best way to flatten large Aluminum slabs
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  1. #1
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    Default best way to flatten large Aluminum slabs

    I've jobs to flatten large aluminum slabs, about 1.5'x4', about 2" thick, it's not always a perfect rectangle, edges may not be straight. Material is cast aluminum, similar to 6 series, tough and somewhat brittle, not sure on exact alloy. The flatness variation tolerance is about 1/64"-1/32", not a precision job. The top surface is rough, occasionally may have hydrogen bubble inclusions and to flatten it, I may be taking anything from 0 to 3/8" to occasionally 1/2" of material.

    So far I've been doing it on a mill, I don't have a table large enough to accommodate complete travel so I had to make a fixture to hold it firm + need to reposition it from time to time. The biggest pain is repositioning the slab, variation in how much material to remove causes end mill bit to either do nothing or bog down on thicker parts. Also, thanks to imperfections in top layer, I've have a good share of carbide bits breaking, because of the sudden change in load.

    I've been thinking about other possible methods, setups specifically a horizontal mill, to make this a more effective operation with less human presence. The problem of varying force needed makes it tough. Taking too much material in one pass will take a lot of clamping and holding force. Rotary cutter vs end mill vs even bandsaw blade? Bandsaw wise, I am not sure that blade won't wander off because of unevenness of the surface. Most machines don't really have tables this big or if they do, the machines are simply huge. Budget wise, I can swing 5k right now, may be more, but I don't want to make a big investment until there is more of this work coming.

    I'd like to get some advice on options to machine these slabs and what kind of machinery would be optimal for this task, I'm sure some members will come up with some interesting options.

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    A head resurfacing mill from an engine shop might just work.

    I have seen a couple older ones that ran in a straight line, for large diesel engines, they pop up on craigslist every once in awhile.

    KWIKWAY 855-5 HEAD AND BLOCK SUR

    If it has a grinding wheel, I'm sure you could sub in a milling cutter,
    some of these have been retrofitted already.

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    Something like a Cinci #4 vertical ? - like this (and for $1500 bucks) No. 4 Cincinnati Vertical Milling Machine | eBay

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    best way to flatten large Aluminum slabs
    The problem of varying force needed makes it tough. Taking too much material in one pass will take a lot of clamping and holding force.
    Planer, hands down.
    Unless you have a horizontal boring mill or a planer mill.

    dsc_0021.jpg
    dsc_0024.jpg

    With the right tool, planer will cut across widely varying depths
    dsc_0030.jpg

    Varying force across steel + Al.
    dsc_0056.jpg
    dsc_0061.jpg



    smt

    Or maybe the mill Sami linked to.
    I used to rent time on a K & T with an 84" table, previously rebuilt at the Hardinge plant. It only had 32" long travel IIRC. (Might have been 36") It was later offered to me free, but I bought the planer instead. If you already have a mill or 2 for your "typical" size work, the planer takes up about the same or less space, weighs less, and is arguably more versatile.

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    I can think of a dozen ways to flatten the rough rectangular castings you dimension. How you go about it depends of what machine tools are available. Face mill them on a HBM or a planer mill seems most suitable for the size. Facing cuts 3 or 4 at a time on a VBM is doable but less efficient. Vertical spindle grind using oil coolant is a very distant third.

    If your resources are limited and your volume is large, I suggest you farm the job out. In the right machine, you can expect floor to floor time of less than a half hour per side: 12" cutter in two passes. plus set-up time

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    Blanchard grind them. Nothing on earth is going to get them flatter, faster.

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    Are you going to shim those spots that don't touch the table? How much will our clamping deform the part? You may get one side milled flat only to find when you release the clamps it bends. Are you doing both sides? Going to sim under the part for the second cut? The side you cut first will probably not lie flat on the table. There is a lot more to think about than than the machine and cutter.

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    Quote Originally Posted by Limy Sami View Post
    Something like a Cinci #4 vertical ? - like this (and for $1500 bucks) No. 4 Cincinnati Vertical Milling Machine | eBay
    this would definitely do it, but at 12K#s I'm not sure I got space and foundation to support this monster.

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    Are you going to shim those spots that don't touch the table? How much will our clamping deform the part? You may get one side milled flat only to find when you release the clamps it bends. Are you doing both sides? Going to sim under the part for the second cut? The side you cut first will probably not lie flat on the table. There is a lot more to think about than than the machine and cutter.
    Another place the planer shines.
    It might not be obvious in the first photo above, but the casting is not, or is barely bolted down to the table for the first/reference side cut. It is wedged between the straps with "moderate" pressure, and some shims stuck here and there under so it does not rock.
    The cutter used puts some down pressure when in the cut, but most of the force is towards the foot dogs.

    smt

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    is metal stress relieved ? i have seen aluminum warp 1/8" per 6 foot piece when unclamped. some requires taking lighter and lighter cuts at lower and lower part holding pressure machining opposite sides.
    .
    for example
    remove 0.100 and it warps .050
    remove .050 and it warps .020
    remove .020 and it warps .005
    remove .005 and it warps .001
    remove .001 and it warps .0003"
    then wait 24 hours and find it warped another .010 over night
    .
    really if not stress relieved it warps easy and often needs time to think about warping some more. like a dog chasing its tail

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    Well, you could always do what the big boys doo...

    In your case a couple of 25 hp motors, some 16" face mills
    mounted directly on the motor shafts.
    Lower the billet down thru a "tunnel" that has the motors opposing each other.

    Or just buy this:
    Cincinnati 430-186 Duplex Production Mill For Sale

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    had a job where 6 foot part was suppose to be flat within .001 and it warped .125 when unclamped after machining
    .
    machinist straightened in a press. no way was it flat to .001 but they got most of the curve out of it

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    The OP did not indicate he was having any trouble with warping or the quality of the cut.
    What he asked for (alluded to) was something with adequate travel so he does not have to reposition & cut in multiple set ups & probably something faster.

    smt

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    yup that would be meat for a planer
    great machine for getting that rough casting flat.

    might be surprised what kind of work would come your way once
    people found out you had one.

    same could be said of the big cinci Limy linked to

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    now if you have to do it on a smaller machine

    get a piece of fixture plate large enough to accommodate the rough casting
    attach the casting to the plate, clamp the plate to the table as needed.
    down side is added weight and still need to reposition the plate.

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    Honestly if your that tight budget wise a simple gantry router set-up might get you there, won't be fast or pretty but you can just leave it to it.

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    This is probably a wacky idea, but this company Electric Wood Planers & Molding Machines | Woodmaster Tools ) sells inserted spiral cutter heads ( Quiet Indexable Wood Spiral Cutterhead | Woodmaster Tools )for wood thickness planers(as do others). They make machines that are wide enough. Drive speeds would have to be adjusted and cuts would have to be very shallow, but if it could be made to work, it would be pretty unbeatable for speed since you are not working to tight tolerances. The inserts are "Shear Action Carbide Inserts from highest-quality European tool steel" which would be an advantage for cutting forces. Carbide is available as well.

    spiralcutterheadrgb.jpg

    Plenty of other posts about using other woodworking tools on aluminum...

    I think you would want to do something to backup the feed rollers control of the slab.
    Last edited by wheels17; 05-09-2018 at 06:35 PM. Reason: Better Picture

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    Quote Originally Posted by adama View Post
    Honestly if your that tight budget wise a simple gantry router set-up might get you there, won't be fast or pretty but you can just leave it to it.
    that's basically what I am doing on a mill at the moment. I'm still working on figuring out best feed/speed since aluminum just likes to stick onto the cutter no matter what. It's slow going. I was hoping for some magical solution that doesn't involve dual 25HP milling heads but I really appreciate all the suggestions.

    Warping won't be an issue, since like I said, 1/100th flatness will be quiet satisfactory.

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    Quote Originally Posted by _boris_ View Post
    I'm still working on figuring out best feed/speed since aluminum just likes to stick onto the cutter no matter what. .
    What are you using for coolant / lube /

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    Quote Originally Posted by wheels17 View Post
    This is probably a wacky idea, but this company Electric Wood Planers & Molding Machines | Woodmaster Tools ) sells inserted spiral cutter heads ( Quiet Indexable Wood Spiral Cutterhead | Woodmaster Tools )for wood thickness planers(as do others). They make machines that are wide enough. Drive speeds would have to be adjusted and cuts would have to be very shallow, but if it could be made to work, it would be pretty unbeatable for speed since you are not working to tight tolerances. The inserts are "Shear Action Carbide Inserts from highest-quality European tool steel" which would be an advantage for cutting forces. Carbide is available as well.

    spiralcutterheadrgb.jpg

    Plenty of other posts about using other woodworking tools on aluminum...

    I think you would want to do something to backup the feed rollers control of the slab.
    If this works, you could always use the cutters on a "Straight-O-Plane".

    I think Stephen Thomas could comment on this.
    Last edited by digger doug; 05-10-2018 at 04:03 PM.


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