Magnetic chuck for a milling machine.
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    Default Magnetic chuck for a milling machine.

    Any pro's or con's on using a magnetic chuck on a cnc or conventional mill for light duty face milling? I run a job that requires taking a light cut (.015-.020) on hrs to remove the black oxidation layer for better weld quality and it seems like a mag chuck would be an easier way, any thoughts? The parts I am currently working with are 2"x3"x5" hrs.

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    I tried doing that once when I first started and one of the older tool makers almost flipped....to this day I won't even try it.

    That said...it doesn't mean it won't actually work lol

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    I Have seen it done..advantage is square, flat and accuracy better than a vise..disadvantage is you can't hog as much as vise or hold downs. Holding may be adding a good block in arm or bump stop. and cant hold non-mag parts..

    Hold down is crazy hard with a mag-chuck but the part can slide..and that is where a stop block-in is needed..Stop block would be bolted down to the table and bumping high on the part.

    Likely figuring the direction of cutting force, have a block stop in that direction would be fine...

    But yes Mag Chucks are soft top so a rough surface part may wear out the flatness.

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    I've seen it done with a large mains powered electro magnetic chuck. It was fine until a painter was looking for somewhere to plug his radio in and un-plugged the chuck ! I heard the crash about 50 yards away.

    Regards Tyrone.

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    if you are doing the facing operation just to clean up the part for welding,
    the mag chuck is wrong for the reasons sited above, but moreover the mill is totally the wrong tool and process.

    for a part that size, an angle grinder with a "strip and sand" corse scothbrite
    will be 3x faster, remove far less material, and leave a better surface finish.

    A drum or belt dander is an ok second choice.

    who would even think of milling that?

    if a flatness spec is required, starting with a cold rolled product would seem the way to go, and even if I was starting with a hot rolled product, I would strip off the mill scale first.

    mill scale has NO place in any of my machine tools...

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    Make sure that you have stops on the sides of the chuck pressing against the edges of the material and feed only toward the stops or you risk wearing your work. It is convenient for what you are doing but things can easily go wrong. As the cutter dulls or grime builds up on the chuck, bad can quickly happen. Why not just run the material through a Timesaver belt sander? It is faster and far safer.

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    Quote Originally Posted by MARK07747 View Post
    Why not just run the material through a Timesaver belt sander? It is faster and far safer.
    yes, the obvious go to, but if the OP had one I figured they would be using it, don't ya think?.. so I left it out.

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    Sanding does seem like the way to remove the scale from HRS, but unless you can get beneath the scale in a hurry that stuff is insanely hard, dulling belts or discs quickly. BTW, these parts are for a good paying fussy customer and the appearance of a machined surface can justify a sweeter price.

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    QT: [2"x3"x5" hrs.] Now holding in a vise?.. it there a problem with that?

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    believe me, I know well the properties of mill scale, and have come up with a few tricks to bust up the stuff, with minimal tools, equipment, and time, but still find those pads and an angle grinder to be readily available and highly cost effective.

    aluminum oxide "sandpaper" is NOT my first choice, for the simple reason that one of the constituents of some mill scale IS aluminum oxide. (ever wonder why some scale is nearly impervious to a regular sanding disk?)

    thus my go to is a disk with corse silicon carbide grit.

    if it is a relatively small piece for a good paying client, I am having a hard time thinking why cold rolled would not be the starting material, even if it were to be "machined for appearance" ?

    and also, a machined surface, preformed pre-weld on a weldment, (which is going to distort from the welding anyway) where not specified, just looks dumb and un-professional in my book.

    more "what the hell were they thinking" than "nice job" to me.

    not trying to be mean, hope you get it that I'm just latin' it out there the way its gonna come off to a pro..I think. anyone else that would have the same thought?

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    I use Schunk Magnos magnetic chucks. They work great for larger parts that cover most of the surface of the chuck. Each chuck has 20,000 pounds of holding force if the entire chuck is covered. The magnets are permanent, electricity is used to flip the poles, which causes magnetic flux to come out of the top of the chuck. Once clamped the power is disconnected and machining starts. Pole extensions are used to lift the part off the surface of the chuck. 3 fixed extensions are used to support the part. The rest of the extensions are floating to conform to the workpiece. The floating extensions lock when the chuck is clamped. These magnets are best at clamping larger workpieces that are thick enough that most of the flux stays within the workpiece.

    Magnos - Shunk - YouTube

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    Removing mill scale is difficult with hand tools.
    I use a lot of HRS and I get almost all of my material wheel abraded from my supplier, it is very inexpensive and convenient. I get my material wheeled only, no primer.
    Second best is to sand blast and I do that quite often if it a rush order and I can’t get wheeled material in time as it does take extra time after ordering.
    I would not choose a mill to remove scale, and if I did then why not clamp in a vise?

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    Quote Originally Posted by Bluechipx View Post
    Any pro's or con's on using a magnetic chuck on a cnc or conventional mill for light duty face milling? I run a job that requires taking a light cut (.015-.020) on hrs to remove the black oxidation layer for better weld quality and it seems like a mag chuck would be an easier way, any thoughts? The parts I am currently working with are 2"x3"x5" hrs.
    .
    magnetic vise used to hold parts that get blanchard coarse ground. usually removes .001 to .005 in less than a minute and removing .20" can take many minutes but often used on difficult to hold parts.
    .
    thinner metal has less holding power, sometimes parallels are stuck to magnetic to give extra so parts dont slide along vise.
    .
    vacuum vise is used sometimes instead

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    Alphaworkholding.com

    They build magnetic milling fixtures

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    bluechipx,
    Back in the day the go to way to remove the bark or scale from
    hot rolled steel was the good old shaper. A properly ground High
    Speed tool bit would give you a good finish and easily remove
    .015-.020 in one pass. For the part you described a small shaper
    would work well. I have a 7" Logan that takes up very little space
    and I use it often to square up & debark cast iron. Old
    school for sure but a satisfying machine to use and it
    earns it's keep.
    spaeth

    dscn2254.jpg dscn2253.jpg

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    Quote Originally Posted by michiganbuck View Post
    QT: [2"x3"x5" hrs.] Now holding in a vise?.. it there a problem with that?
    A vise would work, one piece at a time, but I have a mag chuck that is 16"x48" and a cnc mill that has 30"x52" travels and there are several hundred pieces.

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    Quote Originally Posted by cyanidekid View Post
    believe me, I know well the properties of mill scale, and have come up with a few tricks to bust up the stuff, with minimal tools, equipment, and time, but still find those pads and an angle grinder to be readily available and highly cost effective.

    aluminum oxide "sandpaper" is NOT my first choice, for the simple reason that one of the constituents of some mill scale IS aluminum oxide. (ever wonder why some scale is nearly impervious to a regular sanding disk?)

    thus my go to is a disk with corse silicon carbide grit.

    if it is a relatively small piece for a good paying client, I am having a hard time thinking why cold rolled would not be the starting material, even if it were to be "machined for appearance" ?

    and also, a machined surface, preformed pre-weld on a weldment, (which is going to distort from the welding anyway) where not specified, just looks dumb and un-professional in my book.

    more "what the hell were they thinking" than "nice job" to me.

    not trying to be mean, hope you get it that I'm just latin' it out there the way its gonna come off to a pro..I think. anyone else that would have the same thought?
    I'll have to disagree with this one. My customer is an aircraft research facility. The appearance of the work we do, whether necessary or not is critical. Over the years so-so machinists have slowly faded from the list of go to's. When a job requires the touch of perfection, who do you think they will call? Major companys such as Pratt Whitney, GE, Westinghouse and many more send reps to the facility almost daily. My customer has a world class reputation for leading edge quality and appearance is very important to their professional image.

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    bluechip I was asking what the current holding Re:QT: [2"x3"x5" hrs.] Now holding in a vise?.. it there a problem with that?

    The magnet chuck could be loaded full with a high bump stop to the opposite of the cutting force and with mill trammed well could use a fly cutter. Yes likely to still get .001 or .0005 dish in the part
    Use of end mill and a special sharpening would serve well. That is a 1/16 flat at the end coming in from the OD..then the normal end mill dish to center.

    IMHO it would be good to have a cutter sharpening ability to end-only sharpen end mills.. Light skim ends only takes 5 minuets and can save a lot of money... End mill ODs can be sharpened out of a tube or bushing for near absolute flat and true..much better than out of a work head and a holding device like a collect or other holding device..with such you get all the flutes cutting ..not just the high one..Likely you would only take .020 or so to sharpen so that would be a piece of cake..sharpening across in your end for that kind of work center-gash to end-cutting or just watching center is not even needed. You jut wipe out the center for faster sharpening.

    Running the full 48" chuck your operator would have plenty of time to sharpen a few end mills.

    Qt: [but I have a mag chuck that is 16"x48" ] Oh, does that mean you are already using the mag chuck?

    QT: [have a cnc mill that has 30"x52"] ..good you have that but seems this job would be as well done on a good quality manual mill having power feed and possible a shut down at end of travel.. Seems here in the USA we need a $100k machine to do most everything and that may be part of the reason we can't compete. Also indexable tooling In some cases good and in some cases a waste of money..

    Here a $320 3/4 carbide end mill could be resharpened perhaps 40 times in house and be less that $8.00 per use and less than $10 peruse including sharpening..and a much better surface finish than an indexable cutter. A shell mill with a cutter grinder tickle also gives a better surface finish and longer life. Yes for an indexable a corner and a small end tickle works wonders..even faster the setting inserts as like on a insert setting mill like a value mill.

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    its like using a portable magnetic drill. the magnet is strongest when metal you stick too is flat and at least 2" thick. as metal is thinner the holding power is less. same with using a lifting magnet. you try using with sheet metal and it will bend from its own weight and peel itself off and load fall.
    .
    thus why on a blanchard grinder typically used to clean sole plates 1.5" thick in the 1 foot to over 4 foot size how thick the parts are influences how much you can push on them. blanchard grinder typically on the coarse side and normally tolerance is a .001 or .002" buts thats often the best for cleaning hot rolled plates which can be wavy often 10x that amount

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    Quote Originally Posted by Bluechipx View Post
    I'll have to disagree with this one. My customer is an aircraft research facility. The appearance of the work we do, whether necessary or not is critical. Over the years so-so machinists have slowly faded from the list of go to's. When a job requires the touch of perfection, who do you think they will call? Major companys such as Pratt Whitney, GE, Westinghouse and many more send reps to the facility almost daily. My customer has a world class reputation for leading edge quality and appearance is very important to their professional image.
    I agree, im just a hack running out of a single car garage, but customers absolutely love my surface ground parts, totally unneeded, just shiny sells!!!

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