Re: [math-fun] 3D printing puzzle
Allan, you raise an excellent point. What holds these damned things together? Here's Rohan holding up a tubecube: gosper.org/Photo on 4-21-16 at 8.01 AM.jpg ,which he's convinced me comes right apart if all six [s simultaneously depart radially. And presumably, 3/4 of an octopus could slap it right back together. Admittedly, with wear it's getting a bit delicate. If I build another, it will have pairs of subtle, diamond shaped ridges in the middle of the long sides, to provide detents. Rohan: with an infinite Young's modulus, would these detents render it inseparable? Yet it's amazing how well simple friction facilitates secure but removable lids on jars and bottles, e.g. (Although I do notice drugstore prescription bottles now having detents.) --rwg And for centuries we've have corks securing wine bottles, probably down to the molecule. Note added in 24 proof, gosper.org/IMG_0204.JPG is now so worn that it flies apart with the slightest twirl. But the uninitiated never manage to pull it open. On 2016-05-27 12:34, Allan Wechsler wrote:
I think I am having trouble with the desiderata for this problem. If we are not allowed to depend on friction, then the "assembly" path through configuration-space can certainly be time-reversed to provide a "disassembly" path, which will make the box liable to wiggle apart. Are spring-snap fasteners of any kind allowed? I would think all of these would tend to be a bit fragile.
On Fri, May 27, 2016 at 3:19 PM, Henry Baker <hbaker1@pipeline.com> wrote:
Dear Joerg:
I appreciate the offer, but I didn't design the box & don't have access to the STL file.
I know the fellow who did, but I don't think that you want to do all of his production! :-)
I was just trying to think of all the cool 3D puzzles I've seen in my life -- some of whom were made out of wood -- and try to recall if any of them would fit this particular bill.
About the only thing I've thought of so far is a cylindrical device made out of two (identical) helical pieces of plastic that screw together; think of a DNA double helix.
This shape more-or-less works for for a USB device, because the connector is a bit boxy anyway.
At 11:03 AM 5/27/2016, Joerg Arndt wrote:
* Henry Baker <hbaker1@pipeline.com> [May 27. 2016 18:43]:
People are using 3D printers more & more for prototyping.
I received a small electronic gizmo which plugs into a USB port whose plastic case was 3D printed.
The problem is, the plastic case keeps falling apart, due to the relatively poor tolerances of current gen consumer 3D printers.
It seems you want something for actual use. Hence no PLA, instead use ABS. If a consumer model is used, the operator will need some skill (and quite possibly luck).
ABS prints tend to warp, especially with cheaper printers.
If you can have what you want made from a more expensive printer your chances are much better, the operators will know very well what to do for every requirement (my Uni bought one for 750 K Euro recently, they had to take the wall out of the room to deliver it with a crane; that one can do metal (sinter) prints with close to no restrictions).
Alternatively, send me the STL file and I'll talk to the guys that have bought a very decent printer that is good with ABS. Payment is beer (this is Bavaria), I'll take care of that.
Mit besten Gruessen, Joerg Arndt
So...
The challenge is to come up with a way to print a little rectangular plastic box -- probably in 2 pieces -- that can be put together in such a way that it won't fall apart under normal handling (e.g., carrying it in your pocket banging up against your house keys), but can still be easily disassembled w/o any special tools, screws, etc.
Note that current 3D printers have the following characteristics:
* the plastic isn't very strong and isn't very flexible, so "fingers" that interlace may be too weak and may easily break off.
* the plastic deforms slightly during printing, so registration isn't terribly good.
* the resolution in different dimensions is different, so the tolerances have to be quite wide.
If printing the box in 2 pieces won't produce a satisfactory answer, how about 3 pieces?
Somebody at G4G showed me something that looked like the frob Rohan is holding, except that the tubes were circular in cross-section. I think the circular cross-section prevents the pure radial disassembly. On Fri, May 27, 2016 at 5:12 PM, Bill Gosper <billgosper@gmail.com> wrote:
Allan, you raise an excellent point. What holds these damned things together? Here's Rohan holding up a tubecube: gosper.org/Photo on 4-21-16 at 8.01 AM.jpg ,which he's convinced me comes right apart if all six [s simultaneously depart radially. And presumably, 3/4 of an octopus could slap it right back together. Admittedly, with wear it's getting a bit delicate. If I build another, it will have pairs of subtle, diamond shaped ridges in the middle of the long sides, to provide detents. Rohan: with an infinite Young's modulus, would these detents render it inseparable?
Yet it's amazing how well simple friction facilitates secure but removable lids on jars and bottles, e.g. (Although I do notice drugstore prescription bottles now having detents.) --rwg And for centuries we've have corks securing wine bottles, probably down to the molecule.
Note added in 24 proof, gosper.org/IMG_0204.JPG is now so worn that it flies apart with the slightest twirl. But the uninitiated never manage to pull it open.
On 2016-05-27 12:34, Allan Wechsler wrote:
I think I am having trouble with the desiderata for this problem. If we are not allowed to depend on friction, then the "assembly" path through configuration-space can certainly be time-reversed to provide a "disassembly" path, which will make the box liable to wiggle apart. Are spring-snap fasteners of any kind allowed? I would think all of these would tend to be a bit fragile.
On Fri, May 27, 2016 at 3:19 PM, Henry Baker <hbaker1@pipeline.com> wrote:
Dear Joerg:
I appreciate the offer, but I didn't design the box & don't have access to the STL file.
I know the fellow who did, but I don't think that you want to do all of his production! :-)
I was just trying to think of all the cool 3D puzzles I've seen in my life -- some of whom were made out of wood -- and try to recall if any of them would fit this particular bill.
About the only thing I've thought of so far is a cylindrical device made out of two (identical) helical pieces of plastic that screw together; think of a DNA double helix.
This shape more-or-less works for for a USB device, because the connector is a bit boxy anyway.
At 11:03 AM 5/27/2016, Joerg Arndt wrote:
* Henry Baker <hbaker1@pipeline.com> [May 27. 2016 18:43]:
People are using 3D printers more & more for prototyping.
I received a small electronic gizmo which plugs into a USB port whose plastic case was 3D printed.
The problem is, the plastic case keeps falling apart, due to the relatively poor tolerances of current gen consumer 3D printers.
It seems you want something for actual use. Hence no PLA, instead use ABS. If a consumer model is used, the operator will need some skill (and quite possibly luck).
ABS prints tend to warp, especially with cheaper printers.
If you can have what you want made from a more expensive printer your chances are much better, the operators will know very well what to do for every requirement (my Uni bought one for 750 K Euro recently, they had to take the wall out of the room to deliver it with a crane; that one can do metal (sinter) prints with close to no restrictions).
Alternatively, send me the STL file and I'll talk to the guys that have bought a very decent printer that is good with ABS. Payment is beer (this is Bavaria), I'll take care of that.
Mit besten Gruessen, Joerg Arndt
So...
The challenge is to come up with a way to print a little rectangular plastic box -- probably in 2 pieces -- that can be put together in such a way that it won't fall apart under normal handling (e.g., carrying it in your pocket banging up against your house keys), but can still be easily disassembled w/o any special tools, screws, etc.
Note that current 3D printers have the following characteristics:
* the plastic isn't very strong and isn't very flexible, so "fingers" that interlace may be too weak and may easily break off.
* the plastic deforms slightly during printing, so registration isn't terribly good.
* the resolution in different dimensions is different, so the tolerances have to be quite wide.
If printing the box in 2 pieces won't produce a satisfactory answer, how about 3 pieces?
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