Domino Jointing system - what are "Extremely high pull-out and load forces"?

[sdes]

I'm interested in the possibility of using the Domino Jointing System to hold in treads on a wooden spiral staircase.

I cannot find any data on their strength or range of pull out forces. The Festool website simply says "Extremely stable with dowel and clamping element for strong connections. High pulling and tightening distance. Extremely high pull-out and load forces"

I'm trying to find out what do Festool rate as an "extremely high pull-out force", is that 100N or 10,000N?  I understand there is probably considerable variance depending on the variety of timber, but even a general range for a few conevntional joinery timber types would provide a valuable indication.

The website page I am looking at is this one:
"https://www.festool.com/Products/Accessories/Pages/Detail.aspx?pid=201827&name=Connector-for-DOMINO-joining-machine-EV-32-Set"

Having contacted Festool UK, who then contacted HQ (Germany I assume), they say

"We have deliberately not listed strength data,  because they are always dependent on various factors such as the type of wood, construction or design of the connection.

For such statically loaded connections as in staircase construction one needs an approval. Unfortunately, we do not have them.

To hold the treads on a wooden spiral staircase, the DOMINO connector is exposed to dynamic forces.

For this application the Domino is not to use"

I'm a bit confused that Festool HQ seem to be saying that the Domino Connector is not suited to dynamic forces / loading, apart from a wooden sculpture, there are not many applications where such connectors are not dynamically loaded in some way or another in use.

I'm also not expecting them to in any way guarantee my design, just provide some figures to illustrate their "Extremely high pull out force" claims they make for the connector itself. (The method of use for each connector type is pretty prescriptive) I could then use that info with a significany Factor of Safety to see if the kind of loading I'm anticipating would even be feasible. (I'm not expecting Festool to provide any approval for my design as they seem to suggest, that woud be equivalent to expecting the maker of a rivet to approve the bridge it might be used in)

So, I'm wondering has anyone tested the pull out force that Festool describe as "Extremely high"? There is someone doing, by his own admission, a very unscientific demo of the strength here :

Many Thanks in advance for any info.

Stephen

[attachimg=1]

 

[Birdhunter]

I built a king sized bed for some young friends. I used the Festool 700 connectors to join the bed frame corners.

They have used it for about 6 months. They have a very active 2 year old who uses the bed as a trampoline. I am assuming the bed undergoes regular dynamic stressing.

As of a couple of days ago, the couple reports the bed as totally solid.

The above is not a scientific analysis, but it is real world. I think the 700 connectors are very strong. I’m anxious to try the 500 connectors.

 

[chewy]

Would you still house the treads into the strings, or literally butt the treads up with a domino to join them ? If the latter, I'd have thought shrinkage and movement would cause unsightly gaps.

Sent from my SM-G900F using Tapatalk

 

[epicxt]

I built a king sized bed for some young friends. I used the Festool 700 connectors to join the bed frame corners.

They have used it for about 6 months. They have a very active 2 year old who uses the bed as a trampoline. I am assuming the bed undergoes regular dynamic stressing.

As of a couple of days ago, the couple reports the bed as totally solid.

I thought that was going in a REALLY different direction![emoji6]

 

[Gregor]

I'm a bit confused that Festool HQ seem to be saying that the Domino Connector is not suited to dynamic forces / loading

That IMHO is a case of CYA.

(I'm not expecting Festool to provide any approval for my design as they seem to suggest, that woud be equivalent to expecting the maker of a rivet to approve the bridge it might be used in)

You're not, I'm not... but I'm certain that, at least in the US, lawyers could be found that would happily try to extort insane amounts of money out of Festool in case someone used the connectors in something and something comes apart with (whatever magnitude of) casualties.

 

[sdes]

Would you still house the treads into the strings, or literally butt the treads up with a domino to join them ? If the latter, I'd have thought shrinkage and movement would cause unsightly gaps.

Thanks for the response. I would anticipate trying to conceal the connector completely if possible. It is for a Larch staircase in a 300 Year old French ruin that a friend is restoring, so ideally it would still appear "traditional" even while using contemporary joining methods.

[attachimg=1]

Attached is just a very quick diagram of a possible cross section. My point is that at some point if either reducing the leverage or increasing the number of connectors, it must be possible to make the treads well enough supported to give a Factor of Safety that will give a safe stair. It might be that by that point it uses so many connectors or has such a deep "bracket" (see diagram) that it becomes rediculous / unfeasible. But given that Festool claim  Domnino joints have a claimed (but seemingly totally undocumented) "extremely high pull-out force", perhaps it would not be so rediculous, but without info, and clearly Festool are, for CYA or other reasons, reluctant to give any, its tricky to guess.

Obviously the product has been through design and development cycles in Germany or elswhere, during wich they must have undertaken significant prototype testing and then testing of the production items, they must have the information, but don't wish to publish anything beyond the non specific "Extremely high" touted by their marketing blurb which might actually be of assistance to anyone doing more than decorative woodwork. Ho hum. The results of our (UK) and your (USA) blame / litigation happy society. Easier to sue someone else than do something yourself to make ends meet I suppose.

[attachimg=2]

 

[sdes]

I'm a bit confused that Festool HQ seem to be saying that the Domino Connector is not suited to dynamic forces / loading

That IMHO is a case of CYA.

I think you are, how would you say, "Right on the money".

 

[grobkuschelig]

@sdes why you would want to rely on the Domino connector in the application you are showing is beyond me.

Just the plain thought of a stair tread being only supported by a couple of dominos is ridiculous in my opinion. There is not really any physical support for the loads you might encounter. Thinking past pure „weight of people“ what about possible loads being carried up the stairs?

There is a reason why we have been using interlocking (dovetail etc) and through-bolt constructions for decades and even centuries.

I would not want to trust my life with the small Domino connect and would strongly advise against doing so yourself.

Be safe in whatever you do! [emoji4]

There are ways to hide bolts etc, if it is just an optical issue...

Edit:
One additional thought:
The “extremely high” might also just be in comparison to other similar systems like what IKEA uses...

 

[Rob-GB]

Having built many staircases including a geometric windered stair (spiral) the forces that are imposed on the stair is multi directional and loading can be quite high at times.
For the domino fittings to be asked to work under all the stresses that can be imposed in such an application is just asking too much.

Just for the exercise of it the main points are:-

Passive load: The stair needs to support its entire weight

Active load: The stair could have many heavy adults on it at one time or heavy items being moved up or down it.

Shear: The load effect on the components in a downward direction, this would include the strength of the timber above the domino fixing mortice.

Twist: Action between components when weight is applied to one corner of a tread

Spread (between strings): The treads will flex, in use dependant on loading and can act against the strings pushing them apart, which seems easier with a "spiral" stair as they seem to want to oppose each other anyway [eek]. An Inny and Outy conflict perhaps  [big grin]

Not surprised that Festool don't want to give a nod to using them in this application but maybe they could have given a decent reason as to why not.

Rob.

 

[sdes]

[member=64706]sdes[/member] why you would want to rely on the Domino connector in the application you are showing is beyond me.

Just the plain thought of a stair tread being only supported by a couple of dominos is ridiculous in my opinion.

There is a reason why we have been using interlocking (dovetail etc) and through-bolt constructions for decades and even centuries.

Thanks for the response. You are correct that things are done in a traditional way for a reason, but that is also often because they didn't have a particular technology or materials available to them at that time. The Festool Domino is supposed to offer a revolution in joining for timber - I was hoping to use that potential.

I totally agree that "the plain thought of a stair tread being only supported by a couple of dominos is ridiculous in my opinion", but that is not what I suggested, you will see I said the joint "might become rediculous before there are enough connectors". I'm asking to quantify what force / loading this particular fastener can carry, I would then, as stated, see if, allowing for a significant Factor of Safety, as previously noted, it would be feasible to use them in this situation, as many as would be needed to get to that Factor of Safety.

I wouldn't rely on one thread of Spectra line to hang from, but put enough together and they are used for parachute manufature all over the world, but if the manufaturers of the Spectra line geave no clue as to breaking strain, the parachute maker would have to do their own tests.

Why use Dominoes for construction and not traditional Mortice and tennon / dovetail joints etc, well, time, simplicity, carry the tool to the job etc, basically all the reasons in the Festool Domino marketing literature I suppose.

I agree I'm not proposing a traditional approach to joint fabrication, but isn't making robust connections in a new, quick and elegant way the whole point of the Festool Domino Machine?

I suppose I should never have mentioend the staircase, all I really wanted is some figures for pull out forces for the
connectors! Don't worry, I shant kill myself, or more importantly anyone else. I'm really just trying to establish feasibility of different approaches. Given I have the 700XL machine, it seemed logical to at least see if using it was a viable option.

I would also add I'm not a complete numpty. I built a steel spiral stair with separate cantilevered treads 15 years ago that has had many heavy people use it and carry stuff up and down without issue. But in that case I did have the ability to calculate the forces, because I knew the specifications of the four stainless steel bolts that carry each tread, the thickness of the wall of the centre mild steel tube and hence the strip out force of those threads in that steel. A factor of safety of 3x for a 250kg loading, and each trad was capable of supporting something over 750kg before failure. But I did need a bit of information about the connectors!

The claim of "Extremly high pull-out and load forces" seemed to indicate to me they might be suitable, but if as you suggest Festool should have added a : "compared to a much smaller IKEA connector" or similar, then yes, I should give up this path immediately.

Anyhow, I've just purchased a 300kg / 600 lb "crane guage" from Amazon, so if there are no users with specific info, and Festool don't reply further, which perhaps I was being optimistic about (It has now been escalated aparently, so perhaps some limited info might be forthcoming), I will do my own pull out tests on some different timber varieties and see what evaluation I can do.

I will then obviously keep those results secret - as I won't want to be sued!

Cheers

Stephen

 

[Michael Kellough]

I’d use the tie bolt with a deep bracket.  Large Domino’s would be okay for the lower connection of the deep bracket if the tread wraps around the column to negate twisting loads. Just sink the tie bolt a little deeper and cover with a plug.

I’d also set the tie bolt and especially nut a bit lower (than in you drawing reply #5) so you keep some continuous long grain wood above the nut so the whole corner of the strut doesn’t split out.

 

[Phil Beckley]

Hi Stephen
I have replied to your enquiry via email.
rg
Phil

 

[HarveyWildes]

I'm with [member=63474]grobkuschelig[/member] and [member=7330]Rob-GB[/member] on this one.  You're not getting much mechanical advantage from the domino as you would with through bolts and washers, and you're not even getting the advantage of increased glue area from using wood dominos as loose tenons.  People have done strength tests on dominos for rail and stile cabinet doors (lightweight compared to stairs), and they are not as strong as traditional mortise and tenons, although still plenty strong for the application - just do a search on "domino strength test".  Of course, a lot depends on what size domino is being used, and the tests are for wood dominos, not the new connectors, so you must take the tests with a grain of salt in terms of absolute results.  Still, the results are consistent enough that I would want tests that proved the strength of the connection before I would use dominos on stairs per your diagrams.

If you do more testing, I'd also test for the repetitive "shock" forces that stairs are subject to, not just a single joint failure test.  I could see the repetitive shocks loosening the fit of the connector in the wood very gradually over time, until it suddenly fails.  Think of teenage boys running up or down the stairs two steps at a time.

 

[sdes]

Yes, I have seen some of the videos on the wooden dowels, but as per the link in the original post, the elements I'm intersted in are the Connnector system ones they make the "extremely high pull-out force" claims for.

They are only available in one size currently, for the 14mm diameter cutter. These ones:

[attachimg=1]

Spax for example have a 40 page document about their screws with differnt multipliers to be used when used in various different natural or composite timbers and applications. I'm not seeking that level of detail, one page or even a few lines of info would do it, but just something empirical / objective to back up the subjective "extremely high"

This is the sort of info Spax give:
[attachimg=2]

 

[semenza]

Hi,

    That looks like quite a restoration project. It would be great if you wanted to start a topic and share some on going pictures and such as it progresses. It looks pretty interesting.

Seth

 

[sdes]

Hi,

    That looks like quite a restoration project. It would be great if you wanted to start a topic and share some on going pictures and such as it progresses. It looks pretty interesting.

Seth

Yes, it is, not mine unfortunately but a good friend's who coincidentally introduced me to Festool - I've sadly become adicted.

Festool UK have come back to say:

“The connectors have never been marketed as a construction fixing to take high loads that may carry the load bearing potential of a human. They are designed as a KD fixing for furniture and not any other application. “

...but they do posess "extremely high pull-out force", but it is unquantified and should not be relied upon. So, nothing that supports a human. Quite limiting what with at least half of all furniture being designed to support people.

Anyhow, if we make anything during the restoration that is Knock Down, out of 30mm+ thick material, that does not need to support the weight of a human then I'll be sure to share some photos. At the moment I can't think what that would be.

Ho hum. Topic closed I think as it seems to be stone and blood out of teritory from the "official" direction at any rate.

Thanks for the responses anyhow and good luck with your non human carrying Domino XL Connector projects

Stephen

 

[Svar]

I would not use domino connectors for stairs, not in the design in your #13 post. The anchor part is too shallow, does not even compare to a large (8-10 mm diameter) wood screw in terms of pull out force. If you think tie bolts are ugly use wooden plugs or screw studs.

 

[Cheese]

I think Festool is only suggesting that these Dominos can withstand a high pullout force relative to the standard knockdown components that are currently available. 

I understand you would like these to work in your application but that’s just not feasible.

The Domino has 3 ridges on each side that digs into the wood, consider these to be the equivalent of 3 screw threads. How much load will a 14mm screw support when only 3 threads are engaged?

Also when using a screw, a pilot hole is drilled and the screw manufactures its own internally threaded coupling. There is line-to-line contact between the wood and the fastener for 360 degrees. 
With a Domino, a clearance hole is used and the only line-to-line contact are the sides of the 3 ridges. Maybe...maybe there is 180 degrees of contact. However you’re still relying on the 3 ridges to “push themselves” into line-to-line contact with the wood as opposed to being “driven” into contact. 

So take a 14mm screw, engage only 3 threads, derate it by at least 50% for lack of peripheral contact reasons and you’ll probably be close to the pullout spec of the Domino. I don’t know what that is but it’d be interesting.

 

[Phil Beckley]

Festool UK have come back to say:

“The connectors have never been marketed as a construction fixing to take high loads that may carry the load bearing potential of a human. They are designed as a KD fixing for furniture and not any other application. “

...but they do posess "extremely high pull-out force", but it is unquantified and should not be relied upon. So, nothing that supports a human. Quite limiting what with at least half of all furniture being designed to support people.

Anyhow, if we make anything during the restoration that is Knock Down, out of 30mm+ thick material, that does not need to support the weight of a human then I'll be sure to share some photos. At the moment I can't think what that would be.

Ho hum. Topic closed I think as it seems to be stone and blood out of teritory from the "official" direction at any rate.

Thanks for the responses anyhow and good luck with your non human carrying Domino XL Connector projects

Stephen
[/quote]

Hi
The quote above is from my series of emails today with Stephen - the connectors for the DF700 have never been designed for any  high load bearing application such as a staircase or even similar. They are a KD fixing for use on tables, frames for beds and should be used with that in mind
rg
Phil

 

[Rob-GB]

Festool UK have come back to say:

“The connectors have never been marketed as a construction fixing to take high loads that may carry the load bearing potential of a human. They are designed as a KD fixing for furniture and not any other application. “

...but they do posess "extremely high pull-out force", but it is unquantified and should not be relied upon. So, nothing that supports a human. Quite limiting what with at least half of all furniture being designed to support people.

Anyhow, if we make anything during the restoration that is Knock Down, out of 30mm+ thick material, that does not need to support the weight of a human then I'll be sure to share some photos. At the moment I can't think what that would be.

Ho hum. Topic closed I think as it seems to be stone and blood out of teritory from the "official" direction at any rate.

Thanks for the responses anyhow and good luck with your non human carrying Domino XL Connector projects

Stephen

Hi
The quote above is from my series of emails today with Stephen - the connectors for the DF700 have never been designed for any  high load bearing application such as a staircase or even similar. They are a KD fixing for use on tables, frames for beds and should be used with that in mind
rg
Phil
[/quote]

Seems Stephen while asking for advice is only asking for justification in using these fittings for whatever application he has in mind and not interested in reasonable advice that is being given by anyone else.
My advice after seeing the sketchup drawing is ..use the DF700 as a morticer and peg the tenons of the brackets.
Rob.