Replies

1. 
   SteveSchoene | Jan 17, 2010 08:34pm | #1

   Great question. I'm afraid I
   Great question. I'm afraid I have no idea about the answer. I wonder what Mack Headley and the crew at Colonial Williamsburg would say about springing joints.

2. 
   joinerswork | Jan 18, 2010 09:54am | #2

   Don,
   From Jos. Moxon's
   Don,

   From Jos. Moxon's Mechanic Exercises, or, The Doctrine of Handy-Works (1704):

   "Of the Joynter...fo will two edges of two Boards, when thus fhot, lie fo exactly flat and square upon one another, that light will not be difcerned between them..." and

   "Of ufing the Glew...And before you are to fet them as they are to ftand, you must jostle them one upon the other, that the Glew may very well touch and take hold of the Wood...then fit the two Joints as they muft ftand; And when you fet them by to dry, let the one ftand upright upon the other; For if they ftand a-flope, the weight of the Stuff when it leansupon two extream Edges, maymake one end of the Joint open."

   Glue lines were typically rub joints, according to Moxon. What we call clamps are not even discussed in his treatise on joinery; the only "clamp" described is what we in the US call bread-board ends. I found no mention of what the Brits today call our clamps- "cramps"- either. Now, Moxon himself was a printer by trade, not a joiner. And he was writing what those in the joiner's trade told him, which may not have been exhaustive, or even honest- the "Art and Mystery" of the trades was a closely kept secret at least in some circles at that time. I'm pretty sure that Diderot in his Encyclopedia shows panels in clamps in one of the carpentry plates though I don't have time to search for it this minute. Even if it did show that, that doesn't address whether they were sprung joint or not.

   Intuitively speaking, using a sprung joint is a good way to attain more clamp pressure with fewer clamps, so I'd guess that the technique didn't just fall off the turnip truck yesterday.

   Ray

1. 
   SteveSchoene | Jan 18, 2010 12:35pm | #3

   Interesting. So Moxon is speaking as if the norm is not a sprung joint (that light will not be discerned between them0 and that clamps aren't mentioned. But, sprung joints don't work unless you are clamping the joint

1. 
   joinerswork | Jan 18, 2010 08:11pm | #7

   Steve,

   Just so. All he discusses are what we call a rub joint or rubbed joint, today.

   Just looked at My reprint of Diderot's Encyclopedia of the trades (1763), and saw not a clamp there. I know I've seen somewhere a pic of a panel in "clamps" made of a pair of slats with crossbars, sandwiching the panel, and wedges driven between panel edge and crossbar to provide the pressure.

   Ray

   Edit: It'd be interesting to see what Nicholson says in his how to wooodworking book from early 1800's. Alas, I don't have a copy. And it'd take forever to download on my dialup connexion, from googlebooks. Hint hint.

3. 
   SgianDubh | Jan 18, 2010 04:08pm | #4

   Don, Ernest Joyce in The Technique of Furniture Making discusses sprung edge joints, but this only takes you back to the 1960s. I was taught it by old farts in the workshop I trained at, and they all learnt the techniques from old farts before them ad infinitum I suppose.

   The discussion at this link to a page at my website doesn't answer your question about history either; it does discuss panel glue ups and goes into a little discussion on sprung edge joints. You may find it interesting and useful. Slainte.

4. 
   brucet9 | Jan 18, 2010 04:43pm | #5

   For the benefit of those ignoramuses who don't know what a spring joint or sprung joint is, please tell me, what is it?

   Google let me down, as the only explanation I could find was a confusing entry on Wikipedia that said that using slightly concave boards "increases tension [my emphasis] at the ends of the join [sic] which assists in creating a seamless joint."

   Thanks,

1. 
   joinerswork | Jan 18, 2010 08:08pm | #6

   Bruce,

   An edge joint is said to be sprung when it is intentionally made with one or both of the edges to be joined slightly concave, so that when the edges are offered to one another, a very slight gap remains in the center when their ends meet. Clamp pressure sufficient to close the gap during gluing provides even more compressive force to the ends. This allegedly helps to prevent the joint opening at the ends during times of low humidity (and shrinkage of the panel), which takes place at the ends before equalising over time throughout the length of the boards.

   Ray

1. 
   brucet9 | Jan 19, 2010 02:11am | #8

   Ah, now I'm a little less
   Ah, now I'm a little less ignorant.

   Now that I think of it, I have seen some glued-up panels with joints starting to fail just at the ends; one a 3-year old glued up pine shelf, the other an 80-year old oak desk top.

   It must take a deft touch to taper a little from both ends to the middle wile jointing a pair of boards.

   In a multi-board panel do you spring all of the joints or just the outside pairs?

1. 
   Lataxe | Jan 19, 2010 04:11am | #9

   Bruce,

   All my plank-panel joints get the sprang treatment, as I swallowed the wisdom concerning it helping to prevent the plank ends from separating if and when the moisture was sucked out of their end-grain by a period of dry atmosphere.

   However, the more I think about this claimed benefit, the more I wonder if it is so. Surely the differential moisture exhalation between the middle and the end of the planks will occur very near the plank ends. The moisture from, say, 4 - 6 inches into the end grain seems unlikely to be sucked out the ends......?

   Perhaps Richard can enlighten us as to just what degree of extra exhalation - how far down the plank from the ends - is affected in such a scenario?

   Anyway, the spung joint will presumably exert a constant internal pressure differential at the ends of the joins compared to the middle. But typically the initial gap is very small - 0.5mm in the middle of 4 - 7 foot planks is what I use. So what is the differential pressure (small I think)?

   Also, when the ends dry out, the differential shrinkage may be atween the outer three inches (from the end grain ends inwards) and the rest of the plank. There is only tiny-to-nil gap between the sprung planks 3 inches in from the end, so there seems little liklihood of there being any differential internal pressure there. So won't the planks open up at the ends anyway?

   It seems a more likely explanation for sprung joints is that they reduce the need for loads of clamps. as those applied in the middle will transmit some of their clamping force to the ends.

   I wonder if anyone has made experiments to see if a rapid drying of atmosphere will cause unsprung joints to open at the ends more than sprung ones?

   Lataxe, wondering if there is a "rationalisation after the fact" going on.

1. 
   SteveSchoene | Jan 19, 2010 08:26am | #10

   I'm afraid I haven't seen any
   I'm afraid I haven't seen any science on the issue.

   I must also report that Peter Nicholson, Practical Carpentry, Joinery, and Cabinet Making, 1826 offered no enlightenment to the issue of when the practise arose, though it contains a lot of interesting material and bits of wisdom, especially on design matters and on traditional finishing. Clamps (cramps) appear in the text only briefly, and not in the context of edge joining. Feather tongues were recommended for edge joining if the material being joined was thick enough. (Those are known to most of us as spines.)

   Bernard E. Jones, ed. The Complete Woodworker, 1926 does mention sprung joints saying, "[i}n long joints, say more than five ft., some workmen deliberately introduce a slight but even hollowness extending to within a few inches of each end, but the amount of the hollowness must only be such that the pressure of the cramps will obliterate it. However, as cramping should be unnecessary in most cases, and as the adoption of the method might be regarded as an admission that the craftsman cannot produce true edges and is actually choosing the lesser of two evils, it is better to see that tha preliminary testing and rubbing demonstrate that there is an end to end contact." It's clear he favors rubbed joints over sprung joints saying elsewhere that "cramping is necessary only in the case of thin woodfor thin boards. That being said, he has a separate chapter on cramping, which shows both commercial cramps including Iron G cramps [sic], sash cramps, hand screws, including the Jorgensen Handscrew which allows angling the jaws, and also shows wedge cramping set ups complete with cauls (called batten clamps). By the way, this bood is one of the most comprehensive works I've seen about using hand tool methods, with a great many joints and variations discussed in some detail. And, who could miss the chapter on "Areoplane Woodwork" including instruction on making a propeller

2. 
   joinerswork | Jan 21, 2010 09:23am | #11

   I would posit that the popularity of springing edge joints might be co-incident with the move away from hide glue for edge joining and towards glues that require clamping...

   Ray

3. 
   DonStephan | Jan 24, 2010 07:11pm | #12

   A side benefit of spring/sprang joints might be eliminating high spots between the ends. Don't know how many people dry fit the boards on edge, push on ends to see if the upper board pivots on a high spot.

   Another factor against spring joints may be that they might be more safely made with long handplane, rather than power jointer. As power equipment became more available hand planes were no doubt disparaged as hard to master, use, and sharpen. "Why use hand planes when a power jointer gives a perfect edge ready for gluing, or even glue line rip saw blades?"

   Sent an email request to Colonial Williamsburg today asking if the woodworking shop had historical info. If there is a reply, I'll post summary.

4. 
   DonStephan | Feb 18, 2010 08:28pm | #13

   Received a very informative and helpful reply from Colonial Williamsburg.  There was no reference to spring joints in woodworking literature they referenced.

   Leads me to wonder if spring joint became common practice after central heating led to low relative humidity in winter.

5. 
   RMillard | Feb 18, 2010 10:08pm | #14

   I think (which is to say I don't really know) that spring joints, dates to the age of PVA glues.  A spring joint doesn't work well with  hot hide glue. I bought into the idea that a spring joint would put the ends into compression and lessen the chance of ends opening up from changes in humidity, but now, I'm not so sure. What I am sure of,  it is easier to plane a slight hollow to the edge, than it is to have them meet perfectly, so that is why I use it.

   Rob Millard

   http://www.americanfederalperiod.com

6. 
   oldhand | Feb 21, 2010 07:32pm | #15

   My '29 model yates/american joiner has a lever you can throw on the outfeed table that cocks said table out of plane with the infeed to create spring joints. I never, ever use it and always figured it may have been a good idea before pva glue. Some comments here make that theory sound naieve but none have posted yet to convince me there is much merit in a spring joint, at least in this common man's  practice.

1. 
   Eef | Feb 22, 2010 04:08pm | #18

   hand,

   if the good folks at yates thought it a practical idea to include that nifty feature on their 19 and 29 jointer, does that  not, in itself, say volumes about the benefit and merit of the sprung joint?

   just asking.

   eef

7. 
   Furniture_Maker | Feb 22, 2010 09:01am | #16

   Hide glue works fine with a sprung joint, it's just not a rubbed joint but a clamped one.

   As for other traditions, they didn't use clamps but they used something just as good - a board of slightly larger length than the width of the unit being glued (they would have had quite a collection of these in various lengths) with two ears where one would tap in wedges between the board and the unit being glued to provide a range of clamping pressures depending on the wedge geometry and how hard it was tapped in.

   This technique is ancient, but used throughout Aldren Watson's book Furnituremaking Plain and Simple.

1. 
   RMillard | Feb 22, 2010 10:10am | #17

   I have used hot hide glue for a spring joint and it works well if I add urea to slow down the gel time, and limit the number of joints I have to deal with, but a spring joint is better suited to a slower setting glue.

   I really like rub joints, especially for thin stock, which has a tendency to fold under clamping pressure.

   Rob Millard

   http://www.americanfederalperiod.com

8. 
   dag2000 | Oct 24, 2010 02:43pm | #19

   Tommy MacDonald talks about spring joints in a video on his website. It's more about technique rather than reasons why, but worth a look.

   The series is on building a nice tool box. Twenty seven segments (mostly short). I haven't watched them all, but they seem pretty informative.