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Magnets for jigs?

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srs

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Long time, not post.... Due to other commitments i've not been near the forum or the workshop for a coulpe of years, but a recent reappraisal of life i've decided to make a bit more effort in this area.

Anyway, I need to make a few featherboards (nothing complicated so far) but instead of clamping them down i would like to insert magnets, but this is where my knowledge fails me a bit, I popped onto ebay to look at magnets and got lost as to the what i would need in regard to stength. could someone with a bit more knowhow advise me what strength / type of magent would be best. I'm guessing somthing fairly strong to stop it walking off, but not somthing that will pull the sun closer.

Cheers

Simon (slowly trying to remember all he has forgotton about woodwork)
 

Jensmith

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I've bought Neodymium magnets from E magnets: http://e-magnetsuk.com/magnet_products/ ... m_magnets/

They have a massive range of sizes, you can even get self adhesive ones and prices are pretty reasonable. I'm not sure what strength you would need but it is listed on their site. I've used some 20mm x 5mm ones and they are really strong!
 

bugbear

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Jensmith":2zmu6rfa said:
I've bought Neodymium magnets from E magnets: http://e-magnetsuk.com/magnet_products/ ... m_magnets/

They have a massive range of sizes, you can even get self adhesive ones and prices are pretty reasonable. I'm not sure what strength you would need but it is listed on their site. I've used some 20mm x 5mm ones and they are really strong!
Strong...

I wanted to make a detachable pointer for knife sharpening; it fixed to the knives using magnets.

My prototype used a large (modern) magnet extracted from a broken hard disc. It held splendidly; in fact slammed onto the knife so hard it tended to mark it.

After some experimentation, I ended up using ... 4 off 2mm diameter by 1mm thick magnets ( :-o ), which hold just firmly enough.

And, yes, handling those tiny magnets presented some issues, but they were perfectly strong enough for my purpose!

BugBear
 

Shultzy

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Not sure that small magnets would be of use as they are not very good at resisting sliding, which is the force featherboards are subjected to. Magswitchs from Axminster are more suitable but pricey.
 

bugbear

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Shultzy":2eihyorc said:
Not sure that small magnets would be of use as they are not very good at resisting sliding, which is the force featherboards are subjected to.
Yeah - while the downforce of a rare-earth magnet is impressive, you need a LOT of downforce to resist sliding - either that of some kind of friction enhancer.

Magnets + router mat perhaps (not tested) ?

BugBear
 

dedee

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I hope this is not hijacking the thread I feel it might be useful.

How does one remove the hard disc magnets from their backing plate?

These are a couple that I have:




Thanks


Andy
 

bugbear

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dedee":q8g5dq5b said:
I hope this is not hijacking the thread I feel it might be useful.

How does one remove the hard disc magnets from their backing plate?

These are a couple that I have:




Thanks


Andy
Normally, they're glued. I remove them by holding the plate in a vice, and striking the magnet with a hardwood punch driven by a 12 Oz hammer.

The plating/coating of the magnet may be removed by the glue when you do this - I've never found a cure for that.

BugBear
 

dedee

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Thanks BB worked a treat



All but one came off easily the last one I hit with a cold chisel which rendered it useless :oops:


Could have had this done in half the time had I not locked myself out of the barn - had to take 4 rows of ship lap off the outside in order to get in.


Andy
 

Digit

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I use the magnets out of scrap Micro wave ovens, they are 50-60mm in dia and can leave grooves in cast iron if you try to slide them. Oh, and you don't want to catch your fingers in between them either! :lol:

Roy.
 

Stoday

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Magnetron magnets are really powerful. I got one when I was a kid and tested it everywhere. It slowed the disk on the electricity meter down to almost a standstill.

A few weeks later, my parents grumbled about their electricity bill. A quarter later still and the bill had sky rocketed. Complaints eventually resulted in a meter change and bill adjustments. The magnetron magnet had weakened the meter's magnet that slowed the disk down.

Years later I started training with East Midlands Electricity Board. Eventually I worked for a bit in the meter dept. I asked the foreman if meters ever went fast. In all my time in meters, he said, only once... :-"
 

Noel

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Digit":2woctax9 said:
I use the magnets out of scrap Micro wave ovens, they are 50-60mm in dia and can leave grooves in cast iron if you try to slide them. Oh, and you don't want to catch your fingers in between them either! :lol:

Roy.
Roy, where are the magnets in micro waves?

Agree that HD magnets are good, all my feathers boards are attached with them. Should be plenty of them in the bin of your local independent computer joint.
 

Digit

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Take the case off Noel and in the area where the switches are you will find a finned 'box'.
There are two magnets inside that 'box'.
If in doubt use a screwdriver etc and poke around till the screwdriver attaches itself to something. They're inside!

Roy.
 

Eric The Viking

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Stoday":3fpkivgo said:
Magnetron magnets are really powerful. I got one when I was a kid and tested it everywhere. It slowed the disk on the electricity meter down to almost a standstill.

A few weeks later, my parents grumbled about their electricity bill. A quarter later still and the bill had sky rocketed. Complaints eventually resulted in a meter change and bill adjustments. The magnetron magnet had weakened the meter's magnet that slowed the disk down.

Years later I started training with East Midlands Electricity Board. Eventually I worked for a bit in the meter dept. I asked the foreman if meters ever went fast. In all my time in meters, he said, only once... :-"
That is such a brilliant story!

:)
 

Eric The Viking

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Digit":1mk1sl1w said:
Take the case off Noel and in the area where the switches are you will find a finned 'box'.
There are two magnets inside that 'box'.
If in doubt use a screwdriver etc and poke around till the screwdriver attaches itself to something. They're inside!

Roy.
Be careful though on two counts:

1. Microwaves have chunky high voltage capacitors inside, connected to the magnetron. These should have a parallel discharge resistor built-in (can be alongside the capacitor too), but sometimes it fails (doesn't affect the microwave's performance!), leaving a definitely-lethal charge on the cap, for days possibly.

2. Some magnetrons use Beryllia insulators, which is a Beryllium compound and rather nasty (read very), and a significant disposal hazard. In taking the magnets off the magnetron you're not directly exposing yourself, BUT make jolly sure you don't break anything ceramic-looking (see below).

On Beryllium: http://en.wikipedia.org/wiki/Beryllium#Toxicity
On Magnetrons: http://en.wikipedia.org/wiki/Magnetron#Health_hazards

Despite the above, have fun!

E.

PS: A tip I got years back was always to keep at least a business card between strong magnets and steel/iron. Because the attraction is inverse to the square of the distance, it's next-to-impossible to separate them once they touch, if you can't get a purchase on them easily. I, too, use hardwood wedges to split them off from their holders in hard disks...
 
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