Replies

1. 
   sawduster | Jul 15, 2003 06:55pm | #1

   I'm sure you will hear from a number of more experienced woodworkers than I, but what I would recommend is that you use the flattest, straightest stock you can put together for your top while getting the best grain match you can. My opinion is that you will get enough stress on the joints from the naturial movement of the wood, so why take a chance. I have recently had some problems with glue creep on a 18X60 (3 boards) table top that I was sure sould stay flat and true since it had biscuts within 8 inches of the edge. I've heard, since I started woodworking, "it's wood, it'll move" and that keeps coming back to mind everytime I rub my hand over that table top.

2. 
   RMillard | Jul 15, 2003 07:05pm | #2

   S2S Lumber often looks flat, but may have a serious twist in it. Whether this will be a problem depends on several factors. First is how the table will be finished, a high gloss finish requires a very flat surface, because the top will act somewhat like a mirror, making every deviation stand out. Second which is sort of related to the first ,is the type lighting in the room where it will go, overhead lighting is not too bad, but raking light from windows, will highlight every bump and twist.

   On the straightness issue, I assuming you are meaning along its face as opposed to the glued edge . The amount you are describing is within what I would consider useable as is. The glued edge on the other hand must fit tightly with minimal hand pressure along its entire length or better yet tightly at the ends and open slightly in the center.

   Here are couple of other things to consider.

   Don’t listen to the common advise to reverse the growth rings, as this does nothing to make a more stable top, and causes some problems. These are uneven coloring, difficultly matching grain, and reversed grain direction.

   When selecting boards for glue ups, I look mainly for the reflectivity of the wood. Wood like carpet has subtle changes in color when viewed from different directions. Wetting the wood with water or mineral spirits will help highlight this. Second, is to try to have the grain run in the same direction. Most of the time reflectivity and grain direction go hand in hand.

   If this were my table, I constructed it in two halves, and hand plane each half flat, and then glue those together, letting any deviation in thick happen on the bottom side. Notice I said hand plane, contrary to Thomas Moser’s claim ( and many others) it is difficult, if not impossible to make an acceptable surface with a belt sander.

                                             Rob Millard

1. 
   DavidP52 | Jul 15, 2003 08:42pm | #3

   Rob, I agree about the belt sander.

   As I was thinking about wood movement, it seems there are two issues to consider. The first is reaction wood since straight boards can be cut from unstraight trees. When you cut the wood to smaller size, that relieves some of the stress, but not all. Residual stress that relieves itself over time needs to be considered.

   Adding to this is the effect of moisture change. Expansion/contraction in non stressed wood is a given, but when added to stressed wood, the net result is going to be even greater movement than normal. Or worse, uneven movement. It would seem best to select only boards where the oval pattern of flatsawn grain is consistent from end to end. I've got two boards where the pattern is clearly bowed tho the board is straight (now!). Movement that involves bending along the length would seem to almost guarantee joint failure. For example, tight wood near a knot will probably have a different movement than unaffected areas. Two boards clearly show an irregularity in the tree trunk, sort of like a bulge or crowned area.

   Therefore, AVOID GRAIN IRREGULARITIES OF ALL TYPES. If you want a highly figured table, use a veneer instead.

   Have I got it right?

1. 
   RMillard | Jul 16, 2003 04:15am | #5

   Boatman

   You present some interesting points that I have really not considered.

   My experience has been that the stress of milling and drying the lumber far exceeds anything it will be exposed to as a finished piece of furniture. As long as the boards for the top are flat or can be brought into flat with minimal hand pressure, and both sides are sealed, you don’t have much, if anything to worry about.

   I have used some pretty wild grain for tops with no problems, but these were admittedly mahogany which is quite stable. I made a federal card table a few years ago, where the top seemed to change shape hourly, yet once the finish was on, it remained flat. I see factory furniture, where no care was taken with stock selection, and these seem to hold up, although they commonly use many narrow boards to make up the tops.

   . I think the rigidity of the glue used, has a lot to do with how well the joints stay together Yellow glue has far too much potential for “creep” while white glue is somewhat better. I like hide glue, since it dries very rigid, but you can really only do one joint at a time with it before it gels. Plastic resin glues are rigid, but make a noticeable glue line.

   Rob Millard

1. 
   DavidP52 | Jul 16, 2003 04:35am | #7

   I agree with you and think that more problems are caused by unstraight edges than anything else. I've never had a glue joint failure. Titebond is stronger than wood, so if the joint fails without breaking the wood, this is not the glue's fault. I'm going to use epoxy which is twice as strong as aliphatic resin. Epoxy is much more tollerant of joint imperfections and is not weakened because you have too much glue in a slight gap. I think that is a good strategy for long boards where perfect edges get increasinly difficult.

   I use varnish on all my furniture, and do all exposed surfaces. such as all sides of drawers, inside cabinets, the works. It has been written that sealing this way isn't that big a help. Probably not when moving from Phoenix to Florida, but places where humidity doesn't take big swings (like Florida for example) sealing cuts way down on even small amounts of movement. I'm convinced it's a big factor.

   BTW, I just finished making a vertical clamping table and did a dry run with it. Looks like it will work real well and is very helpful with selection of stock because you can line up boards in different orders and see easily how they work out. It showed me some things I wouldn't have seen otherwise.

   Edited 7/15/2003 9:39:58 PM ET by boatman

1. 
   mwestenberg | Jul 16, 2003 04:51am | #8

   Would you be willing to share some photos of your vertical clamping setup?  The idea is very interesting to me and I would appreciate info on what others have done and the results they obtained this way.

   Mark

2. 
   DavidP52 | Jul 16, 2003 02:54pm | #9

   Sure would, just need someone to tell me how to post pix. It took me about 6 hours to build mine, but I can tell you how to reduce that to just two hours and $20 of material if you're interested. I made a lot of mistakes and did things the hard way. This idea was found in an old FWW shop tips. I can't find which one at the moment.

   This contraption is highly versatile and can be adapted and used for other operations such veneer pressing and laminating.

   Basically you bolt two 2 x 4s together flat-wise with spacer blocks the width of the boards you are gluing +1/8. The bolts go thru the spacer blocks also, which get placed top and bottom positions on each upright. The uprights are drilled full of holes up the vertical center so clamping can be adjusted to different size work. The idea is that you have 3-4 of these uprights, which have "T" feet on them, and then you slide your boards to be glued up in between them. After you get the first board in place, the whole contraption will stand upright. You draw the bolts tight, but most of the clamping action is done with wedges that you cut (or have saved) for just this purpose. With a 48" table you can get by with three uprights or legs. For 60" or greater you need four.

   You can still use your bar clamps for this table, plus you can use wedges. The advantage of this design is the ability to adjust the alignment of the faces of the boards. So, obviously, the more uprights you have the greater the control of keeping edges parallel and even. When not needed, the legs break down and can be stored away.

   Needed:

   6- 8' straight 2 x 4's (SYP recommended)

   36" of 3/8 threaded rod cut to 6" lengths, 9 pcs

   9 3/8 wing nuts

   9 3/8 standard nuts

   18 large washers

   I used a regular and a wing nut on each end of rod so I dont have to mess with two wrenches.

   Cut all 2x4's to a six foot length. Use the cut-off pieces for the cross bar feet. Screw or bolt on as you wish. For storage, best that feet are removable.

   Cut the bottom spacers from scrap the width of 2x4. These support the table top boards during glue up and the lower bolts go thru the spacer blocks, so be sure to get the lower hole spacing even.

   Use the cut off scraps from the 8' 2x4's to create cross legs. The uprights will look like a "T" and will stay up after you slip the first board between them.

   You need to drill lots of holes and it's best to drill through both upwrights at the same time. Using 3/8 rod or bolts, BE SURE TO DRILL YOUR HOLE SIZE 1/6" larger, otherwise you'll never be able to remove the bolts without a lot of frustration. That was the mistake I made. Also good to chamfer the holes both sides.

   I drilled holes spaced 1" starting 18" up from the bottom cross bolt position. Wedge action takes place at these adjustable cross bolts and spaces, partly in lieu of clamps, so you need to space holes based on what size glue ups you think you will make. I chose 18, 24, 36 and 48 inch positions, PLUS ONE INCH for wedges.

   Contrary to what you might think, this rig doesn't have to be very strong as the greatest stress is in the vertical but you don't want to be using a lot of force to even up boards lest you create a stressed table top. Side wedging is just for making minor adjustments, so one shouldn't use it to force poorly prepared boards together.

   Edited 7/16/2003 8:37:59 AM ET by boatman

   Edited 7/16/2003 8:52:21 AM ET by boatman

3. 
   kenewald | Jul 16, 2003 12:31am | #4

   I agree with everything prior.  Just curious, how long have the boards been sitting around dry?  How were they dried? (slow/fast, kiln/clamped in a room with a dehumidifier)

   Do the boards have alot of "character"?  How likely are they to release energy?

   -Ken

   PS.  I recently made a 55"x95" table.  My biggest challenge was making the lengthwise cut straight.

1. 
   DavidP52 | Jul 16, 2003 04:20am | #6

   These boards are dated 12-09-99 and were air dried. Mine are fairly ordinary flat sawn, some have areas close to knots.

   I did a moisture meter test which showed all figured areas had 3% higher moisture than straight grain. Avg content around 10%. Most of the finished stuff in my always air conditioned house runs around 8-9%, again with higher around figure, so the difference seems to remain the same.