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General Information About Magnets

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

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....

Powerful magnets are extremely useful in a Mercedes Sprinter, which has both a steel interior and exterior. It will be a pity if newer Sprinter models use aluminum in place of steel—no more magnets.

Those who spend large sums on upfitting might find frustration with the interior steel all covered-over—a great loss of functionality. IMO, a showcase-looking van is often far inferior in functionality to my hand-designed interior, even as it draws appreciative compliments for its good looks. This section thus applies mostly to DIY or partly-DIY Sprinter owners like myself.

I use magnets heavily in my Sprinter for all sorts of things; I can move them around at will, and they can be powerful enough to hold quite heavy things even over bumpy roads. Magnets come with and without hooks for hanging things too.

There is only one kind of high grade powerful magnet for everyday use: neodymium, grades N42 through N52. Forget everything else as inferior. High-grade neodymium magnets are relatively expensive. Also, there is a lot of junk on the market purporting to be high quality—some are and some are not. Virtually all neodymium magnets are from China, which has a stranglehold on the rare earth metal supply (neodymium is a rear earth metal).

Size, shape, holding power

These topics are covered on following pages in more detail and with examples.

Excluding the generally useless old-school horseshoe magnets, powerful neodymium magnets are available primarily in three shapes: spheres, cylinders, rectangular blocks. Variants include magnets with holes through which screws or similar can be threaded, countersunk versions so the magnet can be screwed on, etc. Special shapes can be made but for general purpose use are out of scope here.

Rubber or other coatings can be very useful when available and appropriate.

Sometimes one wants an axially magnetized magnet (poles at each end). At other times a diametrically magnetized magnet (poles on sides) can be useful for applying magnetic force along the length (for example, a magnet 2 or 3 inches long, it is much more useful to have the poles on the opposite long faces, rather than the small ends).

Magnet size

Very powerful small or thin magnets are extremely difficult to work with; once attached they can be difficult or even impossible to remove because no grip can be had. Avoid small magnets for most all use cases excepting those where attachment is intended to be permanent and/or where they in effect become mounting points where a thin form factor is important.

If you cannot easily grasp the magnet with two fingers, it will be a hassle to use it. One way to work around this is with small cube magnets with holes drilled in them—insert a strong cord through the hole; this then is your grip for removal.

Where to buy

The best quality magnets can be found at KJMagnetics.com—top quality and many grades, sizes and shapes.

  • KJMagnetics.com: this company has magnets of many shapes, sizes and strengths, all top quality. Unfortunately they offer little or no selection of magnets with hooks (e.g., for hanging clothing and similar).
  • TBD TBD TBD

High quality magnets can be found on Amazon, but the quality is often mixed or false claims made about grade, so choose carefuly—buy a single sample to assess it before buying more. However, the prices are excellent for the direct sources on Amazon. Magnets with hooks on Amazon are generally very good quality, though some have not so good hooks that can be bent or come off too easily—again, test a few first.

Magnet safety

Use extreme care with powerful magnets: they can cause injury (even break a finger bone), or shatter into shards if allowed to accelerate like a bullet, which they can and will do. Store in padded pouches or take similar precautions, and exercise extreme caution in allowing such a magnet to come within a foot of another.

TIP: wrap a powerful block or cylinder or sphere magnet in gaffer’s tape. Use bright green for visibility, or choose a color to match the paint or interior. The gaffer's tape is durable and will have minimal effect on the strength, but adds a slight cushion and better grip. With very powerful block magnets, I wrap the entire magnet in one layer of gaffer's tape.

Use extreme care with powerful magnets: very power magnets like grade N42 and especially N52 neodymium magnets can cause injury (bruising or pinching or even break a finger bone).

  • Store in padded pouches or take similar precautions.
  • Exercise extreme caution in allowing such a magnet to come within a foot of another.
  • Do not keep magnets in pockets near keys or phone or any electronics or similar—they can magnetize these items permanently and possibly damage them as well.
  • A tiny piece or any magnet ingested by accident is extremely dangerous—keep away from children and food.

Neodyium magnets can shatter into shards if allowed to accelerate like a bullet, which they can and will do. Once shattered, bits large and small will stick like glue and are very hard to remove.

TIP: wrap a powerful block or cylinder or sphere magnet in gaffer’s tape. Use bright green for visibility, or choose a color to match the paint or interior. The gaffer's tape is durable and will have minimal effect on the strength, but adds a slight cushion and a much better grip than smooth nickel-plating. With very powerful block magnets, I wrap the entire magnet in one layer of gaffer's tape. Some magnets come with plastic or rubber coating; these are terrifice for some purposes.

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Sizes and shapes of magnets —why to choose each

 

Block (rectangular solid) magnets

I use block magnets for a few 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.

For holding heavy items particular things angled outwards and for when bumps won’t shake things loose, choose a 2 X 2 X 3/4 inch block magnet rated for several hundred pounds. Wrap it in gaffer’s tape before use as per the ealier tip. Apply it to flat sheet metal and it will stick on increditly strongly. Then bolt a countersunk-hold N52 magnet to the desired item and let the two magnets come together. That setup holds a 1+ pound light at 90° even over the hardest bumps on very rough dirt roads.

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

[low-res image for bot]
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]
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]

Sphere magnets

For sphere magnets, go no smaller than 3/4-inch diameter, which work very well, but are still a bit small for my fingers.

For peak holding power, 1-inch diameter N52-grade sphere magnets are best—extremely powerful and with a much better grip. Even so it is difficult to separate two N52-grade 1-inch sphere magnets; put a piece of 3/16" foam between them when storing, or similar.

Sphere magnets work best for holding/pinning things with thickness in place, because their point force is very high, which compresses the material and allows for a much stronger grip for the same rated holding power versus a cylinder or block magnet.

For example as shown below, a sphere magnet easily flattens the air bubbles in the Reflectix for powerful contact with the sheet metal of the van (it wll be a shame if Mercedes switchs to aluminum).

I strongly recommend high quality N52 grade 1-inch sphere magnets for this purpose because the pulling force is needed to keep the Reflectix in place and without movement (which would scratch the paint). Moderate-strength magnets are no good—even a mild wind will drag them around and maybe rip the shield off entirely.

Before any upfitting, temporary mobile computing workstation setup
f1.8 @ 1/2500 sec, ISO 20; 2018-07-11 10:16:08
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]

Below, an N52-grade cylinder magnet is used. Its holding power is strong, but nowhere near as strong as a sphere magnet because it cannot make as close a contact through the air bubbles in the Reflectix. I got this one on Amazon and while it is claimed to be N52-grade, its holding power seems to be much less than true N52 grade magnets from KJMagnetics.com. Beware of bogus claims for magnets on Amazon. Still it is a very strong magnet; I bought one to see how good it is—good but not as strong as claimed.

Mercedes Sprinter van high in the White Mountains of California at 11,500' elevation
f1.8 @ 1/2700 sec, ISO 20; 2018-07-11 10:16:45
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]

Magnets holding on exterior shade panels

See Keep it Cool by Blocking the Sun’s Heat.

Over the windshield, four one-inch grade N52 nickel-coated sphere magnets from KJMagnetics.com hold things in place. On the side I’ve used 3 instead of four; I would use four of them if windy. The N52 spher magnets are extremly powerful, and if the material is stretched snugly, it will take a very strong wind to dislodge it.

Below, an N52-grade sphere magnet holds the Reflectix in place. Move the magnet further up if the door will be opened.

Reflectix used as side shade in Mercedes Sprinter van
f1.8 @ 1/2300 sec, ISO 20; 2018-07-11 10:16:29
iPhone 7 Plus + iPhone 7 Plus 4.0 mm f/1.8

[low-res image for bot]

 

 

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