Over the years, I’ve done my share of beam work, but I didn’t get a taste of real timber framing until a few years ago, during the recession, when a friend and I salvaged an old barn—there wasn’t much work around and the opportunity presented itself. Even though the barn had outlived its useful days and the roof had failed, most of the timber framing was still stable. And here’s why—joinery.
Every corner post in the barn was cut with a tenon, mortised …etc. etc. Long beam spans were joined with scarf joints, and also secured with mortise-and-tenon joints to the posts. There were some bolts but very few nails (40d) to be found anywhere in the barn—all the joints were secured with hand-hewn wooden pins or dowels. That barn couldn’t fall down unless every post rotted out completely from the bottom to the top.
Ever since that teardown, I’ve wanted to use scarf joints and mortise-and-tenon post connections with Glulams. Glulam beams are nice because you can order any size—they’re readily available, economical, and fairly straight and square. Sometimes in life, you get what you wish for. Not long ago, a big job of Glulams came up and before long, instead of using steel plates and connectors, we were cutting mortise-and-tenon joints.
Layout for scarf joint and post
In this article, I’m going to describe how we used two of the joints found in that old barn: mortise and tenon joints, connecting the corner posts and beam-headers; and scarf joints—together with mortise-and-tenon joints—to join the long beam spans.
For all the joinery, we started with good drawings.
To determine the length of any scarf joints on the job, and to be sure the proportions stayed symmetrical, I took the depth of a beam and multiplied it by 1.5. In the example included in this article, we were using 12-in. beams, so the length of the scarf joint was 18 in.
I centered the overall length above the post. To avoid a sharp point that might splinter, I designed the top with a 1-in. plumb cut and the bottom—beneath the scarf joint—with a 22-degree bevel cut, which also helped transfer bearing.
To support the scarf joint beam splices, and secure the joint, I designed a tenon on the top of each bearing post, cut with a minimum 1-in. shoulder on the sides. To secure the entire joint, we used 1-in. diameter pegs driven in holes drilled approximately half way between the top and bottom of the beam and the intersection of the scarf joint.
While we were dismantling that timber-frame barn, I found a series of very fine pencil marks or scribe lines at each peg, on each timber, which led me to believe the those carpenters drilled the holes before they assembled the beams. So I followed the same approach, which might have been more difficult but provided a few advantages—especially when it came to drawing the joinery tighter during installation, but more on that later.
I made a pattern for the scarf joint with a piece of plywood ripped to the same width as the beam. I used the center of the post for all calculations. After laying out and measuring the centers of the posts on the building, I was ready to mark the beams.
I lined the pattern up to the bottom of the beam. It’s critical that the bottom of the beams line up. If there is a slight difference in height, you can deal with it at the top of the beams by using shims.
After tracing good pencil lines, I used a straightedge and a knife to score the layout lines and help prevent tear out. And then I was ready to cut.
Cutting the mortises
To cut the mortises, I used a chain mortiser—a great tool that makes mortising extremely easy.
|I adjusted the machine so it would cut precisely on my layout lines.|
Then I just let the tool do the work. All I had to do was crank the handle.
|I have a Makita Mortiser, which I think we paid about $1,200 for, though there are other models out there that adjust for angled mortises, too. The Makita I have goes about 8 in. deep, so rolling the beam over is often necessary.|
My Makita cuts up to 4 1/2 in. wide in one pass, without having to reset the machine, which allowed me to make the mortise and tenons match—a definite advantage.
For big beams, where the mortise can’t cut deep enough even from both sides, I used a chainsaw to finish the cut. Because the mortise isn’t visible on these joints, I gave myself a little wiggle room and allowed for slight adjustment and an easier installation. I always try to make jobs easier on myself and speed up installation time.
|A little wiggle room also helped because I had to cut the mortises first, before cutting the scarf joints, otherwise I wouldn’t be able to clamp the mortise to both sides of the beam.|
Without a machine like this, you could drill out the mortise and finish with a timber-framing chisel. I’ve also seen old-time drilling apparatuses on eBay that would be perfect for this and would probably work well if they’re tuned properly.
Cut the scarf joints
There’s no special tool I know of that makes it easy to cut scarf joints. A beam saw, a Big-Foot saw, a worm-drive saw, a hand saw—if you have the game. Whatever works best for you.
For the length of the scarf joint, I started from the open end of the scarf and cut from each side of the beam, then finished up with a handsaw, cutting the butt joint and bevel joints last. I set up multiple saws for the top and bottom cuts—one for depth and angle to square-cut the top, and one to bevel-cut the bottom. I made those cuts each time I rolled the beam over. I got as close as I could to the line—never “taking” the line, then used a grinder with a 36-grit sanding pad to fine tune each cut.
Cutting the posts and tenons
I calculated my post length including the length or height of the tenons. I intentionally made the tenons a bit short, so I wouldn’t have to grind the tops off later, up in the air. As soon as I’d finished laying out the tenons, I knew exactly what size the mortises would need to be, so I could cut either one first. Like I said earlier, I always leave a little wiggle room for play, but only as much as is practical—not enough to weaken the joint. A little bit of soap or paraffin doesn’t hurt if the joint is really tight.
Mitering and notching corner beams
The corner posts and beam connections were probably the trickiest—even harder than the scarf joints because of the different levels of joinery. The outside corners needed to be mitered, so no end grain would be visible. But the inside corners had to be butt joints, otherwise any wood movement at all would cause those joints to open up.
|I designed a half-miter half-lap butt joint for the corners that also captured the post tenon so we could use the same pegs to secure all three components. I started by drawing very careful layout lines.|
|I used the beam saw to rip along each shoulder and cheek cut.|
Beam saws are slow-going—you can’t push them. And they spin so slowly that you can almost count the teeth at top RPMs. The trick is to push lightly and keep the RPMs up.
I finished the miter with a worm drive after all the steps were cut.
Drilling holes for pegs
The barn I took down used 1-in. pegs. I figured that would work for this job, too, so I laid out the holes on the beam and the posts using my full-scale drawing. In some instances, I left out the upper hole on the beam’s scarf joint, in case I had to adjust the cut a little. But I made sure that both holes were aligned vertically—after all, this part of the joinery was visible. A sharp paddle bit seemed to cut the cleanest hole without tearout. I did learn that if the holes are offset a little in one direction, driving the peg in helps suck the joint tighter—which is a good thing. But if the holes are offset in the wrong direction, you have to make a correction in the air and drill out the holes, or the peg can pull the scarf joint open. Like I said earlier, I try to do everything as precisely as possible, on the ground, so I can avoid excess ladder or scaffold time later. But like most jobs, nothing is perfect and stuff happens.
Cheap dowels might work for looks, but they snap like toothpicks—trust me.
|Since the pegs from the salvaged work I did were hand-carved, I followed suit, at first. I cut a nice, straight grain piece down with the table saw, making it 1 in. square, and then I mitered the edges off to make an octagon and minimize carving.|
I usually cut them to stick out an inch or so on either side, and sometimes I cut them flush or leave a little proud for a more rustic look.
Once all the layout and cuts were made, it was time for the fun part—if all my homework and cutting were done correctly!
|I temped the posts up and braced them carefully, but again, with a little wiggle room, which allowed me to move them around a bit if necessary.|
|I started with the center span joints, so I could fine-tune the fit. The ends that were buried in the walls definitely helped provide some adjustment.|
|Then I worked my way across each span, using my Pettibone to swing each stick into place.|
|If all the joinery is laid out and cut carefully, and correctly, assembly goes extremely fast.|
|We usually try to properly prepare so that weather will rarely slow us down.|
Sunny days can be distracting, what with the beauty of the mountains in winter…
…but we still got a lot of work done.
The corners were sometimes the most challenging. Though the beams fit perfectly around the tenons, the varying width and height of the beams required some real attention—after all, for appearance, the bottoms of the beams had to be flush, which meant minor alterations to the cheek cuts, and later, some planing and shimming at the tops of the beams.
On the corner posts I used 3/8-in. GRK timber screws so that I could lock all the joinery/elements together. Then I covered the timber screws with short pegs.
It’s not surprising for a beam or two to need a little fine-tuning, especially on the scarf joint.
|But diligence in layout and precise cutting paid off in some sweet moments, where joints went together without any adjustments, even though I tried to leave a backdoor open for those moments when joints might not cooperate.|
The joints came together easily, for the most part, but there was still some adjustment required. After all, the beams weren’t milled perfectly and neither am I! We had a lot of techniques at our disposal for aligning the joints, and we often used all of them. Pry-bars, chisels, and bar clamps all helped cinch the joints together.
In my experience, this type of joinery is a great option both structurally and aesthetically. And it’s not very difficult once the layout is done and you get going. Considering most other options involve square butts with exposed brackets or knife plates that don’t perform well when hogged out, I think this is a great option and a great example of how old techniques are sometimes the best techniques. One thing’s for sure: like that old barn I reclaimed, that post-and-beam home is never going to fall down.
Personally, I enjoy learning how carpenters used to work, and I enjoy re-introducing those skills to contemporary jobsites.
I think we’re even seeing the practice establish a new architectural style, what I call “refined rustic.”
Stay creative and when you can, enjoy the craft.
• • •
David Lemke owns Frame to Finish LLC in Bend, OR, and has been a licensed contractor for around seventeen years. Like a lot of contractors, he started in construction working with his dad on remodeling projects, and then moved on to different framing, siding, and finish crews before getting licensed. David likes to specialize in fine, upscale custom homes, but working in a somewhat limited market, and in tough economic times, over the years he’s jumped into anything and everything, from small remodels to commercial framing. When David’s not on a job or project, he likes to fish, play baseball, and go snowboarding with his kids.