milling a very narrow slot
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  1. #1
    JJJack Guest

    Default milling a very narrow slot

    Hello, I am developing a prototype and to do so I need to simulate the pour flap groove in a typical aluminum beverage can (see attached sketch). The requirement for accuracy is high because the dimensions involved are small. Normally the forming of a can lid is done by a sequences of dies or punches. However, this is a very expensive proposition, and at this stage there are a lot of issues I need to iron out on a small scale before I get to any tool and die operations.

    I have narrowed my choice down to 2 options and I am looking for opinions to confirm these choices and to make sure I have not neglected any other.

    I have landed on the Tormach PCNC 440 and the Accurate PCB prototyping CNC A432. The accurate machine can achieve the precision required and I am having difficulty getting information from Tormach. From the information I gathered, it seems that making small slots requires high spindle speed, speeds that Accurate can provide (i.e. 50,000 rpm +) but not Tormach.

    Thanks
    Attached Thumbnails Attached Thumbnails score-line-top-2.jpg  

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    Uhhhm....what is your question?

    If you want to send out an RFQ try this guy;

    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by JJJack View Post
    From the information I gathered, it seems that making small slots requires high spindle speed
    You're not asking any questions here, just making a statement.
    And it would seem that machining is new territory for you.
    There is more to it than high spindle speed and buying some shitty hobby grade cnc.
    It really makes my day when engineers think this line of work is so easy a caveman can do it.

  4. #4
    JJJack Guest

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    The question is: are my 2 choices reasonable and are there other options that I need to consider?

    I am not looking to shop this out, there are too many trials that have to be made in the course of the development.

    J

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    Those machines are hobby level, I think I would find a competent shop with quality equipment and know how to help with your project rather that buy cheap machines to learn and test on.

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    Quote Originally Posted by JJJack View Post
    I am not looking to shop this out
    What is your budget for buying a new machine? This will affect the advice we can give on machines.

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    Quote Originally Posted by JJJack View Post
    The question is: are my 2 choices reasonable and are there other options that I need to consider?
    No, they are not reasonable. Yes, there are other options to consider.

    The link I provided is a guy maned Marcus (member here) who specializes in doing the type of prototyping you are looking at. He is one of the most talented guys on the planet. The consternation arises because you want to do it, but all you have is a cheese grater and a shovel.

    Even if you had the funding to buy the equipment needed, you would still need to commit a lot of time learning how.

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    JJJack Guest

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    Huuum, I am thinking it requires around $20K to buy a sophisticated cheese grater. And yes I do have the time to invest. I would love to talk to Marcus, and maybe hire him as a consultant to ensure that I set off on the right track.

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    The machines that can do this sort of work reliably and hold the tolerances required start in the $150,000 price range. Best of luck.

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    Quote Originally Posted by JJJack View Post
    Hello, I am developing a prototype and to do so I need to simulate the pour flap groove in a typical aluminum beverage can (see attached sketch). The requirement for accuracy is high because the dimensions involved are small. Normally the forming of a can lid is done by a sequences of dies or punches. However, this is a very expensive proposition, and at this stage there are a lot of issues I need to iron out on a small scale before I get to any tool and die operations.

    I have narrowed my choice down to 2 options and I am looking for opinions to confirm these choices and to make sure I have not neglected any other.

    I have landed on the Tormach PCNC 440 and the Accurate PCB prototyping CNC A432. The accurate machine can achieve the precision required and I am having difficulty getting information from Tormach. From the information I gathered, it seems that making small slots requires high spindle speed, speeds that Accurate can provide (i.e. 50,000 rpm +) but not Tormach.

    Thanks
    just put it on a 45o fixture and cut it with the corner of a sharp 1/2" endmill.

    edit: Your drawing is wrong, very wrong... calculate the angles for a .07" deep .022" wide slot. You drew it like it was 90o you need to put it on a 90o and use a side slot cutter at least 1/2" diameter, ground to the proper angle (16.26 o).

    Here is half of your slot:

    side a = 10 side b = 70 hypotenuse h = 70.71067811865476
    angle A = 8.130102354155978o
    angle B = 81.86989764584399o
    angle C = 90o

    dee
    ;-D

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    Quote Originally Posted by JJJack View Post
    The question is: are my 2 choices reasonable and are there other options that I need to consider?
    Your application isn't well suited to being milled. I suspect that a skilled toolmaker could produce some kind of draggable cutter that can peel off a repeatable strip.

    From a milling perspective RPM is almost secondary to stability, any vibration in the machine will snap the cutting tool since it will be so delicate. Tormach will not do this. Accurate 432 - Milling And Drilling Machine For PCB Prototyping or GX - Features - MINITECH MACHINERY CORPORATION might, with proper setup.

    You need to be able to hold down the sheet of aluminum and it has to be extremely flat. This probably needs vacuum.

    Finally, endmills will be a problem. Its hard to cut a V shaped slot like that because as the radius decreases so does the speed at the edge. At zero diameter you cannot cut at all. I can't find suitable endmills for your application and am not sure they exist. You might have to cut with the corner of a square endmill, but that only works if the line is straight.

    I would be looking at other methods of producing this feature.

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    so you think an aluminum framed machine is accurate to 5um?

    you will be pissing in the wind trying to hit that tolerance without getting a real machine and a temp controled building to keep it in!

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    Give the guy a break, he came here asking for advice, didn't try to snowball anyone into thinking he was an expert. The machines you mentioned are really hobby grade machines. As some have said, there is a steep learning curve to machine this kind of thing and will take a much bigger budget. Good advice to find a shop with the equipment and know how to do it. Faster and cheaper in the long and short run.

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    Stupid question, but can you plunge EDM aluminum? Seems like this might be a better route to go if possible.
    $20k isn't a lot of money for this project to be honest, especially if you're wanting to do this in-house.

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    Quote Originally Posted by JJJack View Post
    The question is: are my 2 choices reasonable and are there other options that I need to consider?

    I am not looking to shop this out, there are too many trials that have to be made in the course of the development.

    J
    Shop it out. Period. The tolerances of a Tormach seem to be greater than the thickness of the material you're using. If you want to make a real production product, send this to a shop that has the capability, pay the price and have a part back in a few weeks. You will still be tens of thousands of dollars cheaper than buying a crappy hobby mill and pulling your hair out buying tooling left and right and trying to get things to work that never will.

    If you're inventing the world's next best soda can, do it once, do it right, hire the work to the guys that can make the prototype. If the net return is going to be millions of dollars, do it accordingly. If the net return is one prototype that you think won't ever go anywhere, don't make a super intricate feature in it.

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    JJJack Guest

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    WOW! Thanks for the break, I'm a little shell shocked.

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    Tough crowd. There is good advice to be had, but some are more tolerant than others. We get all kinds that have grandiose ideas but no real world experience or idea what it takes to make things. Personally I think you expressed a reasonable question, although you don't seem to have the knowledge to be handling a project like this (because of the caliber of machines you are asking about).

    Yes you can EDM aluminium. You can EDM anything that is electrically conductive. Brass, aluminium, steel, carbide, titainium. No plastic, glass or ceramic.

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    You might want to think more about the tooling than the machine to cut this?

    I know next to nothing about about what cuts are required to form can end seams -- but don't see a pointy end mill running at high (50,000?) rpm as the way to go. You'll have all sorts of problems, including chip welding or smearing, chip evacuation, just measuring where you are, and holding that thin aluminum flat and stable.

    As suggested above, you'll likely need a vacuum fixture to hold the sheet down. A large diameter multi-tooth cutter (say 3") ground to the required "V" angle could provide at least some possibility of reproducibility. You can buy them already ground to 30, 45, 60, and 90 degrees -- and any local cutter grinder shop should be able to easily make up in-betweens. This is assuming, as shown in the pix, that you can run the experiment on a linear cut. Otherwise, the drag-tool idea might be better.

    Once you figure out how you're going to hold and cut this, then the choice of machine for playing around with prototypes might come into view??

    I'd also suspect that the geometry developed from cutting this feature won't directly translate to how a similarly stamped feature might perform. Still, might get you in the ballpark.

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    Quote Originally Posted by PeteM View Post
    You might want to think more about the tooling than the machine to cut this?

    I know next to nothing about about what cuts are required to form can end seams -- but don't see a pointy end mill running at high (50,000?) rpm as the way to go. You'll have all sorts of problems, including chip welding or smearing, chip evacuation, just measuring where you are, and holding that thin aluminum flat and stable.

    As suggested above, you'll likely need a vacuum fixture to hold the sheet down. A large diameter multi-tooth cutter (say 3") ground to the required "V" angle could provide at least some possibility of reproducibility. You can buy them already ground to 30, 45, 60, and 90 degrees -- and any local cutter grinder shop should be able to easily make up in-betweens. This is assuming, as shown in the pix, that you can run the experiment on a linear cut. Otherwise, the drag-tool idea might be better.

    Once you figure out how you're going to hold and cut this, then the choice of machine for playing around with prototypes might come into view??

    I'd also suspect that the geometry developed from cutting this feature won't directly translate to how a similarly stamped feature might perform. Still, might get you in the ballpark.
    His problem is that he has bad geometry . If he wants the top opening of the slot .022" wide and .07"deep his angle is too pointy if he is willing to go wider or shallower the job becomes easier. As you said, doing it with a vertical V bit is not feasible, a large, horizontal cutter is the way to go.



    dee
    ;-D

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    Quote Originally Posted by dcsipo View Post
    His problem is that he has bad geometry .
    That's just his first problem ...

    a large, horizontal cutter is the way to go.
    Beg to differ, for what he said, a graphite machining center and a ram type edm is the way to go.

    Or at least a way to go which will actually do the job.


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