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?

Perce

On Thu, 07 Aug 2014 10:45:11 -0400, "Percival P. Cassidy"
wrote:

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?

Perce

If the screws are not brass you might try rare earth magnets.

An X-ray would find it but not be cheap.

Would an ultrasound like a fishfinder show them?

"Oren" wrote in message
...
On Thu, 07 Aug 2014 10:45:11 -0400, "Percival P. Cassidy"
wrote:

..

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?

Perce

If the screws are not brass you might try rare earth magnets.

I was thinking along the same line. Maybe one of the magnets out of an old
hard drive. They are strong enough to penetrate a short distance.

On 8/7/14, 12:42 PM, Ralph Mowery wrote:

"Oren" wrote in message
...
On Thu, 07 Aug 2014 10:45:11 -0400, "Percival P. Cassidy"
wrote:

.

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?

Perce

If the screws are not brass you might try rare earth magnets.

I was thinking along the same line. Maybe one of the magnets out of an old
hard drive. They are strong enough to penetrate a short distance.



Or the magnets from a fuel-injected engine throttle body. I have
several that are so strong you need a wedge to pry 2 of them apart !
They beat any standard stud-finder.

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 a problem.

On 8/7/2014 2:22 PM, nestork wrote:

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
a problem.




I had insulation put under the floors.
The installers got tired of catching their clothes on the flooring nails
and decided to just bang them up flush.
I had nails sticking up at various heights under the rug.

Used a harbor freight stud finder

http://www.harborfreight.com/5-in-1-...ter-92375.html

Found 'em no trouble.
Used a center punch to bang 'em back down thru the rug weave.

On 08/07/14 06:48 pm, mike wrote:

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
a problem.




I had insulation put under the floors.
The installers got tired of catching their clothes on the flooring nails
and decided to just bang them up flush.
I had nails sticking up at various heights under the rug.

Used a harbor freight stud finder

http://www.harborfreight.com/5-in-1-...ter-92375.html

Found 'em no trouble.
Used a center punch to bang 'em back down thru the rug weave.

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.

Perce

On 08/07/14 12:42 pm, Ralph Mowery wrote:

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?

If the screws are not brass you might try rare earth magnets.

I was thinking along the same line. Maybe one of the magnets out of an old
hard drive. They are strong enough to penetrate a short distance.

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).

Perce

On Thu, 07 Aug 2014 17:25:06 -0700, Percival P. Cassidy
wrote:

...snip....
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.

Perce


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
screws/nails.

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.)

On 08/07/14 09:11 pm, Mayayana wrote:
| 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?

And some 3/4" holes that are not deep enough to use for bench dogs but
will collect sawdust and wood shavings, etc.

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.)

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.)

Perce

| 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
laminate.

On 08/07/2014 04:22 PM, nestork wrote:

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
a problem.







The best magnets I've ever used are those taken from SCSI drives.

On 08/07/2014 07:35 PM, Percival P. Cassidy wrote:
On 08/07/14 12:42 pm, Ralph Mowery wrote:

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?

If the screws are not brass you might try rare earth magnets.

I was thinking along the same line. Maybe one of the magnets out of
an old
hard drive. They are strong enough to penetrate a short distance.

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).

Perce




Yep, you found them.


The easy way to find them of course is with a drill bit.

Perce,

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.

Dave M.

On Thursday, August 7, 2014 10:45:11 AM UTC-4, Percival P. Cassidy wrote:
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?



Perce

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.
http://www.heavenlyswords.com/produc...roductid=32298

In article op.xj80ztko2cx0wh@ajm,
RobertMacy wrote:

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
screws/nails.

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
sensitivity.

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.

Fred

On Fri 08 Aug 2014 11:44:53 -0700, Fred McKenzie wrote:

...snipped to keep AIOE happy, very interesting approach!
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.

Fred

There's lot's of free software to run the soundcard so all is 'kind of'
free.

if using two coils, might wrap on 16 penny nails, makes for VERY cheap
core material, and has the right shape.

On Fri, 08 Aug 2014 14:44:53 -0400, Fred McKenzie
wrote:


If Perce's swiveling-magnet nail finder won't find them, they may be
brass screws.

He already posted they were not brass. I brought that up in the first
reply to him. Next!