When machining or metalworking in general, 90% of the work is planning. A substantial portion of that is workholding and fixturing: how you keep the workpiece secure, while still enabling access to the parts of the material you need to reach. The most common example is the good ol’ screw vise, but those are often unsuitable for the job as they don’t provide very good access. Magnetic chucks can be very useful alternatives, which is why Chris Borge 3D-printed this magnetic chuck for his DIY tapping arm.
Magnetic chucks come in three major varieties: electromagnet, electro-permanent magnet (EPM), and permanent magnet. The first type is the easiest to understand: they’re just powerful electromagnets that you turn on when you need to hold something. EPM chucks are very interesting, as they use energized coils to permanently magnetize the magnets when necessary. The advantage is that they only need energy when magnetizing or demagnetizing — the rest of the time they don’t consume power and will remain in the set state.
Borge’s is the third type: a permanent magnet chuck. This kind has normal permanent magnets, just like the kind you’d use to stick something on your fridge—though usually much more powerful. The neat feature of a permanent magnet chuck is that it can turn “off,” so you can remove the workpiece. That “switching” feature works by physically moving material with low magnetic reluctance into or out of the magnetic field, effectively “shorting” the magnetic circuit and eliminating outward magnetic flux. Robert Murray-Smith has a fantastic video on this subject if you’d like to know more.
In this project video, Borge improves upon an old permanent magnetic chuck design. In fact, it is quite similar to the design Rober Murray-Smith provided as a demonstration in his video. It consists of six steel nuts arranged in a hexagonal pattern, with permanent magnets between the nuts. A second, almost identical, assembly sits on top of the first. When rotated into the “on” position, there is strong magnetic flux. When rotated into the “off” position, the magnetic field becomes very weak—non-existent, if perfect.
Borge 3D-printed the parts to hold those assemblies in place. That includes a cam mechanism that translates linear motion into rotary motion for switching the chuck. A layer of poured epoxy on top helps to keep the work surface relatively flat and smooth.
This isn’t very powerful, as magnetic chucks go. But it is sufficient for holding a tiny screw vise in place when Borge needs to tap something. Thanks to the magnetic chuck, he can easily move that vise into position and then hold it securely in place.
