Hollow-jointing - Woodworking Talk - Woodworkers Forum
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post #1 of 30 Old 07-20-2012, 08:35 PM Thread Starter
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Hollow-jointing

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.
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post #2 of 30 Old 07-20-2012, 09:07 PM
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This is new to me. I am interested if this technique is used by others.

I normally try to get a tight fitting joint.
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post #3 of 30 Old 07-20-2012, 09:20 PM
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Quote:
Originally Posted by JBSmall View Post
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/...riend/page/all

John

If I strive for perfection, I can generally achieve good'nuff, If I strive for good'nuff, I generally achieve firewood
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post #4 of 30 Old 07-20-2012, 09:26 PM
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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!
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post #5 of 30 Old 07-20-2012, 09:40 PM
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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.
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post #6 of 30 Old 07-20-2012, 11:11 PM
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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.
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post #7 of 30 Old 07-21-2012, 07:58 AM
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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
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post #8 of 30 Old 07-21-2012, 08:21 AM
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My out feed table tilts to make the joint.
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post #9 of 30 Old 07-21-2012, 12:04 PM Thread Starter
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Quote:
Originally Posted by GeorgeC View Post
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.
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post #10 of 30 Old 07-21-2012, 12:08 PM Thread Starter
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Quote:
Originally Posted by firemedic View Post
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!
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.
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post #11 of 30 Old 07-21-2012, 12:11 PM Thread Starter
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Quote:
Originally Posted by WarnerConstInc. View Post
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...
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post #12 of 30 Old 07-21-2012, 02:42 PM
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Originally Posted by JBSmall View Post
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.
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post #13 of 30 Old 07-21-2012, 03:26 PM
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Quote:
Originally Posted by firemedic View Post
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!
+1. 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.




.
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post #14 of 30 Old 07-21-2012, 05:28 PM
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Quote:
Originally Posted by JBSmall View Post
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

Last edited by GeorgeC; 07-21-2012 at 05:32 PM. Reason: added last 2 PP.
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post #15 of 30 Old 07-21-2012, 05:36 PM
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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

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #16 of 30 Old 07-21-2012, 08:01 PM
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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.
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post #17 of 30 Old 07-21-2012, 09:04 PM
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Is This prosses done by hand or with a power jointer?
Lee
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post #18 of 30 Old 07-21-2012, 10:16 PM
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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....
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.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #19 of 30 Old 07-21-2012, 10:54 PM
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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.

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post #20 of 30 Old 07-21-2012, 11:01 PM
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fence?

Quote:
Originally Posted by Leo G View Post
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?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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