HexDome - Magnetic models

Magnetic models

Introduction

Combining ball bearing hubs with magnetic struts makes constructing geometric models simple and easy.

Strong magnets have become inexpensive - and their use as modelling materials has now become practical.

Galleries

To illustrate the potential of the medium, here are a couple of galleries:

Neodymium magnet gallery

Plastic magnetic construction toy gallery

Strut length limitations

The plastic kits typically offer struts in a limited range of lengths. While one manufacturer claims to offer seven different lengths, to construct a reasonable range of models, you would probably need to have struts of configurable length.

The pure-neodymium route provides that capability without much effort - since cylinder magents are available in widths down to half a millimeter thick - allowing for strut lengths to be varied with that sort of granularity without much difficulty.

Magnet strength tests

The neodymium magnets were all N38 magnets (a common-but-fairly-weak grade).

Stronger magnets help when building bigger models.

I did some strength testing of the various magnetic modelling materials I had available:

Name	6mm Rod	6mm Cyl	Uni Mag	Geo Mag	Sup Mag	Mag Stx	Sup Sml	3mm Rod	Stx Bls	Mag Max	Wit ka
Strength
Strength	11	10	10	9	9	8	7	7	7	5	5
Mass/l	2.08	1.43	1.77	1.98	1.14	0.68	0.76	0.51	0.48	0.43	0.43

These tests all used 6mm ball bearings as the test weights.

Note that the strength scale is non-linear - the further away each ball is, the greater increment in magenetic strength it represents.

The mass/length figure doesn't make any attempt to factor in the weight of the steel ball bearings. They make up a lot of the weight in many kinds of model.

I dissected a couple of rods - to see how they were made:

Supermag

Geomag

Geomag (and Unimag) use a 5mm diameter steel rod - to transmit magnetic force between the poles of two 6mm diameter magents.

Supermag uses a single 5mm diameter solid magnet.

A few notes in summary:

The "raw" neodymium magnets are strongest. They also have configurable lengths - and some have reasonable weight.

Of the commercial systems, Unimag was the strongest I tested.

Supermag scores highly in both strength and weight. It comes in a range of lengths - and has a neat ability to fit many rods around one ball.

Contention

Strong magnets can interfere with each other when placed in close proximity to one another. Contention issues do crop up with the neodymium models - but essentially, it's usually no big deal.

Typically the magnets know which way around they are best positioned, and they leap from your fingers onto to the model while adopting that configuration. Sometimes they leap to the wrong location - but they can be pulled off again without too much bother.

Hollow cylinders

Most of the 6mm neodymium magnets have a 3mm hole bored into them - which works well at keeping the magnet aligned with the centre of the ball - and allows some parts of the magnet to move slightly closer to the ball bearing.

Some magnetic strength is lost in the process of removing the magnet's core - but the hollow tubular magnets seem preferable to the solid cylindrical ones overall.

Scaling

To explore the possibilities offered by different size materials, I purchased some 3mm tube magents and some 6mm ball bearings.

3mm neodymium magnet spaceframe

3mm neodymium magnet ring

Making the components larger or smaller seems unlikely to make much difference to the range of models which could be constructed.

Size does make quite a difference to construction cost, though. Neodymium magnets are not yet so cheap that cost is a negligible factor.

Unfortunately, there are some disadvantages to using smaller magnets:

They are more difficult to manipulate with your fingers;
Hollow cylindrical versions are not easily available much below 6mm;
The thinnest magnet is still 0.5mm thick - so there are more length-quantization issues;

Generally, the 6mm magnets used in most kits seems like a reasonable size to me.

The modeling stratgey would benefit somewhat from the use of hollow ball bearings.

However, unfortunately, hollow and light ball bearings do not yet seem to be widely available.

Spheres

Neodymium magnetic spheres

Modelling with magnetic spheres is also possible.

See the neodymium magnetic sphere page for more details.

Hazzards

There are various dangers associated with neodymium magnets. The small ones seem pretty safe to me. I smashed a few thin ones while making these models, but none of them sent shards of neodymium into sensitive parts of my body.

Some people have sensitivities to nickel. I don't seem to be one of them, and am not too concerned about absorbing heavy metals through my fingers from these components.

Magnetic modelling can be fun - and doing too much of it might waste your time and or give you RSI. Nontheless, I rate magnetic modelling as a fairly low addiction risk activity - and a moderate-to-low RSI risk hazzard.

If you have small kids, you might want to think twice about leaving these components lying around.

There are a number of other potential hazzards with magnets - read the warnings and take appropriate care.

Introduction

Galleries

Strut length limitations

Magnet strength tests

Contention

Hollow cylinders

Scaling

Spheres

Hazzards

Links

Neodymium modelling

Magnet suppliers

Bulk magnet suppliers

Plastic magnetic kits

Models pages

Non-magnetic construction kits