How flat and parallel can I machine 1.25x18x27in aluminum plate?
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    Default How flat and parallel can I machine 1.25x18x27in aluminum plate?

    Guys looking to machine 1.25x18x27inch plate as flat and parallel as possible in either 6061 or 7075 skimming off as little as necessary to get it right. I could possibly go up to a 1.5" thick plate. How flat is realistic? Would .001" flatness along the whole plate even be possible? Machine is a fairly low hours Haas. Thinking of using a vacuum chuck and dialing down the PSI as low as possible.

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    Is there a reason Mic-6 or similar is not a consideration?

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    I have machined 0.625" aluminum plates to within 0.001" on a haas. About 2 feet by 4 feet. There were leftovers which I then used as long parraleles for other jobs.

    So yeah 0.001" is quite possible. But machine must be well levelled and not have any drops.

    Didn't have a vacuum chuck just dropped on the table and pushed with side clamps against stops to keep it in place

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    Quote Originally Posted by Lazyman View Post
    Guys looking to machine 1.25x18x27inch plate as flat and parallel as possible in either 6061 or 7075 skimming off as little as necessary to get it right. I could possibly go up to a 1.5" thick plate. How flat is realistic? Would .001" flatness along the whole plate even be possible? Machine is a fairly low hours Haas. Thinking of using a vacuum chuck and dialing down the PSI as low as possible.
    "Flat as POSSIBLE?" is all?

    ?? Surely you must have some FEATURES to mill as well?

    Otherwise, you can just ORDER flat rounds and rectangles from shops that do nothing else, all-day, every day to set sizes and specials for not much more per mass and area.

    They have it nailed as to what their stock is going to do as it is machined (or even ground).

    Seriously. Your machine is dead-average, it can hold better than the alloy being worked, given it is wont to MOVE on yah from machining and temps, both.

    That's why folks BUY it ready finished from those specialists. And why they have "a bizness" doin' that, year in, year out.

    Surely you can find other work they WONT do that puts more coin in YOUR pocket, locally for the time put into the tasking?

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    Quote Originally Posted by thermite View Post
    ...Otherwise, you can just ORDER flat rounds and rectangles from shops that do nothing else, all-day, every day to set sizes and specials for not much more per mass and area.

    They have it nailed as to what their stock is going to do as it is machined (or even ground)....
    Yeah, I've had quite a few pieces of steel plate Blanchard ground over the years. It's a pretty cheap way of getting
    a nice flat surface. Come to think of it, I've never had aluminum ground. Can it be done? I would think that 7075
    or Mic 6 would take to grinding OK...

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    Quote Originally Posted by LKeithR View Post
    Yeah, I've had quite a few pieces of steel plate Blanchard ground over the years. It's a pretty cheap way of getting
    a nice flat surface. Come to think of it, I've never had aluminum ground. Can it be done? I would think that 7075
    or Mic 6 would take to grinding OK...
    Absolutely! I used to grind chunks of alum in a blanchard grinder no problem. Flat AND Parallel ... well it depends on what you need most I suppose... But yes, find a shop that has a big blanchard (ours was a 42"? chuck) and they should be able to do it. A little tip, if this is for fixturing, and you don't need a certain thickness held (because it is hard to do flat, parallel, and thickness to +/-xxx) give them +/- 1/32" and it will be cheaper/easier to get what you need...

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    Quote Originally Posted by Lazyman View Post
    Guys looking to machine 1.25x18x27inch plate as flat and parallel as possible in either 6061 or 7075 skimming off as little as necessary to get it right. I could possibly go up to a 1.5" thick plate. How flat is realistic? Would .001" flatness along the whole plate even be possible? Machine is a fairly low hours Haas. Thinking of using a vacuum chuck and dialing down the PSI as low as possible.
    .
    unless annealed rather than T6 you have like 99.9999% chance it will easily be not flat over .001" and .050 to .100" warpage after machining not unheard of. and of course machined plate will often warp some more after a few days giving it time to think about warping some more. even flatten in a press to .001" quite normal to warp back .010" after a day.
    .
    normally even when annealed how you hold it will affect its relaxed flatness. usually held at airy points at very low torque when machining the last .001" at a time. vacuum chuck you have to use shims to not have vacuum pull it down flat as obviously when vacuum released it will spring back. and as tempting as using a big facemill is if cutting force too high it will push plate when machining and plate will deflect back when cutter it gone. even if 100% support with vacuum chuck obviously vacuum chuck would need indicating to confirm its flat to say .0003" per 40" unless you are machining or shimming vacuum chuck before mounting part. just saying the ability to bolt on anything like a vacuum chuck and have it repeat flat <.0003" is not easy

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    Quote Originally Posted by DMF_TomB View Post
    .
    unless annealed rather than T6 you have like 99.9999% chance it will easily be not flat over .001" and .050 to .100" warpage after machining not unheard of. and of course machined plate will often warp some more after a few days giving it time to think about warping some more. even flatten in a press to .001" quite normal to warp back .010" after a day.
    .
    normally even when annealed how you hold it will affect its relaxed flatness. usually held at airy points at very low torque when machining the last .001" at a time. vacuum chuck you have to use shims to not have vacuum pull it down flat as obviously when vacuum released it will spring back. and as tempting as using a big facemill is if cutting force too high it will push plate when machining and plate will deflect back when cutter it gone. even if 100% support with vacuum chuck obviously vacuum chuck would need indicating to confirm its flat to say .0003" per 40" unless you are machining or shimming vacuum chuck before mounting part. just saying the ability to bolt on anything like a vacuum chuck and have it repeat flat <.0003" is not easy
    Yeh but no but...
    Anneal...you do realise that 6061 is a heat treatable aluminium that naturally ages? So if you annealed it, over a little time it will re-hardening itself...
    Did you mean stress relieve?

    OP - if you buy 6061 mtl in T6511 condition, it is controlled stretched (2%) which straightens and massively helps stability in a stress relieve way.

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    The local blanchard grinding guys are saying .002"/ft. There will be probably 16 1/4-20 holes tapped on both sides. My customer is designing something and wants to know whats going to be doable. MIC-6 could be a possibility but it would have to be machined better than the +-.005" they spec. How about stress relieved A36?

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    Quote Originally Posted by LKeithR View Post
    Yeah, I've had quite a few pieces of steel plate Blanchard ground over the years. It's a pretty cheap way of getting
    a nice flat surface. Come to think of it, I've never had aluminum ground. Can it be done? I would think that 7075
    or Mic 6 would take to grinding OK...
    Just go onto eBay and search "fortal" or "aluminum ground plate".

    There are some "real companies" back of some of those listings, and they have competition as well.

    Yah didn' REALLY think you were the first person ever had the NEED of a hunk of shiney-wood that was at least temp'rarily flat, didja?

    'Coz "temporary" is about all as is reasonable to ask.

    Stuff thinks it is so alive there are not-so-shiney woods as can be more stable...


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    Designers that design too close to "doable" usually end up with expensive designs and high failure rates. Start with what's typical for a given process, then add a safety factor. If the answer isn't satisfying, change the design or change the material. Did you ever wonder why serious metrology equipment is so beefy, far beyond what you'd think is necessary?

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    Quote Originally Posted by Conrad Hoffman View Post
    Designers that design too close to "doable" usually end up with expensive designs and high failure rates. Start with what's typical for a given process, then add a safety factor. If the answer isn't satisfying, change the design or change the material. Did you ever wonder why serious metrology equipment is so beefy, far beyond what you'd think is necessary?
    Given there were "invar" goods under-roof before I was old enough to eat solid-food? WTH, USC&GS surveyor a dozen years before Dad even MET me Mum? Nah. Got the lectures as a kid...

    'member the day I asked Dad what "plastic" was at the breakfast table. I must have been about five years old?

    One of his many loves being organic Chem, he simply warshed out his cawfee cup, puttered around the kitchen and MADE some, right there in his cup.

    Not bad, considering that house didn't even get 'lectricity nor an indoor toilet for another four years.

    Hillbillies and flat-land farm-boys. Not always as dumb as we look!

    Thank God in her infinite mercy!


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    Quote Originally Posted by barbter View Post
    Yeh but no but...
    Anneal...you do realise that 6061 is a heat treatable aluminium that naturally ages? So if you annealed it, over a little time it will re-hardening itself...
    Did you mean stress relieve?

    OP - if you buy 6061 mtl in T6511 condition, it is controlled stretched (2%) which straightens and massively helps stability in a stress relieve way.
    .
    i usually get jig or fixture plate usually its 6061 T0 or annealed and its usually fairly flat as is. but its strength or tensile strength is much less. 7075 usually for higher strength applications and i have seen 6 foot long pieces after machining curled or warped over .100" in center.
    .
    are their special jig or fixture plate alloys thats are higher strength and more warp resistant ? probably but many places selling metal have limited alloy options unless you special order a particular alloy and you might need to buy the whole sheet

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    Quote Originally Posted by LKeithR View Post
    Yeah, I've had quite a few pieces of steel plate Blanchard ground over the years. It's a pretty cheap way of getting
    a nice flat surface. Come to think of it, I've never had aluminum ground. Can it be done? I would think that 7075
    or Mic 6 would take to grinding OK...
    We grind aluminum all the time on our big 32x80 Okamoto. Just need to make sure the wheel doesn't load up, which can be prevented through good coolant pressure and plenty of wheel dresses.

    6061, 7075, and MIC6 all grind fine. MIC6 of course comes out the flattest, but all of them can be ground parallel when bolted to a steel reference plate that is known to be flat.

    My issue with MIC6 is that it doesn't anodize well and has low tensile strength.

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    point is if you want part flat in relaxed "unclamped" on its airy points or minimize sag from its own weight. thick sheet metal supported on its ends sagging. if done on a horizontal mill on a angle plate ,part on its side, gravity sag is less
    .
    most parts as soon as unclamped or unchucked it goes bong or curl or warp. if you final machine with very light clamping pressure often talking finger tight to machine final .001" or even .0005" you maybe can get it flat. checking a unclamped plate if its flat on a surface plate its not easy to get flat to .001"

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    We don't know how flat and parallel your machine can cut. With a reasonably good shape Haas, then yes, with a few flips you should be able to cut a plate of that size flat and parallel on a vac plate that's been dressed to the table.

    The material may bow out over time depending on how stable the plate was and how carefully you balance cutting on both sides. Your best bet may be starting at 1.375", then making about three flips per side down to 1.25". When I can justify it, I prefer to use 7075 for larger parts, just because the harder Al holds up better under use before scratching or having threads get damaged.

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    Quote Originally Posted by Mud View Post
    Thanks. Bookmarked.

    Gots to buy the metal "somewhere", then deal with drops & waste?

    Whom is it making YOUR profitable parts whilst you be messing about with the basic s**t as dasn't make yah as much money as it WASTES, time-value-wise?

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    Quote Originally Posted by Mud View Post
    I've gotten material from them, as well as McMaster (who stocks a limited range of pre-ground material), and while the product's good, you'll pay through the nose for it. In the OP's shoes, I'd do it myself and save the time for delivery and keep the ~$700+ extra in my pocket.

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    Quote Originally Posted by LKeithR View Post
    Yeah, I've had quite a few pieces of steel plate Blanchard ground over the years. It's a pretty cheap way of getting
    a nice flat surface. Come to think of it, I've never had aluminum ground. Can it be done? I would think that 7075
    or Mic 6 would take to grinding OK...

    The local grinder here said they can't really blanchard grind MIC-6 better than it already comes. I guess the MIC-6 +-.005" flatness spec is on the entire full sheet material which but perhaps if you cut smaller sections you may get much better off. Makes me wonder what the flatness spec on a haas table is in the first place considering they are machining them on a bigger Haas mill.


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