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Thread: Mafell DDF40 Duo Doweller - Domino now has some competition

  1. #16
    Keegan is correct about loose tenons being stronger than dowels. Like him, I've repaired a lot of chairs and almost every one that had a failed joint (and it's almost always the joint where the seat attaches to the back) it was a joint of two dowels.

    Let's look at the mathematics. The numbers used are as follows:

    Length of the dowels and the loose tenon = 3"
    Diameter of the dowels = 3/8"
    Number of dowels = 2
    Space between dowels = 1/8"

    The two dowels and the space between them will occupy a space 7/8" wide. We'll make the loose tenon fit into that same space. So the loose tenon will be 7/8" wide by 3 inches long.

    I'm going to compute the long-grain-to-long grain glue surface for both the dowels and the loose tenon.

    The area of a dowel is 2*pi*r*h, where r is the radius and h is the length of the dowel. I'm going to compute the long grain surface area in each side of the joint so h will be 1.5 inches.

    The area of the two dowels is 3.534292 square inches in each side of the joint. However, only half of the surface area is long-grain-to-long-grain surface area. The other half is long-grain-to-end-grain. You can visualize this by considering the dowels to be square with the same surface area. Only half will be long-grain-to-long-grain.

    The resulting long-grain-to-long-grain surface area is 1.767146 square inches. This is for one side of the joint.

    The loose tenon long-grain-to-long-grain surface area can be computed as follows. The loose tenon will be 1.5 inches into the wood and 7/8" wide, giving 1.3125 square inches. Since there are two sides to the loose tenon, the total area is 2.625 square inches. This is for one side of the joint.

    The loose tenon has 48.5% more long-grain-to-long-grain surface area than the two dowels.

    Additional comments: Most of the wood we work with and most chair parts are about 3/4" thick. It's difficult to put bigger dowels into 3/4" material without compromising the strength. And in the world of commercial chairs, they use 3/8" dowels.
    The space between the dowels has been reduced to the minimum in this example. In real chairs, the space between the dowels is much larger. Increasing the space between the dowels allows for a wider loose tenon which provides more surface area to the tenon. The example given here is about as good as it gets for the dowels.

    I have a spreadsheet that computes this stuff so if you want me to run other numbers, let me know.

    Mike
    Last edited by Mike Henderson; 07-26-2021 at 4:31 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  2. #17
    Quote Originally Posted by Keegan Shields View Post
    ... Every cheap chair I’ve had fail has failed at a dowel joint. ...
    Quote Originally Posted by Mike Henderson View Post
    ... I've repaired a lot of chairs and almost every one that had a failed joint (and it's almost always the joint where the seat attaches to the back) it was a joint of two dowels. ...
    I think we've leaned back in chairs ever since they were first built, so I wonder sometimes if ^this^ is just manufacturers being cheap, or if perhaps 135lb offshore chair designers just haven't caught up with American's passionate love affair with our spoons? (Thus endeth my drift off topic.)

  3. #18
    One reason I make my own tenons is I like them to be wider when that fits the project. That gives me even more side grain contact area in the joint. It is easy to make longer mortises by making multiple side by side plunges. While you could put in more dowels, and maybe offset them so they are not so far apart but you still have the issue of limited side grain on the dowels.

    I've never liked dowel joints much. So that bias may influence my belief that the domino makes a better joint. But I agree it is nice Festool is getting some competition. It's a shame the domino costs what it costs.

  4. #19
    Quote Originally Posted by Jim Dwight View Post
    One reason I make my own tenons is I like them to be wider when that fits the project. That gives me even more side grain contact area in the joint. It is easy to make longer mortises by making multiple side by side plunges. While you could put in more dowels, and maybe offset them so they are not so far apart but you still have the issue of limited side grain on the dowels.

    I've never liked dowel joints much. So that bias may influence my belief that the domino makes a better joint. But I agree it is nice Festool is getting some competition. It's a shame the domino costs what it costs.
    When I need wider tenons with my Domino, I just make the mortise wider (with multiple plunges) and then cut one domino tenon so that it, with one full size domino, fits into the mortise. I don't even try to glue the two together.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  5. #20
    Quote Originally Posted by Malcolm McLeod View Post
    I think we've leaned back in chairs ever since they were first built, so I wonder sometimes if ^this^ is just manufacturers being cheap, or if perhaps 135lb offshore chair designers just haven't caught up with American's passionate love affair with our spoons? (Thus endeth my drift off topic.)
    Not at all. US made chairs - made in the 20th century - use two 3/8" dowels. Two dowels will hold the chair together for a while, but if the chairs are used a reasonable amount, the rear joint will fail. It's just a cheaper method of manufacture than using a mortise and tenon and that's why they do it. By the time the joint fails, the chair is out of warrantee and someone like Keegan or me gets it.

    If the people want a cheap repair, I drill out the dowel holes and put in slightly larger dowels*. If they're willing to spend a bit more, I'll put in a loose tenon.

    Mike

    *When the dowels fail they tend to fail on one side of the joint. The other side is still glued so that part of the dowel has to be drilled out. That almost always makes a bigger hole so you have to put in a bit larger dowel. I sometimes turn a dowel to size. Chairs have corner blocks and by the time I get the chair, all that's holding it together are the corner blocks.
    Go into the world and do well. But more importantly, go into the world and do good.

  6. #21
    And, by the way, when a dowel joint fails on a chair, it's not the glue that fails - it's the wood. When you separate the joint, you'll see wood attached to the dowel. What happens is that the stress on the joint exceeds the shear strength of the wood and the wood fails. The glue is actually stronger than the wood. So the failed dowel mortise is always larger than the original size because some wood has been pulled out around the hole. That's another reason you have to put bigger dowels in for a repair, if you're going to repair with dowels.

    Many people think the hole gets bigger because of movement of the dowel in the hole after the failure of the joint. That may be partially true, but the big reason is the failure of the wood around the hole. After failure, the hole is no longer round so that's yet another reason you have to go bigger - you need to drill out the hole to get it round so the dowel and the wood make good contact.

    And, of course, the reason for exceeding the shear strength of the wood is that there's just not enough long-grain-to-long-grain glue surface. Maybe if they would put more than two dowels in that joint it might last longer. Anything to increase the long-grain-to-long-grain surface area.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  7. #22
    I agree completely with Mike on this one. Some of 3/8” dowels probably failed just because the grain was not straight. I’m betting the
    dowel factories don’t check dowel orientation, but….strangely they probably have an orientation for new employees !

  8. #23
    Join Date
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    I’m curious where you guys see the Duo Doweler fitting in. We’ve debated the domino, but there are nice stationary industrial doweling machines that are more suited for high volume economy priced furniture than a hand held doweler. What is the Mafel for? Those times when the workpiece is to big to get on a doweling machine?

    It seems like the Domino units are far more prevalent than the Duo Doweler. Are they more common in Europe where Mafel has more market share and wider distribution? Is the target cabinet shops?

  9. #24
    Quote Originally Posted by Keegan Shields View Post
    For load bearing joinery, the Domino has superior strength as a true loose tenon. Dowels have very poor strength but are cheap and fast. Every cheap chair I’ve had fail has failed at a dowel joint.

    The Domino, Duo Dowler, and biscuit joiner can all do alignment, but only one has the strength of a loose tenon. That’s my thinking anyway. That might not be important to everyone.
    Your cheap chairs failed because they were cheap chairs, not because of dowels. Dowel construction has proven itself for eons and is still practiced today in fine furniture and construction. That said, I think dowels come with the inherent drawback of not allowing for any error. I think the Mafelle machine falls short in that it doesn't really improve upon a drill and a doweling jig in any real way.

  10. #25
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    Again, my point was that the Domino provides a stronger joint than a similarly sized dowel joint. Just because a dowel joint has been used for a long time doesn’t make it stronger than the slot mortise type loose tenon. Perhaps dowels have been used for a long time because it’s pretty easy to drill a circular hole? Design decisions are also made with other factors than quality in mind, (cost? speed?) even fine furniture.

    Like all joinery, dowel joints have their place. However, evidence suggests that dowels are, for instance, a poor choice for attaching rails to rear chair legs if you want them to last.

    I appreciate that Mike went through the math. I would add that his scenario is probably on the generous side when it comes to the amount of side grain contact in a 3/8” hole, and the dowel still looses.

    As further proof, in most of the failed dowel joinery I’ve repaired, the dowel was still firmly glued into the rail (almost 100% side grain contact) but failed in the leg.

  11. #26
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    Oct 2015
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    I see it as just an alternative but a very good one. I own a Domino but the Mafell has got me really interested. It has features that are an improvement over the Domino. It has a sliding scale for 2 independent depth adjustments not just preset lengths. It has a very solid rack and pinion fence with a better locking mechanism. The extension (cross stop) is a lot more solid, better engineered, more versatile and locks in to the unit more precisely. The dowel cutters are not limited to 6mm to 8mm but 3mm to 12mm. That 3mm dowel would suit me for the small boxes I make. The included extra stops means you're not limited just by the pins/paddles like on the Domino (37mm/20mm with base support) so needing to reference off pencil lines is at an absolute minimum if at all. Also and obviously dowels are cheap and readily available but I know some make their own loose tenons. Put simply, it is a precision engineered machine with a lot going for it from a very reputable brand. Now for the disadvantages. Its still expensive, it doesn't have the wiggle room setting, (you could drill a bigger hole eg 8.1mm instead of 8mm), there's a lack of resources eg videos, documentation, accessories and as said above its more prevalent in Europe/UK. In Australia, there is only one Mafell authorized supplier and they don't stock anything but order on consignment. Its that lack of a local presence that has stopped me buying it. I can practically get any Festool product same day, I can even take a small drive to a Festool service center but with Mafell its constantly waiting a few weeks for any delivery. I'm really impressed with the Mafell and would even sell my Domino if I had better local support. This is entirely a personal thing.

    I think the strength argument is a non argument. Some joints work better with tenons eg chairs and some work just as well with dowels eg joining boards. Some tests I've seen have shown 4 or 5 dowels work just as well as a couple tenons depending on the type of joint. So its not a matter of one or the other, it depends on what you're making, your budget and whether you're a professional, serious hobbyist or a weekend warrior. Dowels suit me and the way I work just as much as Dominos, once again a personal thing.
    Last edited by Johnny Barr; 07-26-2021 at 8:56 PM.

  12. #27
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    I wouldn't be buying/using either if I were making chairs.

    If I were making cabinets, the Duo would be the easy choice.

    FWIW - I own a domino.

  13. #28
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    Quote Originally Posted by johnny means View Post
    Y I think dowels come with the inherent drawback of not allowing for any error. I think the Mafelle machine falls short in that it doesn't really improve upon a drill and a doweling jig in any real way.
    ,
    I've used all the dowel jigs from the Dowelmax and Jessem down to the cheapies and their major problem is speed and precision. You think how quickly you can do a mortise with the Domino. The Mafell is just as quick and it even does two holes at once but when you've got a lot to do a doweling jig becomes very slow. Also when doing edge to face joints like with drawers the whole jig has to be rearranged and readjusted and once again this is slow. Doweling jigs even the better ones can't compare with the speed and consistent accuracy of butting up against a pin/paddle like you do with the domino and duo. As for no error I don't see that as a drawback at all with a precision machine. 99% of my mortises with the domino are with the tight setting. I remember Peter Parfitt saying he never uses the wide setting.

  14. #29
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    Keegan and Mike, note this part of my post "An appropriate sized dowel that cannot be subjected to twisting force, is just as strong as any other loose tenon. In fact a dowel made of the same wood as a domino would actually have higher shear strength than a domino if you chose size based on equal surface areas."

    That's the key, do the math. A dowel of equal surface area as a domino will have more cross sectional area then a somewhat oval shaped domino. A bigger cross sectional area equals more shear strength, as I said all other things being equal.

    Mike, you're doing the math wrong. The correlation of the space it takes to fit the dowels and empty space between as to equaling a domino that occupies the same total area is the wrong way to look at it. Like I said, use surface area. To take you analysis to the absurd, why not use 1/8" dowels in the theoretical situation? It'd still justify using the same enormous domino following your logic.

    Dominos are fine, so are dowels. Fixed tenons are better. That is the art of good craftsmanship, knowing when and how much.


    Quote Originally Posted by Mike Henderson View Post
    Keegan is correct about loose tenons being stronger than dowels. Like him, I've repaired a lot of chairs and almost every one that had a failed joint (and it's almost always the joint where the seat attaches to the back) it was a joint of two dowels.

    Let's look at the mathematics. The numbers used are as follows:

    Length of the dowels and the loose tenon = 3"
    Diameter of the dowels = 3/8"
    Number of dowels = 2
    Space between dowels = 1/8"

    The two dowels and the space between them will occupy a space 7/8" wide. We'll make the loose tenon fit into that same space. So the loose tenon will be 7/8" wide by 3 inches long.

    I'm going to compute the long-grain-to-long grain glue surface for both the dowels and the loose tenon.

    The area of a dowel is 2*pi*r*h, where r is the radius and h is the length of the dowel. I'm going to compute the long grain surface area in each side of the joint so h will be 1.5 inches.

    The area of the two dowels is 3.534292 square inches in each side of the joint. However, only half of the surface area is long-grain-to-long-grain surface area. The other half is long-grain-to-end-grain. You can visualize this by considering the dowels to be square with the same surface area. Only half will be long-grain-to-long-grain.

    The resulting long-grain-to-long-grain surface area is 1.767146 square inches. This is for one side of the joint.

    The loose tenon long-grain-to-long-grain surface area can be computed as follows. The loose tenon will be 1.5 inches into the wood and 7/8" wide, giving 1.3125 square inches. Since there are two sides to the loose tenon, the total area is 2.625 square inches. This is for one side of the joint.

    The loose tenon has 48.5% more long-grain-to-long-grain surface area than the two dowels.

    Additional comments: Most of the wood we work with and most chair parts are about 3/4" thick. It's difficult to put bigger dowels into 3/4" material without compromising the strength. And in the world of commercial chairs, they use 3/8" dowels.
    The space between the dowels has been reduced to the minimum in this example. In real chairs, the space between the dowels is much larger. Increasing the space between the dowels allows for a wider loose tenon which provides more surface area to the tenon. The example given here is about as good as it gets for the dowels.

    I have a spreadsheet that computes this stuff so if you want me to run other numbers, let me know.

    Mike
    Last edited by Chris Padilla; 07-26-2021 at 10:52 PM.

  15. #30
    I doubt chairs made in a factory somewhere in Asia would fair any better if the were made with Dominos. If your describing failures in which the glue surface was the point of failure, you're describing a failure of workmanship and not a failure of dowels. All the glue surface in the world is useless if all you do is squeeze in a drop of glue and bang in your dowel/tenon. Also, just measuring the glue surface doesn't tell nearly the entire story. Two dowels spaced apart will often provide more resistance to twisting or racking forces than a single tenon placed in the middle of a joint. Then, of course, there is the problem of comparing those cheesy pine dowels to beech dominos.

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