Thread: Fein magnetic broach core drill

Hi Marc,
does the drill still hold ok on unpainted steel?

Phil

Good question, I did not try since yesterday, should give it a go, but I am sure it will.

Originally Posted by Marc

... how is it possible that a coat of paint, conceded, a rather slick and slippery paint would counteract the strength of the electromagnet? Is there something wrong with it? May be got weaker with time?

I can't give a definitive answer but just about all clamping works by increasing the friction between the two clamped objects, so the slippery paint may cause problems that way. One place I worked we had to put a paper shim in between a chromed part and a powder coated part just to improve the coefficient of friction present. Magnetic fields will loose strength over a gap (whether air or filled with a non-magnetic material), so if the paint is thick or the magnet is suspended on some high spots...

Michael

Yes, the coat of paint is thick in relative terms however the power of the magnet is supposed to be 12000 N. If my memory is correct about this moronic unit, that is 120 tons aprox.
According to Wiki, the force of a magnet reduces inversely to the square of the distance, so F= 1/d2, that is a dramatic reduction but starting from 120 ton a couple of millimeters shouldn't make that much difference. I think the epoxy is the culprit.

Originally Posted by Marc

the power of the magnet is supposed to be 12000 N. If my memory is correct about this moronic unit, that is 120 tons aprox.

12,000 Newtons is 1.2 tonnes. Still a respectable amount of force tho.

If I remember my physics correctly the magnetic field strength falls by the square of the distance between the two faces. So yes a coat of paint a millimetre thick would be the equivalent of a four times reduction in strength per millimetre of area.

Eletro plated gal or hot dip? the laterI assume, it can be pretty thick in places.
Your 1.2 tons is vertical, as Micheal.said, without friction there is nothing stopping the magnet moving sideways. It can side along happily supporting much of the 1.2 ton load vertically*. If paper doesn,t work I,d try a sheet of wet anbd dry( I think I,ve do that in the dim distance past but cant remember the detals)

Stuart

* thats how you get two magnets apart. Though with two magnets there is a force resisting siding

Depends on how far the power lead is run to Marc,
I have had problem before with volt drop not powering the magnetic


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Originally Posted by RustyArc

12,000 Newtons is 1.2 tonnes. Still a respectable amount of force tho.

Doh, 1k = 9.8 newtons not the other way around. Didn't I say its a moronic unit? What's wrong with kilogram force?

Never mind, yes, still a lot of force and even if halved or 1/4 by the paint should be able to keep the drill in place. I lowered the leavers a millimeter at the time really slow to no avail.

Yes hot dip gal plus two thick coats of luxepoxy4 however I am thinking votage drop now, combined with the increased distance from the steel. I used two 20m leads supposedly 15 amp leads but hey, probably 2mm.
PS
Correction they are 1.5 mm 15amp my foot
Should have used the generator

My fein mag base drill stickiness to the work piece is only effective when it is on the workpiece, a mm or two above it and it is weak as... As others have pointed out magnets and an insulation gap do not go well together...

Originally Posted by Marc

Hi there!

When I went to install the channels, two out of the 16 holes needed to be corrected some 5 mm. No problem I thought, got the drill, positioned it and switched the magnet on and as soon as I lowered the broach the whole contraption moved. What? I thought, didn't I switch the magnet on? Tried once more with the same result. Ended up using a die grinder since fortunately had enough hose to reach the job.

So the question to the metal work experts on the forum is ... how is it possible that a coat of paint, conceded, a rather slick and slippery paint would counteract the streanght of the electromagnet? Is there something wrong with it? May be got weaker with time?

Your reply is appreciated.

Marc, I'm pretty sure that the pin at the centre of the rota broach needs to be supported by the pilot hole that you drill first, without
that hole to guide the broach you would have buckleys trying to mill the egde of the hole out.
Of coarse all that depends on whether we are talking about the same beast ?

Fortunately the broach cutters don't need any guide or they would be rather useless. No pilot hole either. In fact I bent the centering pin against the side when the drill slid on the paint because I forgot to take it out.
I think that a combination of thick galvo and paint plus low voltage did the deed.

Originally Posted by Marc

Fortunately the broach cutters don't need any guide or they would be rather useless. No pilot hole either. In fact I bent the centering pin against the side when the drill slid on the paint because I forgot to take it out.
I think that a combination of thick galvo and paint plus low voltage did the deed.

You could test your hypothesis by boring another hole on a fresh lump of uncoated PFC, then move the unit back
5mm as before, and then attempt to move the hole back 5mm as before, I'm betting you will get the same result.
If you do this the cutter will only be cutting on one side, maybe 1/3 or 120 deg of the cutter, as soon as the cutter
contacts the PFC it will come under load and push sideways as the full 360deg of the cutter is not cutting and you
have no pilot pin to stop the sideways thrust.
No doubt the gal and the paint have made a small difference to the holding power of the magnet, but the magnets main
function is to stop the drill from lifting as you apply pressure to the cutter, holding power in shear is nowhere as great.

good luck, shed

When it is not the easiest thing to do, cutting half a hole on the edge of a plate or another hole with an annular cutter is perfectly possible if the magnet works as it should. The centering pin has nothing to do with it and it's only purpose is to center the hole over a mark. The pin retracts as you lower the cutter and there is certainly no pilot hole.
You are probably thinking in a hole cutter.
https://www.youtube.com/watch?v=U8yWMfq69gE
Not a broach cutter
https://www.youtube.com/watch?v=d_KiYfKc-iw
https://www.youtube.com/watch?v=O1zG73Mtol4