KV D8 Connector pullout strength vs screws.

[ChuckM]

I appreciate your concern for safety and it is something we take very seriously.  While in the shop, she is supervised, always wears closed toe shoes, long pants, and eye/ear protection.  I've owned a tree service for 22 years and we have a perfect safety record there too.  Immediately after this, I talked to her about the hazard of getting too close.

I think the concern was about her being seen close to where the steel wire was in tension as the joint was being pulled. The wire and the hook could fly towards your child as the joint broke free.

About racking, I've built a workbench for a neighbor, and he has had no complaints about anything after a year of use. Let me dig up some photos about the construction.

Edit: Photo added
[attachimg=1]

 

[Cheese]

The connector manual states that the connectors are suitable for both solid wood and chip board. Using the Domino connectors on end-grains is a standard application.

Just to add to Chuck's input, these photos were taken from the Domino manual that Festool produced for distributors about 4 years ago.

Note that for KD connections, Festool recommends at least 2 Dominos for shear and racking purposes and a KD connector to keep the joint tight. This is an example of a bed frame.

[attachimg=1]

[attachimg=2]

 

[bwehman]

FWIW, I built a bed for our kid using the D700 connectors, and only one on this key joint (one connector and one domino) and it's been rock solid over the three years she's had it. I just don't think the D8 connectors were ever meant for substantial furniture like a bed.

They're fantastic for other things, of course, but bed isn't one of them.

 

[ChuckM]

Snip.

I agree that pullout strength is not the most critical force, but it is relevant and easy to measure. Racking will be the primary stress. Here is a picture of the frame:

View attachment 1

Snip.

I'd dry-assemble the whole bed with the flower boxes, etc. in place while they're still in the shop (which btw looks spacious!) and rock it to see how it stands up to the racking test. If needed, fix the problem before doing the final assembly in the bedroom.

 

[ChuckM]

The question of whether the DF500 connectors are strong enough for beds has popped up from time to time, and most posters advised against such an idea. But no empirical proof was given in those discussions.

I do think the actual design and purpose matter, and for a children's bed with low clearance, the concern of using KVD8 connectors may be less. In a comment to a video (DF700 connectors) posted two months ago, one woodworker who had built a bed with the KV D8 connectors seemed to be quite happy with the results. But he didn't provide all the details about the bed or design:

"@kurttalert
2 months ago
@joethiele I just put together a king bed frame with 500 connectors tonight. Used 2 in each end of each rail, plus 2 more 10x50 dominos which will just be loose, for added resistance against shearing forces. Super tight connection, and I have even added my center rails for extra support yet. DF500 connectors are more than good enough I’d say!"

 

[smorgasbord]

The connector manual states that the connectors are suitable for both solid wood and chip board. Using the Domino connectors on end-grains is a standard application.

I've not seen a full-blown manual, just a single sheet of paper guide that says this:

Only suitable for connecting wood or wood-like materials for furniture construction (no lightweight construction materials). The Domino connector is only a connecting element and not a supporting element. Observe the minimum routing depths and edge clearances. Use indoors only.

And like the one picture you included, it shows only sheet goods, and show at least two connectors plus a domino per joint.

Between that and "no lightweight construction materials" I'd say the joint being tested doesn't meet the guidelines.

 

[ChuckM]

In this guide (https://www.festoolownersgroup.com/festool-tools-accessories/festool-domino-connectors-guide/ reply #3) -- same as yours? -- solid wood (including a small diagram) as well as chip wood is mentioned at the beginning of the page.

The illustration in the guide of the joinery doesn't specify any wood species and with the inclusion of solid wood in the guide, I wouldn't construe it as applying to plywood only.

In the workbench I referred to earlier, because the boards were under 5" (130 mm) in width, I used only connectors:

[attachimg=1]

 

[smorgasbord]

In this guide (https://www.festoolownersgroup.com/festool-tools-accessories/festool-domino-connectors-guide/ reply #3) -- same as yours? -- solid wood (including a small diagram) as well as chip wood is mentioned at the beginning of the page.

Here's the link:https://www.festoolusa.com/-/media/tts/fcp/festool-usa/downloads/manuals/707754_002_domino_kvmsv.pdf

We're talking about the same guide.

The illustration in the guide of the joinery doesn't specify any wood species and with the inclusion of solid wood in the guide, I wouldn't construe it as applying to plywood only.

In the workbench I referred to earlier, because the boards were under 5" (130 mm) in width, I used only connectors:

Yes, I acknowledged the guide does say "wood" or "wood-like materials." But, the pictures uniformly show sheet goods, with two connectors per joint plus a domino. A single connector for use with 2x4s doesn't, in mind anyway, conform to the guide.

Glad the workbench you built has held up.

 

[Jim_in_PA]

I don't know if the 8mm connectors are enough for a bed project, but I have used the 14mm version for a TwinXL over Queen bunk bed project for a client a few years ago and it was "darn stout". The setup was like in the illustrations from the Festool connector booklet that was posted above. I know that bed has been moved three times since I handed it off to the client and they said it's remained secure and tight.

 

[bpbolde]

In this guide (https://www.festoolownersgroup.com/festool-tools-accessories/festool-domino-connectors-guide/ reply #3) -- same as yours? -- solid wood (including a small diagram) as well as chip wood is mentioned at the beginning of the page.

Here's the link:https://www.festoolusa.com/-/media/tts/fcp/festool-usa/downloads/manuals/707754_002_domino_kvmsv.pdf

We're talking about the same guide.

The illustration in the guide of the joinery doesn't specify any wood species and with the inclusion of solid wood in the guide, I wouldn't construe it as applying to plywood only.

In the workbench I referred to earlier, because the boards were under 5" (130 mm) in width, I used only connectors:

Yes, I acknowledged the guide does say "wood" or "wood-like materials." But, the pictures uniformly show sheet goods, with two connectors per joint plus a domino. A single connector for use with 2x4s doesn't, in mind anyway, conform to the guide.

Glad the workbench you built has held up.

Last I checked, Eastern White Pine is "wood"  [wink] Like I mentioned in the original post, I know the DF500 connectors are not ideal/recommended for heavier applications like a bed.  Unfortunately, a 700 isn't in the budget right now with a bathroom remodel and new well happening this spring.  Someday, I'll add one to my collection. 

The joint I tested fits my guidelines exactly. It also fits Festool's guideline of "wood or wood-like material" and the method of installation. I couldn't find any specific info on the strength of the connectors, so I experimented to find out what the pullout strength is of a single connector versus a single through-screw as well as a single pocket screw. I wanted to compare each method of connection fairly against each other with no other variables.

Since others might be interested, I decided to share my findings. Pullout force is only one force furniture may endure, but since the KVD8s are designed to connect, not support, that implies pullout strength is relevant, since resistance to that is what keeps two pieces held together.

In any case, twisting/racking will be largely mitigated with the bed base (3/4 plywood) screwed into the frame pieces.  That will also hold together the 4 sides of the bed. My goal is to have minimal visible fasteners and these will be hidden beneath carpet under the mattress.

View attachment 1

There will also be a modular stair/shelving unit on this side that will help stiffen the whole assembly.

View attachment 2

 

[Cheese]

Here's a strength chart that may help you in your journey.

[attachimg=1]

 

[ChuckM]

The screwed base should significantly add to the structural integrity.

 

[squall_line]

Far be it from me to allow a horse that appears to have no life remaining to lie still without striking it again...

When I mentioned "in end grain", I was talking specifically about the expanding connector.  I'm aware that the vast majority of 90-degree butt joints usually consist of one piece of end grain and one piece of long grain wood or substrate (unless using MDF).

That said, when people are talking about "suitable for end grain", all of the connection visual examples provided show that expanding connector is in the long grain piece and the grub screw / cross connection is in the end grain piece, not the other way around.

Which in many ways is as much to do with locating and fixing the grub screw as it is the strength of the connection, but both knock downs are purposely built to favor putting the expanding connector into the long grain.