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

On Jun 22, 6:07*pm, 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.
....
Tom

Round holes, then wire EDM?

On Jun 22, 6:29*pm, Jim Wilkins wrote:
On Jun 22, 6:07*pm, 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.
....
Tom

Round holes, then wire EDM?
That was a reality check.

If I had to do this on less than an aerospace budget I'd look into
milling molds of the unit cell and casting them in wax, gluing them
together and making a lost wax casting. Since the outer surfaces are
flat they could be cast a little oversize and fly-cut smooth to remove
the joint lines.

If the metal is soft, like aluminum or pewter, a home-made square
broach of unhardened tool steel should cut at least a few holes before
it dulls and jams, then you could resharpen it by taking a light cut
to the face of each step in a lathe.

On 22 Jun 2008 23:07:10 +0100 (BST), 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.


Stereolithography
http://www.bathsheba.com/math/

--
Ned Simmons

Won't be cheap, but I've seen production broaching done with a rotary
broaching unit. here's some info I googled up for ya
http://www.sommatool.com/manuscripts/broaching.asp

Karl

On Sun, 22 Jun 2008 17:43:02 -0500, "Karl Townsend"
wrote:

Won't be cheap, but I've seen production broaching done with a rotary
broaching unit. here's some info I googled up for ya
http://www.sommatool.com/manuscripts/broaching.asp

Karl

========
These rotary/wobble broaches work pretty good, but be advised
that the hole won't be exactly square/straight (if this matters)
such that a square straight gage (like a tool bit) will go
through, the square hole will have some amount of twist to the
cross section. If you are doing cnc, you can minimize (but not
eliminate) this by running clockwise and then counter clockwise
over short feed distances.


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

On Sun, 22 Jun 2008 23:07:10 +0100, 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.
[big snip]

If I were making something like this, I'd start by writing a program to
dissect it into castable layers. Patterns could be made up of short
pieces of square stock in two or three standard lengths, locked up in a
matrix, in the same way that movable-type letters were used to print
newspapers long ago. Most patterns would be used several times per
sponge.

[snip re low-melting alloy]
[snip re round-to-square broach]
If on a limited budget, you might consider buying square files or rasps
and adapting them via a grinder or sander.

[snip re expensive EDM shop for 648 holes]

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.

Or (as before) dissect the sponge into layers that have long surface slots
and short cross-holes and some supporting structure, ie, two or three units
of thickness. Starting with plate stock, either mill the slots and broach
the holes, or punch small holes with a square punch and saw or mill outer
rectangular perimeters as needed. Then epoxy the layers together, or bolt,
or oven braze, or if you did good work, just wring them together.

-jiw

On Jun 22, 4:07*pm, 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 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

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

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.

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




"Thomas Womack" wrote in message
...
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

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 **

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

--If its purpose is purely decorative howzabout doing a lost wax
casting to a near-net shape and calling it done? ;-)

--
"Steamboat Ed" Haas : "Hold on! we're passing
Hacking the Trailing Edge! : through the moronosphere!"
www.nmpproducts.com
---Decks a-wash in a sea of words---