Re: Who is a good supplier for small 3-jaw chucks



Jeffrey Lebowski wrote:

"BottleBob" <bottlbob@xxxxxxxxxxxxx> wrote in message


I just hope all these magnetic
holding devices are not powered by wall current. I mean if you had a
severe brownout... Yikes! LOL


Bob,

Electroperm magnets don't lose their magnetism upon power loss...rather, a
single pulse reverses the poles instead.


JL:

Heh, yeah, that'd certainly be safer. That's *IF* the magnetic chucks
in question were permanent electro-magnetic and not just regular
electromagnetic. I don't have any personal experience with permanent
electro-magnetic chucks since the two surface grinders I've been using
for over a decade are electromagnetic. (If you leave them on for any
extended period of time they get warm to the touch)

Here's an excerpt from the site listed below that explains the three
different kinds of magnetic chucks.

==============================================================
http://www.industrysearch.com.au/Features/Increase_Profitability_with_Magnetic_Workholding-407

What Are Magnetic Chucks?

The three types of magnetic chucks are permanent, electro-magnetic and
permanent electro-magnetic.

Permanent magnets switch on and off through the alignment of magnets
within the chuck to the mild steel surface on top of the chuck. These
magnets are restricted in their clamping force by one?s ability to
overcome the magnetic resistance in turning the chuck on and off.
Historically, permanent magnets were only used for grinding and EDM work
due to the limited clamp forces resulting from magnetic resistance.

Electro-magnetic chucks use a constant supply of electricity through a
coil to create a magnetic field perpendicular to the coil.
Electro-magnets can generate large magnetic fields, but if power is
lost, so too is the magnetic clamping ? making them impractical for use
on pallet changers and machining centres. It is important to also note
that electricity through an electro-magnet generates significant amounts
of heat within the chuck and on the surface.

Permanent Electro-magnetic workholding has come a long way in the past
10 years, especially with the advancements in neodymium magnets.
Neodymium iron boron (NdFeB) magnets are smaller and more powerful than
other types of permanent magnets, therefore magnetic fixturing is more
powerful and more compact. In addition to neodymium, permanent
electro-magnets also use alnico magnets as the magnetic switch so that
the magnet can be turned on and off via a pulse of electric current.
This switching cycle takes less than a second as permanent
electro-magnets only require electricity to turn the magnet on and off
?.no electricity is required to maintain the magnetic field.
==============================================================

--
BottleBob
http://home.earthlink.net/~bottlbob
.

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