If your first stop is a thrift store, (and it probably should be) you might notice most of the available tripods are missing their quick release plate. These plates might cost three times as much as your bargain tripod for a new one. More than likely you won't even be able to find one.
Fortunately, most of these pieces are very simple. Chances are you have all the tools you need lying around.
Step 1: Parts and Tools
We're going to need these tools:
Hand Saw and Miter box (these can be and are replaced with a table saw)
1/4" drill bit
Chamfer bit (nice to have, but I used a christmas tree stepped bit.)
A stack of thick card stock or similar
Of course, some materials are also handy:
1/4" - 20 threaded bolt
Captive bolt ring
Length of Hard Wood approximately the correct size for your tripod (Use hard wood, I used pine, but it was what I had at hand. I will replace it when I get a chance.)
Step 2: Measure the Tripod
My favorite method is to push a stack of card against the angled surface and then copy the slope for measuring with a protractor.
It's also good to keep a reference diagram handy. I scrawl one on a mini whiteboard so it's easy to edit.
Step 3: Layout the Material
Go for a hardwood if you can. I used pine here and it's likely I will have to replace it sometime in the future.
Step 4: Cut the Wood
DO NOT USE A TABLE SAW! Table saws are statistically the most dangerous tools in your shop. I don't want to hear about anybody who loses the ability to touch type. A much better tool for this task is your standard pullsaw and miter box combo.
Now that the disclaimer is out of the way, cut along the marks you made for yourself. The angle isn't critical, but the closer you can get the better.
Step 5: Adjusting the Pattern Because You Overlooked a Simple Piece While Measuring
Always cut away from yourself with chisels and make sure that your work is properly clamped down.
Step 6: Drill the Hole
Step 7: The Bolt
Once you've inserted the bolt, you want to clip a captive ring onto the other side of it so it stays put. I didn't have one, so I used a welder. Remember that excuse should not apply to auto maintenance
Step 8: Success
Disclaimer Numero Dos:
I accept no liability if your camera falls off of your tripod, your tripod falls over, your house is struck by lightning, or aliens invade the earth. Use your brain. This was designed to hold up a light that weighs less than a pound and can be repaired for less than a dollar.