Replies

1. 
   nikkiwood | Dec 08, 2006 08:20am | #1

   Yeah, I have --- back in the early days before I knew any better.

   But I take your point. If you have made a decent joint, used mechanical fasteners (nails, etc.), it is pretty unlikely that joint will fail (as in fall apart) because you clamped too hard and too much of the glue squeezed out.

   ********************************************************
   "It is what we learn after we think we know it all, that counts."

   John Wooden 1910-

2. 
   RickChristopherson | Dec 08, 2006 09:06am | #2

   You can't starve a glue joint using hand clamps, unless the joint is smaller than the clamps (i.e. 2-inches wide). It is too late at night to go searching for the specifications from glue manufacturers, but if memory serves me, it takes well over 250 psi to starve a joint (possibly higher). So that means if your joint is a moderate 12 inches wide, then you would have to apply 3000 pounds of clamping pressure with the clamps to starve the joint.

   This myth originated because commercial facilities using hydraulic and pneumatic clamping systems were capable of applying huge clamping pressures to their joints. Unfortunately, Norm keeps repeating this same misinformation on a regular basis. The net result of that, is that many woodworkers end up complaining that they keep getting visible glue lines.

   I don’t remember who posted after you, but if they claim to have starved a joint, it is likely that the glue had skinned over before the joint was clamped. This is not starving the joint in the same sense, but the results are similar.

3. 
   RMillard | Dec 08, 2006 02:41pm | #3

   For edge joints, this one is in the tall tale category. Typical woodworking glues ( white, yellow, hide glue etc.) work by being absorbed into the wood and keying into the cell structure. With that in mind, as long as sufficient glue is applied in the first place, clamping couldn't starve the joint, because the act of tightening the clamps would only serve to force the glue into the cell structure of the wood. Still, I strive to have my joints come up tight with minimal clamping pressure; if excessive clamping pressure is required to close a joint, then you are building in stress, and that's not a good thing.

    I can see dovetails and especially mortise and tenon joints, being glue starved. In the case of the M&T, if you were to spread glue only on the tenon, and shove it into the mortise, the tight fit would squeegee off the glue and starve the joint. This is why I apply a thin coat of glue to both the tenon and the mortise (likewise with dovetails).

   I'm not sure, but I believe some of the more exotic glues like polyurethane and epoxy, could be glue starved, but I have very limited experience with these glues.

   Rob Millard

1. 
   nikkiwood | Dec 08, 2006 06:09pm | #6

   The one time years ago when I had a problem, it was when edge joining boards for a table top. I was careful about getting the the boards fitted properly with the jointer, but when gluing up I really torqued the clamps.A few more years down the line, two of the boards came apart at the seam, and I attributed that to "glue starvation."If I am reading your comment correctly, the problem was not that at all -- and despite my best efforts, probably due to improperly jointing the boards. Is that right?********************************************************
   "It is what we learn after we think we know it all, that counts."

   John Wooden 1910-

1. 
   JimV | Dec 08, 2006 06:15pm | #7

   Although you haven't given any specifics concerning the construction and design of the table top, I had similar experiences in a couple of my earlier efforts, which I now contribute to not allowing for wood movement. Without actually seeing your table, it's nothing but wild-*assed guessing as to why it split.Jim
   "There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other is that heat comes from the furnace." - Aldo Leopold

2. 
   RMillard | Dec 09, 2006 05:33am | #12

   Nikkiwood,

   There are so many things that could cause joint failure, such as burnished surface from dull knives, old glue ( yellow glue is especially prone to this), or allowing the glue to skin over before pressure is applied, that it is hard to say what caused the joint to fail.  I can say that over-clamping wouldn't cause the joint to fail.

   I also don't think wood movement could be the cause. A good glue joint is always at least as strong as the wood itself. I often break off-cuts on glue ups, just to see where it will break; they almost never break at the joint.

   Rob Millard

1. 
   4quarter | Dec 09, 2006 06:34am | #14

   Hello all, I'm new here to your forums and would first just like to say hello.  Second, interesting thread - thought it looked like a good one to peep my head out of my hole.

   I often break off-cuts on glue ups, just to see where it will break; they almost never break at the joint.

   I find myself doing this almost everytime and have yet to get a cut off break at the glue joint. 

   For joints, be they edge joints, dovetails, mortise and tenon, etc, I work to have the pieces fit together with minimal clamping pressure.

   I must agree here, if I can't make it fit right with hand pressure before glue I'm going to fix why the peices won't meet up as desired.  Tying to put it in words I apply enough pressure on the clamps the make the peices meet (no visible glue between, when you feel the bind) then about a 1/8 to 1/4 turn more.

   I am confused about somthing here though, I'd never dream of making a joint without some kind of helper besides glue (biscut, mortise/tendon, dowel, dovetail, etc).  There were posts about  edge joints splitting, I'd never make an edge joint without biscuts and have yet to see one split.  I guess my question is am I over building always jointing with something helping the glue surface area?

1. 
   sapwood | Dec 09, 2006 06:40am | #15

   It seems that the consensus is that this starving thing IS a myth. That's pretty much my feeling since I read it many years ago. So, since the solstice is close upon us (Dec. 21, 3:22 pm ADT), lets all take a couple of glued-up boards and throw them on the bonfire!

2. 
   dherzig | Dec 09, 2006 07:10am | #16

   There are arguments back and forth as to whether biscuits add to the joint strength or merely help alignment. Supposedly a well-fitted joint without a helper is as strong as it need be. I will use biscuits when gluing up a long table top to help in aligment as I work my way down the joint. Otherwise only a well-planed surface that meets properly, often with a slight spring to the middle.

2. 
   RickChristopherson | Dec 08, 2006 06:27pm | #8

   Still, I strive to have my joints come up tight with minimal clamping pressure; if excessive clamping pressure is required to close a joint, then you are building in stress, and that's not a good thing.

   Even the concept of over-clamping causing stress at the joint is a misconception. I am not sure where this got started, but I have read Ian Kirby mention it before. The misconception is that people think that all the pressure (hence stress) is located at the joint, but it is not. The compressive forces are spread out equally throughout the entire volume of the boards, not isolated at the joint. The greatest area of stress and compression is right at the clamp head where all of the force is localized to the contact surface between the clamp head and the board.

   This concept may have originated for a discussion where the joint was not perfectly made, and isolated surfaces were experiencing greater forces than other areas. In this case there would be stress, but the joint will have more problems than just stress.

1. 
   dherzig | Dec 08, 2006 07:21pm | #9

   I wonder how much of the problem that the myth refers to is due to the fact that over tightening the clamps could lead to some imperceptible twisting and cupping of the boards leading to a somewhat imperfectly formed joint.

2. 
   RMillard | Dec 09, 2006 05:19am | #11

   Rick,

   I was meaning that clamping should not be used to overcome poor workmanship. The only time I apply a lot of pressure when clamping, is when gluing up inlay bandings. For joints, be they edge joints, dovetails, mortise and tenon, etc, I work to have the pieces fit together with minimal clamping pressure.

   Rob Millard

   http://www.americanfedralperiod.com

4. 
   VeriestTyro | Dec 08, 2006 02:55pm | #4

   Can't be done with hand clamps.  The only way to exert enough pressure to starve a joint is with pneumatic clamps.  Read the manufacturer's recommended clamping pressures - these glues are optimized for factory use - not backyard woodworker use.  The stuff is sold by the 55 gallon drum to large manufacturers.  Those are their real customers.  Franklin couldn't keep the doors open selling 8 oz. bottles to guys building a Shaker piece every six months. 

   The stuff they put into the small bottles for you and I represents the drip off from the manufacturing equipment.

5. 
   jackplane | Dec 08, 2006 05:06pm | #5

   Never experienced it, often read about it.

   But then I don't use hydraulic clamps.

    

6. 
   gmoney | Dec 08, 2006 08:53pm | #10

   debunked myths is always interesting here in knots.  i would have never known those things but for reading it here.

7. 
   Quickstep | Dec 09, 2006 05:56am | #13

   Interesting thread. I posted a while back about a problem where I had a wide glue up in which one joint had failed where I had used epoxy. Someone who responded indicated that I had probably applied too much clamping pressure for epoxy and starved the joint by not leaving enough glue film thickness. Since then, when using epoxy, I apply only enough pressure to juuuuust close the joint. No failures since. I've never had a failure with yellow glue.

1. 
   EF | Dec 09, 2006 07:14am | #17

   Maybe epoxy joints can be glue starved by hand?? Maybe it easier/possible to push the epoxy out of the joint whereas yellow glue penetrates the wood so that it take more force to glue starve? Or epoxy needs a thicker layer to work right? I'd bet pressure to "glue starve" varies from glue type to glue type.

1. 
   user-211435 | Dec 09, 2006 07:20am | #19

   It may be that with the older types of glues that we no longer use regularly, like plastic resin or resourcinol, that it was possible to squeeze too much glue out of the joint. 

   It certainly is possible with epoxy.  Especially when gluing white oak.

   Hal

   http://www.rivercitywoodworks.com

    

1. 
   philip | Dec 09, 2006 12:33pm | #20

   Well, Ah beelive that the way to a starved glue joint is by means of A) using wood glue such as PVA and the like that is waaaaaaay to thick especially on hard woods(dense woods)-here the glue cannot penetrate the wood as required and squeezes out .
   B)Using glue that is too thin especially on softwoods-it merely penetrates and disappears because it is spreading over too great an area i.e it is thinned out.
   C)By simply not applying enough glue. Simple but true- have seen this in factories staffed by unsophisticated but cunning gentlemen who either did not want to have to remove squeeze out , or required the glue for own use ....
   D) As mentioned by previous posters, epoxy type glue should not be used as though it were wood glue.
   The proof of the pudding when clamping is the rubbed joint, for smallish panels, assuming one has got to grips with #7 or nice surfacer....Philip Marcou

2. 
   user-211435 | Dec 09, 2006 07:17am | #18

   Hey Quickstep,

   Epoxy is the one place that I know of where you can squeeze the glue out of a joint.

   With epoxy, the bigger the joint full of epoxy, the stronger the joint (as long as the epoxy is thick enough to stay in until it dries).

   Just curious, what do you make that you need to glue panels with epoxy?

   Hal

   http://www.rivercitywoodworks.com

    

    

1. 
   Quickstep | Dec 09, 2006 04:44pm | #21

   I started out using epoxy on stuff I made for boats, then expanded it to use on anything that would be outdoors. I now use it for almost everything. I like it's very predictable cure time. I can glue up big projects without having to worry if the glue will evaporate before I get done since pot time can be adjusted by using a slower hardener. Epoxy squeeze out is easier to sand than resorcinal. If I were a production shop, I wouldn't be able to afford this luxury, but as a hobbyist, the cost difference between resorcinal and epoxy is probably less than my mistakes. :)

   Also, now that I have a good jointer, this is less of and issue, but epoxy forgives a bad joint......... as long as you don't overclamp.......

1. 
   user-211435 | Dec 09, 2006 07:13pm | #22

   I really like using epoxy too.  Especially for large doors (house doors) with mortise and tenon joints.

   And resorcinol is really nasty to sand.  It's also really hard on hand planes or any edge tools for that matter.  I don't like it at all.  Even the color is nasty.

   Hal