Spring joints for panel glue ups - concave, convex, expansion, etc.

[Eric Arnsdorff]

I've never used a spring joint for panels. I'm wondering if it is worth trying on my next panel glue ups that I'll be doing.

I can see a nice advantage of a slightly convex (gaps at the ends rather than the center) as it would seem to provide a tight joint with less clamps. However, it seems more effective way of doing this is with cauls.

I'm struggling to understand any advantage of the concave (gap in the middle). I've seen the indication of humidity expansion/contraction and such. I'm not following this reasoning though. Once the glue dries without a gap, it seems if there is uneven wood expansion/contraction would be the same issue if there was no spring joint used. I'm just not following the thinking and I'm curious if there are any studies done or case studies. It seems this is considered the more common spring joint. Or maybe I just have come across more of these on the internet.

I do wonder if creating a joint that is consistently slightly convex may be easier than trying to create a flat joint (which is my normal attempts). My "flat" joints will often end up either slightly convex or concave in areas. Granted these are small. But I have to pay attention to where these are to clamp it such that they are removed. This is the one thing that has my interest in these. But then I debate with myself if cauls are really the better answer.

Then I wonder if simply putting the joints together and running them over the jointer is the simpler and best method. I'm not that great with a hand plane. If I were I could definitely see just making a pass or two with a hand plane.

My conclusion that I haven't tested is to clamp my boards with the joints matching then run them over my jointer. The make cauls to help minimize the number of clamps needed.

I'm interested in your experience and thoughts. I have come up with things like this before and when I tried them, I quickly realize I'm struggling to get it all to work.

[Mel Fulks]

We have a recent and long thread on this subject.

[Eric Arnsdorff]

I did a search but I didn't see anything recent or anything discussing the convex versus concave.
Maybe I'm not using the search on this forum properly.
I'd appreciate a link to the thread if you have it.

[Eric Arnsdorff]

I did just figure out that the search bar I've been using at the top of the window is not the correct one. I just saw that there is a second search that is for the forum.
If nothing else, I learned that and that helps!

[John TenEyck]

I've never seen a good reason to use spring joints. The argument about needing fewer clamps is false if you believe the glue manufacturers who tell you you need a clamp nearly as close together as you can get them to get enough force. Seasonal expansion/contraction arguments are less than convincing to me. If I could shoot a perfectly flat and 90 deg edge on a long board I would superman. So the jointer is my tool of choice and I make the mating edges as perfect as I can. Sometimes they are not quite perfect, but never off by more than maybe 1/64" over several feet and that is easily drawn tight with clamps.

The best way I've found to verify you have jointed a 90 deg edge, or at least complimentary angles that will yield a flat panel is to stack the boards vertically on edge. If you can stand them on edge, one on top of the other, on your workbench and a square fits perfectly against the face of them then you know the jointed edges are correct. Any bow in the panel means you need to take corrective action. When boards stack up straight they glue up flat without the need for cauls to force them that way. If cauls are needed then the angles aren't correct and you likely will end up with a gap on one side or the other of the panel.

John

[Mel Fulks]

It was slightly concave versus straight . But yes some can only make convex, since they can't make proper jointer
adjustments. I'm sure it's the freshest and most complete anywhere.

[Mel Fulks]

John, I hope you read my posts in that thread ,they are the best available anywhere.

[Robert Engel]

Its concave & the theory is the it counters the tendency of panels tend to shrink more at the ends due to endgrain moisture loss, which would result in an open joint.

Bear in mind this originated in the says of hide glue. It does save on clamps, so that could be a factor especially in days of yore.

With modern glues I don't think its necessary.

[Brian Holcombe]

Convex is sure to gap at the ends. Flat or concave.

I spring anything important, and it’s working well I have nice tight joints.

I use a ton of clamps.

[Kevin Jenness]

In theory a concave spring joint held together in the middle will exert continued pressure on the ends and keep them together even if the panel is shrinking, which it will do faster on the ends due to higher end grain moisture transmission. The most important thing is to use acclimated lumber and then you don't have to worry about it.

[Mark Bolton]

Im with Brian and Kevin. We spring everything possible. Having continuous closing pressure on the ends of a panel (where they will inevitably see the first, and most movement) is a no brainer. It has nothing to with less clamps. We clamp as close together as reasonable and reef the clamps down as hard as possible. If you have open joints and the ends that you are pulling closed with clamps your pretty much guaranteed they will open over time. If your boards are boutique jointed and perfectly straight, you'll likely still risk them opening at the endgrain. Keeping those ends in compression is a good thing.

[Mel Fulks]

Mark ,thanks for the comment on spring joints. As a smart and practical shop owner ,your advice has weight.
This thread has a lot of good stuff , I don't think anything was left out. It could be edited to be a most informative and
useful pamphlet . I would be happy to edit authors draft at no charge or print credit.

[Michael W. Clark]

I know you guys mention that some jointers have a “spring joint” setting. If a jointer doesn’t have this, how would you recommend doing a spring joint? Would it still be practical on a jointer or would you recommend using hand tools?

[Mel Fulks]

That's in the thread, You raise outfeed table just a couple thousandths. If you have a jointer that is adjusted with a hand
wheel, Not a stick it's pretty easy

[Michael W. Clark]

Thanks Mel, I’ll read the other thread again. I’ve been contemplating a new jointer and this would be a plus for handwheel vs stick adjustment