Festool Domino vs. Traditional M&T

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Forum topic by ErikATX posted 06-23-2020 03:19 PM 435 views 0 times favorited 11 replies Add to Favorites Watch
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4 posts in 47 days

06-23-2020 03:19 PM

Topic tags/keywords: festool domino mortise tenon loose tenon joint strength tenon length mortise depth

Like a lot of people, I’ve been tempted to get a Festool Domino. And I suspect like a lot of people, the next issue is whether to go for the DF 500 or the XL 700. Obviously, the 50% (plus more if you want to get the Seneca adapters and extra cutters to use it like a 500) price difference is a deterrent to getting the 700, and so is the added weight and bulk.

My general takeaway from researching the issue is that people tend to claim that you can get away with an awful lot with the 500 and that the XL is only required when you are making really big projects like beds and doors and maybe some large dining tables.

What I am having difficulty with is trying to reconcile this with the 500’s specs when compared with rules of thumb for traditional mortise and tenons, particularly with regard to mortise depth/tenon length. I know that mortise and tenon sizing is a whole debate unto itself, so I hope I can get away, for purposes of this discussion, with citing this article from Christopher Schwarz: Also, I am assuming that these same rules apply for loose tenons, just acting two ways.

Here is Schwarz’s summary of the rules of thumb for M’s & T’s:
-Tenon thickness: 1/3 to 1/2 of the stock being mortised;
-Tenon width: 1/2 the width of the rail you’re cutting it on (with some caveats about when the tenon gets too wide compared with the width and adding a haunch);
-Tenon length: 5 times its thickness, or often longer.

Tenon thickness is the thing that most discussions of the 500 vs. 700 seem to focus on. Because max cutter size on the 500 is 10mm, and the discussion generally seems to get simplified to people saying you are limited to stock about 3×10mm = 30mm = about 1 3/16” thick. Obviously it is more complicated than that, especially when the stock you are joining is of difference thicknesses, but limited to this one aspect—thickness—it does seem like the 500 would cover a lot of ground and you could probably use parallel sets of less-thick dominos in thicker stock. So the thickness issue is not a major concern for me (feel free to educate me if it should be!).

Tenon width: This is the most convoluted rule of thumb in Schwarz’s discussion, but the Domino, both 500 and 700, give you a lot of options with respect to mortise/tenon width and it seems like in almost every situation you could come up with a solution that gets you a total width of all tenons that more or less ‘satisfies’ the rule. You are not going to be making haunches with the Domino (although I guess you could probably get creative and try to combine a haunch with Dominos but that’s beyond the scope of what I’m trying to get at). In general though, when comparing the 500 vs. the 700, it doesn’t seem that tenon width should be a limiting factor since with the smaller unit you could almost always use multiple narrower tenons to add up to the total width you need and provide plenty of glue surface.

So, finally, and thanks for bearing with me if you made it this far, you get to tenon length/mortise depth. This is my real question. On the DF500, literally none of the cutters will make a joint that comes close to satisfying the 5x the thickness rule of thumb. The closest, somewhat oddly, is the 6mm x 40mm domino, which gets you a 3.33x-thickness tenon on each side. But in terms of dealing with larger stock, the 10mm cutter for the 500 maxes out at 50mm, so a 2.5x-thickness tenon on each side. On the XL, all but one of the Dominos get you to at least 4x-thickness, but more importantly, to my mind, every cutter size has a corresponding Domino length/ that will allow you to get at least 5x.

I realize there are situations where the design of the joinery will not allow you to use a 5x-thickness tenon. I realize also that for something like cabinet doors that are going to be bearing much weight or subject to serious racking forces, that it may not be necessary to have a tenon that satisfies these rules of thumb.

But I see people all the time using the 500 on pretty substantial furniture projects and in cases where they could easily satisfy the rules of thumb with a traditional M&T or custom floating tenon joint. In trying to search for information about this, I’ve seen strength test comparisons, but they always compare the domino to a traditional M&T of the same dimensions (it’s generally weaker, but not by enough for me to be concerned about). But this seems to me to miss the point. The strength comparison should be between what the Domino allows you to do for a given joint and the M&T you would create at that joint, following the rules of thumb or your own experience as well as the situation allows.

So, to summarize, with respect to the 500:

Are people just tempting fate with these joints?
Are the rules of thumb just overkill, especially with improvements in today’s glues?
Is there something I’ve missed about the Domino joint that meaningfully distinguishes it from traditional M&T/floating tenons and allows the tenons to be shorter while providing comparable strength?

Sorry it took me so long to get to finally get to these questions. As you can probably tell, this has been eating at me for a while. Thanks for reading and in advance for any insights.

11 replies so far

View Fred Hargis's profile

Fred Hargis

6315 posts in 3298 days

#1 posted 06-23-2020 03:53 PM

I have both the Domino mortisers, I bought a well used 500 some years ago that gets the most use. Then about 2 years ago I bought a used 700 for what I thought was a great price. I use it on larger projects. But it’s not the only M/T joint I do, I still use traditional integral tenon joinery frequently. On to the questions: Nope, I don’t feel I’m tempting fate with Festool tenons…I do think that the Schwarz’s rules are old and proven…and also not always needed. As for the domino cutting depth, even if you cut these with a router and spiral bit, you aren’t going to get much deeper; and there have been a lot of mortises cut that way (router). As for the width of the Festool tenons (notice I call them tenons, instead of “Dominoes”), the Domino will cut wider slots to allow some side to side movement for slight alignment errors. When I cut the 14 MM mortises I used (twice) I cut the widest mortise the tool would do. Then I made my own tenons, and made them to fit the wider mortises. This created very strong joints on a heavy bench and it’s what i would do if I ever built an entry door. If the narrow width really bothers you, you can overlap the cuts and make a wider tenon. The convenience of the Domino is the taking the tool to the workpiece, so don’t feel you are limited to using the Festool tenons. I’m a fan of the Domino, but not a fanatic…and it’s price does almost put it out of reach of most hobbyists. Plus, there’s a lot of other ways to accomplish the same thing. I doubt any of this helped, maybe didn’t answer your questions (and they are fair questions), but if I had the concerns you expressed I’d erase the tool from my acquisition list. One other thing to consider, all the Festool tenons are expensive, but that takes on a whole new definition with the largest ones…they approach $1 ea., the last time I looked.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Aj2's profile


3178 posts in 2603 days

#2 posted 06-23-2020 04:00 PM

I also sometimes use my Festool to only cut mortises. Then I square up the ends with a chisel and cut my tenons the traditional way. Cutting very accurate mortises is the key.

It’s a expensive tool for sure.

-- Aj

View ErikATX's profile


4 posts in 47 days

#3 posted 06-23-2020 05:23 PM

Thanks for the replies. Fred, your post was definitely helpful, thanks. I think my post got so convoluted that it wasn’t clear, but I think the 700 does generally allow you to fulfill the rules of thumb in almost all cases. I guess I was just trying to understand why people think they can get away with the 500 in a joint that requires real strength since it is impossible for it to ever fulfill the rule of thumb re: tenon length. Your point about routered mortise depth is well taken; I suspect that this rule of thumb may not be widely followed with or without the Domino.

View ErikATX's profile


4 posts in 47 days

#4 posted 06-23-2020 05:32 PM

Also, Fred, I don’t know if you’ve seen this, but I believe somewhat recently Taylor Toolworks started selling knock-off dominos in some of the more common (i.e. 500) sizes:

Haven’t tried them since I don’t have the machine, of course, but might be worth a try.

View shampeon's profile


2154 posts in 2988 days

#5 posted 06-23-2020 05:57 PM

Seems to me like if you have a table saw, router table, and a roundover bit you could make loose tenon stock and just trim to length as needed.

As for tenon length, I can think of very few projects that absolutely require the full 5x tenon length. Maybe a bed frame. Since it’s a hand-held tool, it is a lot more convenient to have a lighter and smaller 500 that covers most of the possible uses you’ll encounter 360 days a year, and then hand cut the mortises and tenons that exceed the capacity on those other 5 days. Don’t buy for the exception. That’s like driving around a dump truck all year because you’re thinking about landscaping your yard one day.

-- ian | "You can't stop what's coming. It ain't all waiting on you. That's vanity."

View avsmusic1's profile


652 posts in 1490 days

#6 posted 06-23-2020 08:31 PM

I’ve had both dominos and continue to use M&T cut other ways

Simply put, the 500 is the tool the typically person will reach for more. It may not quite satisfy the rules of thumb but it makes joints plenty strong and, as others have noted, there are small tweaks or workarounds that can make them even stronger. Personally I used to just double up on joints that needed more and never ever felt like the structural integrity of the joint was in question.

I’m convinced there will be rock solid furniture in regular use 50 yrs from now that was built with the domino 500

View Fred Hargis's profile

Fred Hargis

6315 posts in 3298 days

#7 posted 06-23-2020 08:46 PM

Thanks for that link to Taylor tool, I was nor aware of them. At the moment I’m pretty well stocked, but will keep that link on on hand. Besides, they may broaden their offerings over time.

-- Our village hasn't lost it's idiot, he was elected to congress.

View ErikATX's profile


4 posts in 47 days

#8 posted 06-23-2020 09:27 PM

Thanks for the additional replies. I’m not doubting the convenience—no doubt that is why people are so eager to reach for the 500 in spite of the short tenon length. I’m concerned about the strength of those convenient-to-make tenons. Seems like people are leaning toward the ‘the rules of thumb are overkill’ explanation.

View Rich's profile


5689 posts in 1394 days

#9 posted 06-23-2020 10:36 PM

Seems like people are leaning toward the the rules of thumb are overkill explanation.

- ErikATX

Rules of thumb are simply a place to start. Every situation is different and no one “rule” will fit each one. Attaching an apron to a table leg does not carry the same load bearing concerns as a bed rail mortised to a post.

You’re talking about two different things. The article linked is referring to integral tenons, not loose tenons. Single dominoes are rarely used for a joint of any size. The manual states guidelines for spacing them in a joint.

What matters the most is the surface area of the glued joint and the orientation of the grain, not simply the length of the tenon.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Woodknack's profile (online now)


13439 posts in 3185 days

#10 posted 06-24-2020 12:37 AM

We’ll know in 20-30 years whether the Domino is any better than dowels. A lot of that dowel furniture from the 60s came apart on its own or can be easily pulled apart by hand. Dowels just don’t have much glue surface. My guess is the Domino will be better. Many people overestimate how strong furniture needs to be for everyday use and underestimate the benefit of being easily repaired. I would have no qualms about using a Domino for run of the mill furniture because most will be in a dump before the glue dries out. For something I really care about, pinned mortise and tenons.

-- Rick M,

View pottz's profile


10326 posts in 1789 days

#11 posted 06-24-2020 01:16 AM

i bought a used 500 a few years back and can say i love it and it was money i consider well spent.ive thought about getting the 700 but for the cost just not sure it would be justified,but then again i buy a lot of tools that i cant justify.hey if you can afford it do it.

-- working with my hands is a joy,it gives me a sense of fulfillment,somthing so many seek and so few find.-SAM MALOOF.

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