Tipping force and Center of gravity for wall fitted furniture

[tivva]

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!

 

[berkeman]

Welcome to PF.

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

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?

 

[tivva]

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.

 

[berkeman]

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)...

 

[tivva]

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.

 

[tivva]

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…

 

[berkeman]

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?

 

[jrmichler]

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.

 

[Tom.G]

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!

Cheers,
Tom