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Making lots of square holes

I'd like to make a Menger sponge

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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

Reply to
Thomas Womack
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Round holes, then wire EDM?

Reply to
Jim Wilkins

Stereolithography

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Reply to
Ned Simmons

[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]

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

Reply to
James Waldby

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

Reply to
stans4

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.

Reply to
texasjim1093

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

Reply to
Flash

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.

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Reply to
William Noble

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.

Reply to
Jim Wilkins

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

Reply to
Jon Elson

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

Reply to
steamer

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