Making a huge 3D Printer! January 05, 2014 09:57PM |
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Re: Making a huge 3D Printer! January 13, 2014 07:36PM |
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This is correct it's why when you build a bigger machine you have to go quite big on the cross-section of the members but preferably hollow. Especially on horizontal members gravity alone makes things SAG in the middle from their own weightQuote
garyhlucas
The stiffness of a long narrow part comes from the material on the outside. Steel has a tensile strength of 50,000 psi or greater. Concrete 5,000 psi in compression, a couple of hundred psi at most in tension. So your frame will be much heavier but not stiffer. Doubling the circumference of a part about quadruples it's stiffness, and only doubles its weight. Making a part twice as long reduces it's stiffness by about 4 times. Hence making something twice as long requires making the circumference about double to handle the same load at the same deflection.
Re: Making a huge 3D Printer! January 14, 2014 01:55AM |
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Re: Making a huge 3D Printer! January 14, 2014 10:07AM |
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Quote
bobc
I like the idea of Makerslide, I have an Ordbot which uses it. The makerslide is quite stiff and the trucks roll really easily.
However, I bought a 1 meter length of makerslide for a custom machine, but over 1m the makerslide has a distinct bend. Not sure whether this is a one off fault, or a general feature of extrusions, but it's not really good enough for precision work.
On this I would agree with dick, if you are going "big" the robustness and precision of CNC equipment is desirable, if expensive. I guess the alternative is a somewhat flexible frame which requires a lot of adjustment to get it true.
The biggest printer I could find in this sort of class has a 600x600x600 print volume, although people have discussed building big printers before, I'm not sure much came of them.
Re: Making a huge 3D Printer! January 15, 2014 09:07AM |
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Re: Making a huge 3D Printer! January 15, 2014 04:12PM |
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he said he had got 3 x 3 x 10' long my guess would be that even if was perfectly straight with a 3 x 3 it probably end up with about .070 SAG in middle with absolutely no weight on member just supported on both endsQuote
garyhlucas
Aluminum extrusions are actually stretched as they are extruded otherwise they would be wavy in all directions. So ones that are not straight suggests a manufacturing issue.
Re: Making a huge 3D Printer! January 19, 2014 03:10AM |
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Quote
cnc dick
It's nice to see somebody else attempt this With very long running times reliability is more important than speed take for example if the printed parts take one hundred hours and it fails at 90 hours just lost 90 hours. Versus if it was a little slower will say 150 hours and print was successful obviously you'd be much better off. To achieve that kind of reliability you are going to have to use all industrial quality machine parts that are meant to be reliable for millions of cycles in production which makes it is expensive. Supported linear rails not the round one's ballscrews and machine operating system from a CNC machine such as Mach 3. You're probably going to have to design your own hot end and extruder very important to be reliable
Quote
bobc
I like the idea of Makerslide, I have an Ordbot which uses it. The makerslide is quite stiff and the trucks roll really easily.
However, I bought a 1 meter length of makerslide for a custom machine, but over 1m the makerslide has a distinct bend. Not sure whether this is a one off fault, or a general feature of extrusions, but it's not really good enough for precision work.
On this I would agree with dick, if you are going "big" the robustness and precision of CNC equipment is desirable, if expensive. I guess the alternative is a somewhat flexible frame which requires a lot of adjustment to get it true.
The biggest printer I could find in this sort of class has a 600x600x600 print volume, although people have discussed building big printers before, I'm not sure much came of them.
Quote
TheTechnicalNoob
I have no idea if anybody has tried this. But here's an idea: use square box stainless steel or aluminium extrusions and fill them with cement for rigidity.
Bearings with delrin or machined teflon rollers could be used as guides if you use soft extrusion like aluminium.
Heck, if you make it really big on the order of meters you could even use concrete reinforcing steel! That way it'd holds its strength in case the cement inside cracks.
Something like this: [secure.flickr.com]
Some pictures illustrating what I had in mind: [forums.reprap.org]
As for a heated bed. Lots and lots of resistors on the bottom of a sheet of metal could work. If you go this route make sure to use plenty so the heat is spread evenly and use a material that conducts heat well. I wouldn't use glass, as it gets to hot where the resistors are and cracks ( mine did ).
Making an enclosure and using an oven heating element with fans to circulate the hot air might be an idea. But just the hot bed in an enclosure might be enough heat. Just try with only a heatbed and take it from there I'd say..
Good luck!!
Re: Making a huge 3D Printer! January 19, 2014 03:14AM |
Registered: 10 years ago Posts: 118 |
Quote
garyhlucas
The stiffness of a long narrow part comes from the material on the outside. Steel has a tensile strength of 50,000 psi or greater. Concrete 5,000 psi in compression, a couple of hundred psi at most in tension. So your frame will be much heavier but not stiffer. Doubling the circumference of a part about quadruples it's stiffness, and only doubles its weight. Making a part twice as long reduces it's stiffness by about 4 times. Hence making something twice as long requires making the circumference about double to handle the same load at the same deflection.
Re: Making a huge 3D Printer! January 19, 2014 03:24AM |
Registered: 10 years ago Posts: 118 |
Quote
cnc dick
Yes pretty much so I don't think 20 x 20 mm is strong enough for even a small machine. And other things that are going to be mounted to the structure are also going to get heavier. For anything horizontal I think you should use rectangle with the largest side taking gravity load
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