The spring joint

All of a sudden I’m kind of hungry… Spring rolls and “flied lice”, baby! But for now, I’m building a birdhouse with my daughter. I had to glue up some wider boards, and soon I found myself on a roll. So to speak…

Kudos to those who took the Lethal Weapon reference, by the way!

There is several ways to join two boards to make a wider one. But the spring joint, once mastered (which takes no time at all – and very little skill), is really easy, fast and reliable. It also has a hidden benefit to it – the ends of the boards changes over the seasons, more so than the middle. This can cause stress on the glue line at the ends, leading to cracks. By deliberately creating a gap in the middle of the boards, we remove (most of) the problem as there will be no stress build up. In stead, we put the ends of the boards in compression, which will prevent the joint from opening up over time.

I’m building a birdhouse with my daughter, but first I needed 15cm wide boards, but I only had 10cm wide boards. I cut two extra pieces which I ripped down the middle with my hand saw. This gave me four pieces roughly 5cm wide.

Jointing for glueup of a panel

I proceeded to clean the sawn face with my scrub plane (two sweeps and done, it is VERY fast!). I then placed the two boards to be joined, in the vice. I quickly jointed both edges at the same time, so that they will match each other perfectly.

You do this by imagining the joining faces to be the back of a book. Place them like a closed book in the vise and plane both faces at the same time – and by the way; note that this method does not require 90 degrees to the sides. You could use 78.6 if you wanted to, and the result would be perfect. But we try to be accurate and train ourself to maintain as close to 90 degrees as we can – even for the modest birdhouse. If you joint two pieces like this at 89 degrees, one of the pieces will be 91 when you open the «book», which makes this work.

I then made the spring in the boards.

The markings shows where to plane

I started a small distance in from the end and took a shaving with my smoothing plane. I stopped short of the far end, roughly the same distance in from the edge as my starting point. I then took a swipe of the middle of the board. In the image above, I’ve marked the starting points and the end points. Lastly, I took one long swipe across the entire length to smooth it out.

Just a gnat’s nadger of a gap is enough.

As you can see, there is barely a gap there. I had to hit the angle just right in order to take the picture. The gap can be closed with moderate clamping pressure.

Let’s cook a horse then!

Time for the sticky stuff! In Ye Olde Times, you cooked a couple of horses and got a bucket of hide glue. At some point somebody cooked a horse that acted like a lunatic, and crazy glue was invented.

Joke aside: if for some reason you might want to take a joint apart in the future, hide glue is the way to go. These days, you can buy the cooked horse in a can, so there’s nothing to it. I prefer more modern alternatives. I recently converted from regular Casco white wood glue to Titebond. I get the hype. I am a convert. This stuff is great! Try it. You won’t regret it.

Some gravy…

Run a line of your preferred sticky mess along the joint. Place the two boards together then slide and wiggle them around.

You take your left part out, you put your right part in, then you wiggle it all about. You do the gooey glue-y!

-Scrooge McGoofy

There is NO NEED for fancy gizmos, doo-hickeys or thingamabobs here. No disposable brushes, rollers or what have you. Your finger works great. For hard woods, spread glue on both pieces to aid the bonding. Another thing: do not use too much glue. There is no point in having the joint drooling glue until you have half a bottle of sticky stuff all over your bench and almost zip left in the joint. It really doesn’t take much! A tiny amount of squeeze-out along the length of the glue line tells us we’ve used a smidgen more than the correct amount. Just perfect.

You can be generous with gravy – in fact, I encourage just that – but not so when it comes to glue. Anyway, time for some depressing instructions.

Put the pressure where it counts!

One single clamp is all it takes. It closes the gap and the boards stay in place. Very easy to do and very stress free. Cheap, too….

There are a few options for longer boards. You can use pinch dogs to hold the ends of the boards, more clamps or a couple of cauls at both ends. This will keep the boards from sliding around until the glue bites. You could also shoot a couple of brad nails into the soon-to-be-glued face of a board and cut’em off close to the surface – they will keep the pieces in check, but you need to be accurate when joining the pieces. You also need to do it after you’ve smeared the glue. Sounds like work to me…

I’d use one single clamp for boards up to 100cm, but for longer boards I would use more.

Some people say use salt to add friction sonthe pieces won’t slide around. I have some salty comments on that I’ll keep for myself. But I don’t condimen.. compl… condone such practices!

In some cases the only viable option is a bucket of clamps. You will never have enough clamps.


Panels glued up
All boards done!

Now it is just planing the boards flat, cut to length and then make the parts for the bird Astoria. Some father – daughter time to assemble the house, some finish, and the birds can move in.

A spring joint is a good choice when you’re using rough prepped boards to make a table top or a panel. I would get the boards roughly to 4S, with at least one face planed smooth to act as a reference face. The final smoothing should be done after the panel is made. It will move on you anyway, and you will most likely need to fix the glue line.
And remember: there is NO NEED to flatten and smooth the underside of a table top, the inside of a panel in a chest of drawers and so on. There is really not even necessary to get an even thickness. Machines has made accuracy easy to achieve in every single part of a furniture piece. You just jam the wood into the thing, and it spits out flat and true boards on the other side. But how many times in your life have you ever checked if the underside of the dining table at your inlaws was flat and smooth? Have you ever checked the thickness of the table top on your grandma’s coffee table?
Flatten the area where the aprons meet the table top and get the edges down to an even thickness (but you can always do it at an angle and feather it out to zero. Do not sweat that 2mm at the center! Just make it smoothish. It is good enough.

Which meat do you prefer in your spring rolls? (vegans: stop eating the food my food eats!!)

I am a fan of chicken, and I foresee a future source of free fowl…..

2 thoughts on “The spring joint

  1. Morsom og nyttig lesing. Jeg trenger nok mer overbevisning ang Titebond, da jeg mener mange slike produkter skjuler hva de er og bare skal ha mer penger. PVA er PVA uansett hva slags merke det er… Men jeg har ikke satt meg inn i Titebond familien. Så det kan være en morsom utfordring i fremtiden. Takk for en underholdene og informativ artikkel 😉
    Kopierer kommentaren inn på FB for å skape litt blæst rundt bloggen din.

  2. Pingback: The support table, part 1 |

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