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Block Magnets: Mounting Items, Holding Power

Last updated 2018-07-11 - Send Feedback
Related: Mercedes Sprinter

Photographer and cyclist and Mac expert and software engineer Lloyd Chambers is available for consulting on general Sprinter considerations at his usual consulting rates via phone, or in person in the Palo Alto, CA area. Save yourself hours and mistakes by discussing issues up-front. More about Lloyd....

Block (rectangular solid) magnets can be cubes or rectangular solid shapes.

  • Flat surface makes them excellent for mounting heavier items (magnet attached to item which latches onto the block magnet).
  • Excellent choice for hanging small tools or similar.
  • Longer rectangular shapes are excellent for holding fabric or material spanning roof or similar.

In use

I use block magnets for several different purposes.

For holding fabric or similar in place, grade N52-grade 3-inch-long and magnetized along the length are excellent. Be sure to get these at least 1/4-inch thick or they will be too difficult to grasp for placement/removal.

Below, a number of these ~3 X 1/2 X 1/4 inch epoxy-coated magnets hold a large silvered insulating pad against the ceiling beams. The epoxy coating is excellent for preventing breakage and containing it if broken.

Epoxy-coated N52-grade rectangular block magnet holding metallized material in place
f1.8 @ 1/60 sec, ISO 32; 2018-07-11 11:53:43
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

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I was experimenting; the 2 X 1/4 X 1/4 grade-N52 magnets are very strong, but harder to handle. I wrapped them in bright green gaffer’s tape for easier handling. Two of them broke just trying to separate them, so I gave up on this size as too fragile and hard to handle.

N52-grade rectangular block magnet wrapped in green gaffer's tape holding metallized material in place
f1.8 @ 1/30 sec, ISO 25; 2018-07-11 11:48:37
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]
3 X 1/2 X 1/2 inch N52-grade rectangular block magnet wrapped in green gaffer's tape holding metallized material in place
f1.8 @ 1/25 sec, ISO 32; 2018-07-11 13:57:02
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]

Powerful block magnet for mounting heavier items

TIP: wrap block magnets in gaffer’s tape. This provides much better grip for handling, and adds a bit of shock absorption. If the magnet were to break, the tape will keep pieces from scattering and making a mess that can be extremely difficult to clean up.

The about 2 X 2 X 3/4 inch block magnet shown below has a holding power of about 300 pounds. It is partially wrapped in the dark green gaffer’s tape, for easier handling and reducing abrasion potential between the magnet and the painted steel interior.

In this particular case, the magnet attaches to the sheet metal of the Sprinter van wall. As powerful as it is, the ballhead and light are angled away at 90°, which exerts a strong lever-arm torque far greater than the actual weight of the assembly; this has the effect of wanting to peel-off the assembly from the magnet. Worse, hard shocks as on rough dirt roads exert far greater force for an instant, which can instantly peel-off the light*.

* Peeling off when hitting a bump proved to be an issue with an N52 magnet on the ballhead directly on the steel chassis; rated for 50 pounds, it could not hold the light even over a modest bump, even if the light was hanging down from the ceiling. The magnet would just peel off. I had just about given up on magnetic mounting when I though up this dual-magnet idea.

Below, an extremely powerful block magnet was used, along with another N52 magnet with a countersunk hole, screwed onto the base of the Really Right Stuff mini ballhead. The light then attaches to the ballhead and the ballhead allows aiming the light as desired.

Powerful N52-grade block magnet holding N52 countersunk-hold magnet bolted to Really Right Stuff ballhead with Cineo Matchbox light
f1.8 @ 1/30 sec, ISO 25; 2018-06-29 10:23:44
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]

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