Magnetic Chucks Revisited
pent...@yahoo.com
magnetic chuck shown on youtube
http://www.youtube.com/user/tryally#p/u/30/avUkGTNqUtk.
This chuck used three sets of triple stacked computer HDD
magnets. Unfortunately the magnetic design is not optimum so it
can only achieve a fraction of the hold down power ofprofessional
magnetic chucks. However the idea seemed worth following up. The
results are shown in
http://i801.photobucket.com/albums/yy291/pentagrid/MagbeticChuck.jpg
http://i801.photobucket.com/albums/yy291/pentagrid/MagnetAssysideview.jpg
http://i801.photobucket.com/albums/yy291/pentagrid/Spacerlayout.jpg
This again uses HDD magnets, only two pairs this time but
now arranged to achieve a properly closed magnetic circuit.This
results in a big increase in hold down force.
With a 22mm diameter 1/2 " thick mild steel test piece the
results were;-
youtube triple magnet design
with 2mm thick top plate 4Kg
New design 17Kg
Eclipse 18"x 6" Chuck 20Kg
The JPGs are largely self explanatory but a few points
may help.
The unwanted parts of the original HDD magnet mounting
are sawn and filed away leaving just enough meat to bolt through
to the 1/8" mild steel mounting plate.. This plate is part of the
magnetic circuit and must be at least 1/8" thick.. Brass end
pieces bear on the eccentrics and also locate the magnet assembly
centrally within the chuck body
The chuck top layout depends on the actual magnet size.
A 5/32" wide brass spacer mounts acros the center line of the
chuck. The centre line between the two sets of magnets lies
directly under this spacer.Two more 5/32"spacers are added, each
directly above the centre line of the arc of the magnet pair that
it covers.
1/8" thick mild steel pole pieces are then machined to
the correct widths to fit in the empty spaces.
To deal with the larger "magnet switch off" forces the
youtube cranks are replaced by a pair of 7/16" dia 3/16 offset
eccentrics running on 1/4" bearings,
To keep the overal height low these eccentrics are located
beyond each end of the magnet assy
The eccentrics move 180deg for full "on" to full "off.".
magnetic forces retain them in either the "off" or "on"positions.
"full off" is a misnomer. The chuck is still partly on but
with reduced downforce for workpiece removal.
Jim
Tony Jeffree
>youtube triple magnet design
> with 2mm thick top plate 4Kg
>
> New design 17Kg
>
>Eclipse 18"x 6" Chuck 20Kg
Impressive results.
I have a few of these kicking around - might give it a try.
Regards,
Tony
Bob Engelhardt
great.
In the previous thread (http://tinyurl.com/ydxaobn), you said that hdd
magnets were really pairs with opposing poles (NS-SN) & to break them
apart. But you haven't done that?
How do your eccentrics engage the backing plate?
You sawed & filed the magnet's original mounting plates to be thinner.
Is that necessary? IOW, what is the purpose of that?
The chuck in the video had pieces to prevent x,y motion - is yours
strong enough to not need them?
Could you send this to the DropBox, so it will be available for "all
time"? Stuff loaded to places like Photobucket tends to get deleted
after a while.
Thanks!
Bob
Tony Jeffree
<bobeng...@comcast.net> wrote:
>In the previous thread (http://tinyurl.com/ydxaobn), you said that hdd
>magnets were really pairs with opposing poles (NS-SN) & to break them
>apart. But you haven't done that?
You would break them apart if you wanted to build a more conventional
design with a sliding magnet assembly, as opposed to this design where
the magnet assembly is simply moved away from the top plate. The
magnets are effectively horseshoe magnets with very short arms, which
is just right for this approach.
>
>How do your eccentrics engage the backing plate?
I believe that the eccentrics merely hold the magnet plate away from
the top plate - the magetic attraction is sufficient that the magnet
plate doesn't fall to the bottom. The brass pads at either end serve
as bearing surfaces and also help to keep the magnet plate centered.
>
>You sawed & filed the magnet's original mounting plates to be thinner.
>Is that necessary? IOW, what is the purpose of that?
Smaller, not thinner, if I read his post correctly. The point is that
you want to be able to mount the magnets as close to each other as
possible, but you still need enough of the original backing plate to
allow you to attach them.
Regards,
Tony
pent...@yahoo.com
<bobeng...@comcast.net> wrote:
>Cool! My mill's table is so small (1 T slot), that your vise would be
>great.
>
>In the previous thread (http://tinyurl.com/ydxaobn), you said that hdd
>magnets were really pairs with opposing poles (NS-SN) & to break them
>apart. But you haven't done that?
The magnets do not need to be broken into two pieces
because,this design with its mild steel magnet mounting plate and
top surface pole pieces, properly utilises both the NS and the
SN magnetised areas . Mild steel can be regarded as an extremely
low resistance magnetic conductor so this configuration turns the
flat HDD magnet into a short powerful horshoe magnet.
>
>How do your eccentrics engage the backing plate?
The eccentrics are not used as in the steam engine valve
gear sense but as cylindrical cams. The magnet assembly is always
strongly attracted to the top pole pieces and considerable force
is needed to pull it away. This is provided by the cylindrical
cams bearing on L shaped brass extensions at each end of the
magnet assembly.
>
>You sawed & filed the magnet's original mounting plates to be thinner.
>Is that necessary? IOW, what is the purpose of that?
>
As rescued from a HDD the magnets are bonded to odd
shaped backing pieces which locate them with the required gap.
The full thickness of the backing piece behind the magnet is
still required but the outer parts should be cut away to permit
the modified magnets to be mounted as close together as possible
on the mild steel mounting plate.
The standard backing piece is not thick enough to carry
the maximum flux of this design and it needs the extra thickness
of the 1/8" mild steel mounting plate. This is easily
demonstrated. As removed from a HDD the backing is inert - it
doesn't behave as a magnet. If the magnetic circuit is now closed
by a lump of mild steel in contact with the magnet face the
backing piece saturates and N and S poles appear on the back
surface.
>The chuck in the video had pieces to prevent x,y motion - is yours
>strong enough to not need them?
The hold down force in this design is nearly strong as in
professional chucks so stops are not normally needed for light
grinding (0.0005" downfeed). Very thin workpieces and even light
milling require stops of some sort. Surface grinder magnetic
chucks usually have an end plate that can be lowered or raised to
act as a stop. It's usually quicker to backup any problem
workpiece by a much larger thinner piece(s) of mild steel
spanning several pole pieces.
>
>Could you send this to the DropBox, so it will be available for "all
>time"? Stuff loaded to places like Photobucket tends to get deleted
>after a while.
Posted in the DropBox under the heading Magnetic Chuck
Jim
Bob Engelhardt
> On Mon, 14 Dec 2009 22:34:39 -0500, Bob Engelhardt
> <bobeng...@comcast.net> wrote:
> The magnets do not need to be broken into two pieces
> because,this design with its mild steel magnet mounting plate and
> top surface pole pieces, properly utilises both the NS and the
> SN magnetised areas . ...
OK
>> How do your eccentrics engage the backing plate?
> ... The magnet assembly is always
> strongly attracted to the top pole pieces and considerable force
> is needed to pull it away. This is provided by the cylindrical
> cams bearing on L shaped brass extensions at each end of the
> magnet assembly.
Alright - I was thinking that the assembly had to be pushed both ways.
I can see the brass bearing plates in the 2nd pic, MagnetAssysideview
>> You sawed & filed the magnet's original mounting plates to be thinner.
> As rescued from a HDD the magnets are bonded to odd
> shaped backing pieces which locate them with the required gap.
> The full thickness of the backing piece behind the magnet is
> still required but the outer parts should be cut away to permit
> the modified magnets to be mounted as close together as possible
> on the mild steel mounting plate....
OK, I don't know why I was thinking thickness removal (that wouldn't
have been an easy job).
>> The chuck in the video had pieces to prevent x,y motion - is yours
>> strong enough to not need them?
> The hold down force in this design is nearly strong as in
> professional chucks so stops are not normally needed for light
> grinding (0.0005" downfeed). Very thin workpieces and even light
> milling require stops of some sort. ...
Ah - *surface grinding*. The video showed the chuck being used on a
mill & that's what I thought yours was for. And what I was planning on.
Would it be useful on a mill, with x/y stops? Or, would it be the
case that, even with the stops, you would be limited to light milling?
> Posted in the DropBox under the heading Magnetic Chuck
Thanks
Bob
pent...@yahoo.com
<bobeng...@comcast.net> wrote:
>pent...@yahoo.com wrote:
>> On Mon, 14 Dec 2009 22:34:39 -0500, Bob Engelhardt
>> <bobeng...@comcast.net> wrote:
>
>> snip
>
>>> The chuck in the video had pieces to prevent x,y motion - is yours
>>> strong enough to not need them?
>
>> The hold down force in this design is nearly strong as in
>> professional chucks so stops are not normally needed for light
>> grinding (0.0005" downfeed). Very thin workpieces and even light
>> milling require stops of some sort. ...
>
>Ah - *surface grinding*. The video showed the chuck being used on a
>mill & that's what I thought yours was for. And what I was planning on.
> Would it be useful on a mill, with x/y stops? Or, would it be the
>case that, even with the stops, you would be limited to light milling?
>
>
>> Posted in the DropBox under the heading Magnetic Chuck
>
>Thanks
>
>Bob
x/y stops would be needed for milling. In this case increase
the thickness of the mild steel pole pieces to 1/4"and provide as
many tapped holes as is convenient to secure x/y stops.
Jim