Hi Matt, I built my workbench just on 4 years ago. If you like I'll talk you through the reasons behind each decision, and how those decisions are travelling after 4 years of use. I'm a self-taught woodworker going on 9 years now, who likes to dabble in all sorts of different aspects of woodwork, mostly with hand-tools; so the bench has been put to varied uses. Currently I'm using it to build a 2.5m long dining table.
1. Tail Vise. I built a wooden, L-shaped tail vise, using a cheap metal vise screw. Best Decision Ever. I have not found a reason to regret it. The top is 1.9m long; with the vise extended I can support work from underneath up to 2.5m long. the standard tail vise task of clamping between dogs is extremely useful, not just for planing, but for light carving, stabilising for chisel work, holding the drop saw in place and lots of other handy tasks. One thing I have found really useful is having a vise that is open on 3 sides - particularly when holding oddly shaped work, or holding onto my turning chuck and having a bowl I am carving/dremelling hanging out the side for easy access.
2. Split top. I started out building a single top, then when I realised I didn't have enough long clamps, changed it to a split top. I haven't regretted it. The cons were in the added complexity of the build - getting things coplanar, flattening tops and undersides, attaching an endpiece for the L-vise. No cons so far in the use, only pros. On the back piece I put a metal woodworker's vice as the split top afforded me the ability to be able to cut either side of the jaws. I have added flexibility in clamping (very handy), the centre till lifts up to be a back-board/planing stop (also surprisingly handy). No problems with rigidity/flexing/movement - but both pieces are securely fastened to an over-engineered base, and joined together with an endpiece/breadboard.
3. Vise Choice. I have 3 vises - an L-shaped tail vise, a leg vise as a face vise and a metal woodworking vise on the opposite rear end. twin dog holes in the back vise's chop allows for holding curved work (opposite holes in the bench top). The leg vise I made myself using another cheap vise screw, with the bottom support made from some all-thread and a foot wheel (because bending down to move a pin is so 20th Century). $40 AUD all-up for a rock-solid, easy to use, versatile vise. I had never used one before, but have found a leg vise to be a very, very good addition to the bench - advantages are the depth of the screw; I can put even larger items in them, provided they stay to one side; it has an insane opening width; it has exceptional holding power compared to a metal woodworking vise. If I build another bench, I might replace the metal vise with a patternmaker's vise, but the other two vises would be the same. I haven't used a twin-screw vise, but am yet to find the
necessity for it in my work - every problem it solves, I have been able to with my current setup (albeit not always as easily as it would have allowed)
4. How thick? About 85mm (3 1/3 inches). I built it out of 90x45mm construction pine, which limited my thickness. I wouldn't want thinner. It's rock-solid at this thickness.
5. Base Joinery. Drawbored Mortise and Tenon. It's immovable, interlocked and not hard to do.
Other considerations - I made provision (but ploughing a groove in the underside of the top) for later installation of a deadman, but haven't had the need. I have just tended to drill holes in the leg for the holdfasts to go into if the wood is long enough to need extra support. Twice now I have regretted not having a front apron (or at least a lip) to clamp against, but it was a minor irritation that was quickly worked around. Having the legs in line with the top, though, has been really handy.
And a couple of pictures, to give you an idea what it looks like.
wb 121.JPG
wb 122.JPG
But ultimately, it is your bench for your uses. Make it to please you and meet your needs, not to please us and meet ours!