Edge Jointing Question - So-called "Spring Joint"

[Darius Ferlas]

By any chance do you know if the maximum cutting depth/height of your newly installed knives is flush with your outfeed table or slightly higher?

Darius,
Sounds like your jointer knives might be a little high. Check how high they are off the cutterhead. John White's book is a good reference.

Gentlemen, as I said the results I get are purely accidental. I wish I could say I whip them spring joints with ease, but it's just a side effect of, apparently, faults in my jointer set up.

To my knowledge the knives are flush with the out feed table. I use one of those "glass plate plus magnets" jigs. I am pretty sure the reason for my "spring joints" is that the tables are not perfectly coplanar. I have a parallelogram jointer, but I find it extremely difficult to benefit from its alleged superiority. The the little bolts (no idea what they are called) used to regulate the height of the tables keep on slipping on me, so what I have now is about the best I can get. Unless I get real straight edge and try again.

[Dru Dron]

Hi Bill,

I appreciate your insights. I didn't mean to come across as overly sensitive and apologize to Pat and Jack again if that's the case. I was just surprised that my original question would be referred to as "silliness". I was just hoping to learn a little more about this technique in case it was beneficial to my project. I've always felt asking questions is the best way to learn and I've certainly learned a lot by reading this forum.

I'm getting the impression from some of the responses to my original post that I may not really need to worry about achieving a sprung joint, and if that's the case, so much the better. I'll glue up my panels and move on. If they start cracking a few years from now I'll know that I didn't do a good enough job on the joints and I'll try again if I ever need to replace these doors.

Thanks,

Dru

[John Downey]

If you want to spring the joint, a couple swipes with a hand plane is all that is needed.

The purpose of springing an edge joint is to use the tension in the center to compress the ends a little more. Whether it is necessary or not is, as you see, open to debate. I've seen all of one table top joint fail under normal conditions, ie: not due to water damage during storage, etc.

Springing an edge joint certainly isn't a requirement of good woodworking practice. That said, I often will do it on joints longer than about 3', as it doesn't do any harm either, and its very easy to do if you have a sharp plane handy. I don't recommend fooling around with the jointer to do this, but that's just me

[Myk Rian]

Drop the outfeed table of the jointer a tad. That will do it.

[glenn bradley]

Gary R is one of my favorite gurus and I'll stop and read or watch pretty much anything he has to say or show but, I don't bother with spring joints at all.

[John Thompson]

I used to years ago but.. find as long as you are getting "butt kiss" joint alignment the entire lengh it is not necessary from my experience with them.

[Frank Drew]

Dru,

I'm with the group that doesn't believe that sprung joints are in any way necessary or superior to ordinary, well-fitted glue joints. In over a quarter century making furniture, I never saw one of my glue joints open up, not at the ends or anywhere else along the glue line (I never got a call-back, at least ).

However, I believe that some of the older heavy-duty jointers had settings to create sprung joints.

[Chip Lindley]

Dru, the purpose of any "sprung joint" is to insure that the ends of panels do not open up during the glue/clamp process. Unless stock contains excess moisture that will allow it to shrink faster at the ends after the glue-up, there should be no problem with gluing up perfectly straight-edged stock. I have never had a problem with panels which were prepared with stock edge-jointed as perfectly straight as I could possible manage.

A very simple method to spring a joint is accomplished by pressing down harder on the center of the board! An extra smidge can be removed in the middle but not the ends. This too-simple technique requires no misalignment of your jointer whatsoever.

Personally, once I get a jointer set up to cut perfect straight at 90 degrees, I ain't messin' with it!! Not until knife-changing time! Finding the elusive set-up which will allow your jointer to cut straight again, may be more trouble than it is worth, in trying a new technique which may be of small value in the grand scheme of things.

Please do not "read too much" into responses by others, as to what you sense as terseness or rudeness. Folks from different parts of these United States communicate in different ways. "Normal" for a New Jerseyite may offend a mild-mannered Midwesterner. "Everyday" for a Longshoreman may offend a PhD. No doubt, some here are Qwerty-challenged, and elaborate as little as possible. Unless explicatives or epathets or direct attacks are included, take it all with a grain of salt.

[Eiji Fuller]

Say you have a table top you need to glue up with 8 boards if you spring all those joints you will have to delfect the joints on the outside by about a 1/16" or more to get them all to close up. I just dont see the point.

If your jointer leaves a gap between 2 boards than it needs some adjustment. no gap is best. The only joints I have ever had fail are when I used polyurethane glue for some exterior columns. I will never touch the stuff again.

[Howard Klepper]

A jointer doesn't just automatically produce a perfect edge when it's set up well. The stock has to be fed well. Different users will have a different set up, depending on how hard and where and when they press when feeding.

That being said, I agree the best joint is dead straight. If you have to be off, it's better to have the gap in the center, but that's IF.

[John Downey]

Say you have a table top you need to glue up with 8 boards if you spring all those joints you will have to delfect the joints on the outside by about a 1/16" or more to get them all to close up. I just dont see the point.

This assumes the wood is un-compressible, and in that case I would agree. The idea is to put the ends of the boards under a slight cross grain compression because they swell before the middle as they acclimate. I'd bet this is a hold over from the days of hide glue, which I still use. I would also guess your example is over-estimating the amount of spring, but I'll admit to never having measured when I've done it

Part of the problem with evaluating the effectiveness is that of the table tops I've seen fail (thought of another, I'm up to two now ) I have no idea if the joint was a.) sprung, b.) straight, or c.) convex. The other problem is that all our glues have a long enough expected life span that you're unlikely to ever see one of your own joints fail. One of the two tables I've seen fail was 40 years old, high quality factory stuff. The other was less than 10 years old, but was 8/4 mesquite - problem was caused by gnarly grain shearing the joint as it moved. I wouldn't really count on any technique or kind of glue to save that one.

I still chalk it up to personal preference. There's a bit of theory behind it, but I've never known anyone to make a serious study of the question.

Now that I think of it a bit longer, springing must be a more modern practice, as it requires good clamping pressure. Pre-industrial revolution that would have been much harder to achieve, steel clamps being either non-existent or absurdly expensive.

[Mike Wilkins]

I have read about this technique in the past, and thought it was kind of foolish to go through all this trouble to glue up a panel. As long as the edge of each board is straight, and your jointer technique is proper, there should be no need to use a sprung joint. I could see using this method if your lumber is not at a proper moisture level, but you should not be attempting to make panels with wet wood anyway.
Joint straight, glue up your panels, and enjoy the efforts.
Just my nickels' worth.

[John Thompson]

[QUOTE=Howard Klepper;1429490]A jointer doesn't just automatically produce a perfect edge when it's set up well. The stock has to be fed well. Different users will have a different set up, depending on how hard and where and when they press when feeding.

That being said, I agree the best joint is dead straight. If you have to be off, it's better to have the gap in the center, but that's IF.[/QUOTE]

Couldn't agree more... the reason I used to spring joints before I got technique down to an art on the jointer. And you are absolutely correct about gap in the center as opposed to ends. That gap will compress and lock the ends tight but.. gap on ends are very difficult to work with and if you have them you are pretty much dead in the water from the git-go for the most part IMO. haha..

[Michael MacDonald]

A very simple method to spring a joint is accomplished by pressing down harder on the center of the board! An extra smidge can be removed in the middle but not the ends. This too-simple technique requires no misalignment of your jointer whatsoever.

Dru -- +1 for this. I wouldn't think that misaligning the outfeed table is a great idea.... I can't remember where I saw this... but it was probably a video on the intranet.

By the way, when I read Pat's comments on "wasting time on this silliness", I didn't take it as rude... just a clear comment on his opinion for the value of this technique... Since I discovered the technique myself, I have wondered if it was really worthwhile. Pat's point may be right or wrong, but it is a sound idea to evaluate what you are trying to do--is it worthwile, or is it overthinking that which is already good enough. It looks to me like there are mixed thoughts on the creek about that conclusion.

[Cliff Rohrabacher]

Don't waste time on this silliness.

What he said