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Posted by on June 22, 2008, 7:35 pm
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wrote:
> I'd like to make a Menger sponge
> (http://en.wikipedia.org/wiki/Menger_sponge) in metal; that is, I want
> to make a number of intersecting through holes of square cross-section
> through a cube of metal.
>
> I don't know what the relevant metal would be; it's a decorative item
> with a lot of operations done on it, so ease of machining is the major
> requirement and attractiveness a secondary one. =A0Free-machining brass
> looks good.
>
> Even the base cube of metal seems quite hard to find; I can find
> various suppliers for two-inch square aluminium bar stock, and one
> ebay auction for an offcut of four-inch square aluminium bar stock,
> but I can't find brass square bar stock of more than one inch, which
> would be too small.
>
> With four-inch square stock I could presumably produce a cube with
> 97.2mm sides by face-milling, and it looks as if the big square holes
> would not be too hard to mill - what sort of radius is it reasonable
> to get on the corners of a 32.4mm x 32.4mm hole?
>
> But I don't have a good idea how to make the third-level holes - 3.6mm
> square holes, 97.2mm deep. =A0It seems both a bit small and a bit deep
> to mill, and I've no idea how happy milling machines would be with a
> hole that repeatedly broke into air - I presume the edges around the
> break-throughs would be horribly burry. =A0And I'd need 216 holes to
> that spec.
>
> [for second-level holes I could fill the first-level holes with
> square-section dowels, mill, then remove the dowels; would it make the
> third-level milling easier to fill the first- and second-level holes
> with some kind of low-melting alloy that could be melted out
> afterwards?]
>
> Could I drill them and then make them square with a broach of some
> sort? =A0Custom broaches sound likely to be crazy expensive, so I
> presume I'd have to size the project for the size of the nearest
> round-to-square broach, and I'm not sure where to look for a
> round-to-square broach.
>
> I presume the fourth-level holes, 1.2mm x 1.2mm x 97.2mm, would be
> completely impractical by any affordable means - it's 80 times
> diameter, which looks barely possible in a good EDM shop, but 648
> holes at a good EDM shop would leave me vastly out of pocket.
>
> Plan B is to glue together eight thousand 1cm^3 plastic cubes, which
> would involve some trivial jig-making and a lot of very tedious
> assembly, and lose a lot of the gee-whizz of fractal geometry machined
> in metal, though would make a nice big block in the end. =A0It looks as
> if eight thousand little cubes would cost a few hundred dollars; I'm
> getting a feeling that small deep holes with reasonably sharp corners
> are not to be had for a dollar.
>
> Tom
Cast them. Square core holes wouldn't be tough to do. Could use
aluminum or brass. Want sharp inside corners, get the file out.
Stan
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Posted by texasjim1093 on June 22, 2008, 7:49 pm
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Legos is maybe best answer or generic equivalent bought in mass
quantity. I think if someone machined this out of block of metal to
reasonable tolerances the cost would be in the hundreds of thousands
of dollars regardless of size. I have seen those 3-D photo polymer
machines on TV that could make this but I am not sure of the
tolerances or setup costs.
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Posted by Flash on June 22, 2008, 10:45 pm
Please log in for more thread options Two questions did not resolve exactly to my mind:
Question #1:
Resolution, (exactness).
MUST this be a thoroughly *EXACT* item, following all the mathematical
hole-structure throughout??
- - - - - - - - OR - - - - - - - -
Could there be some part of it that is "hidden", therefore, not viewable,
and by reasonable extension of that thought, "not necessarily exactly per
mathematical description?
By that I mean, could there be some sort of surface-layer that could be
"correct", while internally, the invisible parts could be non-existent? In
other words, is "appearance" more important or is it paramount to adhere
exactly to formula?
If you could do with appearance, it might be possible to make the outside
layer of brass (of a thickness to equal the smallest hole diameter), cut the
holes properly in the outer layer, assemble the cube by brazing, and polish
accordingly. You might have to make surfaces inside the big holes through
the middle, if visibility were deemed an issue. But at a 4" cube, I think
you might be able to do the outside with a degree of precision, and as for
the inside, it would be much easier to create the "appearance"" without
having the exact substance.
Question #2: SIZE.
You did say a 4" cube, but you seem to suggest that you might perhaps want
bigger. In that case, you would have to take much more pains with the
interior structure.
Flash
> I'd like to make a Menger sponge
> (http://en.wikipedia.org/wiki/Menger_sponge) in metal; that is, I want
> to make a number of intersecting through holes of square cross-section
> through a cube of metal.
>
> I don't know what the relevant metal would be; it's a decorative item
> with a lot of operations done on it, so ease of machining is the major
> requirement and attractiveness a secondary one. Free-machining brass
> looks good.
>
> Even the base cube of metal seems quite hard to find; I can find
> various suppliers for two-inch square aluminium bar stock, and one
> ebay auction for an offcut of four-inch square aluminium bar stock,
> but I can't find brass square bar stock of more than one inch, which
> would be too small.
>
> With four-inch square stock I could presumably produce a cube with
> 97.2mm sides by face-milling, and it looks as if the big square holes
> would not be too hard to mill - what sort of radius is it reasonable
> to get on the corners of a 32.4mm x 32.4mm hole?
>
> But I don't have a good idea how to make the third-level holes - 3.6mm
> square holes, 97.2mm deep. It seems both a bit small and a bit deep
> to mill, and I've no idea how happy milling machines would be with a
> hole that repeatedly broke into air - I presume the edges around the
> break-throughs would be horribly burry. And I'd need 216 holes to
> that spec.
>
> [for second-level holes I could fill the first-level holes with
> square-section dowels, mill, then remove the dowels; would it make the
> third-level milling easier to fill the first- and second-level holes
> with some kind of low-melting alloy that could be melted out
> afterwards?]
>
> Could I drill them and then make them square with a broach of some
> sort? Custom broaches sound likely to be crazy expensive, so I
> presume I'd have to size the project for the size of the nearest
> round-to-square broach, and I'm not sure where to look for a
> round-to-square broach.
>
> I presume the fourth-level holes, 1.2mm x 1.2mm x 97.2mm, would be
> completely impractical by any affordable means - it's 80 times
> diameter, which looks barely possible in a good EDM shop, but 648
> holes at a good EDM shop would leave me vastly out of pocket.
>
>
> Plan B is to glue together eight thousand 1cm^3 plastic cubes, which
> would involve some trivial jig-making and a lot of very tedious
> assembly, and lose a lot of the gee-whizz of fractal geometry machined
> in metal, though would make a nice big block in the end. It looks as
> if eight thousand little cubes would cost a few hundred dollars; I'm
> getting a feeling that small deep holes with reasonably sharp corners
> are not to be had for a dollar.
>
> Tom
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Posted by William Noble on June 23, 2008, 1:25 am
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so, perhaps you might look in the archives - within the last few months we
discussed a special drill that makes square holes, and I uploaded the
instruction manual and price list to the drop box.
** Posted from http://www.teranews.com **
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Posted by Jon Elson on June 23, 2008, 1:56 pm
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Thomas Womack wrote:
> I'd like to make a Menger sponge
> (http://en.wikipedia.org/wiki/Menger_sponge) in metal; that is, I want
> to make a number of intersecting through holes of square cross-section
> through a cube of metal.
>
I think wire EDM is the best solution, but it appears that sinker EDM
could also do the job. Doing it with sinker sould take a LONG time, but
could rub unattended for long stretches. Commercial wire EDM systems
have automatic piercing, but this particular project could be
pre-drilled for a more home-brew system.
Jon
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> (http://en.wikipedia.org/wiki/Menger_sponge) in metal; that is, I want
> to make a number of intersecting through holes of square cross-section
> through a cube of metal.
>
> I don't know what the relevant metal would be; it's a decorative item
> with a lot of operations done on it, so ease of machining is the major
> requirement and attractiveness a secondary one. =A0Free-machining brass
> looks good.
>
> Even the base cube of metal seems quite hard to find; I can find
> various suppliers for two-inch square aluminium bar stock, and one
> ebay auction for an offcut of four-inch square aluminium bar stock,
> but I can't find brass square bar stock of more than one inch, which
> would be too small.
>
> With four-inch square stock I could presumably produce a cube with
> 97.2mm sides by face-milling, and it looks as if the big square holes
> would not be too hard to mill - what sort of radius is it reasonable
> to get on the corners of a 32.4mm x 32.4mm hole?
>
> But I don't have a good idea how to make the third-level holes - 3.6mm
> square holes, 97.2mm deep. =A0It seems both a bit small and a bit deep
> to mill, and I've no idea how happy milling machines would be with a
> hole that repeatedly broke into air - I presume the edges around the
> break-throughs would be horribly burry. =A0And I'd need 216 holes to
> that spec.
>
> [for second-level holes I could fill the first-level holes with
> square-section dowels, mill, then remove the dowels; would it make the
> third-level milling easier to fill the first- and second-level holes
> with some kind of low-melting alloy that could be melted out
> afterwards?]
>
> Could I drill them and then make them square with a broach of some
> sort? =A0Custom broaches sound likely to be crazy expensive, so I
> presume I'd have to size the project for the size of the nearest
> round-to-square broach, and I'm not sure where to look for a
> round-to-square broach.
>
> I presume the fourth-level holes, 1.2mm x 1.2mm x 97.2mm, would be
> completely impractical by any affordable means - it's 80 times
> diameter, which looks barely possible in a good EDM shop, but 648
> holes at a good EDM shop would leave me vastly out of pocket.
>
> Plan B is to glue together eight thousand 1cm^3 plastic cubes, which
> would involve some trivial jig-making and a lot of very tedious
> assembly, and lose a lot of the gee-whizz of fractal geometry machined
> in metal, though would make a nice big block in the end. =A0It looks as
> if eight thousand little cubes would cost a few hundred dollars; I'm
> getting a feeling that small deep holes with reasonably sharp corners
> are not to be had for a dollar.
>
> Tom