The Magswitch Magjig is a very clever magnetic clamp. It's made in a way that the magnetic field can be switched off or on by turning the knob on top. They are very useful for fixing featherboards or jigs to table saw tops or other steel or iron surfaces.
Unfortunately, the Magjig is also pretty expensive for a clamp.
This is my design for a similar magnetic clamp that is simple and cheap as chips to make.
Step 1: Materials
I have a 3D printer so designed a body for the Magjig using Fusion 360. You can download the STL file (and a featherboard design) from Thingverse here: https://www.thingiverse.com/thing:2964752
If you don't have a 3D printer you could make a suitable body from a block of wood or even aluminium.
You also need are a rare earth magnet. I bought some 32mm magnetic hooks from Ebay The hooks can unscrew from the base and have a M6 thread.
You will need a M6x40 clamping knob similar to what you can see in the photo (Ebay) and a couple M6 nuts.
You could make a knob with your 3D printer and a M6 bolt but I had these knobs already.
Step 2: Assembly
After printing the body, push a M6 nut into the recess on the top. This was easy to do using my drill press.
Next, screw in the knob and add a nut on the underside about 5mm from the end. Screw on the magnetic base and tighten against the nut using pliers to get a good grip around the base. This will prevent the magnet unscrewing easily during use.
Finally, I added a piece of masking tape to the magnet to prevent it scratching the table saw top.
Step 3: How to Use
A real Magjig uses magnets configured in such a way that the magnetic field cancels out when turned off, but when turned on the magnets align to provide a strong holding force.
This DIY version isn't that clever. The magnet is powerful but always on. The screw knob provides leverage to easily remove the magnet when required.
Simply place the magnet on the metal surface and wind in the screw until the magnet touches the surface and holds securely. To remove, wind out the screw until the magnet can be removed.
Besides the featherboard, this magnetic clamp can be used in other jigs. The base is curved at two ends and will fit in a 45mm hole. The other two sides are flat and can be place flush against a board for example.
Let me know in the comments of any other ideas this can be used for.
I hope you find this Instructable useful!