A quick captive nut how-to, for when you are making a wooden box that has a lid you need to remove on an irregular basis. Wood screws tend to maul the wood after a while and then the lid falls off, these captive nuts are easy to do and just work.
You will need:
- Nut and bolt
- two part expoy adhesive
- drill bit as large as the nut and a drill
- Vaseline or any other petroleum jelly
In this example I am using an M4 nut and bolt and an 8mm drill bit. You may need to cut your bolt to length.
1. Drill your hole
in this case about 1 cm, deep enough so when you insert the nut and bolt the expoy will cover the nut. Clean it up, removing wood shavings and other debris.
2. Grease Up
To prevent the expoy sicking to the bolt smear some Vaseline onto your bolt, only a small amount is required, but you should get it into the thread, make sure you keep the nut clean. Thread the nut back onto the bolt, leaving 4-5mm of bolt protruding, as shown:
3. Mix up the Expoy
Mix a blob about the size of a marrowfat pea, enough to fill half of the hole. Drizzle this into the hole.
4. Plunge the nut and bolt into the hole
Wiggle it about a bit to make sure the expoy is well distributed. Position the bolt how you would like and leave to set. If you see the bolt moving use some sticky tape to hold it in place.
5. Remove the bolt
After about 10 to 15 minutes, the expoy will have set (unless you got that weird stuff). Use a screwdriver for at least the first turn as there will be a little adhesion, but it’ll come out cleanly.
If you have any excess expoy protruding it’s still quite soft at this time so cut it way with a Stanley knife as I have done in the example. Once fully cured expoy makes a hard plastic that can be difficult to cut.
The amount to cut off your bolt is the length of your bolt less the thickness of your lid less a bit of wiggle room, I use a cutting disc on a Dremel, and file the cut edge smooth. You need to ensure its long enough to go through the nut once cut as the expoy has a thread that gives a misleading nutness (technical term!) that soon wears away.
I hope you enjoy your captive nuts, I am sure they will give you many years of service. The same principle can also be applied to making captive bolts, especially if you wanted to use Wing Nuts for easier access.