Replies

1. 
   _mj_ | Jul 08, 2020 05:23pm | #1

   You will not need any added strength to your top glueup, but the domino will make life easy when you get going on it. They are great for alignment, and hold against lineal slippage better than biscuits or splines. Use the tight setting on all of one board and one tight domino in the center and a sloppy fit for the rest on the second board.

   With 3/4" material don't use much glue in the domino slots, the wood will swell from the moisture pockets and you'll be forced to wait to surface the top. I sanded one flat and wound up with depressions after it fully dried out. Live and learn.

2. 
   The_Official_Tyler | Jul 08, 2020 06:16pm | #2

   Short answer to your question is "yes." A loose tenon like a domino will add more glue surface and increase the strength of the joint. I don't think anyone will argue that (though it is the internet so who knows!).

   The longer answer is that I don't forsee you needing any extra strength than just a long grain glue joint on a panel glue up of 3/4" walnut. The glue alone will be plenty strong to hold. Dominoes in this instance - as MJ pointed out - would typically be used to help keep the boards aligned during glue up and reduce the amount of flattening you'll need to do later.

   On a separate note, if you're worried about strength (or movement) on a 26" wide panel, you may consider bread board ends. Not strictly necessary for that width, but wouldn't hurt either and I really like the look of them. Something to think about at least.

3. 
   pintodeluxe | Jul 08, 2020 07:12pm | #3

   Tabletop glueups are actually easier without any joinery. The glue alone on long grain surfaces is plenty strong.

   It's only guaranteed for the first hundred years though.

4. 
   lat_axe | Jul 09, 2020 03:12am | #4

   Dominos, biscuits, splines, router-cut lock-joints et al will strengthen a joint via both more glue surface and often via the internal-clamp action of a domino, biscuit or spline that swells internally with the glue. But you don't need the long-grain glued edge-joints of such a small item as that you mention to be strengthened unless you're so bad at making edge joints that they're likely to spring and go gappy with time.

   Using such things as dominos for alignment in such a small item also seems redundant. Alignment only becomes an issue with long or unwieldy planks being edge-jointed. Many will anyway shout, "Use cauls" which will help avoid misalignment but can themselves be unwieldy and difficult to apply to a big glue-up, unlike a few dominos or biscuits.

   But that item o' yourn is easily manageable without any alignment aids other than a nipper or two over the ends of the joins down each side of the end-grain edges (if that).

   Lataxe

5. 
   gulfstar | Jul 09, 2020 09:48am | #5

   The glue joint is stronger than the wood , we will never know if the biscuit makes it stonger as the wood will break away from the glue joint when stressed.

6. 
   lat_axe | Jul 09, 2020 10:46am | #6

   I once did an ad hoc "test" of a biscuit joint with two size 20 biscuits in a "leg" joined to matching slots in "an apron". (Two bits of scrap, in fact). This was some 14 years ago, when I used biscuits quite a lot rather than make M&T joints of the traditional kind.

   After leaving the test piece glued up with Cascamite for 48 hours, I anchored the "leg" part in the vice and put a hole through the "apron" part with a chain through it attached to a hand winch jammed behind an immovable kerb.

   Tugging broke the joint but it needed quite a lot of tug. The end grain of the "apron" was glued to the long grain of the "leg" but cracked away from the long grain of the "leg" part first, as you'd expect. After more tug, the biscuits broke in half and the two jointed parts were ..... parted.

   The biscuits didn't leave their slots; the glue retained them there but the (Trend beech) biscuits themselves broke in two across their slanting grain, leaving most of their half-bodies in the slots into which they'd been glued.

   As with the simple long-grain to long grain joint that's just butt-glued, the glue joint is stronger than the wood. This applies to wooden biscuits as well as to ordinary planks, it seems.

   As a substitute for traditional M&T biscuits were OK but definitely not as strong when first made. A traditional M&T has the long grain of a fully-attached tenon glued into the mortise, rather than a couple of wooden wafers. But I suspect that the M&T will loosen over time as small seasonal moisture change movements cause the glue join to weaken and eventually part. This can be seen in a lot of older furniture.

   Drawboring and wedged tenons were invented for a reason.

   Will the same glue-join breakdown happen with biscuits over a few decades? They do tend to be tighter in their slots than a tenon is within a mortise, as they're compressed when dry then expand in the joint as the water in the glue is absorbed and permanently re-swells the beech or birch biscuit. There's mechanical as well as glue grab, with biscuits. Same with Dominos.

   Lataxe

7. 
   suburbanguy | Jul 09, 2020 12:09pm | #7

   If you're worried about alignment, sprinkle a bit of salt on the joint. The two parts won't move during glue-up. Don't use sugar, though. The crystals don't have sharp corners/edges and won't bite into the wood.
   The salt crystals simply dissolve or are crushed into the wood grain, so there won't be any effect on the final project.

8. 
   DRBWWing | Jul 09, 2020 06:26pm | #8

   Trust me, Dominoes will not add any strength to a panel beyond what the glue does. Long grain to long grain is THE strongest glue joint there is. Their function in a panel glue up is for alignment.

   This is a pretty small panel. If your boards are straight you don’t need alignment aids. Personally I rarely use alignment aids. I incrementally add clamping pressure and a very intentional whack with a rubber hammer corrects any minor discrepancies.

   I recommend either clamps across the joints on the ends or cauls. On the ends, small blocks covered in packing tape in each side of the joint will do the trick.

9. 
   geedubbee | Jul 09, 2020 06:55pm | #9

   I use splines or dominoes for alignment on pieces large enough to present a challenge. If there is any appreciable add to the joints strength I have yet to see an testing that yields empirical data. Two boards, well joined and edge glued will break in the wood more often than at the joint.

   It is easy to get over-focused on the numbers. In reality you want to be concerned with is the joint strong enough for the function. Increasing strength beyond that is of a decreasing value IMHO.