KV D8 Connector pullout strength vs screws.

[bpbolde]

We're building a loft bed for our daughter and have a need for knockdown connectors. I only have the DF500 and the 700 isn't really in the budget right now. I knew the EV/32 connectors would be much better suited for holding a bed together, but wanted to know how strong the KV D8 connectors actually were. While there are a ton of videos and info about the strength of a glued Domino joint, I couldn't find anything about the knockdown connectors. 

I built a test rig out of the same white pine 2x4s the sides of the frame are made of. I attached three vertical pieces of 2x4 joined to a single long horizontal 2x4 with about 5" of space between them all.  One was joined with a KV D8 connector, one with a #10x3 1/8 GRK screwed through the horizontal 2x4 into the vertical, and one with a 2 1/2" Kreg pocket hole screw from the vertical 2x4 into the horizontal 2x4.

I secured the whole assembly to the floor with forks on a front end loader.  Then I pulled each vertical piece to failure with a chain fall to an eye bolt in each 2x4, measuring the tension with a crane scale. Surprisingly, the KV D8 failed at a very low amount of force, only 107 pounds before the split connector pulled out.  The GRK was next at 430 pounds. The pocket hole screw head pulled through the pocket hole and failed at 535 pounds.

Just for fun, I epoxied the split connector in a new 2x4 and will test that tomorrow after it's cured.

I hope this data helps anyone using these connectors. This was my first time using them. They were extremely easy to install and would work great in light duty applications. I'd skip them for anything structural though. 

 

[squall_line]

[welcome] to the FOG, and thanks for the test results!

The split nature of the KV D8 connector lends itself better to plywood and engineered substrates than solid wood, and also to box construction rather than furniture, IMHO.  You'd be better off with cross dowels or the DF700 connectors with solid wood/timber construction.

 

[Packard]

Confirmat screws have the reputation as “knock-down” screws and I see them advertised with that description.

Unlike other screws, Confirmat offers both the pull-out (tensile) strength of a screw with the structural (racking) strength of steel dowels. 

I have used confirmats to assemble, break-down and reassemble.  I don’t know how many times you can do that, however.

This is an engineers report on testing done on Confirmats.  Unfortunately, I don’t have enough of an engineering background to make much use of the data.  I’m sure the information you are looking for is in there if you can decipher it.

From my experience, the confirmats never fail, the material they are screwed into does.
https://publisherspanel.com/api/files/view/1114545.pdf

The video is much more obvious.  I pre-judge YouTube workshop videos based on how much the workshop in the video impresses me.  On that basis, I rate the video A+. [big grin]

 

[ChuckM]

We're building a loft bed for our daughter and have a need for knockdown connectors. I only have the DF500 and the 700 isn't really in the budget right now. I knew the EV/32 connectors would be much better suited for holding a bed together, but wanted to know how strong the KV D8 connectors actually were. While there are a ton of videos and info about the strength of a glued Domino joint, I couldn't find anything about the knockdown connectors. 

I built a test rig out of the same white pine 2x4s the sides of the frame are made of. I attached three vertical pieces of 2x4 joined to a single long horizontal 2x4 with about 5" of space between them all.  One was joined with a KV D8 connector, one with a #10x3 1/8 GRK screwed through the horizontal 2x4 into the vertical, and one with a 2 1/2" Kreg pocket hole screw from the vertical 2x4 into the horizontal 2x4.

I secured the whole assembly to the floor with forks on a front end loader.  Then I pulled each vertical piece to failure with a chain fall to an eye bolt in each 2x4, measuring the tension with a crane scale. Surprisingly, the KV D8 failed at a very low amount of force, only 107 pounds before the split connector pulled out.  The GRK was next at 430 pounds. The pocket hole screw head pulled through the pocket hole and failed at 535 pounds.

Just for fun, I epoxied the split connector in a new 2x4 and will test that tomorrow after it's cured.

I hope this data helps anyone using these connectors. This was my first time using them. They were extremely easy to install and would work great in light duty applications. I'd skip them for anything structural though.

Any photos to share of your setup and of the results?

 

[Michael Kellough]

Too bad the Kreg Jig HD has been discontinued. It used #14 screws which made extremely strong joints in sound wood. They claim the resulting joints are only 50% stronger but that’s low in my experience.

 

[smorgasbord]

Too bad the Kreg Jig HD has been discontinued. It used #14 screws which made extremely strong joints in sound wood. They claim the resulting joints are only 50% stronger but that’s low in my experience.

There's now an XL  model.

 

[Coen]

Confirmat screws have the reputation as “knock-down” screws and I see them advertised with that description.

Unlike other screws, Confirmat offers both the pull-out (tensile) strength of a screw with the structural (racking) strength of steel dowels. 

I have used confirmats to assemble, break-down and reassemble.  I don’t know how many times you can do that, however.

This is an engineers report on testing done on Confirmats.  Unfortunately, I don’t have enough of an engineering background to make much use of the data.  I’m sure the information you are looking for is in there if you can decipher it.

From my experience, the confirmats never fail, the material they are screwed into does.
https://publisherspanel.com/api/files/view/1114545.pdf

The video is much more obvious.  I pre-judge YouTube workshop videos based on how much the workshop in the video impresses me.  On that basis, I rate the video A+. [big grin]

Some nonsense in that video. The "big head" (against pull out) is canceled out by the shoulder of the screw. The fatter shoulder however prevents the hole from widening and provides for a stiffer connections against bending forces.

 

[smorgasbord]

Back to the OP, pull-out resistance is but one type of force on joints. Twisting, racking, etc. are some other forces that joints are subject to, so I think it's hard to quantify different kinds of joint strengths, especially when not used in a particular project - and even then the type of project introduces even more factors to consider.

 

[Packard]

Ikea probably has as much experience with flat pack furniture as anyone. 

Several years back they tested KD joinery.  They found most of them wanting. 

They found acceptable dowels and Confirmats.  Dominoes did not make the cut only because there was no automated system for using them. 

But ultimately they came up with their own design utilizing a wedge fastener.

I would note that while cabinet manufacturers are invested in KD also, much of their (maybe almost all) racking strength comes from the fact that they are mounted to the wall.  The wall becomes an integral part of the structure. 

Ikea, the last time I bought one, used dowels (no glue) for racking strength and confirmats or 1/4 turn fasteners to hold pieces together.

My experience with joining plywood panels using pocket hole joinery is that the screws have a lot of pull-out strength, but not much racking strength.  Putting pocket holes on opposite sides of a single panel helped quite a bit.  But still not my first choice where racking strength is a concern.

Here is a look at IKEA’s patented KD joinery:
https://www.core77.com/posts/59321/how-ikeas-new-joinery-is-advancing-their-design

 

[Packard]

And my earlier rant about drywall screws (only use for installing drywall).
https://www.festoolownersgroup.com/building-materials/dry-wall-screws-are-for-dry-wall-only/

 

[bpbolde]

I redid the test with the epoxied split connector.  Failure occurred at 505 pounds, with the cross anchor pulling through the 2x4.  The split anchor didn't budge.  I'm interested to do more tests on shear strength and racking.  With the epoxy enhancing the split connectors, I'm very confident in their strength for our application.

I'm having trouble with images attaching, so I'll play around with it tonight and try again with pictures.

 

[ChuckM]

The most common problem with loading images is the files being too large. Try reducing the size to under 1 MB/image.

I wonder if CA glue (thick) would have the same or similar additional strength effect.

 

[bpbolde]

The whole test piece:

View attachment 1

End of 2x4 where cross connector pulled through:

View attachment 2

Whole anchor still attached to cross connector after pulling though:

View attachment 3

Split anchor still in wood with no visible movement:

View attachment 4

 

[bpbolde]

The most common problem with loading images is the files being too large. Try reducing the size to under 1 MB/image.

I wonder if CA glue (thick) would have the same or similar additional strength effect.

Thanks! Getting under 1 MB worked.

 

[smorgasbord]

Here's a video:

Man, that was the scariest thing I've watched this year. First hearing your kid's voice and thinking "I hope they're well behind the camera," but then seeing their legs as the thing pops. Scary. That could have gone sideways in all sorts of ways.

Whole anchor still attached to cross connector after pulling though:

Yeah, not surprised to see that 2x4 end grain wasn't able to hold on and failed instead of the connector failing. As was said upstream, those connectors were made for man-made sheet goods. And if you're going to use them in solid wood at least don't go into the end grain.

 

[Crazyraceguy]

That straight pull out is a false flag. That is not a source of failure in any kind of furniture or cabinetry project. Racking, twisting, are what you have to work against.
Cross bolts are used in conjunction with some other type of alignment/registration device, be that dowels, Dominos, etc. The cross bolt is only there to draw the joint together, which is something dowels (and other types of tenons) can't do.

 

[Steve1]

Thank you for taking the time to run the tests and post the results.

 

[Packard]

An oversized (long) drill bit used to drill the length of the 2 x4 blocks and threaded rods would be my approach.

Or, cut a long groove and drop the rod in place and then glue in a strip of wood to retain the threaded rods.

I would probably use 1/4” rods and fender washers.

 

[bpbolde]

That straight pull out is a false flag. That is not a source of failure in any kind of furniture or cabinetry project. Racking, twisting, are what you have to work against.
Cross bolts are used in conjunction with some other type of alignment/registration device, be that dowels, Dominos, etc. The cross bolt is only there to draw the joint together, which is something dowels (and other types of tenons) can't do.

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

It will be able to be disassembled into four pieces: front, back, and 2 sides.  Stairs will go up the left side and there will be some decorative elements like flowerboxes below the windows. It's more practical to build modular components that can be assembled in her bedroom.

Man, that was the scariest thing I've watched this year. First hearing your kid's voice and thinking "I hope they're well behind the camera," but then seeing their legs as the thing pops. Scary. That could have gone sideways in all sorts of ways.

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.

 

[ChuckM]

Snip.

As was said upstream, those connectors were made for man-made sheet goods. And if you're going to use them in solid wood at least don't go into the end grain.

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.

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