Leg vise design and experimentation
Until a few years ago I had never heard of nor seen a leg vise. The buzz around leg vises, in particular the Benchcrafted Glide Leg Vise, has been growing over the past few years. This is likely in response to Oprah, errr Schwarz and his penchant for workbenches and accessories. I chose to go with the vise screw from Lee Valley and build the rest of the leg vise parts myself. This do-it-yourself thing is good on some levels (financial for one) but not so great when you get an idea into your head that won’t go away.
Chris Schwarz has been regaling the community with the benefits of a Croix de St Pierre, or St Peter’s Cross and its incorporation into a leg vise. I was intrigued by the mechanics of this and wanted to pursue making one myself just to see what was involved. I experimented. I used steel L bar, which wasn’t at a true right angle and still has the ability flex quite a bit. Into the scrap bin that went. I tried steel box tubing. I actually got quite a bit of success playing with this on some scraps, using the already purchased vise screw. So why does it not appear below in the pictures? I found other points of failure. I used hinges to hold the bars to the chop and leg, only to find that they were neither strong enough to not buckle under the pressure nor was pine a good substrate for the screws that held them in place. The other setback was how the pine (which is what my base is made of) allowed the bars to compress the leg enough to put the whole mechanism out of square.
Failure? Perhaps, but I learned a lot and could conceive of building one with success at some point, but then along came Benchcrafted again with their own version of the Cross. They had found some unique ways of addressing these issues. So, for this instance of a leg vise, I went with the more traditional glide leg vise style with the guide bar. Drilling the hole for the vise screw before the bench was fully assembled is a good idea, you can do all the work against a leg while it’s up at a decent height on your work surface. I highly recommend doing this. Even though I had this advantage I still managed to need to trim the upper stretcher slightly as I’d ended up with the vise screw rubbing on the stretcher.
Once fitted in place I had the chance to get a little creative. I felt that the chop needed to evoke something that was clearly ‘woodworking’. The design that Benchcrafted has looks a little like a cap iron. I found inspiration just sitting there on my old workbench. My wide bench chisel.
It was a pretty simple matter to draw it out and cut the bevels, with a slight compound angle to get the angular side bevels by shimming the chop while I cut the angle on the table saw. The curves were a snap on the bandsaw and voila it looks like a ridiculously large chisel!
I decided that I wanted to try and duplicate the roller glide mechanism that Benchcrafted uses. I searched a bit and came across some really detailed blog entries that describe this perfectly. Turns out this was the Oud Luthiery blog where Jameel first came up with the idea. I used this as inspiration and went looking for a skate shop!
A skate shop? Yes, skateboard to be exact. I bought a set of inexpensive wheels, bearings and spacers. The wheels were a big wider than I wanted, as they were for Jameel in his blog entry, so I cut them down slightly on the band saw, just wide enough to get the bearing flush with the edge of the wheel.
To mount the wheels, I made the brackets you see here. You can just barely make out that I have a rubber washer between the wooden frame and the wheel. This allows me to tighten the bolt without pinching the wheel. The bearing’s inner wheel and the spacer are clamped tight and the bearings allow the wheel to spin freely.
I also took the approach to have the adjustable slot to allow me to raise or lower the wheel slightly once installed on the bench leg. I did not use a tap and die set, I just used some lag screws and washers and this has so far been pretty good. The lag screws have an aggressive thread on them, which works pretty well in the pine legs.
One bracket is installed on the front of the leg, under the vise chop, to support the guide bar from below. The other is installed on the back of the leg, above the guide bar to push it down from above and essentially take the weight of the entire vise making the vise move very smoothly.
With a leg vise, the main issue is going to be racking. This is what the St Peter’s Cross is supposed to help with by transferring some of that force that the vise screw is creating back down the ‘X’ of the cross so that it essentially counter-acts the inward pressure and pushes the bottom of the chop out a bit. With a guide bar at the bottom, you have to have a pin that you place at an appropriate distance from the leg to help push the force back onto the material being clamped at the top of the vise. It’s physics…if you want me to explain it with diagrams just ask…I will bore you to death with force mechanics, Newton and all that good sciencey stuff.
My guide bar is milled down to about 3/4″ thick and I cut a corresponding through mortise in the leg, with a bit of slop, so that the guide bar will move freely through the leg. The lovely repetitive pattern of holes is there to give you lots of options for where your pin can go to maximize the clamping pressure at the top of the vise. Oh, and yes, I did make mine a bit longer than necessary and drilled more holes than I need. I’m ok with that…I was having fun.
The guide bar has a tenon cut in the end that goes into the the bottom of the chop. I chose to drawbore the guidebar in place as well as glue it. I dont’ think it’ll be going anywhere. A little trimming with a block plane and I get a nice clean, shiny strip of end grain at the bottom of the chop.
My drawbore technique still needs a bit of work, I managed to twist the drawbore pin on the bottom a little and opened up the hole a little bit. Not that noticeable, except for the mice on the floor when I’m not around, and they’re not talking.
Once the guide bar is in place, it’s time to do the final fit and finish of the leg vise. This basically involves installing the chop, screw and guide bar in to the leg. To adjust the wheel brackets I shimmed the chop slightly to allow the guide bar to ‘float’ inside the mortise, roughly 1/16″ from the bottom and the top of the mortise. Once shimmed, I brough the wheels into contact with the guide bar and tightened the lag bolts. A little finessing here and there was in order, but it took a total of about 5 minutes to get the whole mechanism working smoothly and gliding beautifully in and out. Happy camper!
Last, but not least, here’s a wider view of the leg vise installed and ready to go. Once the rest of the bench is done I’ll be putting a finish on the chop and installing a suede or leather strip inside the chop.