After finishing up our Roubo-inspired workbench, one of the first things I wanted to add was a leg vise. There are several ways to go about building one, but after seeing a few example of vises using linear bearings and rods to act as a parallel guide, I thought I'd give it a shot.
One thing to consider before getting started is which side of the bench to mount the leg vise. Since I'm (mostly) right-handed, I'll be mounting the vise to the front-left leg to make edge planing easier, but if you're left-handed you may want to consider mounting it to the front-right leg.
Step 1: Preparing for the Linear Bearing
I got a bit of a head-start on the vise installation while I was still working on the bench by drilling a few holes for the vise screw and linear bearing that I will be using in the leg. If you're working with an existing bench, it should still be possible to drill all the holes with a cordless drill using a square to keep the drill as perpendicular to the front face of the leg as possible.
I decided to go with a 20mm linear bearing and rod, but for a bit more strength you could also use a 30mm linear bearing and rod and possibly avoid needing to add a wedge to counteract racking. (Although I definitely recommend the wedge if you really like cranking down!)
To recess the linear bearing, I started by drilling a larger, shallow hole in the leg a few inches up from the bottom on the front face of the leg. At the center of that hole, I drilled another one that was just slightly larger than the bearing's cylinder so that there would be a small amount of wiggle room to make mounting it perpendicular to the leg face a bit easier.
I then drilled another hole about 9" down from the top of the leg's tenon (the bench top) for the vise screw. Since my Forstner bits weren't quite long enough, I then finished drilling the holes with a spade bit in my cordless drill by clamping the leg down to a few small blocks to prevent tear-out on the back of the leg.
Step 2: Installing the Linear Bearing
Next, I double checked that the linear bearing was perpendicular to the front face of the leg by inserting the linear rod and made a few slight adjustments with the Forstner bit in my cordless drill before pre-drilling and screwing it to the leg.
Step 3: Mounting the Vise Screw Collar
For this leg vise, I decided to go with a Yost 18" Vise Screw. It's plenty strong, relatively cheap, and turns easily.
I mounted the vise-screw's collar to the rear of the leg using four 3" #14 screws. To center the collar opening with the hole in the leg, I mostly just eye-balled it from above while making a few marks at the extents. The goal is to end up with the screw centered in the hole in the leg so that there is no rubbing as it turns. After marking the hole locations, I then pre-drilled and screwed it in place.
Step 4: Painting the Vise Hardware
While the vise hardware is great, it was a bit too blue for me. I first cleaned the paint with some mineral spirits and then masked off the screw with a bit of string and a piece of dowel. After a couple of coats of flat black spray paint, the hardware looked great and matched the hardware that I planned on using for the end vise.
Step 5: Gluing Up the Leg Chop
Next, it was time to start on the chop. I started by rough-cutting a 2x8 into two pieces at the miter saw. I then ran one face from each piece through the jointer and then glued the two pieces together to form one thick piece.
Step 6: Surfacing the Chop
Once the glue dried, I took it back over to the jointer to flatten one face and one edge before surfacing the other face at the planer. I then took it back over to the miter saw to cut it to final length before ripping it to final width at the table saw.
Step 7: Beveling and Trimming the Chop
To make cutting pieces held in the vise easier, I went ahead and cut a bevel across the top of the chop before heading over to the drill press to make it look slightly fancier and lighten it just a bit. To do that, I used a large Forstner bit to cut out a curve about a foot from the top on each side. I then scribed a line along the edge starting at the inside of the curve and cut the pieces off at my band saw.
Step 8: Finishing the Chop
After a little sanding to clean up the bandsaw marks, I added a 1/4" chamfer to the front edge of the chop using my router before drilling out the hole for the vise screw at the drill press and wiping on a little boiled linseed oil.
Step 9: Attaching the Leg Vise
Next it was time to attach the leg vise to the bench. I started by reattaching the screw collar to the back of the leg (after the paint dried).I then inserted the vise screw through the chop and threaded it onto the collar. To ensure the screw was centered in the hole in the chop I shimmed it along the floor, and then pre-drilled and attached the screw to the chop with a pair of 2" #14 screws.
Then, with the chop tightened against the bench leg and centered along the bottom, I inserted the Forstner bit that matched the bearing size and marked on the back of the chop the location for the rod. I removed the chop and drilled a 2" deep hole at the drill press with a 20mm Forstner bit that would hold the rod.
Step 10: Adding a Handle
I decided to keep the handle simple for now (mostly because I don't have a lathe). So I cut a piece of 1" oak dowel, sanded it well, and pinned it in place with a screw. To finish it, I wiped on two coats of Danish Oil.
Step 11: Adding a Guide
After installing the rod (without glue for now) it was time for some tests. Unfortunately, the weight of the chop combined with the slight play in the vise screw caused the rod to sometimes bind in the bearing.
The solution was to simply use a piece of wood as a guide to help keep the rod perpendicular to the leg face. To do this, I removed the shelf and since I'd already glued the inner stretcher in place, I drilled a couple of holes through it and then attached the guide with screws to the outer stretcher.
Another option that I may also try is to add a second linear bearing to the rear of the leg, but so far the simple wooden block has worked great.
Step 12: Adding a Wedge
Although the guide addition made the motion of the vise very smooth, there was still a little racking when clamping work-pieces down hard in the vise. A 30mm bearing and rod probably would have eliminated most of it (also adding drawer liner or leather to the chop helped considerably), but with the 20mm ones I used I decided to try Jay Bates's solution which was to use a wedge along the bottom of the chop.
I found another scrap piece of wood and cut it to 16" long by 6" wide to match the roughly 4" wide by 1.5" deep cut that I would be making in the vise chop. I then used some double-sided tape to secure it to a piece of MDF to act as a tapering jig at the table saw.
After ripping it into two pieces I cut one half down to make a smaller 12" wedge for workpieces up to 3" wide. I then used the wedge to mark off the corresponding piece that needed removing on the chop and cut it out using a hand saw.
Step 13: Finishing the Leg Vise
To finish up the chop I added a little wood glue to the hole for the rod -- mostly just to harden the wood around it as the fit was already tight enough to hold it in place.
I also cut a piece of thick drawer liner to add even more grip to the top of the chop and used some double-sided tape to secure it in place. This actually ended up eliminating the need for the wedge during most clamping operations.
Step 14: Results
With both of these changes, it's now possible to apply a large amount of clamping pressure to a work-piece without fear of damaging the linear bearing. So far I've been really happy with the way it turned out and how well it works. Next up will be a sliding dead-man which should make it even more useful!