3

I'm building a coffee table with legs that are sub-assembled with a miter joint. See photo. The plans call for a Domino or dowels in addition to a spline [edit: key, see link below] for added strength.

I don't own a Festool Domino joiner and I'm struggling to plan out a way to accurately drill for dowels into the miters. My question is whether the miter joints will be strong enough with just glue plus the key glued in? I acknowledge that I could also do pocket holes on the underneath, and they would be hidden well, but if they aren't necessary then I'd like to avoid.

The picture shows in red where the key would go. The Domino/dowels are supposed to go at the bottom of the miter joint.

Author's Edit: I've added a complete picture of the table for additional context. You should now be able to see how the leg in question supports the table.

Leg Sub Assembly

enter image description here

bdots22
  • 31
  • 2
  • Am I the only one that doesn't understand what view this is? "Red shows where the spline should go" is incomprehensible, given my understanding of a spline. If you could provide a sketch of the entire table, this-all might make more sense. – Aloysius Defenestrate Jun 20 '21 at 19:32
  • I agree with Aloysius Defenesrate. I cannot see how this shape for the leg fits to the table which is important for how the force is transferred through the joint. A full table sketch with some dimensions would be very helpful. – Ashlar Jun 21 '21 at 01:21
  • 1
    @AloysiusDefenestrate, The main problem here is one of terminology, one that I go on and on about. The plan is using keys, not splines..... I've attempted to correct a number of prominent YouToubers about this in an attempt to halt the spread of this one particular modern terminology fail and in every case got ignored or had my comment deleted for my troubles :-/ – Graphus Jun 21 '21 at 02:31
  • @Graphus Are you sure that the confusion isn't one of those American vs British word things? You know like getting a draft beer at the bar rather than a draught lager at the pub :P – Ashlar Jun 21 '21 at 22:48
  • @Ashlar. Yes I'm sure. Older American sources exclusively refer to keys as keys, splines as splines. Then some dolt called keys splines at some point (in the last 10 years or so?) and for some odd reason it took off like wildfire! I blame the Internet LOL – Graphus Jun 22 '21 at 06:15
  • @Ashlar, when keys are very thin they might be called feathers, or feather keys and this may be how the earliest sources refer to them, when slips of veneer were used for the reinforcement (meaning you just needed a hand-saw kerf) and they were used to strengthen the corners of picture frames and small decorative boxes. I believe they were never used for larger items until the modern era, when power-tool operations allowed for the easier creation of uniform wide slots, along with the reduction in the use of 'proper' alternative joinery like blind dovetails. – Graphus Jun 22 '21 at 06:22

2 Answers2

4

The plans call for a domino or dowel, plus a spline for added strength.

Just so you know, this is probably overkill.

Many such legs are reinforced by just one means, not two, and the tables survive use just fine. However, you can by all means reinforce in two (or more!) ways because you trust the plan and want to go with it exactly as written, or simply for peace of mind because you like to over-engineer any critical joint, just in case; nothing wrong with this.

Re. how the plan is written, be aware that the writer has fallen into the modern trap of sloppy terminology — what are marked in red are keys, not splines1.

Also regarding the author's specific implementation of keys here, two thinner ones would add more strength than a single fatter key.

I'm struggling to plan out a way to accurately drill dowels into the miters.

Oh this is easy. If you drill the holes separately it's really just a matter of:

  • accurate initial marking out (use a gauge and/or dividers to mark each joint face from the same datum surfaces)
  • then careful drilling perpendicular to the mitre surface.

OR, one of my favourite solutions when it comes to dowel reinforcements, just drill the holes after assembly, i.e. using through dowels. Once a mitre is assembled it's a snap to drill right through the joint to sufficient depth that the dowels seat deeply into the second piece of wood; in this case drill down from the top so you get decent penetration into the legs. Incidentally, the exact angle of the dowels isn't critical, and, each one doesn't have to be consistent with its neighbour.

I don't own a Festool domino joiner

Well you certainly don't need one hehe ^_^

Seriously though, dowel joinery has been shown in multiple tests to be just as strong or stronger, is nearly as fast to do (close enough as makes no odds in some cases), it doesn't require a specialist mono-tasking tool which let's face it, is not cheap (understatement) and doesn't then tie you to a fastener that is also, ahem, not cheap (magically makes beech cost more than ebony!) and is more difficult to source in difficult circumstances2.

On the other hand dowels can more easily be bought from a range of sources and if needed, or preferred, shop-made. Now you can of course make your own floating tenons — that's what a Domino is, a specialist kind of floating tenon — but by comparison dowels are much, much faster to make3 and allow you to use various offcuts and scraps that are smaller so a better frugal option4. Also worth bearing in mind that now that we have easy access to epoxies dowels don't even need to be wood. Comparatively, dowel joinery is full of win.

1 I don't know why but people seem to have trouble keeping track of which is which. But I think it's fairly easy to remember that keys always cross the joint, while splines run along the joint (or splines line up with the joint if you want a mnemonic).

2 Normally this point is a little forced TBH — one usual example being, what if you run out in the middle of a weekend? — but not in recent times when sources of supply have dwindled or dried up entirely and deliveries have been slow (to the point of farce in some cases) or even non-existent.....

3 Using a shop-made dowel plate..... or if money is super tight, just a washer.

4 Can even be quickly, and safely, made from firewood if necessary! [By splitting off chunks and riving them down to approximate cross section in stages, which also ensures the dowels have super-straight grain so are as strong as poss. This process doesn't require a froe, a hatchet or axe, or even a chisel, I've done it by batoning with a stout kitchen knife more than once.]

Graphus
  • 65,691
  • 3
  • 50
  • 139
  • Thank you, very helpful! Apologies for the terminology mix up; I'm still very green to woodworking and was using the terms provided in the plans. I've added a full sketch of the table to address the other commenters concerns, but I think you've answered my question completely. – bdots22 Jun 21 '21 at 13:38
  • +1 for drilling the dowel holes after the joint has been assembled. TBH, I'm not sure which direction the dowels are intended to go in this particular case. I'm thinking that they're to go vertically through the joint so the top of the dowel would be hidden by the table top (though it would probably hit the key, weakening that), but they could go through the leg assembly, holding the key in, too. In either case, drill & install after assembly. – FreeMan Jun 21 '21 at 16:48
  • @bdots22, oh it's not your fault! Numerous woodworkers (not just the younger hungry ones, it includes a few who are long enough in the craft to know better.... I'm looking at you K-M) are now calling keys splines. Anyway, it's a shame about the sloppy terminology because this is a very attractive table with some nice details. Best of luck with it. Oh and P.S. for when the build is completed, have you settled on a finish yet? – Graphus Jun 21 '21 at 17:17
  • @FreeMan, if the original idea was to use two dowels per leg and for them to flank the key, they could still miss it even with it being a full 1/3 the thickness of the stock. But with the legs and mitre angled as they are blind dowels situated in the fat part of the joint could miss the key entirely. – Graphus Jun 21 '21 at 17:23
  • @FreeMan the plan calls for two dowels to run parallel to the key on the inside lower part of the joint. I suspect they are used more for alignment purposes to help with the glue up. – bdots22 Jun 21 '21 at 17:33
  • @Graphus I haven't settled on finish yet. I'm building the table out of hard maple. I've only worked with Rubio Monocoat to finish so far, but am open to suggestions. – bdots22 Jun 21 '21 at 17:41
  • If you've used and like Monocoat then I think you're unlikely to like many other options :-) But wiping varnish is well worth trying at some point as it's a very versatile option and provides more protection (from water and scratching) for high-traffic items. Just to be clear, I mean normal varnish thinned to wiping consistency, not the commercial stuff which is overpriced. Lots of references to wiping varnish here as I'm a big proponent of it and recommend it frequently. I use it myself a lot and love that it's so easy to get a good result + will dry so reliably, even when it's cool and damp. – Graphus Jun 22 '21 at 06:12
0

My main concern with your sketch of the leg is that the key is at the outside corner of the leg segment intersection. The weight on the table will want to cause the two pieces of the leg to splay out increasing the angle between them. The lower inside corner of the leg segments will want to pull away. The "key" (ahem, tribute to Graphus) is located at the top, outside corner and does not extend all the way along the joint to the bottom, inside corner. The key is located at the point in the joint where it is needed least. Since you are including a spline (oops!), I would extend it all the way along the length of the joint. With such glued joint there is no need for dowels. The keyway can be easily cut on both leg segments on a table saw with a proper jig to secure the piece for its saw run.

Ashlar
  • 8,454
  • 5
  • 23
  • 47