The Mystery of Magnetic Blocks - Operation & Use

[paul11273]

At work we have these magnetic blocks which have arms attached to them for dial indicators. They are use to hold the dial indicators like an extra pair of hands. They work great. My question is how do they work!?

The magnetic block has a switch on it. This switch will turn the magnet on or off. When it is on, it is quite strong. When off, you wouldn't really know there was a magnet there at all. There is no power applied to it, so this is completely a mechanically switching of its internal components.

I am amazed at how strong the magnet is, and that it can be turned off.
How does this work? Is is simply an application of a shield inside the housing?
Specifically, the ones we use are made by Mitutoyo. I do not have a model number. They are referred to by the manufacturer as magnetic blocks.

I am very curious about their operation. Does anyone have insight?

Thanks.

 

[berkeman]

Are they electromagnets, with AC power being turned on and off to energize a coil around some ferrous metal? Or are they something more exotic? You could probably make some moving ferrous metal pieces that expose or short out the field of a permanent magnet, but I hadn't seen that done before. I'd be interested in more info if it's not a simple electromagnet.

 

[marcusl]

No it's not electric. I've used them in the machine shop; wasn't going to post since I'm not fully sure what's inside but I'm guessing it's a horseshoe magnet inside with a shorting bar that rotates so it's either across the pole faces ("off") or upright in the middle where it has no effect ("on"). They are quite amazing to use!

 

[paul11273]

Are they electromagnets, with AC power being turned on and off to energize a coil around some ferrous metal? Or are they something more exotic?

No, they are not electromagnets. They are simply a free standing base, which is what makes them (in my eyes) so amazing. They do not plug in, connect, or use batteries. You can simply put them on a para (ferro) magnetic material, switch to "on", and they stick like crazy.

Has anyone else used them, or have any insight as to the physics behind how they operate?

Besides thinking that they may operate by physically moving a shield to block some strong Earth magnets which are permanently installed, I cannot imagine how they work. This has been driving me crazy. Is it that simple?

 

[paul11273]

Does anyone else have an idea of how these magnetic bases work?

 

[berkeman]

Does anyone else have an idea of how these magnetic bases work?

Well, help us out a little here. I googled Mitutoyo +magnet, and got some hits, but please don't make me sort through them to answer your question .

Please post some pictures, links, etc., and we'll be happy to use our physics and EE backgrounds to figure out how they do it if none of the links explain it. There are only a couple ways to do what you describe, after all.

Sorry if my reply is a bit terse. It's been an intense week at work, and at my work, we all expect our collegues to do their homework before presenting us with problems...

 

[berkeman]

Well, help us out a little here. I googled Mitutoyo +magnet, and got some hits, but please don't make me sort through them to answer your question .

Please post some pictures, links, etc., and we'll be happy to use our physics and EE backgrounds to figure out how they do it if none of the links explain it. There are only a couple ways to do what you describe, after all.

Sorry if my reply is a bit terse. It's been an intense week at work, and at my work, we all expect our collegues to do their homework before presenting us with problems...

Okay, I've gotten a bit of sleep and am feeling more my generous self. Sorry again for the late-night tired rant.

I spent more time with google, and got more info:

Sample Stand http://www.nextag.com/Mitutoyo-7010S-Magnetic-Stand-512889513/prices-html

Better Picture http://longislandindicator.com/magbase.html

Other Brands http://www.nolansupply.com/superprecision.asp?supercategory=Indicator+Bases+-+Magnetic

Hmmm, no luck with google trying to find an explanation of how they work. It could just be that they are using the lever to move the internal horseshoe magnet up slightly away from their bottom surface, in order to reduce the holding power enough to make it easy to pull the base off of wherever it's stuck to. Does it seem like maybe that's what's going on? The mechanical leverage of the lever moving several cm in arc translated to moving the magnet inside by a couple of mm?

 

[Gokul43201]

It could just be that they are using the lever to move the internal horseshoe magnet up slightly away from their bottom surface, in order to reduce the holding power enough to make it easy to pull the base off of wherever it's stuck to. Does it seem like maybe that's what's going on?

I don't think so. That way, you'd still have to do as much work as it would take to physically rip the magnetic block off the surface. But maybe the point isn't to reduce the work needed to separate the objects as much as it is to make the removal safer (better constrained).

I believe marcusl has the right principle. Rather than decreasing the PE of the system, you simply change where it's stored by rotating (or sliding) a ferromagnetic "shunt" inside the block. This would mean however, that switching between ON and OFF should be pretty difficult when the block is removed from a ferromagnetic surface (at least, compared to when it isn't).

 

[Gokul43201]

Okay, I've just spent a couple minutes taking apart one of these magnetic blocks. Will report findings later...

 

[berkeman]

Whoot! Post some pictues if you can too!