load on cabinet hinges 1

[MBGraham]

We have new cabinet doors. They are quite wide and somewhat vulnerable. I am thinking about adding a brace to limit the opening to 90deg (hinges go to 105deg.

It's been a long time since I did any structural engineering! What I would like to see, is a load diagram for situation shown in drawing below. And in particular the loading on the main hinge aat C.

- 10lb load denoted is the pushing force on the outer edge of the door
- Blue Line is the door
- Orange line is the cabinet frame
- Green line is wire restraint
- B,C&D are hinged points. The main door hinges are at C

Thanks

 

[jayrod12]

Assuming the stop wire is at 45 degrees, the tension in that wire is 30*1.414=43lbs roughly.

You take moments about point C. Your hinge ends up with reversal of load.

I guess the question is why?

 

[IRstuff]

DIY posts should be posted in the Hobbies forum

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[MBGraham]

Where did the 30 in your formula come from?
When you say reversal of load at hinge (C). Would that then see an upward force of 10lb at the hinge?

Reason? The doors are at low level and vulnerable to someone purposely or accidentally pushing the door beyond 105deg where the hinges are at their limit. This could lever the one screw holding and likely break the 3/4x1.5" frame. This picture shows the hinge almost at it's limit

 

[JoelTXCive]

MBG -

Is your diagram a plan view or side section?

If a plan view, then I don't think the opening angle affects the load on the hinges. It will be the same load regardless of opening angle.

Jayrod summed the moments at point C. [10lbs * (20+10 in)] - (Cable Tension * Sine45 * 10in) = 0

He did some fancy math and simplified the equation by dropping out the 10.

 

[MBGraham]

The diagram is a plan view - or bird's eye view if you like. Added pic below.

What I am interested in, is the difference in load on the single mounting screw with and without the wire restraint. And also, the value of force on the wire mounting screws if the restraint is used.

The case without the restraint is harder to visualize or calculate. Once the hinge gets to 105deg, the door and the hinge mount plate would act as single lever. Only support/pivot is at 1/2 the thickness of the frame (3/8"). Would this mean the 10lb force would result in 10*(30/0.375) = 800 lbs pull on the mounting screw? Very high regardless. Thus the need for a restraint.

 

[WinelandV]

MBGraham,

I have similar hinges on my cabinets. We taught the kids to be nice to the doors and to shut them when done. It's going well so far, haven't had any broken off (yet).

 

[JStructsteel]

Now I wont sleep tonight worrying about my cabinet doors.

 

[phamENG]

Move the attachment out to 5 inches from the end of the door. That will effectively remove prying from the hinge and reduce the tension in the screw to a negligible amount. Set it up initially to be slightly less than 90 degrees for your opening angle - whatever you use will probably relax with repetitive use.

Or you could take winelandv's advice and treat this like nearly everyone else on the planet who doesn't break their cabinet doors off.

 

[MBGraham]

You can make fun of my concern, but they sell thousands of restraints of different types for just this type of use. The face front verticals on our cabinet are particularly vulnerable. They are a soft wood, just 0.75"x1.5". And unlike the clip-top Euro type hinges used on many kitchen cabinets, our Compact hinges use just one screw for mounting.

I can't see having a long wire hanging in the cabinet and obstructing access. I will probably use a solid scissor type. These will likely attach at about 1/3 of the door width.

By the way, we don't have kids or dogs. But the grandkids do visit - with their dog. Training them is not that simple!

 

[rb1957]

A wire sounds like a very "agricultural" (think tractor) solution. I'd've thought there were stops that worked around the axis of the door (through the hinges).

I'd've thought it would be quite easy to pry a door off the casing ?

another day in paradise, or is paradise one day closer ?

 

[phamENG]

I don't mean to make fun of the concern - it is legitimate. That's why I gave a qualitative assessment of what I think is the best solution.

The loads are so small here, I do think engineering a solution is a bit over the top unless you're going to be marketing it for sale. If your grandkids regularly harness the dog and sit on a skateboard and ride through there (I've seen it), then you may want to bump up those loads a bit and then it makes sense to figure on a custom solution...though you may want to consider which is more important, the door staying on the hinges your grandkids staying out of the hospital as it's unlikely to have both. But just opening them a little more vigorously than usual? They're readily available online - no engineering required.

 

[MBGraham]

rb1957 - Agree that the wire restraints are not elegant. And I wouldn't use them. But it seems many do. (see picture below)

PhamENG and rb1957. There are restrictor clips that fit some hinges. But they are only meant to reduce door opening angle so there is no impact with walls etc. They are also hinge type specific (not universal) They would not help to prevent the door from being pried off.

Looking at this problem from an engineering viewpoint may be a bit 'over the top' But it sometimes helps to better understand the physics of a system before jumping to a solution. For example, the wire restrictor seems like it should work. But knowing the tension in the wire might help to determine if the screws holding the wire at each end would hold. I used 10lb in example as the force, just to illustrate the problem. It would likely be much higher, even if it was just someone opening the door aggressively or perhaps leaning against it while open. As rb1957 said - it would be quite easy to pry a hinge off the casing (possibly destroying the casing)

 

[rb1957]

this wire doesn't stop the door being pried off either. The load on edge of the door creates a moment around the hinge. This moment is reacted by a load in the wire. But the hinge still has to react the resultant of the wire and the initial load. If the hinge hasn't bottomed out (ie the door isn't bearing against the casement side of the hinge) the door side of the hinge looks more substantial. If the hinge has bottomed out, then the wire isn't preventing the door being pried off.


another day in paradise, or is paradise one day closer ?

 

[MBGraham]

rb1957 - This is in part why I asked first about the load diagram and the forces on the hinge.

Intuition tells me that without that wire stay, it would be much easier to pry the hinge off by pushing on the edge of the door. The wire prevents the door hinge from getting to it's limiting position at 105deg.

Something like this jib crane homework task I found on the net.

 

[IRstuff]

Huh, you're worried about a single screw getting pried out, and your solution is to use single screws for a restraint?

It seems to me that if you are that concerned, you might consider replacing those hinges with stronger ones



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[Tomfh]

Tension in wire roughly 40lbs
Load on hinge 20 lbs.


Your 800lbs load (or whatever it is) is why it’s easy to pry off a cabinet door. Very short lever arm.

 

[MBGraham]

Irstuff said: "Huh, you're worried about a single screw getting pried out, and your solution is to use single screws for a restraint?

It seems to me that if you are that concerned, you might consider replacing those hinges with stronger ones"

I don't have a solution yet and you don't seem to have grasped the issue. The strength of the hinges is NOT an issue.

 

[MBGraham]

Tomfh said: "Tension in wire roughly 40lbs. Load on hinge 20 lbs.

Your 800lbs load (or whatever it is) is why it’s easy to pry off a cabinet door. Very short lever arm."

Exactly the problem I am trying to resolve. So if those numbers are correct, the restraint screws would see a pull of 40lbs while without the restraint, the single hinge screw might have an axial load of ~800lb. The 10lb load was just a number to work with. It could be 100lb or more. The cabinet frame could be destroyed.

 

[3DDave]

All this so far is true - these hinges are not suitable for the desired resistance. As long as the hinge remains in the load path the screw will likely fracture the frame. Be aware that even the 180 hinge, if the door interferes with the next door or door handle, can be used to pry it loose from the frame. The farthest I see from Blum is 170, but there are some makers claiming 180.

These hinges are designed to appeal on two main factors - they have a spring to hold the door closed without the traditional catches and they are highly adjustable to make up for less than ideal cabinet making. Stylistically, they are also hidden and, being more costly than plate hinges are sold as being exclusive, something the poors cannot afford.

There are many hinge designs that won't allow the door to pry the hinge loose from the frame. This isn't one of them.