Replies

1. 
   JohnWW | Feb 17, 2004 07:29pm | #1

   First guess is that the temperature was too low while the glue was setting.  Some details about the shop conditions might help.

   The second, even stronger possibility, is the top is being restricted from shrinking as it loses moisture to the inside air and the stress is causing the cracking.  What type of braces and attachment did you use to attach the top to the base?  Depending on your climate, the top will shrink almost an inch when brought inside from a cool damp shop to a very dry heated interior.  Measure the diameter lengthwise and crosswise to the grain, I'll bet your table top is no longer circular. 

   In the mean time, to prevent the problem from getting worse move the table back into the unheated shop until you figure out what is wrong.

   John W.

1. 
   utternovice | Feb 17, 2004 09:23pm | #2

   JohnW-

   The shop is an old, uninsulated barn in upstate new york near buffalo.  Top stayed completely flat and circular - at least it didn't appear to suffer that much differential shrinkage.  I will measure the top tonight to see how much shrinkage there is.  The top is held in place with four rockler table irons (the ones that look like the number 8).  There is one on each arm of the base.  The table irons were mounted in 3/4 inch diameter by 1/8 inch deep counterbores made with a forstner bit and were rotable about the attachment screw with slight hand pressure.  I was hoping that this would allow for adequate cross grain morvement.  The table irons are spaced about 3.5 inches out from the center of the table. I have included a picture.  Also, I have not applied a finish to the table yet.  Hopefully this is the type of information that you needed.

   Eric

   Edited 2/17/2004 1:32:28 PM ET by utternovice

   
2. 
   ChasStanford | Feb 17, 2004 09:54pm | #3

   Red Oak is bad about movement.  White Oak would have been a better choice.  W/O is the traditional choice for Arts and Crafts pieces.  The masters chose it for good reason.  Red Oak is a poor substitute.  I refuse to work with it under any circumstance.

1. 
   utternovice | Feb 17, 2004 10:25pm | #4

   Pretty new to the woodworking thing and got a what I thought was a good deal on the red oak and thought it would be good to practice with.  At the time did not know that there was that big a difference between the two other than I couldn't fume the red oak because of differences in chemical composition of the the woods.  Have used it on a couple of smaller projects and had not experienced any difficulties. 

   Currently, I am just trying to make pieces to learn how to do different joints, and proportions and structure.  If it looks OK I use the furniture in the house.  If not - relegated to the shop.  Will probably have a very comfortable lounging area in the shop before I'm done.  :-)  This was a borderline piece because of fit of some of the stretcher tenons into the legs, but since the gaps on in two locations weren't that noticeable it went into the house. 

   When I feel more confident in my skills, I will likely spring for the quarter sawn white oak, which will allow me to fume it as well.  In the mean time I still have about 150 bdf of red oak in 4/4., 6/4 and 8/4 to use up.  

   I suspect that the current problem is an adhesive failure due to improper curing, most likely due to shop humidity and temperature, however, being new to this I thought I would solicit opinions to draw on the collective wisdom of the forum.  To me it seemed unusual that the separation would only occur at the ends of a couple of the boards although come to think, the separation is along the opposite ends of the same glue line.

1. 
   ChasStanford | Feb 17, 2004 11:27pm | #5

   I think asking the average glue to hold RO together is asking too much.  If somebody held a gun to my head and made me build a project with it, a project that had wide glue-ups, I would use epoxy.

   I wouldn't spend a whole lot of mental energy discerning glue failure from other cause(s).  I would simply expect disaster on wide glue-ups using Red Oak.  The ultimate reason for the failure matters little unless you are bound and determined (and you don't seem to be) to build a lot of projects with the species.

2. 
   JohnWW | Feb 17, 2004 11:53pm | #6

   Commonly the separation starts at the ends of the boards because they shrink quickly from moisture loss through the exposed end grain.

   Shop humidity wouldn't cause a problem but low temperatures definitely effect the cured strength of yellow glues, as does the glue being old and/or having been frozen.

   John W.

3. 
   HowardAcheson | Feb 18, 2004 12:31am | #7

   I would suspect a glue failure. What was the temperature during the time when you did the initial glue up? Titebond should not be used when the temperature is under 55 degrees. The clamp and cure time on the label is based on 75 degrees and 50% humidity. For every 10 degree below that, the clamp and cure time doubles.

   What was the moisture content of the wood itself? If it was not fully dry, adhesion problems can also occur.

   Keep in mind for each 12" of width, Red Oak will expand/contract 1/8" (if quartersawn) or 3/8" (if flatsawn) for a change from 30%RH to 80%RH.

   BTW, White oak is even more unstable. It will expand/contract 1/4" (quartersawn) or 1/2" (flatsawn)under the same conditions. That's why front doors are typically made from red oak, not white oak.

1. 
   utternovice | Feb 18, 2004 12:54am | #8

   Temperature was right around 50 during the day when glued.  The top was left in clamps over night but the temperature dropped into the low thirties upper 20's if I am remembering correctly.  I don't know the moisture content of the wood.  It was purchased as kiln dried July 4th weekend 2003 and has been sitting off the ground and stickered in a corner of the barn ever since.  The glue squeezed out from the joint appeared to have fully cured, however, I don't know that its curing is indicative of anything.  I have had other glue failures in colder weather when gluing cold wood, but in that case the glue turned into a white powdery substance when it dried (it was about 5 outside then).

   I guess the lesson is to confine my gluing to warmer temperatures.

1. 
   ChasStanford | Feb 18, 2004 01:24am | #9

   The larger lesson is to not repeat the same mistake over and over.... You mentioned that you have had cold weather glue failures (my emphasis on the plural ending).

   Every woodworker is alloted one cold weather glue-up failure.  After that, it's time to stop and rig up some heat, or take the panel inside your house to cure. 

   Your woodworking will still be better if you eschew Red Oak.

1. 
   utternovice | Feb 18, 2004 02:10am | #12

   Sorry, I was unclear, the multiple failures that I atribute to extreme cold, i.e, the glue turning white and powdery, resulted from a single gluing session.

1. 
   ChasStanford | Feb 18, 2004 02:26am | #14

   All glues have both storage temps. and usage temps.  Become familiar with them and don't push the product.  There is no cushion in their numbers. 

2. 
   JohnWW | Feb 18, 2004 01:35am | #10

   The conditions you described certainly make glue failure the primary suspect with your table top. 

   The fact that the wood was never brought into a heated space until after the piece was made means that there will be considerable shrinkage as I described across the top"s width.  If you don't allow the top to move on the base, it will still crack but, with a proper glue up, the cracks may not occur at the joints between the boards but rather at a weak spot in the wood's grain.

   John W.

3. 
   BG | Feb 18, 2004 01:48am | #11

   Utternovice,

   I'm reading the responses but having trouble understanding.  It been cold and very dry this winter...and I suspect the same for you.  It seems the piece has been outside for the last two months...and inside your house should be warmer and somewhat higher mositure ??....so shouldn't the top be expanding...and not shrinking?

1. 
   utternovice | Feb 18, 2004 02:26am | #13

   Yes it has been cold and very dry, and I thought that the lumber would have been near its minimum dimensions.

   Intuitively I thought that the differences in humidity would not have been that much between outside and inside.  However, I have a 36" wide cherry trestle table that was assembled with hide glue during the summer and sat in the shop until the breadboard ends were finished in December that came into the house in January and it has shrunk about 3/16 along each edge (widthwise).  I think the forced hot air heat really drops the humidity.  Funny thing is there are no cracks in that much larger table just contraction across the grain.  Although, because of the nature of the end supports, I was able to design in table top attachments to accommodate more movement.  It was still surprising to see though.

   It will be interesting to see what has happened to the oak today when i get home.

   A lot of this is still learning for me, which is a good thing, in a lot of areas I know just enough to think I've taken care of something only to find out I've made the problem worse or haven't considered every variable.

   I am beginning to think that purchasing a moisture meter is in my future as well.

   Eric

2. 
   Alan | Feb 18, 2004 02:46am | #15

   BG,

   Relative humidity plummets when you warm up a parcel of air.  "Relative Humidity" is the ratio of how much water vapor the air actually holds to how much moisture the air could hold before the water vapor would condense into a liquid.  Relative humidity is usually given as a percentage:  e.g. relative humidity of 50% means the air contains 50% of the maximum water vapor it could hold.

   Cold air can hold less water vapor than warm air.  So when you heat up cold air its ability to hold moisture increases, so the relative humidity drops--the greater the increase in temperature the lower goes the relative humidity.

   BTW, this is why HVAC units in colder climes often have a humidifier.  When I lived in upstate NY I found the winter air in my place so very dry I bought a little humidifier.

   Alan

3. 
   JohnWW | Feb 18, 2004 02:46am | #16

   BG,

   Unless someone goes to extraordinary lengths to add moisture to the air in their house it will be bone dry this time of the year.

   The reason is as follows:  The air outside being quite cold, doesn't hold a lot of actual moisture in it even at a high relative humidity, such as you might get during a storm.  On clear cold days the amount of moisture in the outside air will be even less.  Once that outside air comes indoors and warms up it can hold considerably more moisture which it will then draw out of everything in the house, skin, sinuses, and wood being the primary sources.  In addition, if the house has older windows that are getting frost on them, all that frost is moisture being taken out of the air though it may evaporate back into the air during the warmest times of the day.

   John W. 

1. 
   BG | Feb 18, 2004 03:11am | #17

   JohnW,

   Between what you and Alan said it all makes sense now.  Utternovice mentioned he had a  hot air heating system...usually they do have humidifiers...but even so, the RH could still be lower than the barn...

4. 
   AlbionWood | Feb 18, 2004 07:39pm | #19

   This kind of thing is one reason I switched to polyurethane glue.  Shop temps are frequently around 50 deg F and often drops into the 40s at night, but hardly ever below 40.  This is too cold for PVA, and combined with high humidity, meant looong clamp times and weak joints.  With PU, I can strip the clamps in an hour, even in cold weather.

   Two other suggestions:  Use splines or biscuits to align and strengthen the joints.  I use biscuits most of the time, and make sure to place one close to each end of the joint (finished end, that is - be careful not to place them where you will cut into them when shaping the panel).   And consider jointing the edges slightly concave, as described by Tage Frid, if you suspect the panel will be subjected to later drying.  This places a compressive stress on the ends, so they are less likely to open up later."Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

4. 
   utternovice | Feb 18, 2004 03:40am | #18

   More info -

   The good news is that the top seems to have stabilized with the largest crack being a little over 1/32 wide.  The top now measures 25 1/4 inches across the grain and 25 3/8 with the grain.  The largest crack is along the glue line right down the center of the table, the next glue line separation occurs at the two adjacent joints and is considerably less.  Even though I thought I had left enough lateral play, I probably should not have used the two table irons on the cross grain rail.

   Thanks to all for the feed back. 

   I have certainly learned quite a bit and realize that I have a lot more to learn.