Tabletop Construction

[jackellis]

I'm attempting to make a fairly simple table for a printer. The top and the shelf will measure approx. 24"x24", so to create a surface that large I'm gluing up narrower boards using biscuits for strength. It's raised a few questions:

1) Clamping tends to pull the glued up boards into a U-shape along their long axis. What's the best way to keep the whole thing straight?

2) Although I took my time cutting the biscuits, there was still a very slight (1/64th) misalignment between boards. Is this typical, or can you expect a perfectly smooth surface using biscuits with enough practice?

3) I'm using a hand plane to try to smooth the surface this time because I don't have a thickness planer. Is it safe/advisable to run glued up boards through a thickness planer? Even if I had a jointer, I couldn't afford/don't have space for one that is capable of handling 24" boards.

4) Is there some handy place where I can read up on the technique for doing this, or is it simple enough that I just need to do some practice pieces?

Thanks

[RayintheUK]

1) Clamping tends to pull the glued up boards into a U-shape along their long axis. What's the best way to keep the whole thing straight?

Too much clamp pressure will often cause the symptom you describe. A simple way to prevent bowing is to put the clamps alternately over and under the workpiece, although even with this method the important thing is not to overtighten the clamps and squeeze all the glue out. An even glue line is the ideal.

2) Although I took my time cutting the biscuits, there was still a very slight (1/64th) misalignment between boards. Is this typical, or can you expect a perfectly smooth surface using biscuits with enough practice?

As with any tool with a motor, there will be some vibration. If your downward pressure on the fence varies, this can cause a little misalignment from time to time. Also, if the tool is not perfectly set at right-angles to the edge, the same effect can occur.

3) I'm using a hand plane to try to smooth the surface this time because I don't have a thickness planer. Is it safe/advisable to run glued up boards through a thickness planer? Even if I had a jointer, I couldn't afford/don't have space for one that is capable of handling 24" boards.

If there is misalignment on the glued-up boards, then a planer will remove it, but all boards will have to be passed through, otherwise the project will end up with differing sizes of stock. On the odd occasion I've run a pair of glued-up boards through a planer, I've done so without problems, but if they're bowed (as in 1) above), then you'll take out the bow and reduce the stock thickness before getting to the glue-line misalignment, assuming that the bow is upwards.

4) Is there some handy place where I can read up on the technique for doing this, or is it simple enough that I just need to do some practice pieces?

Can't help with this one, but you know what they say about practice?

Ray.

[scorrpio]

You can find a number of articles on the internet. Latest Fine Woodworking also has a nice article on how to keep a tabletop flat through its seasonal movement.
Far as thickness planer: running laminates through is fine, but 24" planers are far from cheap.

If you ripped these boards to width on your table saw, it might be that your blade is not perfectly square to the table, producing a slight bevel. When laid out on a flat surface, do the pieces meet perfectly, or is there a slight gap on either top or bottom? If not, you need to square the blade to table.

Cutting bisquit slots, did you use a plate joiner? If you are new to the tool, it takes some practice to learn not to shift the fence slightly as you plunge cut the slot. I don't have a joiner so when cutting slots in stock edges, I prefer do it on a router table with a slot cutting bit.

When you clamp, use caulls. Select either straight wood pieces, or some aluminum or steel stock. I using wood, put some clear packing tape on it to prevent it gluing to workpiece. Put caulls over and under your glueup and clamp them togeather. They will keep your glueup straight and aligned.

[LarryG]

Another important tip on clamping

In addition to alternating the clamps as Ray describes, make sure the clamp is applying pressure at the center of the boards' edges. If the pads on both jaws are not accurately centered, the tendency to pull the panel into a U is greatly magnified. When using cauls (as you should, with most types of clamps), it's all too easy to get the clamp pad slightly off center. Tighten each clamp carefully, and reclamp any that aren't sitting just right.

If you are jointing the edges of the boards, either with a jointer or on a router table, alternate the tops and bottoms of the boards as you run them through so that any slight bevels that may exist due to the fence not being square will cancel each other out.

A little misalignment along a biscuit line is not unheard of. Careful selection of the biscuits, to make sure they all fit snugly, will help, as will careful technique.

[JimD]

I have glued up lots of boards over the 20+ years I've been woodworking and I still get misalignment of the boards. I use a belt sander (a Ryobi I got from Cummins (rebuilt)) to even things up. I've read of people using a cabinet scraper and hand scraper for this. I plane should work but I tend to power tools as much as possible. I start with 80 or 100 grit and often use the sander at an angle at first switching to in line sanding after the top is flat. I belt sand to 150 grit and then use a random orbit sander and sometimes hand sand for the final finish.

You can get by without the biscuits with modern glues (like Titebond) but they do help keep things lined up. You need straight and square edges but you can get those on the BT3100.

Jim

[LCHIEN]

With a table top glue up everythings got to be pretty close to perfect if you want perfect reults.

1. Edges have to be jointed at exactly 90 degrees (either saw or jointer) or the finished board will be cupped (if you keep them same side up) or serpentine (if you alternate boards).

2. the clamping bed needs to be made of stiff, flat rods if you are resting the boards on them. This means Bessey K-body or Jorgenson Cabinet Master Clamps. If you use the cheaper F-clamps the backbone steel member will bend so that the whole table takes on a convex curve to match the backbone or the angles of the jaws. If you have to use the F-Clmaps, make sure you have a caul arrangement that holds the boards in a flat plane (e.g. use several 2x4 on edge top and bottom to clamp them).

3. With the Plate joiner, you have to make sure there's no dust and dirt under the fence, that'll raise up the slot by that irritating 1/64th.

[Ken Weaver]

Recent magazine (FWW?) suggested using dowels same diameter as thickness of boards you are working with. Put them on edge of board and clamp the dowels to the work. This puts the pressure point in the center of the edge and reduces the tendency to warp the top from clamp pressure. I plan on using this on a top I'm roughing out this week. Also, in addition to using a caul, make sure you alternate the grain in the boards to be glued up. That also helps reduce warpage.

[AlanJ]

Nobody has suggested to use a glue line router bit to add strength/align the boards instead of using biscuits. I haven't used one yet (I bought one last month), but I suspect if it's set up properly on the router table it would give a better alignment than biscuits - with equal or even better strength.
Would this be true?

Alan

[BobSch]

2) Although I took my time cutting the biscuits, there was still a very slight (1/64th) misalignment between boards. Is this typical, or can you expect a perfectly smooth surface using biscuits with enough practice?

Are you sure you cut the biscuit slots on the same side of each board? If you accidentally flipped one over and the slot cutter depth setting wasn't exactly half the thickness of the board that could throw things off. BTDT.