How much of a gap for a spring joint?

[Tony Wilkins]

Chasing my tail a little for jointing the boards of my table top. Right now the boards are 102”. How much of a gap is acceptable for a spring joint?
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[David Carroll]

Back before I bought good clamps I used spring joints all the time. I still do. First I would shoot the boards so when offered to one another there are no visible gaps. Then I would run a No. 7 plane along the joint starting a quarter-inch or so from the near end and letting it lift off a quarter of an inch or so from the far end. I'd do this once or twice. So the gap would be roughly 0.003-inches, depending on how thick a shaving I was taking off.

Note: I should mention that while taking this hollowing cut, I bear lightly at the beginning and end of the cut, then bear more firmly in the center.

I read an article in fine woodworking where the author suggested 1/32-inch. I never tried it, but that seems like too much to me. If you have to force the boards that far to close it seems like it would introduce a great deal of stress. But since your boards are so long, I imagine a bigger gap would be acceptable. I still wouldn't go 1/32-inch, but you could certainly try it out and see. It's easy enough to shoot it back straighter if need be.

What was nice about the joint, is that a single clamp in the middle will hold it while the glue sets. These days I shoot the boards flat on my bench sitting on top of, (and overhanging a bit) a nice, flat and parallel pad of wood or plywood, about 1/4-inch thick, using the bench top itself like a long shooting board. It's easy to control the cut this way without worrying about keeping the plane square to the cut. My final pass, once I am taking full width and length shavings all along the edge introduces the spring cut. Then I run match planes on the edges, mostly to help with alignment.

I think for a long table top, I'd be tempted to glue it up in a couple of sections, not all at once, particularly since I don't have a large assembly bench.

Good luck with it!

DC

[Eric Brown]

Mostly agree with what David said. You might try this: Put a clamp on it in the middle, without glue. How much effort are you using to close the joint. Depending on the type of clamps and the leverage they impart, you should be able to close with a medium amount of force. But, you also need to consider how dry the boards are. If they are still somewhat wet, I would wait before final planing and glueing.

[Tony Wilkins]

Mostly agree with what David said. You might try this: Put a clamp on it in the middle, without glue. How much effort are you using to close the joint. Depending on the type of clamps and the leverage they impart, you should be able to close with a medium amount of force. But, you also need to consider how dry the boards are. If they are still somewhat wet, I would wait before final planing and glueing.

Definitely dry. Put a medium duty F clamp and it closed up with two-ish full turns of the handle at the point of clamping.

[Cameron Wood]

The point is to counteract any tendency for the ends to open up, not to build tension in to the piece.

If there are five joints with a fat 1/32" gap each, and it is all glued up at once, the table could be 1/4" narrower in the middle than the ends.

[Richard Coers]

For me it is just seeing a bit of light in the center. Never measured it. I usually check it by putting one board on top of the other and trying to pivot the board on top. If it pivots easily, the center is only touching. If it really drags at first, the ends are touching. Another thing I do is lay out the boards and then mark the mating boards at a joint with inside and outside of the fence. That cancels out any angular error between the table and fence. One board might be 89 degrees and the other 91 degrees, but the joint will be perfectly flat. Use any steep grain boards as a guide for which direction that extreme board should be fed.

[Mel Fulks]

I’ve put as much as an 1/8 “ at center of length on boards 4 and 1/2 feet long. Mainly with soft pines and poplar. Less with harder woods. I have NEVER had
an end open up . Gap would be less with stuff like maple. I used to put a bounty ,10 ,15 dollars, for anyone who could show me
an open end. Never had a claim. Used to routinely face, plane ,joint ,and glue, would not use helper. Sprung joints go way back .
Hot shot new foremen would sometime “ that ain’t necessary “. Real boss always overruled them.

[Mel Fulks]

In recent years there have been a number of online comments such as, “With todays modern glues sprung joints are no longer needed”.
Most likely posted by guys seeking an office job.

[Tony Wilkins]

For me it is just seeing a bit of light in the center. Never measured it. I usually check it by putting one board on top of the other and trying to pivot the board on top. If it pivots easily, the center is only touching. If it really drags at first, the ends are touching. Another thing I do is lay out the boards and then mark the mating boards at a joint with inside and outside of the fence. That cancels out any angular error between the table and fence. One board might be 89 degrees and the other 91 degrees, but the joint will be perfectly flat. Use any steep grain boards as a guide for which direction that extreme board should be fed.

I did match plane plane them after first doing the Charlesworth straightening (where you use stop cuts to get it to stop planing) technique. First time I’ve worked with boards that long.

[Warren Mickley]

In recent years there have been a number of online comments such as, “With todays modern glues sprung joints are no longer needed”.
Most likely posted by guys seeking an office job.

Spring joints were not used in the hand tool era. They arose around 1890 and were originally used on boards that had been jointed by machine. I haven' t used a jointer machine in over forty years and don't understand the mechanics of why they would have spring joints.

18th century cabinetmaker Peter Nicholson says the edges "must be brought as straight as possible" and talks about using rub joints with "very hot" hide glue, no clamps.

[Mel Fulks]

Sure Warren is right about time periods. The Nicholson news was most assuredly right ,given the choices available in those days. But
I’m not persuaded that spring joints have any drawbacks. They were using air dried material. I think sprung joints were used in 19 th
century . Not gonna try to buy a mule to hitch to the buck-board…. unless it’s for a good paying job in a Western movie. And why did
Doctors stop using leeches? They did good work !

[Rafael Herrera]

A skilled joiner would have produced a straight edge with hand tools, and so can a skilled practicioner today. A rub joint is an efficient and simple method to glue two boards together, not even clamps are needed.

A spring joint works too, but from its description it is a joint that rather relies in a bit of brute force. The Charlesworth method is fiddly and you still need a clamp. I would not describe it as a better or advanced method.

I can routinely make seamless joints without purposely creating the hollow for a spring, rather aim for a straight edge. The plane I use is a no. 7 that I took special care to flatten the sole. The last passes are end to end shavings, I don't do the stopped planing of the DC method. I do use clamps.

[Mel Fulks]

Nothing wrong with old ways . Rubbed joints are still used ,but mainly on just short stuff. Brute force is only used by young easily
bored employees. The old workers knew the wood had to be warm . I’ve seen guys bring in wood from a small shed , and glue it up
quickly! “Boss says he needs it fast ! Sprung joints were used on air dried wood, you don’t want the ends to pop open. And sprung
joints make sure they won’t. Some architects plans specifically call for sprung joints, or state that glued up stuff with open ends will
not be accepted. You are not gonna find any holes in the old ways, but you might find faster ways .

[Mel Fulks]

I disagree that sprung joints were all late . They have been found on Cremonese violin tops.

[Derek Cohen]

I do not use spring joints on the whole, only very occasionally. A straight edge and rubbed joint is my preference. I think that the reason for some using a spring joint is when the edge is difficult to get straight, and a slight hollow is better than a high spot, and more likely to close flat.

Regards from Perth

Derek

[Tony Wilkins]

I do not use spring joints on the whole, only very occasionally. A straight edge and rubbed joint is my preference. I think that the reason for some using a spring joint is when the edge is difficult to get straight, and a slight hollow is better than a high spot, and more likely to close flat.

Regards from Perth

Derek

I’ll try for straight then. I think the length of the board led me to plane in more of a hollow than I thought. I was ok with a bit of spring but I think what I have is too much.

[Mel Fulks]

Sprung joints are especially needed for air dried wood. A lot of modern jointers are set up wrong….front table too low. That’s bad.
But it demonstrates innovative thinking. “ now the rough ends won’t hit the front table !” For sprung joints on machine jointer, I straighten all in regular mode , then adjust front table up, and joint again.

[Prashun Patel]

I think it can be tricky for mere mortals like me to get a perfectly jointed straight edge on a long and heavy boards.

My approach is exactly what Derek mentions: aim for perfection, but err on the side of a slight hollow if I must.

Sprung or straight, the test for me is strips of paper placed along the joint. The pieces should be locked in place under moderate clamping pressure on a dry fit. Then I know the joint is ready.

Best efforts may still lead to a visible seam over time if you have not selected a board that is stable or properly dried.

[John C Cox]

When I'm jointing, I aim for flat/no gap end to end. The room for error is a little light in the center which closes readily with light clamp pressure. Loose on the ends is a no-no.