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Magnetic Milling Machine

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Rick Spaidal25/08/2010 19:13:49
12 forum posts
It seems in the last few months my manual milling machine has taken on a magentic charge, all the steel chips are sticking the the cutters, vice and workpiece while held in place to be machined. Has anyone else had an issue like this and what does one do about it ?
Bogstandard25/08/2010 21:52:28
263 forum posts
I would suggest you find the orientation of your mill table.
 
If it is set exactly on or very close to a north/south orientation, cutting material in that orientation will impart a magnetic field to the part, and most probably anything else as well.
 
It is a well known fact that if you put a piece of soft iron in the N-S orientation, and give it a good beating with a hammer, it will turn it magnetic.
 
Just a suggestion that might be causing your problems.
 
Bogs
Richard Parsons26/08/2010 08:33:45
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645 forum posts
33 photos
Rick
Build yourself a demagnitser.  All it is is a coil through which you pass an AC current.  You moe the thing to be demagnitised accross it.  I use the primarys of an old transformer and drive it with a 6 volt bell transformer I dont like 230 volts wandering about.
Gool Luck
Dick

Edited By Richard Parsons on 26/08/2010 08:35:21

KWIL26/08/2010 09:21:40
3681 forum posts
70 photos
The real problem would be making the coil big enough to pass the mill through it
David Clark 126/08/2010 09:43:34
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3357 forum posts
112 photos
10 articles
No, The real problem will be lifting the mill up to pass it through the coil.
Or would it be finding a big enough battery to power it?
Perhaps the cutters and work need demagnetising first?
regards David
 
John Haine26/08/2010 10:16:55
5563 forum posts
322 photos
I had exactly this problem with my Myford VMB.  It seemed that the quill and to some extent some cutters had become magnetised.  I made a demagnetiser which is a bobbin using a short length of plastic drainpipe big enough to accomodate the end of the quill, about 5 cm long, end cheeks made of thin plywood, wound with about 500 grams of 23 gauge enamelled copper wire (a complete spool bought from RS Components).  This is fed from the mains through a 100W lightbulb to limit current and also provide a tapered "inrush"current - when the mains is switched on the current is very high becasue bulb is cold but it dies away as the bulb heats up.
 
Technique is to sit the bobbin on the mill tableon steel packing with a slug of mild steel in it (because the quill won't touch the table at extreme downfeed).  Bring the quill to press on the slug, switch on, then slowly raise the quill out of the magnetic field.  One application fixed the problem and I've never had to repeat it.  Glad to supply photos of how it was done - depending on your location could loan the kit (assuming it would fit your quill).
 
John.
John Olsen26/08/2010 10:44:31
1294 forum posts
108 photos
1 articles
Have the Britsih lost their enterprising spirit? There was a time when they fitted demagnetising coils to whole ships...a mere milling machine would not have caused them any difficulty at all.
 
Then there was that Wellington Bomber fitted with a coil, but that worked the other way around, to set off magnetic mines.
 
BTW the demagnetiser needs to run on AC, not on batteries. But as was suggested, using a low voltage is quite a smart move.
 
regards
John
Richard Parsons26/08/2010 17:44:18
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645 forum posts
33 photos
 

If the whole machine is your worry then wind 5 or 6 turns of cable round the confounded machine and hook it up to a low voltage AC source for a few hours. I have a similar problem over here in Hungary. The soil is full of iron but it is too diffuse to recover and the ‘Variation’ is Zero not 12½°West like back in the U.K. but I only demagnetise  small hand tools. 

BTW Magnetic mine sweeping with a Wimpey was BLOOMING dangerous.  You had to fly at under 50 feet and if a mine went up it was touch and go -they contained about 1 ton of bang stuff-
 
Hi Dave hows the metal plates doing? You have to use AC to demagnetise anything, low voltage, if possable, I would not like to read about a 'fried editor' 
Regards
Dick
 
Billy Mills26/08/2010 18:41:11
377 forum posts
To demagnitise a ferrous object by the AC degaussing method you create an alternating field that has to be greater than the initial field in the object. By then slowly reducing the alternating field  to zero you "sweep out" the field to a small residual value by periodicaly reversing the magnetising field down to zero. If you remember Hysteresis curves then you are running around the curve reducing the B to zero at the origin 0.0.
 
The simplest method is to use an air cored coil  large enough to be passed over the magnetised object then slowly remove the coil to some distance - say 5 diameters- away before switching off the current. ( Slow being 3-5 sec) Do not switch off before or you will magnetise the object!
 
At work we use a coil of 1m diameter and about 380 turns  connected directly across the mains  240 V ac supply. No inrush protection  is needed - it is an INDUCTOR !!!!
The draw is about 3A in air.   It is used to degauss displays using CRT's in steel frames and has been in daily use for 29 years. It has never failed it's task. But it does use 1200m of wire!
 
You need about 1000 Amp/turns to demagnitise most steel objects, any less is a waste of time. Custom degaussers can use iron cores to confine the field to a small working region but they - along with "wand" degaussers will not work on machine tools. Nearly all demagnitisers are rated for intermittent use i.e. they overcurrent the coils so you don't leave them running too long.
 
You don't have to worry about motors or anything containing magnets in closed paths  when bulk degaussing since the closed path is a very much lower reluctance than the demag path.
 
It might be possible to use an arc welder as an AC source running an air cored coil but unless you can reach around 1000A/t you could only touch very lightly magnetised objects.
 
  Don't bother with degauss coils from old colour TV's, the field and their design is not suitable for the task. If you don't understand coil design, insulation and are not happy with electricity seek help with degaussing. Connecting things across the mains may be harmful. If a friend gives you two wires to hold do not trust him ever again.
 
Regards, Alan.
 

Stub Mandrel26/08/2010 20:35:22
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4318 forum posts
291 photos
1 articles
My Dad used to have a degaussing coil about 8-10" across wound between two octagonal formers - it was a commercial item. Used on TVs or anything else you pressed the button, waved it over the object, walked a good 8 feet away and turned off.
 
Hit and miss, but I have degaussed two badly magnetised computer monitors and a TV by waving a loudspeaker magnet at the very fast!
 
Neil
Ian S C27/08/2010 11:58:30
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7468 forum posts
230 photos
My demagnetiser consists of a primary coil from the transformer from a micro wave oven, it has a hole through it about 2" x2 1/2", and  use 12V from a transformer, it works well. Back in my days in aircraft engineering we used a big vesion of this (hole about 12" square), for magna -flux crack testing, I think the coil was surplace RNZAF equipment, and aproved by the CAA. Put the artical in the coil, switch on , then off-magnetised, do the test. Switch on pass the artical through the coil,then back and remove a good distance, switch off, check for residual magnetisim, if any repeat the demag. Ian S C

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