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Roubo: The Base & Top Flattening
Post - March 10, 2012
No one ever accused a Roubo workbench of being skinny! This beauty features some rather beefy 5 3/8″ x 3 1/2″ legs! That’s just how I roll. Each leg receives mortises for the short and long rails as well as large tenons at the top. These tenons will help us locate and secure the top to the base. Interestingly enough, this is one case where we cut the tenons first (most times I like to cut the mortise first). After the base is assembled, I’ll flip everything upside down, mark the locations of the tenons, and then cut the mortises in the underside of the top. This technique really saves me a lot of headache. As massive as these legs are, I was still able to use a fairly standard tablesaw/miter gauge/dado blade setup to cut the tenons.
Although the original Benchcrafted plans call for knock-down joints using some massive hardware, I opted to drawbore all of my base joints. So at the drill press, I drilled two 3/8″ holes through each mortise. The right front leg received a few extra holes for the holdfasts as well as a large finger hole which will later allow me to access the one dog that winds up centered over the right leg. I used a 3/4″ Power Bore bit from Rockler for the 3/4″ holes.
In addition to the legs, the base is made up of six rails. Each receives a tenon on both ends. Once again, the tablesaw/miter gauge/dado blade setup makes this job easy. Since the mortises were all cut on the router, the ends of the mortises are round. So instead of chopping all of those mortises square with a chisel, I opted to round over the tenon using a chisel and a rasp.
When contemplating the flattening of the workbench, I decided to go the power tool route using a router sled. Why? Primarily because I am lazy, but also because I think it is an under-represented user-friendly technique. I have been meaning to demonstrate it for years and this was my opportunity. I should also mention that I certainly didn’t invent this method. If I’m not mistaken, it was first demonstrated by Tage Frid in an old publication, but don’t quote me on that. While I know there lots of us who think flattening a workbench is a great way to spend a Saturday afternoon, I am not one of them. Fortunately though, there are crazy people like Shannon over that the Hand Tool School who seem to thrive on this form of torture. I asked Shannon to do a demonstration of his flattening technique and he obliged. So in the video series, we’ll be showing BOTH techniques.
So here is how the router method works. The router sits inside a very simple plywood sled and rides along two parallel rails. As you move the sled back and forth, a big honkin’ router bit chews up any high spots. The best way to think of this is like a poor man’s CNC machine.
The router sled itself is constructed from three pieces of 3/4″ plywood that are custom fit for the router. The rails are made from construction grade 2×6’s. I jointed one side of each rail at the jointer before attaching them to the sides of the workbench using clamps. Now here’s the only tricky part in the technique. The goal is to get the two rails not only parallel to one another, but also parallel to our bench top. Fortunately, there’s a trick that makes this pretty easy.
I start by making sure the rails are roughly parallel to the bench top by measuring at all four corners. I aim for them to be about 1/2″ above the bench top surface. I then attach two pieces of coated wire from corner to corner creating an X-pattern on the workbench. You can use string for this too but I find using a more substantial wire with a bright colored coating makes it easier to see and thus, more accurate. When attaching the wire to the rails, I used a screw and a washer to ensure a good grip. Notice that the wire is wrapped around the screw in a clock-wise orientation. This is so that as the screw catches, it will actually help to tighten up the wire making it nice and taut.
If those two rails are perfectly parallel the two wires should intersect at the center, essentially traveling through one another. But obviously, the wires touch and the laws of physics prevent that from happening. To get around this, I take two cut-offs and place them under the top wire at each corner. This raises the top wire by one wire thickness. So now we know that the two rails are perfectly parallel when the two wires just kiss each other at the center. Using a hammer, I tap the corners until not only the wires touch, but each rail is approximately the same height above the bench top surface. If your bench top is really out of whack, its a good idea to first know where your high and low spots are and that should help you determine the best setup prior to routing. At first glance, this method might not seem all that accurate. But if you actually try it, you’ll see that just the slightest tap at one corner is all it takes to separate those two wires at the center.
Once the rails are parallel, the wires can be removed and the clamps tightened up. Now it’s time to make some wood chips fly! I like to plunge the bit down through the sled until it makes contact with the workbench at the lowest point. By moving the sled around with the bit extended, you can get a feel for what section represents the lowest spot. Anything that is higher than the lowest spot will be routed away. The process took about 10 minutes and as you can see, it made quite a mess. Even though it looks like I removed a lot of wood, I didn’t take much more than 1/32″ – 1/16″ over most of the surface. The one exception was the back left corner where a some fairly significant twist resulted in the loss of about 1/8″.
Over time, my bench will likely go out of flat again and the minor seasonal changes will be easy enough to correct with my trusty #7 jointer plane. For this initial flattening process though, I am very glad I went with the router method. Furthermore, one of the great bonuses to this technique is that the sled is re-usable. If I ever have a large slab of wood that is just too unwieldy for the jointer and planer, I can achieve a dead flat surface using this system. It’s a handy jig to have around the shop! I highly recommend getting one. They are so choice!
Gap Stop & Shelf
The final treatments for the bench include a lower shelf and a gap stop. The shelf consists of ship-lapped 3/4″ boards sitting on ledger strips that are attached to the inside edge of the rails. This shelf is completely optional and some might prefer not to have one at all. But personally, I could always use the extra storage. And to be honest, I think the bench looks more complete with a nice shelf.
The gap-stop is a pretty neat feature of the bench. It not only fills the gap between the two slabs but also serves as full-length planing stop. When not in use, it sits flush with the bench top. If so motivated, you can actually use the gap stop as a tool rack for your chisels and saws while working on a particular project. This is much better than having them roll around precariously on the bench top work surface.
In the heat of battle, I sometimes forget to snap pictures. So we’ll be skipping over some details like the leg vise assembly, the roller brackets, the shaping of the leg vise chop, and the sliding deadman. You might notice that I opted to pay homage to Greene & Greene with my design choices. Even though it is “just a workbench”, there’s absolutely no reason it can’t reflect my personality and tastes. Below is a current picture that shows the state the bench is in today. I’ll be resuming progress on Monday. There are still some finishing touches to do before we can call this bad boy done, but clearly the finish line is fast approaching. I can’t wait to use this beast!
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