Two leg assemblies are part of the support system for the bench. I was going to use glued up 2×4s, but found some 12/4 poplar, so sawed that to shape instead. The legs are 2.75” thick and 4” wide, and the top rail is 2.75” square. The legs are angled at about 15 degrees. The 2×4 approach would have simplified cutting the angled slots, but then you have the hassle of cleaning up the glued up legs. The large hunks of wood making up the legs give them a nice solid look and feel.
The rails and legs are joined with a half lap joint and then strengthened with dowels. A bridle joint would probably be a little stronger, but due the angles, harder to cut. I had a router jig set up for making the shelf half laps and the same setup worked for this joint. I cut all the half laps with a pattern routing bit and a template jig to maintain the 15 degree angle. For the front legs I wanted to keep everything as flush as possible. On a couple of joints I needed to shim with some scrap veneer and do a little planning till I got it right on. I used epoxy to glue things together. I am sure wood glue would have been sufficient, but I wanted this joint rock solid and gap filled so decided to use the epoxy. While building this I delayed glue up by using bolts to keep things together until final assembly. This allowed me to break things down and work with more manageable pieces along the way.
For the face vise, I drilled a slightly oversized hole for the acme screw and drilled a larger concentric hole to hold the nut on the back. The screw is attached using a pipe flange which is secured to the back of the leg. The opposite leg has a bracket that supports the pipe that the screw is riding in. The rectangular hole is for the chain to pass through. I could have drilled a 5/8 hole instead, but decided to go rectangular to minimize wood removal and allow a tighter fit. The chain works best if it is anchored close to the screw. I used the drill and chisel method to cut this. The recessed rectangular notch below this hole on the back provides clearance for the sprocket which I mounted close to the surface of the leg. If I kept it a little further away from the leg, it would not be needed.
The linear bearing is also mounted on the leg. To install, clamp the leg on the drill press table and drill a hole for the bearing with a Forstner bit, then drill a concentric hole to hold the flange. This takes about 20 min total to complete. I think making and installing a pinned parallel guide takes a bit longer. On the downside it may require more precision in alignment, so I was prepared to tweak and shim as needed to make sure the bearing and screw are aligned.
The lower shelf is attached to the legs with a half lap joint with two bolts per leg holding it in place. I used 3/8 carriage bolts with torque washers to eliminate any rotation. I ground the rounded head a little flat so that they look a little like elevator bolts. I recessed the bolts into the front of legs and glued in a plug to hide the hardware. The flatter head allowed for a shallower recess hole. Nuts/washers on the back secure things and allow disassembling.
The shelf consists of a frame and a top. The frame is built using 2.75” square poplar joined at the corners using pinned bridle joints and notched for half lap joints with the legs. The same jig I built for notching the legs is used to rout out the slots for this joint. The inside edges of the poplar frame are rabbeted to hold a ¾ plywood panel top. Some 1.5” poplar boards were added to the bottom for additional support. Clearly I over-engineered this, but they were offcuts, so I put them to use. The small rectangular notch near the left leg is for the chain to pass through. The linear bearing and chain run under the shelf. It would not be needed if the parallel mechanism ran above the shelf.
I was pleasantly surprised how stable and strong just the legs and shelf were even with no bolts keeping them together. The half lap joints lock things down very nicely. While building this table, I bolted the legs to the shelf, put a board on top and had a great temporary bench halfway into the project.