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  1. #21
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    Quote Originally Posted by Djstorm100 View Post
    Hey guys,


    What this stems from is I need to cut this 7.9" x7.9" part. It's 1/8, although I'm thinking of making it 3/16. Material is 6061 t6. and while not typically thing. I wouldn't do this in a vise because of the span of material. Starting off with 8"x 8" rough stock. How would you do something like this?

    I was thinking dowel pins for locating and strap clamp would help clean up the operations but it doesn't look like it.

    Op1 - strap clamp, drill & counter sink the 4 corners.

    Op2 - Remove strap clamp, use 4 counter sunk heads to hold part down, face it (think this will get ugly since nothing is holding it down in the center), Profile, and chamfer

    Op3 - Flip it over and hold it for facing op and chamfer. How to hold it...still working on that.


    Have someone laser cut this profile for you, that is much easier for them to do this and remove the tabs when done. You can also machine 8" x 8" stock with soft jaws in two positions. machine two ends first and then flip the part over and finish machine the ends and corners.

  2. #22
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    Also, once you have one set up, vacuum is the easiest way imaginable to do this sort of thing. Run your gasket more or less around the part (a minute, maybe) and go to town.

    Why do you want to flip it? If there is any volume at all, back-chamfer it in the mill. If there isn't, use a drill press and a countersink.

    It sure looks like a lasered or punched part to me, too, but I'll take your word for it that it has to be machined.

  3. #23
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    If it is being faced for cosmetics, look into other ways to finish it.

    A scotchbrite pad and some elbow grease will make a very nice grained surface. Or you could throw a wire wheel in the spindle and mess around with finishing it like that. After machining you'll have four holes to screw it down by, so that should be no issue.

    It should look a lot nicer than a bare milled surface in my opinion, especially if it looks bad due to unsupported areas near the middle.

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    Best way I have found for doing one off or very short run parts like this is using super glue. I don't have a vacuum plate..

    1. Take a scrap piece of aluminum say 3/8 or thicker that is larger than your part for a fixture plate. Clamp it in your vice with the top surface above the top of your vice. Face the top of it off for good measure for a clean gluing surface.
    2. Next super glue your stock to the plate. I usually get my supper glue from radio control hobby shops. They call it CA glue. You can get different viscosities and they usually also carry an accelerator and debonder. I have never tried a debonder, acetone works well.
    3. Mill out the profile and holes of your part all at once cutting slightly into your fixture plate to get a clean cut.
    4. Take a razor blade between the bottom of your part and fixture plate and tap with a hammer. If you are careful the part will break free and after breaking the edge of the part you won't have a blemish from the razor blade. You could probably get creative and mill a depression in your fixture plate to break the part off the fixture plate with a soft piece of material but the razor blade has worked great for me.
    5. Clean the cured superglue off your part with acetone.
    6. Clean the super glue off your fixture with acetone or re-face it and make more parts.

    This method has worked good for me for short run parts. If I had to do a lot of the same part I might think about doing it another way. I have heard of using masking tape on the part and then gluing to it so you don't have to clean the super glue off. I have yet to try it this way but I assume it works.

    Here is a video I made. Fixturing Parts for Machining with Super Glue - YouTube

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    I've done the super glue thing, too. Pain in the butt.

    A vacuum plate doesn't have to be a big complicated setup. You need a thick-ish chunk of aluminum. 7" x 12" x 1" thick is nice and fits in a vise. You need a $20 vaccum generator. You need a $5 muffler on the exhaust (the metal screen kind won't clog up like the plastic kind) and you need literally $10 in fittings and air hoses. For occasional use you don't even need a valve.

    Then you need some 1/8" of 1/4" closed cell foam cord, which is $20 for 100 feet.

    You can have the whole setup going for under $100 plus a scrap chunk of aluminum, and make it in an hour or two. They're too handy NOT to have one in your back pocket.

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    You can buy pre-finished aluminum sheet with a brushed finish on one side or both sides. Material like this comes with protective plastic film applied to the finished side(s). If you can't find the right alloy and thickness in pre-finished stock, then you can use a non-woven abrasive drum to put the finish on the stock once the part is otherwise done.

    I doubt any attempt to face mill a part this large and thin is gonna turn out well regardless of the method of holding. If the customer absolutely insists on machined surfaces, I'd expect the labor portion of the job to be 3X to 5X the cost of brush finished surfaces.

    I did a job a while back of 500 pieces of a tapered steel shim made from customer supplied laser cut steel blanks about 3" x 5" with the minimum thickness tapering to the 1/8" thick range. As a flat part with no surfacing required, about a $4 part at most. The tapered face milling requirement kicked my price up to $17/ea and that was good enough to get the job. Seemed awfully high going in, but turned out to be a reasonable price as the work generated a decent shop rate but certainly no windfall.

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    Great suggestions, Thanks you all!


    Going to try my hand at making a fixture vacuum plate so while with 2 parts on it. While one is running I can prep the other vacuum plate.


    Now sure how one would backside chamfer it. Unless in the pallet milled a slot around the part for part for the backside chamfer tool. I would image this slot would have to be pretty deep, no? 1/4" maybe?


    The bottom side, doesn't have to necessarily be milled but if this goes in to production, just can't be raw material. Good enough to put your name on it to send out to customers type thing. It's all bare however.


    The 4 legs that are 8" long with slots in them, are going to be fun to make fixture for. I haven't had to make fixtures like this before but damn eager to learn.

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    Quote Originally Posted by Djstorm100 View Post
    Now sure how one would backside chamfer it. Unless in the pallet milled a slot around the part for part for the backside chamfer tool. I would image this slot would have to be pretty deep, no? 1/4" maybe?.
    Only needs to be .02" or .03" deep if using a true back-chamfer tool.

    Regards.

    Mike

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    Quote Originally Posted by Djstorm100 View Post
    Going to try my hand at making a fixture vacuum plate so while with 2 parts on it. While one is running I can prep the other vacuum plate.
    There's no "prep the other plate." You switch off the vacuum, take the completed part off, position the next blank, switch the vacuum back on.

    If you try to position parts on the " other fixture," they're liable to slide around as you position and affix the fixture, with no vacuum holding anything in place (assuming you have the back-chamfer relief groove all the way around the periphery).

    Regards.

    Mike

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    Quote Originally Posted by Djstorm100 View Post
    The bottom side, doesn't have to necessarily be milled but if this goes in to production, just can't be raw material. Good enough to put your name on it to send out to customers type thing. It's all bare however.
    DA Sander and scotchbrite will give it a good finish without milling and might also prevent having to backside chamfer it.

    Teryk

    Sent from my XT1710-02 using Tapatalk

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    Quote Originally Posted by Finegrain View Post
    There's no "prep the other plate." You switch off the vacuum, take the completed part off, position the next blank, switch the vacuum back on.

    If you try to position parts on the " other fixture," they're liable to slide around as you position and affix the fixture, with no vacuum holding anything in place (assuming you have the back-chamfer relief groove all the way around the periphery).

    Regards.

    Mike
    Mike, You are absolutely right. I've literally have change designs (mostly slight things) to make sure it works the first time around.


    My table only has 18"X, I need to deck the vacuum plate... I have a 2.5" face mill. The concern I keep battle with my self, is this. I'll have the shell mill come in at back corner of the table, The shell mill will plunge in to the stock slightly and start moving in the x+. The material that didn't get cut during the plunge will be picked up by the rear of the shell mill as it passes. Will this cause any issues? Finish pass take .010. just wanting to get the top perpendicular to the spindle is all.

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    I dunno about what all these guys are talking about, unless you have a silly flatness or surface finish spec, start with 1/8x8x8

    drill/mill interpolate whatever all the holes + 1/16 dims from edge, hold it in a vise, perhaps you will need a small bit of fixturing to keep it from bowing, but it is 1/8 and you are not taking a big chip, it will probably be fine. Worst case clamp it to a slightly undersize piece of stock with a pair of cant twist clamps

    drill and tap 4 holes in a piece of aluminum for the 4 corner holes. Use a size that is a close fit for the holes, do not offset them as in the part blanks

    screw it down and mill the edge.

    if volume goes up increase the number of fixtures so you can change while the part runs.

    back burr off line on a drill press

    with 2 fixtures I could run a ton of these a day, maybe 30 seconds machine time for each op and no fooling around or spending money on fixturing

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    Quote Originally Posted by Djstorm100 View Post
    My table only has 18"X, I need to deck the vacuum plate... I have a 2.5" face mill. The concern I keep battle with my self, is this. I'll have the shell mill come in at back corner of the table, The shell mill will plunge in to the stock slightly and start moving in the x+. The material that didn't get cut during the plunge will be picked up by the rear of the shell mill as it passes. Will this cause any issues? Finish pass take .010. just wanting to get the top perpendicular to the spindle is all.
    Program a long shallow lead-in and lead-out instead of just dropping the facemill to final Z.

    Regards.

    Mike

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    Had you to make cubes you could start on any side. A part with a very distinct dimension like this must begin there. Buy correct thickness aluminum and pack several up. You can sandwich both sides with a lost sheet (not drilled). Now give them the 7.9 inches and the five bores. By countersinking the uppermost and replacing one from underneath you can work through the staple. My 2 nuts

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    Quote Originally Posted by Finegrain View Post
    Program a long shallow lead-in and lead-out instead of just dropping the facemill to final Z.

    Regards.

    Mike
    Curve lead in/out got it!

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    Well no, not curved, rather, ramped. Start at, say, X = 0, Y = 0, Z = .015", move to X = 2, Y = 0, Z = 0. Then carry on with a facing toolpath.

    Regards.

    Mike

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    If this is a production thing I would face the fact that it's not a mill part, it's a waterjet part with some drill press ops.

    Just sub the laser or waterjet part out and focus on a simple fixture to do the countersinks. Start with mirror stock and you don't need to face it.

    Hell, get someone with a 5 axis waterjet and they'll just jet in the countersinks.

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    Face a thicker plate. Clamp plate however you want. Blue tape on plate and blue tape on part. CA glue both parts together at the blue tape.

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    Carpet tape from the depot works great just soak in thinner to remove after machine. Super glue trick good also.

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    So, I've hit a snag in my plan to take over the world.

    At this point they are prototypes but would like to set my self up in case it did take off.
    I got, what I though, almost finish making a vacuum fixture then though "how am I going index these parts if it become production"


    Thought about 4 down pins. 2 in between the two flat parts (locate y) and one in the middle span of each part (to locate x). This would allow me to push the stock together, turn vacuum on and hit go. Then flip the part and using the machined edges as stop again the pins. Removing the bottom material off.


    Then I got to thinking...why not just mill a pocket in the fixture slightly bigger, to accommodate the raw stock size. File the cut edge (I have 0.050 to play with). Push the stock to edge of the fixture plate, turn vacuum on and hit go.







    With the pocket idea.


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