Tipping force and Center of gravity for wall fitted furniture

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Discussion Overview

The discussion revolves around the stability of a wall-fitted MDF furniture unit and the calculations required to determine whether it will tip over when fixed only to the wall. Participants explore the implications of mechanical fixings, the center of gravity, and the potential need for additional structural support such as a deeper plinth or legs.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks assistance in calculating the tipping force required for the MDF unit fixed to the wall.
  • Another participant questions the manufacturer's recommendations for affixing the unit and suggests the possibility of adding legs for additional strength.
  • A participant identifies that the wall studs are 600mm apart and mentions the option to extend the plinth for stability.
  • Concerns are raised about the spacing ribs on the back of the unit, which may hinder secure mounting to the wall studs.
  • Participants discuss the use of metal L brackets for securing the unit and the implications of these brackets on stability.
  • One participant expresses uncertainty about their calculations, particularly regarding the center of gravity and its relation to the tipping point.
  • Another participant highlights the complexities of furniture calculations, including factors like additional forces from users and potential points of failure in the installation.
  • A suggestion is made that practical testing may provide better insights than calculations alone, proposing a test involving a heavy person sitting on an open drawer.

Areas of Agreement / Disagreement

Participants express various concerns and suggestions regarding the stability of the furniture unit, indicating that multiple competing views remain on the best approach to ensure safety and stability. There is no consensus on the calculations or the necessity of additional support structures.

Contextual Notes

Participants note limitations in the calculations due to factors such as installation quality, the nature of the load, and the design of the furniture unit itself. The discussion highlights the need for clearer problem definitions and the potential variability in installation practices.

tivva
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Hi All

I was wondering if anyone can assist with a task of calculating whether an MDF unit will tip over if fixed only to the wall behind it with mechanical fixings as shown below. And what force will be required to do so. I've given it a try. Let me know your thoughts, would be much appreciated. Thanks!

 
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Welcome to PF.

What does the manufacturer recommend for affixing that unit to the wall? What is the spacing of your wall studs?

tivva said:
whether an MDF unit will tip over if fixed only to the wall behind it with mechanical fixings as shown below.
And why do you say "if fixed only to the wall"? Is there an option to install legs under the front edge to add strength? Is there a maximum load specified in the manufacturer's documentation?
 
We are the manufacturer and we are advising the designer in this case. Wall studs are 600mm apart.

There is an option to extend the plinth and make it deeper but we need to prove to the designer that it is necessary.
 
Sorry, what is a plinth?

Also, looking at the mechanical drawing, it looks like there are spacing ribs along the back of the unit? That will hold it away from the wall and make it difficult/impossible to tie the back of the unit to the wall studs. I've hung a fair number of cabinets, and that's how you make the mounting strong -- deep screws through the back of the cabinets into the wall studs (and lots of them)...
 
berkeman said:
Sorry, what is a plinth?

Also, looking at the mechanical drawing, it looks like there are spacing ribs along the back of the unit? That will hold it away from the wall and make it difficult/impossible to tie the back of the unit to the wall studs. I've hung a fair number of cabinets, and that's how you make the mounting strong -- deep screws through the back of the cabinets into the wall studs (and lots of them)...
They will be using metal L brackets. 50mm angle shoulder and 150mm tall with 6 screws in each. They tie the “offset” ribs woth the brackets, then screw the back panels to them.

My main question is though are my calculations correct? And how to convince client to have a deeper plinth.

Plinth is the box that the drawer carabiners sit on.
 
I’ve done all my calculations based on this video:



There is part 1 and part 2 as well.

However, my center of gravity is past the tipping point which makes me think that perhaps I should put in the distance to it with a minus and the result will be not 95kg but -95kg…
 
tivva said:
They will be using metal L brackets. 50mm angle shoulder and 150mm tall with 6 screws in each. They tie the “offset” ribs woth the brackets, then screw the back panels to them.
Sorry, I still don't understand. What is the purpose of the ribs in the back? They can't be seen from the front, so they can't be a cosmetic feature. And they eliminate the possibility of using traditional mounting practices like is done all the time for cabinets, bookshelves, etc.

And is adding a few legs to the front side a possibility to add even more strength?
 
Furniture calculations are very difficult for several reasons:

1) The real load is not the weight of the furniture plus the weight of the drawer contents, but all of that plus the force from the heavy person that stumbles against the fully loaded open drawer.

2) There are multiple points of failure. The unit itself can break. The brackets can fail. The screws can pull out of the wall. The wall can fail. The weakest of those points will be what fails. This requires more than just one calculation.

3) You cannot control the workmanship of the installation. The instructions can specify screw size, screw length, and fastening into wall studs. The installer can drill the wrong size pilot hole, miss the stud entirely, fasten into the very edge of the stud, get less penetration because of thick drywall, and find other ways to get a substandard installation.

4) We have a communication problem here. We know how to calculate, but we need to start with a better defined problem. For example, it is difficult for us to explain exactly why the exact location of the mounting screws is important.

This is a case where a good test is better than any calculation. A good test would be to build a unit, install it, fully load the drawers with heavy stuff, open the drawers, then have a 100 kg (or heavier) person sit on the drawer. Make a video of the test and show it to anybody who questions the design or installation instructions.
 
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jrmichler said:
This is a case where a good test is better than any calculation. A good test would be to build a unit, install it, fully load the drawers with heavy stuff, open the drawers, then have a 100 kg (or heavier) person sit on the drawer.
Make whoever does the calculation and says it is safe be the seated part of the first trial.

Nothing like "having skin in the game" to get excellent results! :doh:

Cheers,
Tom
 
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