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Eclipse 934 magnetic V block

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Massimo Dalmonte04/12/2021 15:57:02
33 forum posts
18 photos

Good afternoon everybody,

I recently bought an old V block, the magnet was stuck and I managed to have it move again by soaking it in ATF fluid and then hitting the magnet with a wooden dowel alternatively from both sides.

Doing this, the major part of it was always in its cavity, protruding about 1.5 cm over the total of 10.

I don't know if this was enough to loose magnetism, anyway now it works, but, once set on the milling machine table, I can move it rather easily with my hand.

Is it possible to restore the original magnetism and could you tell me which kind of firm I should turn to?

Thanks,

Massimo

Mark Rand04/12/2021 17:26:52
1272 forum posts
28 photos

I have a large Eclipe magnetic V block. I don't know the number, but it's 4" long by 3.75" high.

It has an Alnico magnet. These are potentially very strong, but can be demagnetised very easily (That's how I got it as scrap from work).

My plan is not to remagnetise it, but to make an aluminium or brass carrier for a number of square neodymium magnets as a new rotor, I think that this will be a better long term solution. I have bought the magnets, but have not got aroung to doing the work yet.

SillyOldDuffer04/12/2021 18:22:18
Moderator
8692 forum posts
1967 photos
Posted by Mark Rand on 04/12/2021 17:26:52:

...

It has an Alnico magnet. These are potentially very strong, but can be demagnetised very easily (That's how I got it as scrap from work).

...

Sorry, I don't know the answer to Massimo's question. Maybe a magneto remagnetising firm could do it? Several of them on the web, but the magnet is created inside the assembled V-Block, and I'm not sure how that's done, or if a magneto remagnetiser is suitable.

I've always wondered about Alinco magnets being easily demagnetised, even by dismantling. Didn't seem likely to me that removing a magnet would damage it: seems I'm wrong. This website explains:

Putting the Alnico magnet in open circuit may be enough to cause self demagnetisation (the working point is taken beyond the ‘knee’ of the Intrinsic curve, causing demagnetisation). The working point is changed if the magnetic circuit changes. Self demagnetisation occurs because the magnetic field from the magnet can pass back through the magnet itself (the magnetic path is more preferable than the air surrounding the magnet), which is thus an external demagnetising field applied by the magnet itself...

As I understand it, in a device like a magnetic vice, a block of un-magnetised Alinco alloy is assembled in a structure that as a whole creates a stable magnetic circuit after the whole is whacked with a massive electric pulse. Pulsing creates an Alinco permanent magnet that depends on the surrounding structure. If the permanent magnet is removed from the assembly, the magnetic circuit alters and it starts de-magnetising itself. How fast it declines depends on the magnet's geometry: short fat magnets fade faster than long thin ones.

Dave

DiogenesII04/12/2021 19:01:46
561 forum posts
221 photos

..kind of a 'Schrodinger's Magnet' then..?

Massimo Dalmonte08/12/2021 11:26:28
33 forum posts
18 photos

Mark, I think we have the same:20211208_092629.jpg

the magnet in the "on" position:

20211208_092921.jpg

looking with a gadget which should give an idea of the magnetic field lines, we see that these do not look very "healthy":

20211208_093005.jpg

for a comparison, this is a stack of magnet as found in hard disks

20211208_094722.jpg

the idea of the neodimium magnets stack is good, but I'm afraid that if there is not a complete path of high magnetic permeability material, with the minimum of air gap, but some brass or aluminum, the magnetic effect could be strongly reduced ( anyway I could be wrong Dave, magnets are almost black magic for me smiley).

Massimo

Mark Rand08/12/2021 13:26:11
1272 forum posts
28 photos

Sorry, I should have said that I intended for the neodymium magnets to be held in an aluminium or brass frame that was sandwiched between two steel pole pieces. The plan was to bolt the pieces together, turn the assembly to the right diameter for a close fit, then insert the magnets in it and assemble it into the V block,.

The good thing about the Neodymium magnets is that their coercivity (resistance to changes in magnetic field) is enormous compared with Alnico, steel etc., so they don't demagnetise at all easily (except if you get them hot). Their maximum possible magnetic field is actually slightly less than that of Alnico, but you'll never see a fully magnetised lump of Alnico because it's so easy to demagnetise.

Your one does look identical to mine, apart from the handle being different.

RobCox08/12/2021 14:20:15
59 forum posts
20 photos

This might be a bit of a mad idea, but...

If you could get a transformer a bit bigger than the V block, take it apart so you have the E laminations and the windings left. Connect the thickest windings to a DC supply, put 2 limbs of the E laminations in contact with the V block and pass as large a current as the windings will stand from the supply. There should be a large magnetic field generated by the transformer coil which you are arranging to pass through the V block (with it in the ON position). This might reinforce the magnets strength (check which way round first, otherwise it'll try and demagnetise it or push the electromagnet away).

I'm guessing this is a bodge version of what would be done commercially.

Massimo Dalmonte11/12/2021 15:41:01
33 forum posts
18 photos

An update: I went to an old school car electrician, a gent in his eighties, who owned an antique remagnetizing contraption and treated my block with it for a few minutes.

A nice guy, did it for free, but alas I didn't notice improvements; didn't have the courage to tell him...

On the other hand, I read on the net:

"don't bother to buy any of the small homemade magnet chargers - they will not saturate an AlNiCo magnet."

(as I suspected).

peak411/12/2021 20:57:02
avatar
1713 forum posts
183 photos

Where do you live?
If in the UK Eclipse in Sheffield will do it for you.

Bill

Massimo Dalmonte12/12/2021 22:34:06
33 forum posts
18 photos

Hi Bill,

yes, this would be the logical approach, but I live in Italy and the round trip must be costly, it's a rather heavy item (and probably I would have to pay the customs too on the return leg), that's why I hoped about a local solution.

I'll try to enquire with Eclipse anyway, to get an idea, thanks.

Massimo

peak412/12/2021 22:46:04
avatar
1713 forum posts
183 photos
Posted by Massimo Dalmonte on 12/12/2021 22:34:06:

Hi Bill,

yes, this would be the logical approach, but I live in Italy and the round trip must be costly, it's a rather heavy item (and probably I would have to pay the customs too on the return leg), that's why I hoped about a local solution.

I'll try to enquire with Eclipse anyway, to get an idea, thanks.

Massimo

I'm guessing that it will be cheaper, and easier, to buy a replacement; particularly considering the customs and tax implications post Brexit.
I made tentative enquiries about getting a 12" diameter magnetic chuck re-magnetised.
I could deliver and collect personally, and was looking in the region of £150

Bill

Edited By peak4 on 12/12/2021 23:15:06

Mark Rand13/03/2022 12:41:25
1272 forum posts
28 photos

An update on this topic. I've spent the last few days making a new rotor for my V block. It seems to have succeded.

roughing.jpg

I glued (with Loctite 648) and screwed two surface ground lumps of steel to a milled block of aluminium. Mounted the assembly with a Myford dividing head on the milling machine and roughed off the corners. The reason for using an MT2 drill chuck rather than the three jaw lathe chuck was that the lathe chuck fouled the milling chuck.

separated.jpg

This is what the innards look like. It wasn't an intentional dissassembly, I got it a bit warm when turning is on the lathe with a chipped insert and the glue came apart. But it does show the general arrangement.

turned.jpg

This is the finish turned rotor.

match marked.jpg

I match marked the ends with one dot at one end and two at the other to simplify reassembly

gluing.jpg

After cooking it in the oven to release the Loctire, I cleaned it up and reassembled the bits. This took some care, the 30x30x15mm magnets are extremely strong and want to sit on top of each other, not side-by-side. I actually used the bit of wood, clamped with two, distanced, G cramps to sit over the first magnet while pushing the second magnet into its pocket. The edges of the steel pole pieces are also razor sharp and need respect. More Loctite 648 was used as glue.

assembled.jpg

At this point I learned that it would have been better to use a taper reamer in the screw holes before separating the parts, so that they could be accurately realigned with a couple of taper pins. I had to turn a couple of thou off the assembled rotor to get it to fit in the V block. Not a nice thing to do with a strong magnetic assembly.

test.jpg

After getting it all together I gave it a little test. It happily holds up a 27kg electromagnetic chuck. With the original magnets, I could pull the V block off with my hands.

Edited By Mark Rand on 13/03/2022 12:45:52

Michael Gilligan13/03/2022 23:24:59
avatar
20182 forum posts
1053 photos

Superb result, Markyes

MichaelG.

bernard towers14/03/2022 09:14:32
618 forum posts
109 photos

Mark, I think you may have started something here! I know several people who have these weak v blocks.

bernard towers14/03/2022 09:14:32
618 forum posts
109 photos

Mark, I think you may have started something here! I know several people who have these weak v blocks.

Henry Brown14/03/2022 10:20:07
avatar
552 forum posts
117 photos

Excellent Mark, thanks for taking the time to document your project, delighted it worked out ok.

Massimo Dalmonte15/03/2022 08:38:01
33 forum posts
18 photos

Hi Mark,

nice step by step report, I think this is the best solution for me too; I initially thought I would have used 3 taller cylindrical magnets, but your approach has "more magnet" and is to be preferred.

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