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View gauntlet21's profile

French Cleat Fail

by gauntlet21
posted 10-27-2018 09:35 PM


10 replies so far

View bilyo's profile

bilyo

906 posts in 1660 days


#1 posted 10-27-2018 09:57 PM

This is not a failure of the french cleat. it is a failure of the design. The downward force of the weight of the shelf and tools rotates around the lower edge of the shelf against the wall. This causes the upper half of the cleat to lift out from behind the lower part. You will need a bracing component extending downward against the wall for a distance approx,. equal to the width of your shelf for this to work. What you have done is much like trying to mount the shelf to the wall with a hinge. It won’t stay horizontal unless you put a brace against the wall farther down.

View lumbering_on's profile

lumbering_on

578 posts in 1048 days


#2 posted 10-27-2018 09:58 PM

I have a cough modified French cleat system. I had something similar to what you had, and the issue is where the centre of gravity is for the part you are attaching to the cleats. I just ended up doing something similar to what you did, but I used wooden ‘clips’ [small rectangular pieces of wood that rotate around a screw]. This way you can still move the cleats easily, but still have things fastened securely.

View Kazooman's profile

Kazooman

1386 posts in 2510 days


#3 posted 10-27-2018 10:05 PM

Dan, French cleats are terrific at bearing a lot of weight when the force is pretty much straight down, like hanging a very heavy mirror. In you case, the extension of your screwdriver holder out from the wall results in forces that are not pressing the faces of the cleat together, they are causing a rotation that it drawing the faces of the cleat apart. Your second image shows this very well.

This is hard to describe in words, but here goes. A simple solution would be to have a part of your holder that extends downward from the face of the cleat and then has a spacer added to press against the pegboard. You need to counteract the rotational force. When you see things like shelf units that are supported by French cleats, they usually have enough in the vertical dimension to provide the bearing point against the wall at the bottom.

There could be some modified designs that would suffice to support the small load that you are going to see, but the simplest fix would be even a small “outrigger” that extends downward and against the pegboard to balance the rotational forces.

Gotta love this Forum. Two similar replies while I was typing. Your application is “fixable” if you absolutely must have the French cleat for the ability to remove the holder. The easiest alternative is two wood screws.

View waho6o9's profile

waho6o9

8798 posts in 3135 days


#4 posted 10-27-2018 10:17 PM

Corbels spring to mind.

View clin's profile

clin

1072 posts in 1554 days


#5 posted 10-27-2018 10:34 PM

The problem us you have almost nothing below where the cleat meets or grabs at the top and the bottom of the shelf. There are forces pulling down on the cleat, but there is also a force pulling the cleat away from the wall. This force exists in every mounting technique.

Bottom line you need more distance from where the cleat grabs at the top and where the shelf pusheses back at the bottom. It’s a leverage type problem. To fix this, remove the cleat from the shelf. Attach the shelf to a board that is say 4” tall and then attach your cleat to the top of this board. Or add wood to the bottom of the shelf so it at least meets the bottom of the wall cleat.

Also, since your wall cleat is narrow, it would. Be better still to extend your shelf down past the bottom of the wall cleat and the add a spacer to this so it can push against the wall.

For a more detailed explanation you can keep reading if you want:

For something easier to understand, think of a simple kitchen wall cabinet. There is weight pulling down on the cabinet, but all this weight is also out some distance from the wall. So if the cabinet is screwed to the wall near the top and bottom, the screws will support the weight pulling the cabinet down. This is trying to shear the screws.

But because the cabinet is also out away from the wall, the top of the cabinet is pulling out near the top screws. It is trying to pull away from the wall at the top. So the cabinet is trying to rotate forward. Because the cabinet is being pulled back by the screws at the top, there must be an equal but opposite force at the bottom of the cabinet. Therefore the cabinet is pushing into the wall at the bottom.

So how much is the force? Assume the cabinet and all the plates in it weigh 200 lbs and the center of this weight or mass is half the depth of this 12” deep cabinet. This causes a moment equal to 200 lbs x 1/2 foot = 100 ft-lbs. think of this as the torque trying to rotate the cabinet.

Assume to top screws are 2 feet from the bottom of the cabinet. At this point the cabinet is pulling out from the wall wth a force of 100 ft- lbs/2 ft = 50 lbs. but the bottom is pushing against the wall with this same 50 lbs. However, none of this is extreme and it all works fine.

Now, a cleat system is the same thing. But your system is like a cabinet that only has a 1/2” or so from the screws on top ( the cleat) and the bottom of the cabinet ( bottom edge of your shelf where it meets the wall).

So let’s take the cabinet, and instead of 2 feet from the screws on top and the bottom of the cabinet, let’s make it about 1/2” which is 1/24 foot. Taking the 100 ft-lbs of moment, but now dividing this by 1/24 th of a foot and what was 50 lbs is now 100 ft- lbs/(1/24 ft) = 2,400 lbs of force. This 2,400 lbs is the force try to pull the top of the cabinet from the wall and also the force pushing in at the bottom. Note how this 2,400 lb force is much greater than the weight of the cabinet.

Now, you aren’t supporting a 200 lb cabinet, so of course you aren’t getting that much force. But the point is the distance from where it grabs at the top to where it pushes back at the bottom matters a lot. The greater the distance, the lower the force pulling it out at the top. In your case you probably have much more force pulling it out than the weight pulling it down. So the net effect is even with the 45 degree slope in the cleat, it is pulling out so hard relative to the weight pulling down that it is actually lifting out.

I hope this wall of words helps some. I know a diagram would make it easier.

-- Clin

View WoodenDreams's profile

WoodenDreams

829 posts in 469 days


#6 posted 10-27-2018 10:36 PM

Looks like you tried making a floating shelf with French hangers. Your French hangers will still work if you add a support to keep from tipping, from above or below your tool holder.

View lumbering_on's profile

lumbering_on

578 posts in 1048 days


#7 posted 10-27-2018 10:49 PM

@Clin – this should help go along with your explanation.

http://www.schoolphysics.co.uk/age11-14/Mechanics/Statics/text/Stability_/index.html

View shampeon's profile

shampeon

1900 posts in 2741 days


#8 posted 10-28-2018 04:48 AM

So here’s your problem. You want the load to be pressing into the wall, not at a pivot point that will lift the cleat out of the base. That same shelf 2 inches lower will press all the load into the base, and the pivot point will be below the bottom of the cleat.

Imagine a shelf attached to the bottom of a 4 foot long board with a cleat attached to the top of the 4 foot board. Even if you hung a bowling ball from the shelf, it’s all going to press into the wall. Assuming the shelf could hold something of that weight, the cleat will not lever out.

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

View TheFridge's profile

TheFridge

10859 posts in 2044 days


#9 posted 10-28-2018 05:01 AM

I like cake. Like a lot.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View gauntlet21's profile

gauntlet21

69 posts in 768 days


#10 posted 10-28-2018 06:10 PM

Yeah I figured a few modifications (that weren’t screws) would fix it. I realize that the French Cleat isn’t “failing” and that there’s user error involved (probably close to 100% user error). I was just thinking that if I were to make a YouTube video depicting how easy French cleats are to use, I’d probably add a little tip as to what types of things work best for French cleats and a simple formula as to what can go wrong (I’m not trying to blame anyone despite the fact that I’m basically blaming YouTube woodworkers). I’m not upset at all, it’s all part of the learning experience and it’s a simple fix. I’m obviously new to the mechanics involved in woodworking and will add this to my tool box. I just wanted to try out the French cleat and going forward will know what not to do and what scenarios the French cleat excels at. At least I wasn’t putting an urn or porcelain antique on that shelf before it came crashing down.

Thanks for your comments and suggestions!

Dan

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