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Thread: Magnetic Chucks

  1. #1
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    612

    Default Magnetic Chucks

    We are getting good results with a vacuum chuck on our Men's Shed Router.
    During an idle moment today, the subject of magnetic chucks arose.

    Our vacuum chuck uses a tyre pump backwards to achieve -50 kPa over an area of 6400 mm sq (80x80).
    The stock is 95x95 mm 3 mm MDF.
    A 2 mm cutter trims the outer shape to a coaster 86 x 86 mm in steps of 0.4 mm.
    We have not seen any movement over about 10 jobs so far.

    Is it likely a small magnetic chuck, permanent or electric, could achieve the same result using, say, a piece of 5 mm steel plate 80 x80 as the top clamp ?

    John

  2. #2
    Join Date
    Apr 2013
    Location
    Toowoomba Qld
    Posts
    363

    Default

    Hi John

    My understanding is not all magnetic chucks are created equal, there can be different setup's with magnet size and spacing, the different layout is dependent on the intended use of the chuck. For example one with small magnets generally is designed to hold smaller / thinner parts where bigger magnets would be better suited to holder larger / thicker material.

    The cut you are describing, 3mm depth of cut at 0.4mm step over in MDF is a tiny cut unless you are moving at some crazy travel speed, which I'm guessing you are not. At that small of a cut load you could probably get away with just putting a couple Kg lump of steel on top to hold it down (not suggested you actually do this...)
    So to answer you question I'd say it is probably possible with the correct Mag Chuck to get it to hold, I have to ask the question tho, why would you ?
    At the moment you may only be routing the outside but you have access to the face if you decide to do something more later. It's like using a sliding panel saw to cut up your firewood, sure it could probably do it. But it's not the best tool for the job.

  3. #3
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    612

    Default

    We have a process:
    - cut raw blanks 95x95 out of sheets of MDF on a vertical bandsaw,
    - hold raw blank on vacuum chuck to cut coaster outline into a blank coaster,
    - clamp blank coaster on a fixture,
    - change tool and engrave the shed logo and initials,
    - on demand, re-load initialized coaster and engrave the name of the visitor.

    At each step we accumulate a buffer stock to make it easier for the next step.
    Our annual open day for visitors is this coming Saturday, and we have it pretty slick to date.

    Cutting individual blanks is easier than trying to combat the out-of-flatness platen affecting a sheet of MDF.
    The magnetic chuck was just idle discussion.

    Plug: Penrith Community Men's Shed, Baptist Church, Caddens (Morelli Tce).

    John

  4. #4
    Join Date
    Apr 2013
    Location
    Toowoomba Qld
    Posts
    363

    Default

    Guessing you are not punching out great numbers of these ?

    If you are have you considered making a larger vacuum plate where instead of raw cutting them down individually you could load a sheet that you get say 6 or more out of and use the cutter to bring them to size and separate them ? Just sounds like it would be a time consuming job otherwise.

    95 x 95 to 86 x 86 = 9mm reduction / 4.5mm off each side, 0.4mm per pass = 11.25 so 11 roughing + 1 finishing pass = 12 passes
    86mm side x 4 sides = 344mm, going to guess by how conservative on the other numbers feed rate likely no more then 200mm min, each pass between 90 to 120 seconds
    12 x 90 = 1,080 seconds / 18 minutes

    Am I right on my calculations ? that sounds like a long time just to profile the outside

    I'd be going to a larger routing bit, maybe something like a 6mm, rigidity of a 6mm vs 2mm is crazy, you will also get higher SFM on the cutting edges so should be able to feed faster, I believe timber likes higher SFM also. This is of course assuming your vac table is strong enough, Vac tables are capable of pretty damn strong holding force tho
    Eg https://www.youtube.com/watch?v=FcRGvB6dYw0#t=11.610882

  5. #5
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    612

    Default

    We cut through the MDF in 8 passes, no tabs or niceties.
    The excess surround peels away OK.
    Milling passes don't work, the MDF deflects and forms large burrs.

    Remember, this is currently only an interest for old farts to play with.
    Right now, all we want to do is demonstrate operation.
    Our machine is frankly too flimsy for serious work, and there is a vibration in the Y direction that must be researched.

    After the open day, we will start on some flatpack critters for Xmas presents.

    John

  6. #6
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    612

    Default

    The open day went well, engraved over 25 coasters for visitors.
    Background job is making a coaster for every member of the shed.
    Trouble is, some of the guys want multiple copies, and/or, the wife's name - this will all take some time.

    Didn't make any operator mistakes today, and our cycle time is improving.
    But, had a limit switch operate for no reason and a loss of communication put down to a loose USB cable.
    Neither fault actually caused any problems but it just adds to the list of areas to be investigated.

    John

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