# Hollow-jointing



## JBSmall (Jul 6, 2012)

Anyone else hollow-joint?
I was taught to raise the far table of the jointer a hair, which would produce a hollow in the edge, which, when doubled with its mating board done the same way, allows a crack of light through in the middle when held up together.
The reason for this is to build-in some pressure at the ends, so that the glue-joints won't fail and open.
I do this also by hand by clamping the mating-boards' faces together and planing both at once, so any square-error will cancel.


----------



## Dave Paine (May 30, 2012)

This is new to me. I am interested if this technique is used by others.

I normally try to get a tight fitting joint.


----------



## jschaben (Apr 1, 2010)

JBSmall said:


> Anyone else hollow-joint?
> I was taught to raise the far table of the jointer a hair, which would produce a hollow in the edge, which, when doubled with its mating board done the same way, allows a crack of light through in the middle when held up together.
> The reason for this is to build-in some pressure at the ends, so that the glue-joints won't fail and open.
> I do this also by hand by clamping the mating-boards' faces together and planing both at once, so any square-error will cancel.


Hi - I think it is better known by the term "spring joint". Here's some info
http://www.finewoodworking.com/item/26796/spring-joints-an-edge-glue-ups-best-friend/page/all
:smile:


----------



## firemedic (Dec 26, 2010)

That's more commonly referred to as a "sprung joint." if my memory serves me right it became a common practice for commercial panel clamping operations. 

Hide glued panels have a propensity check or split on the ends, modern glue doesn't. Old solution to an old problem which no longer exist is not uncommon in woodworking. This one in particular is oddly amusing though and I'll get to that in a bit. The issue in this case is the solution to old glue is a problem for new glue. Sprung joints with modern glue result in glue starved edges on the panel ends due to the excessive clamping force needed to close the center of the panel.

The old solution in modern use actually causes the old problem!

So, no I don't use sprung joints with modern glue but it's not a bad idea if using hide glue... Won't work for a rubbed joint though!


----------



## Bonka (Mar 24, 2011)

*Spring Joint*

I spring joint edges. It is good to know that a starved glue joint with modern glues could result using this method. I use mostly hide glue but I will remember this when I use Tite Bond.


----------



## WarnerConstInc. (Nov 25, 2008)

I have a lever on my outfeed table of my jointer for making sprung joints.

The gap in the middle is tiny, you can use less clamps and I have not had an issue with modern glue and sprung joints.


----------



## GeorgeC (Jul 30, 2008)

Would someone explain to me how raising the outfeed table produces a hollow joint. I presume you are saying that the side of the board being jointed actually looks like a very shallow "u."

George


----------



## WarnerConstInc. (Nov 25, 2008)

My out feed table tilts to make the joint.


----------



## JBSmall (Jul 6, 2012)

GeorgeC said:


> Would someone explain to me how raising the outfeed table produces a hollow joint. I presume you are saying that the side of the board being jointed actually looks like a very shallow "u."
> 
> George


I imagine that the technique is geometrically imperfect. The amount above top-dead-center depends on the lengths of the boards being joined, and the hold-down technique of the millman.
But essentially, the board kinda rocks its way past the cutter, which results in the near end raising a bit off the near table. You know you've raised the far table too much if the cut runs out before you reach the end of the board.


----------



## JBSmall (Jul 6, 2012)

firemedic said:


> That's more commonly referred to as a "sprung joint." if my memory serves me right it became a common practice for commercial panel clamping operations.
> 
> Hide glued panels have a propensity check or split on the ends, modern glue doesn't. Old solution to an old problem which no longer exist is not uncommon in woodworking. This one in particular is oddly amusing though and I'll get to that in a bit. The issue in this case is the solution to old glue is a problem for new glue. Sprung joints with modern glue result in glue starved edges on the panel ends due to the excessive clamping force needed to close the center of the panel.
> 
> ...


Cool. Thanks.
I've never had any glue-starvation problems, though I have heard of such a thing. 
Glue, that it works at all, baffles me.


----------



## JBSmall (Jul 6, 2012)

WarnerConstInc. said:


> I have a lever on my outfeed table of my jointer for making sprung joints.
> 
> The gap in the middle is tiny, you can use less clamps and I have not had an issue with modern glue and sprung joints.


Is that an old jointer? Never saw that feature.

The slight added pressure does participate in helping to hold things in position during some awkward glue-ups, during which the phone usually rings...


----------



## WarnerConstInc. (Nov 25, 2008)

JBSmall said:


> Is that an old jointer? Never saw that feature.
> 
> The slight added pressure does participate in helping to hold things in position during some awkward glue-ups, during which the phone usually rings...


Well, it is not as old as my other stuff, but it is from the 40's.

Most 12"+ jointers seem to have the spring joint function.


----------



## cabinetman (Jul 5, 2007)

firemedic said:


> That's more commonly referred to as a "sprung joint." if my memory serves me right it became a common practice for commercial panel clamping operations.
> 
> Hide glued panels have a propensity check or split on the ends, modern glue doesn't. Old solution to an old problem which no longer exist is not uncommon in woodworking. This one in particular is oddly amusing though and I'll get to that in a bit. The issue in this case is the solution to old glue is a problem for new glue. Sprung joints with modern glue result in glue starved edges on the panel ends due to the excessive clamping force needed to close the center of the panel.
> 
> ...


+1. :yes: Yep...woodworking is definitely a personal thing, and how and what we get subjected to may seem to make sense. I prefer to have just good fitting joints.








 







.


----------



## GeorgeC (Jul 30, 2008)

JBSmall said:


> I imagine that the technique is geometrically imperfect. The amount above top-dead-center depends on the lengths of the boards being joined, and the hold-down technique of the millman.
> But essentially, the board kinda rocks its way past the cutter, which results in the near end raising a bit off the near table. You know you've raised the far table too much if the cut runs out before you reach the end of the board.


Are you are saying that this is an end to end (end of board to end of board)_ curve? And not a side to side (edge of board to edge of board on one side) curve? I was imagining that it was the latter.

OK, I just did what I should have done sooner. I "googled" and found that it was and end to end "spring."

Do not really see the desirability of this. Jus plain old wood dynamics will often cause this and the opposite.

George


----------



## woodnthings (Jan 24, 2009)

*allow me*

The 2 edges are planed concave. When placed together on a flat surface flat sides down, there will be a gap () like that. You have to clamp with more pressure in the center to close up the gap. The ends squeeze out the glue first and then are starved when the gap is finally closed up.  bill


----------



## Keith Mathewson (Sep 23, 2010)

Gary gives a good explanation of the joint. The comment on hide glue however is incorrect. Hide glue comes in several strenghts, 252 and 312 are as strong as pva glue. This technique works well with both pva and hide glue. For most appliaciations a straight joint is all that is required.


----------



## Icutone2 (Nov 4, 2011)

Is This prosses done by hand or with a power jointer?
Lee


----------



## woodnthings (Jan 24, 2009)

Icutone2 said:


> Is This prosses done by hand or with a power jointer?
> Lee


Either way. The jointer is easier and faster. Hand planing requires more skill....except when I do it.... the first piece is either concave or convex and the next piece is either convex or concave.... :blink:
The venerable 6" Craftsman jointer with the fixed outfeed table won't work in this case, you need an adjustable outfeed table.
Apparently that is one of the main reasons for it being adjustable, making spring joints.


----------



## Leo G (Oct 16, 2006)

Correct me if I'm wrong (I'm not) if you want an open in the center of the 2 joining boards you would need to lower the outfeed fence not raise it. Raising the fence will make the board be convex, not concave.


----------



## woodnthings (Jan 24, 2009)

*fence?*



Leo G said:


> Correct me if I'm wrong (I'm not) if you want an open in the center of the 2 joining boards you would need to lower the *outfeed fence* not raise it. Raising the fence will make the board be convex, not concave.


did you mean table, not fence?


----------



## cabinetman (Jul 5, 2007)

Somebody once said it's OK to disagree. Well, I disagree with this method of joining edges. I don't believe craftsmanship starts with creating an ill fitting joint. When the edges are jointed to fit, and the clamping pressure along its total length is fairly equal, there's no reason the ends should separate.









 







.


----------



## Leo G (Oct 16, 2006)

woodnthings said:


> did you mean table, not fence?


Ya, outfeed table.:icon_redface::icon_redface:


----------



## WarnerConstInc. (Nov 25, 2008)

Leo G said:


> Correct me if I'm wrong (I'm not) if you want an open in the center of the 2 joining boards you would need to lower the outfeed table not raise it. Raising the fence will make the board be convex, not concave.



It drops the far end of my table for a concave joint.

I can lift that end up for a convex joint.

Another reason for a spring joint, as I have read in some older books, was for when the panel drys out more in the winter (or whenever) the ends of each board in the panel would shrink more. A spring joint was to help make sure the panel joints would not separate due to seasonal wood movement.

This is just coming from a guy that has to oil his machines before he uses them.


----------



## JBSmall (Jul 6, 2012)

Leo G said:


> Correct me if I'm wrong (I'm not) if you want an open in the center of the 2 joining boards you would need to lower the outfeed fence not raise it. Raising the fence will make the board be convex, not concave.


 You are wrong.


----------



## Leo G (Oct 16, 2006)

Been doing it for 20 years. Nope, I'm right.

If you raise the front (outfeed) table as you push the wood forward it will keep lifting it off the back table making a convex board.

If you lower the front (outfeed) table then the board keeps falling cutting a hollow in the board, and at the end it will leave a small snipe.


----------



## JBSmall (Jul 6, 2012)

Well.
Alrighty, then.


----------



## woodnthings (Jan 24, 2009)

*correct me if I'm wrong...*



Leo G said:


> Been doing it for 20 years. Nope, I'm right.
> 
> If you raise the front table as you push the wood forward it will keep lifting it off the back table making a convex board.
> 
> If you lower the front table then the board keeps falling cutting a hollow in the board, and at the end it will leave a small snipe.


Don't we work with the out feed table for the concave/convex issue and leave the front table for the depth of cut? That's what I've been doing for 40 years, but I could be wrong.


----------



## Leo G (Oct 16, 2006)

I consider the front table the outfeed table and the back the infeed. The infeed table determines depth of cut and the outfeed is suppose to be perfectly in line with top dead center of the knife.


----------



## woodnthings (Jan 24, 2009)

*no wonder then*



JBSmall said:


> Well.
> Alrighty, then.


Not me. The front table is the infeed table and it's the one you stand in front where the switch is, on the front. 

The rear table is the outfeed table where the work feeds out after passing over the cutterhead. That's why the older Craftsman 6" which has a fixed outfeed table, gets some scorn. I find that for every jointing process I need, a fixed outfeed is just fine, but for the "hollow or spring joints" I would use a different jointer, my Jet 6" or my Grizzly 8".

The outfeed table on my table saw is at the rear, behind the blade. The switch is on the front where I stand to feed the work in....... But I could be wrong on this and would like to hear what others say. :huh: bill


----------



## Leo G (Oct 16, 2006)

Just the way I look at it I guess. On the jointer the outfeed is in the front to me. I guess I should just say in and outfeed.


----------

