Lee Valley has a little bit on the use of cups around their magnets to
increase their strength.  Click on the "tech" highlight in the ordering
section.

http://www.leevalley.com/US/wood/page.aspx?p=58750&cat=1,42363,42348

These may help, if you embed these in the far jaw of your vise, away from
the magswitch.   Also, what about 2 Magswitches, or are they opposed and
push each other away?  Could you reconfigure them to be a pair?  Or two on
the same side to pull your plate?

Here is a page on magnetic field strength that may give more clues.
https://www.kjmagnetics.com/blog.asp?p=surface-fields-101

We did a thing back in HS on field shape, with metal shavings on top of a
thin piece of ?plastic? and could see the shape of the field change wiht
the magnets.  We didn't have supermagnets back then, so I don't know if it
would be as dramatic as now, or more so.  I had an industrial magnet that
the teacher wouldn't let near his setup.

Finally, when trying to separate two magnets, go sideways, not away.
Rather than lifting them like LPs on a spindle, slide them and scratch the
LP.  Much easier.

KE




On Sun, Apr 21, 2019 at 12:56 PM Ed O'  wrote:

> Kind of on the periphery of the charter so please do a direct reply if you
> have info and think it is too far afield.
>
> I am attempting to create a work holding device or jig to hold some stuff
> while I work on it with hand tools.
>
> I think the basic question is:  do any properties of what a magnet
> attaches to affect the strength of the bond?
>
> Short question that gives a feel for what I want to do:
> Magnetic bases for dial indicators are switched so you can engage or
> disengage the magnetism.  Is the hold strength of the magnet affected by
> the mass or thickness of the iron that it will attach to?  In other words
> if I use a piece that is 2 x 3 x 1/8 will it result in less grip than say
> using a piece that is 2 x 3 x3/8?
>
> Longer question with more specifics:
> When using a hand screw the reach is limited by the length of the jaw from
> the threaded rods.  I am attempting to create something that would not have
> this throat limitation.
>
> I am using a Magswitch (
> https://www.amazon.com/Magswitch-8110005-MagJig-150/dp/B001B8HMKG/ref
=sr_1_2_sspa?keywords=magswitch&qid=1555873085&s=gateway&sr=8-2-spons&psc=1">htt
ps://www.amazon.com/Magswitch-8110005-MagJig-150/dp/B001B8HMKG/ref=sr_1_2_sspa?k
eywords=magswitch&qid=1555873085&s=gateway&sr=8-2-spons&psc=1)
> in one jaw and a piece of mild steel in the other jaw.  I am currently
> using 1/8 thick steel.  If I try and hold two pieces of veneer between the
> 2 jaws it holds well, 2 pieces of 1/8 thick stock and it holds, but not
> well.  Does altering the thickness of the mild steel side effect anything?
>
> Here is a picture of the prototype holding some 1/4 inch stock (it
> actually will be 2 x 1/8+ pieces that I want to work, that I need to
> maintain the orientation of and cannot use glue or carpet tape to hold
> together)
>
> https://www.edoii.com/auction/magswitch/img_1981.jpg
> https://www.edoii.com/auction/magswitch/img_1982.jpg
> https://www.edoii.com/auction/magswitch/img_1983.jpg
> https://www.edoii.com/auction/magswitch/img_1984.jpg
>
> I bought a piece of 3/8 flat bar stock from HD and the hold appears to be
> slightly  better than with the 1/8 bar stock I already used.  I don't want
> to cut it up and make another prototype just to find out the hold is going
> to be just nominally better.
>
> Any engineering types out there that can point me in a direction?
>
>
>

-- 
Kirk Eppler in HMB, CA