I built a workbench with a four-layer MDF top and did not keep close
track of the location of the screws securing each pair of layers
together (in addition to the glue), thinking that I could locate them
afterwards with a stud finder and ovoid them when drilling holes for
bench dogs. I do know that I ensured that screws were placed so that the
later ones did not collide with the ones already connecting other layers.
BUT neither the electronic stud finder nor the swiveling-magnet nail
finder will locate these screws.
I know that fancy and expensive devices exist that are claimed to be
able to find nails in lumber, but is there some simple and cheaper way
to do what I need?
The screws are steel rather than brass.
I thought I still had several magnets from dead hard drives (mostly
Western Digital), but I've found only one small pair. Sliding one of
these (one half of the pair) along the surface of the workbench, I do
find some spots where it wants to stay put and swivel rather than slide
further along, so I think it is doing the job. When I have more time,
I'll mark the spots and see whether they are at regular intervals: I
can't be sure where I drove the screws, but I am reasonably confident
that they were equally spaced (or close enough to).
Lee Valley sells Rare Earth magnets.
However, I'd expect the magnet in a magnetic stud finder IS a rare earth
magnet, and if it's not responding to the presence of steel screws, then
another rare earth magnet won't either.
I think this is one of those cases where there isn't a good solution to
I'm not sure why the Hazard Fraught one would work better than the
Stanley. Keep in mind that we are talking about screw that were driven
in from what is now the underside of the bench top, so only the points
of the screws are within 1/2" or more of the surface.
On Thu, 07 Aug 2014 17:25:06 -0700, Percival P. Cassidy
you need a 'tiny' metal detector! A small version of those things people
scan around over the ground, but only 1/2 inch in diameter. I've got one
with a 1/4 inch diameter in my lab. If you want a LOT of details, contact
me offline. From memory it can 'see' a nail something like 6 inches away.
or was that a foot? can't remember now.
you can make one with some effort. A coil and your soundcard. Power the
coil with the soundcard drive while monitoring the 'response' of the coil
with the input of your soundcard 'listening'. Then moving the coil around
on top the bench will find stainless steel as well as ferro iron
To really add some 'gain' to the system, use two coils one to transmit and
one to send. put the transmit under the table and move it around, put the
receive on top and move it around at the same time. When you line up on a
screw/nail the signal(s) will be greatly enhanced.
[Haven't tried but might work, try using a 'cable locator', one of those
$25 thingies from HD, launch the tone into a small coil under the bench,
and move the probe around on top at the same time, might really hear it
get louder when you line up on a screw/nail.]
| The screws are steel rather than brass.
| I thought I still had several magnets from dead hard drives (mostly
| Western Digital), but I've found only one small pair. Sliding one of
| these (one half of the pair) along the surface of the workbench, I do
| find some spots where it wants to stay put and swivel rather than slide
| further along, so I think it is doing the job. When I have more time,
| I'll mark the spots and see whether they are at regular intervals: I
| can't be sure where I drove the screws, but I am reasonably confident
| that they were equally spaced (or close enough to).
Why not just drill out the holes and take a chance?
What have you got to lose other than maybe a
cheap drill bit or two?
I wonder about using MDF, though. It chips easily
on the edges and it's very sensitive to water. I'd be
inclined to put something like fir plywood on top. (Or
maybe birch plywood if it has to be very smooth.)
Look at Mayana's solution again ad think about it. There are very few
screws in the wood so, most likely, you won't hit any screws. If you do hit
a screw get a metal bit and finish drilling the hole. Losing a screw is not
a tragedy and you can certainly off-set and put in another screw. You seem
to be looking for a difficult solution to a simple problem.
| It has 1 1/2" solid wood all around to protect the edges. MDF was
| recommended specifically because of its smoothness and flatness. (It's a
| woodsmithshop.com design.)
I'm surprised. It won't be smooth and flat if you spill
your coffee on it. It will swell up. It is very nice in
terms of compressive strength and smoothness, but
really not good for much other than a substrate for
On Thursday, August 7, 2014 10:45:11 AM UTC-4, Percival P. Cassidy wrote:
Get one of these spherical rare earth magnets and roll it around in the area. It will stop when it finds a nail. I have a "solid" desktop and it works on that. Also finds the nails in my hardwood floors.
If Perce's swiveling-magnet nail finder won't find them, they may be
brass screws. Either way, the metal detector approach may be the best
way to find them.
You can build a simple oscillator circuit that operates near the
frequency of a local AM broadcast station. You would use the
oscillator's coil as a probe to detect metallic objects, assuming it is
an air-core coil.
You would tune the oscillator to produce a whistle when listening to the
station on an AM radio. When the coil gets close to a metal object, the
whistle pitch will change. Use the lowest pitch you can hear for best
I have not tried the sound card approach, so do not know how sensitive
it may be. It should be easy to try with two coils of wire, if you know
how to generate and detect a tone.
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