Tuesday, February 3, 2009

Roubo Bench - part 2: The Base

In this episode, I describe how I built the base. I decided to begin with the base for a very good reason, unfortunately I can't quite remember what it was, but it was good, I assure you.

Here is the page from my Visio plans for the base.


I wanted to keep the leg dimensions the same, each is made of 5 4/4 boards, each 5" wide. Glued up together they make a true 5x5 leg. I laminated them allowing for the open mortise to go through the leg for the long stretchers. This saved me the trouble of cutting a 2"x3"x5" deep mortise through the leg. That was a lot of trouble saved.

As you can see from the plan, I toyed with making the long stretchers longer and then possibly putting wedged tusks through because from the beginning I wanted to make the bench so I could knock it down for moving. I ended up trying something different to the same effect.

I began by cutting all the leg parts to size.

I determined outside faces and began gluing. At this point I still hadn't learned the very basic lesson of ensuring all boards grain is going in the same direction. Fortunately, it's not as important on the legs. If there's a little tear-out, not such a huge deal.

The glue-up was a little more tricky than I anticipated. For one thing, with only short times in the shop, less than two hours a week, you really can get much glued up in that time. It also didn't help that right after I got the first leg finished I ended up having to have surgery, twice, and then radiation treatment all covering from March through June. When you can't even lift the weight of one leg, it's not so easy to make them. I managed to get some parts glued up and get some of the legs finished.

Once I got the legs put together I then finished them a bit, smoothing down some of the roughness, and beveling the bottom edges to avoid tearing out chunks as you drag it across the floor.

Next it was time to make the stretchers. I began with the short stretchers. I built them to the plan. Then I bothered measuring the wood. Oops. The boards in my drawn plan were 8/4 (2-inches) thick. The boards I ended up getting were 7/4 (1.75" thick). This kind of threw off the measurements of my top. I decided to go with 14 boards wide, thus giving me 24.5" exactly. But I had drawn my design for 12 2" boards thus yielding a 24" wide top. I had just built stretchers just .5" too short. Back to the lumber pile. This is why you buy more lumber than you need!

Because of this blunder, one of my long stretchers has two pieces butted up together to make the inside section of the laminate. (BS1 on the diagram)

It was at this point that I came up with the idea of how I was going to make this a knock-down bench. Instead of through tenons with wedges, I was still going to make them through tenons, but I was going to pin them. I thought about wooden pins that I could then drill out should I wish to move, but then had an idea.

I'm not sure where I got the idea from, whether I came up with it totally on my own or something gave me the idea but I thought about the large pins that hold door hinges together. They're about 1/4" in diameter, 4" long and have a head to give you some leverage when pulling them out. I mused on this idea all during the even slower period of intense end-of-season gardening that cuts into my already meager shop time as I help my wife get the beds ready for the winter.

I went to the Woodworking in America conference in November and absolutely loved it. While there I got to meet Chris Schwarz (and many others) and see the original bench he had built in the book. I ran the idea of the brass pins by him and others and while the reception was generally "sure, I guess you could do that, but not sure why" I got the impression it was something just not thought of before. I wasn't encouraged, nor was I discouraged. But seeing the original bench was very inspirational to get mine done!

I finished the stretchers and began to put the base together. First I began with the (new) short stretchers.

I cut my own pegs from some tough, straight-grained pine I had. I first tested it for shear strength by putting one peg into my vise and whacking it with a mallet. I have two mallets, one round carving mallet that I use for everyday whacking, and then the one you see in the photo, my "Persuader" that I bought at an antique store for $20. The store is one of those that get "antiques" by the container load from Britain. The head is about 2-pounds and very hard. It's wonderfully persuasive, and when it took some really hard whacks with the persuader to break the pin, I was satisfied.

What looks like a crack along the pins is actually just uneven glue-up. This was planed down smooth later.

The brace and bit in the picture represent the wonderful time I had cutting the 1"x3" by 2" deep mortises into the maple legs. The mortises go all the way through to the long stretcher mortise, which helped for figuring out depth, but man, that's a huge mortise to cut out. Taking down the sides to be smooth and straight proved to be a real challenge at times. At least one is not terribly straight and has a small gap where the wall is undercut at the bottom. I could wedge it, but I figured after pinning and once it's all together with the top on, the stress on that particular joint will not be such that the gap will compromise any strength.

This was a really exciting moment. For the first time, this pile of wood began to look like something. It was fun to have a leg. It was more fun to have four legs. This was now even better.

The next step was to begin and fit the huge tenons of the long stretchers into the massive mortises. I had to fare the mortises and sometimes the tenons to get them to fit. The mortises had been created by just gluing shorter pieces and I had used patterns of the tenons to help keep spacing, but it's never perfect.

Then there was the fateful day when I was ready and used my persuader and several sacrificial blocks to protect the ends of the tenons to pound these great suckers into the mortises. Getting one end together was harder than getting the other. Once I had one end on the floor with two long stretchers sticking out, I put the other end on top and saw more evidence (as if I needed it) that wood is a living material. What you couldn't see with casual inspection became obvious at this point, that one of the stretchers had a slight amount of twist to it.

This is where the mass of the whole thing comes into play. I just torqued the base around to get the tenon started, then used the mass of the end piece to help drive the whole thing down onto the tenons. It was much easier with the weight of the two legs helping me.

I now had the whole base put together.

Now that was a moment to celebrate. It is so massive and tightly put together that it is just not coming apart. The mass also overcame any issues with not quite even bottoms on some of the legs. The base does not rock or wobble even a hair's breadth. It is as solid as I could wish it.

So, despite feeling like I didn't really need them, I still wanted to experiment with the brass pins. I justified it by being concerned that racking of the base from planing might begin to work the tenons loose. When looked at dispassionately, I think the odds of that are pretty darned low considering the size of the joints, but we all have our caprices.

I obviously wanted the heads of the pins to sit below the level of the wooden leg to keep any metal off the surface of my bench, even the leg surface. I first marked out where the pins would go and drilled the countersink hole for the head of the pin with some of my wonderful center bits. I picked up a set of these some years ago and every time I use them I wonder why I don't use them more. They work so well.

You can see this picture was taken on the vise leg. The notch in the leg will be where the parallel guide will go. I cut out this notch on each individual board before glue up since cutting it in a 5" leg with a handsaw seemed to be much more fraught with peril than doing it on five 1" boards. And I want as little peril as I can get.

I then cut the ramp that will allow me access into the hole to pry up the head of the hinge pin. I had experimented with this whole setup before starting this on my bench, and I found out a couple of things. One of which was that cutting this ramp with a mortise chisel was really very easy, with a bench chisel, not quite as much. I just used the size of the mortise chisel to determine the ramp size since it was sufficient for the screwdriver I already had marked out as my prying tool.

I drilled the holes for the pin itself. I found in my experiments (I'm big on experimenting before doing anything terribly new, and that has paid off tremendously) that my Jennings bit made a hole that was too perfect and the fit was so tight that it really made it hard to get the pin out. My Irwin bit, on the other hand made a hole just perfect. There was some bite but I could also easily get the pin out.

The tenon in this picture looks worse than it is. That is not a gap you see, but actually the long stretcher is a fraction of an inch proud of the leg.

And voila, using a wooden "nail set" I drove home the pins with my persuader (overkill, but it's so much fun to use) and I have an amazingly stable and exciting (I know, I have a problem) bench base.

It was so satisfying to get to this point that I'm afraid I could easily develop "a bench problem" as Chris Schwarz talks about. And I haven't even built the top yet.

The next steps are figuring out some issues around the wagon vise and getting ready to make the top. But that's for next time.



  1. Nice descriptions there. A couple questions:

    1. Did you drawbore the holes for the pins?
    2. Did you need a corner chisel to clean up the mortises post-drilling? Or just your mortise chisels?

  2. I did not drawbore the holes for the pins. I didn't want the pins to be too tight in the holes. The idea of the pins was NOT to draw the joint tighter together, there's no way I could make that joint more secure. It was merely to give me that extra feeling of security that the tenon would not work its way loose.

    Now that I've worked with the bench with the top on it, I'm convinced that the pins are over-engineered. (like that's never happened before!) If I did it over, I might not put anything in there. The tenons are so long, and it was such a challenge to get them through the mortises to begin with, I just cannot envision them working their own way out.

    If I were doing this again, what I'd do is just leave them as is, and after use if I found them starting to creep out, I'd then drill a single hole all the way through and drive in a single wooden pin. If I needed to break down the bench, I'd just drill out that pin and be done with it.

    I was going to fix the top to the base with this pins too, but once I got the top on, I just don't see a need at the moment, so I've held off. Once I get the leg vise on and start using it in earnest, I'll see if the top and base rack at all. If so, then I'll pin them down, but as it is, I haven't bothered. It's pretty darned solid.

    I still like the hinge pin idea, and still think it's a possible solution to a bed frame to avoid bed bolts, which I just don't like, for some reason. I just don't think it was truly necessary for the five-inch through tenons. If you were doing shorter ones, then they'd be more useful.

    As for cleaning up the mortises, I don't have corner chisels. I use my mortise and bench chisels. I am sure I don't do it the best way, but I keep getting better at cleaning up the corners. You just have to nibble your way to square with whatever works.

    Thanks for your comments.



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