We purchased a tray table, but we didn't notice at the time that there was nothing to hold the legs in the open position. So if you pull it in the wrong way the legs will fold up and drop your meal squarely in your lap or on the floor. We lived with this for a couple of months, but today I decided to change this situation. Here is how I did it.

Step 1: Tools and Materials

I made the locking mechanism with a salvaged grippy clamp thing. These are little clamps that are used to hold brooms on walls, and I have no idea what they are actually called, but you can get them at most hardware stores. The only criteria I used in selecting the clamp was to make sure it gripped the crossbar of the tray leg assembly completely. I had intended to use E-6000 for added security in mounting the clamp, but decided against it.

Materials used:

Grippy clamp thing
Small Phillips head screw

Tools used:

Hacksaw
Ballpeen hammer
Metal punch
Drill bit sizer
Drill and bits
#1 Phillips head driver bit
Files
Pliers
Marker
Bench vise
Work piece protectors

Step 2: Clamp Preparation

My salvaged clamp had a tab sticking off its base that wouldn't allow it to sit flushly against the surface of the leg stop. I secured the clamp in my bench vise and used a hack saw to trim the tab off. I used pliers and a file to remove residual pieces of the tab.

Step 3: Making a Hole

In order to mount the clamp I needed to make a hole in its base. I used three criteria in the screw selection process:

A flanged head so more of the clamp base would be covered for a secure hold
A small shaft that wouldn't require a big hole
The screw couldn't pass through the wood once mounted

Once I found a screw in my parts stash that met these criteria I checked the diameter of the shaft with a drill bit sizer. This let me choose the proper size bit for drilling the base. In my case this was 3/32".

I secured the clamp in my bench vise with the opening facing the floor. I then used a metal punch and ballpeen hammer to dent a spot in the approximate center of the base. This dent will keep the drill bit from "walking" when the hole is drilled. I then used a power drill and 3/32" bit to drill a hole in the clamp base.

A flat file and a round file were then used clean up the edges of the hole.

Step 4: Attaching the Clamp

With the clamp finished I needed to attach it to the tray table. I snapped the clamp onto the crossbar of the leg assembly. This allowed me to make a reference mark on the edge of the wooden stop that was approximately level with the hole in the base. I then used the edge of my drill bit sizer to transfer this mark to the inner face of the stop. With the mark transfered I drilled a pilot hole in the wooden stop. I then used the Phillips head driver bit to secure the clamp to the wooden stop with the screw I picked out of my parts stash earlier. The clamp now snuggly grasps the crossbar when the legs are deployed. This ensures that the tray table won't collapse unexpectedly so the only food in my lap will be what falls out of my mouth.