DIY specimen holder

lothman · Post by **lothman** » Sat Feb 01, 2014 8:06 am

Hi,

I just wanted to share the idea of my magnetic specimen holder since it works so perfect.

I used a strong magnet ø14x3 with a countersink holding a ball bearing ball. In the ball I drilled a hole (you need tungsten bits) for a ø4mm pin. On the pin you can slip an electronic clamp.

All you need is a magnetic surface (steel) to position the holder where ever you want.

Because the ball bearing ball is hardened and polished, the movement is very smooth and good to control. You can shift the magnet lateral, turn and swivel the ball - all parts less than 10$.

Best regards
Lothman

Ichthyophthirius · Post by **Ichthyophthirius** » Sat Feb 01, 2014 10:47 am

Great idea!

Olympusman · Post by **Olympusman** » Sat Feb 01, 2014 11:13 am

Very clever.

ChrisR · Post by **ChrisR** » Sat Feb 01, 2014 5:47 pm

You can use a second identical magnet, with a 4mm countersunk screw in it, whose threaded part goes into the crocodile clip.
It saves drilling the ball. You can use a selection of different screw lengths.

jazzper · Post by **jazzper** » Mon Feb 03, 2014 12:27 pm

Looks nice! I just wish you could get these parts in black - they shine like crazy! Of course you can paint them with a permanent marker, but it rubs off

ChrisR · Post by **ChrisR** » Mon Feb 03, 2014 5:38 pm

There's always "gun blue" which makes a black if you're careless enough

.

elf · Post by **elf** » Mon Feb 03, 2014 11:35 pm

Powdercoating would work well for the non-magnet pieces.

lothman · Post by **lothman** » Tue Feb 04, 2014 7:15 am

ChrisR wrote:You can use a second identical magnet, with a 4mm countersunk screw in it, whose threaded part goes into the crocodile clip.
It saves drilling the ball. You can use a selection of different screw lengths.

but you need the countersink - at least its rim - for the ball. This creates friction and guide for the ball. If the ball cannot get deep enough into the countersink because this is blocked by the screw head this will not work. But you could glue the screw on the backside of a second magnet, then this should work.

Edward Ruden · Post by **Edward Ruden** » Tue Feb 04, 2014 7:47 am

jazzper wrote:Looks nice! I just wish you could get these parts in black - they shine like crazy!

Alligator clips often come with a Black Boot. The pin can be covered with back shrink tubing. The ball can be hidden behind a washer made of flocking material slid over the pin.

ChrisR · Post by **ChrisR** » Tue Feb 04, 2014 7:55 am

Sure - the magnets I have (somewhere) have a deep countersink so it isn't hard. Or file the screw head lower.
Or, as I found while looking for a drawing, use these - which I didn't realise existed

Magnets with TWO countersumk holes !!

Those might provide some useful additional articulation, and a better base if a lump of iron isn't available.

jazzper · Post by **jazzper** » Tue Feb 04, 2014 8:46 am

Lots of good ideas in this post - excellent!

elf · Post by **elf** » Tue Feb 04, 2014 7:53 pm

You could also eliminate the need for drilling the ball bearing if you use these. I used similar magnets in this positioner

Edward Ruden · Post by **Edward Ruden** » Tue Feb 04, 2014 9:12 pm

ChrisR wrote:You can use a second identical magnet, with a 4mm countersunk screw in it, whose threaded part goes into the crocodile clip.
It saves drilling the ball.

The steel ball will become strongly magnetized when in contact with the magnetic base, essentially becoming a magnet itself. So, you don't actually need a second magnet attached to the pin for it to stick. You can just countersink the top of a flat head steel machine screw, with a shaft serving as the pin.

There are lots of choices for bases:
Magnets with Countersunk holes on eBay

ChrisR · Post by **ChrisR** » Wed Feb 05, 2014 4:01 am

Countersinking the top of a screw, or drilling the ball or the magnet, are all things I'd find hard to do without facilities.

Perhaps the easiest would be to countersink a screw head, if one started with a hex-socket headed screw, because the starting depression is already in the middle.

The circular countersunk magnets I had were deeply countersunk, but that's not something generally specified. I've never tried drilling those magnets. I know they're brittle, but how easily they'd drill for a deeper hole, I can only guess. They usually have a hard corrosion resistant plating.

Doodling in Word shows about how much space one has. A slotted screw could have its slot sawn deeper and the top filed, a certain amount, without any machinery.
Intended to represent 1mm squares:

Clearly d= R-√(R² – r²)
So with R=10, r=5; d=1.34
I've "stolen" a little from the top corner of the countersink, because they're usually rounded. That makes it worse for clearance.
I think with these dimensions there's scope for normal, if slightly hand-modified, screw heads.

Edward Ruden · Post by **Edward Ruden** » Wed Feb 05, 2014 7:56 am

ChrisR wrote:Doodling in Word shows about how much space one has.

The ball will rotate smoother if it sits on the conical surface instead of the rim. You need a smaller ball or larger countersink for that. Your sketch is for a magnet with a 4mm hole. I've found on US eBay a few with up to 7mm holes.

On the other hand, if a design is chosen to have the pin with an integrated or attached countersink, It's redundant for the ball to rotate on its base at all. You could just sand/grind a flat on the ball and epoxy it to a flat magnet (sand magnet too for better adhesion). The magnets are brittle ceramics. They can only be modified by sanding or grinding. You could do this to the flat of a round countersunk magnet and epoxy it to a flat head screw if countersinking the screw itself is difficult. That will stick with more force than magnetized steel to steel since the magnetization of steel saturates at less the intensity of the magnet itelf.

DIY specimen holder

DIY specimen holder

Specimen holder