Automatically catching mechanism for drop leaf table

Question

I need to build a changing station. We have a great location for it between two walls in our bathroom (they are only about 4 feet apart). The table will span from the one wall to the other.

We need to be able to remove the table when not in use. It would be much better if the table top could go down rather than up for stowing. But the parent carrying a baby, the table must go from the stowed downward position to the locked horizontal position by a one-arm movement. So the challenge is how to receive and automatically support the table top on the right-hand side wall.

Getting the table back to stowing position may require two hands, but that is fine. We just need to be able to go and change that diaper without putting the child down first.

Essentially, this is like a door lock. You can close the door by a push. But you need to turn the handle to open it.

I am very open to suggestions for how to obtain this mechanism. The mechanism needs to be fairly strong so it can easily carry a 2-year old troublemaker. Also, it would be great if it can be released from one handle/lever/whatever.

Answer 1

First off I would suggest that you not hinge the top on the narrow end. Instead hinge it along the long side that is against the wall in the alcove. This will make it much easier to swing it up into position. Something like this:

For supporting the hinge up shelf I would have a wood strip mounted into the side walls of the alcove that was positioned in a horizontal manner such that it was located where the top comes when it is hinged up into position. Near the outside ends I would install two striker plates that were basically the same as a regular door plate. You would install the curved side of the striker plate in the down position. Something like this:

The wood strip has two advantages here. First off it allows some clearance of the shelf from the side walls of the alcove. Secondly it makes it easier to mount the door catch than trying to put it into drywall or other wall materials. You may very well find it advantageous to install a continuation of this strip along the back wall of the alcove so you have a decent surface to mount the hinge. The strips can be secured to the walls at the stud locations.

For the catches that you would mount on the bottom of the hinge up shelf you would use a product that looks like this:

Picture Source

These catches are often called "slam latches" and can be found at trailer parts stores among others. You will want to find lighter duty catches that the spring is not too stiff. A catch designed for a trailer gate that retains a 3000 pound load would be unsuitable for your application.

Obviously the catch tapered part is mounted to align with the door striker plate described earlier. Once you realize that the tongue of the latch sticks out beyond the end of the shelf you can see the reason for the first installed wood strip to provide for clearance as the shelf is swung up into position.

Once the two latches are mounted on the two sides of the flip up shelf you would interconnect the two handles with a light piece of chain that was fairly taught when the shelf latches are in their relaxed position. A pull on the chain from the center should allow both catches to be released to lower the shelf when it has been in the raised latched position. Chain like this is strong but light duty and will not have the tendency to have its links bend while being tugged on.

Picture Source

Answer 2

Consider the wonderful world of the gusset. In its usual guise, it supports and strengthens a corner formed by a pair of otherwise weak members. Gussets are used in truss construction, building framing and many other locations.

In the simplest form, it's a right-triangle shape. For your application, one square side of the triangle would be hinged to the wall, with the other square side aligned with the shelf in the deployed position.

In the image above the green wall supports a yellow backing plate containing the hinge for the red/brown shelf (missing a hinge circle). The blue gusset is on a hinge visible in the top view. It's more practical in normal use to have the hinge at the top of the yellow in the drawing, but easier to draw at the bottom.

When the gusset is flush against the wall, the shelf will fall. The gusset should be either lightly spring loaded or the hinge tilted in such a way as to bias it to the open position. When the shelf is lifted, the gusset will reach the position shown in the side view, allowing the shelf to be supported.

Lifting the shelf slightly and pushing the gusset toward the stowed position begins the reversal. Once the gusset has a bit of angle to it, pressure of the shelf will assist the retraction. Wear surfaces could be protected by a plastic strip or panel on which the gusset would slide. Inexpensive poly cutting boards are handy for applications of this sort.

Piano hinges would provide reasonable strength as well as ease of alignment. The gusset need not be full depth in either direction, depending on the materials used.

Answer 3

This is a pretty easy question for general use, the challenge is doing it fail safe.

There a number of hinges that do just this - the hinges on folding tables do just what you want

that mechanism has been very reliable as far as I have seen, but I don't know if I would trust it with a baby.

If you have a high enough ceiling, and the walls above the tabletop are clear, you could make something that folds down across the open area and is supported by a cleat / ledger on three sides. It would work something like a built in ironing board

I'd have a lot of confidence in that being sturdy and reliable in the open position. However I'd worry about the surface falling down and hitting someome. To prevent that I'd use something like these torque hinges

These hinges are typically used on chest lids, they have enough friction in them that they can either slow the lid and prevent it from slamming or if the lid is light enough even stop it in any position. Normally you'd use two and wouldn't think much about it, but I might use three for this purpose so that if one fails, you still have two hinges working properly.

Goes without saying, I'd work the thing thoroughly and test it well, and inspect it very carefully for any signs of failure, before I'd use it.

Answer 4

There are a lot of "off the shelf" options for accomplishing this. Some use the gusset theory mentioned in other answers and are quite strong. Look for items related to "locking shelf bracket", "locking support bracket", "folding wall bracket", and the like.

This type will lock in the raised position and requires you to press a lever to lower it: standing desk folding bracket

There are other types where you simply lift the shelf to lower it, but with a child on it I would feel more comfortable with a positive locking mechanism...