enough, this is a prime candidate for a glued-up piece that uses up multiple scraps, or board-stretching technique (using a long diagonal cut) if you have one board that is close to the length needed but not quite.

² They can be a much-magnified version of wide mitre joints, which became something that carpenters preferred not to do because of their proven likelihood of opening up at the inside or outside over time.

Answer 2

A few small changes will likely make a significant difference in the rigidity of the desk. I added some doodles to your diagram, to go with my notes.

First, a slightly thicker top (7/8" or 1") will give significantly more strength. Personally I've found that 3/4" for tops or shelves is right on the cusp of being too thin--that extra 1/8" is worth a little extra weight.

Second, an apron inside of the legs will be very helpful to act as a gusset to keep the legs from flexing. It should be fastened to the tops as well as the legs, and the larger it is the better (for hardwood I'd suggest something around 1" thick by 3" tall). It's the long yellow boxes on my doodle.

A third considering would be to move the two legs in the corner apart, so the one near the seam can support the seam, and there could be gussets between the legs to help support the tops. If you plan to belly up to the desk these might bump your knees--I'd keep them set back about 12" from the front edge to avoid this--but it will depend on your posture and body dimensions. These are the orange boxes in my doodle.

Perhaps an alternative to the long gussets would be a plate, permanently attached to the longer top, with the shorter top resting on it as a ledge with a limited number of fasteners (expansion and contraction of the shorter top will need to be considered--fasteners may need to be in slots to allow some movement).

PS) Yes, my doodle has overlapping boxes--it's just meant to convey some options that might be competing and would need some more detailed thought.

PPS) The Sagulator (sag calculator) is an interesting tool to estimate sag. It's geared towards shelves and might not provide much value here--but it can demonstrate that a little extra thickness can make a significant difference.

Answer 3

While your design certainly has adequate legs distributed adequately to support the top, it is the connection of the legs and the location of the joint at the top that concerns me.

You should consider the top end of each trapezoidal leg assembly as a hinge. While the corner legs, at right angles, are very important in stabilizing the desk each individual leg can rotate unless the connection to the top resists. This is especially important if you attempt to shift the desk by dragging at any time. The simplest way to connect the legs would be to screw them to the top from the top surface. This, of course will expose the screws and would be undesirable if this is intended to appear finished as a piece of furniture. An alternative approach would be to glue wood rails to the underside of the top and screw the legs into the rails at their side face. These rails would be mostly concealed and should not interfere with clearances below, although they might interfere with horizontal clearance to something like a file cabinet. If you add an apron, it will help stabilize the leg assemblies against rotating. If you are concerned about clearance for cabinets or seating, you may want to only add aprons at locations where they are not visible or in the way.

I see two locations for the top plywood joint. The first is at a 45-degree angle at the corner. This may be more desirable for appearance, if you are considering a clear wood finish and want the grain to appear so. If you are not interested in that appearance or are painting the surface, I would recommend running one sheet the full 75" and the other at 35". This arrangement will make cutting the pieces to get a square intersection easier. In either case I would recommend creating a spline at the connecting edges and reinforcing the joint with a wood strip running the length of the joint below, glued to one side and screwed with shallow screws from below to the other.

One other possibility short of a full depth apron is to apply a 1x3 glued at the edge to the open areas between legs creating a 1 1/2" edge on the top to which you could apply a thin piece of trim as a face trim. (Or apply a 1x2" to the face of the plywood top to create a slightly stronger and more attractive edge.)

Additional response:

In a comment you added that you would make the top from hardwood. This adds another consideration in the design. Note that, unlike plywood, the hardwood will expand and contract in the width, but not in the length. The result is that you cannot make fixed joints when connecting the wood in different directions. In your design that would produce stress between the top of the legs and the top in the 25" directions. The connection should allow for expansion differences. This is usually accommodated by slotted connections between the top and an apron frame at the top of the legs making the aprons more important. (Sorry!) IF you search through other answers on this site, you will find plenty of discussion about this issue. Also note that making the directional change of the top at 45 degrees will eliminate the issue of expansion between the two top pieces since both will then expand and contract the same amount.