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# Building Large Stuff

Building Large Stuff [message #52401] Wed, 08 August 2012 23:34 UTC
Need some advice concerning Large structures. Lets assume i want to fill the entire bounding box of WSF using as little material as possible and making a structure that has at the same time maximum stability from a vertical vector (gravity).

I've been doing some research into this and the shukhov tower seems like the best candidate.

http://en.wikipedia.org/wiki/Shukhov_Tower

So hypothetically speaking, very roughly how much weight can i put onto such a structure (see attachment) before it breaks?

I know its hard question, i am not looking for specifics, just some very vague boundaries. Lets say the wires are 1mm thick, and there are many (64) of them.

1kg 5kg 10kg 20kg ?

if all of this is to outlandish, then let me simplify, instead of the shukov hyperboloid lets just have a simple tube, 60cm high 35 cm in diameter, and a wall thickness of 1mm. Lets increase stability by slightly coning it towards the top.

Now same question, roughly, how much kg can i carefully place on top of it ?

[Updated on: Thu, 09 August 2012 01:59 UTC]

Re: Building Large Stuff [message #52403 is a reply to message #52401 ] Thu, 09 August 2012 02:33 UTC
If I may, let me give you an indirect (non-scientific) answer...

My train layout is 0.75 by 1 meter and weighs about 7kg

I designed this bridge and printed it in Alumide.

The model is here: http://shpws.me/3Ugk

All the struts are 2mm thick. The bridge is 5cm wide and 4cm tall, 18cm long. It is anchored to my layout with a product called Liquid Nails.

I can pull up on the bridge, and lift the entire layout without deforming the bridge in any manner.

Patience, Persistance, Politeness - the 3Ps will help us get us to Perfect Printed Products
Re: Building Large Stuff [message #52407 is a reply to message #52401 ] Thu, 09 August 2012 05:30 UTC
1mm thickness is only allowed for small things and it's really flexible anyway, it would crumble. There is a calculator for this and you would have to use 3.6mm for 600mm long (Anybody knows how do you reach that page with the new site redesign?)

Also you have take into account the different behavior against comprension and extension, vibrations, impact... Someone built a part for a RC, it broke under use. Lacking analysis software, only way is build and test.
Re: Building Large Stuff [message #52420 is a reply to message #52407 ] Thu, 09 August 2012 11:02 UTC
 stannum wrote on Thu, 09 August 2012 05:30 1mm thickness is only allowed for small things and it's really flexible anyway, it would crumble. There is a calculator for this and you would have to use 3.6mm for 600mm long (Anybody knows how do you reach that page with the new site redesign?) Also you have take into account the different behavior against comprension and extension, vibrations, impact... Someone built a part for a RC, it broke under use. Lacking analysis software, only way is build and test.

The link was on the Materials Comparison Page until I pointed out that was the only link to the 'big parts calculator' via the feedback forum ( http://www.shapeways.com/forum/index.php?t=msg&th=10390& amp;start=0&), after which it was removed

Re: Building Large Stuff [message #52425 is a reply to message #52420 ] Thu, 09 August 2012 15:59 UTC
thanks, anybody know any software that can display the parts of a model that are exposed to the most stress ?

Also, i would like to reapeat my question, a tube with a wall of 3,6mm, diameter 35cm, hight 60cm, how much weight can i put on it ?
Re: Building Large Stuff [message #52427 is a reply to message #52401 ] Thu, 09 August 2012 17:50 UTC
You should be able to calculate the answer via the material data sheet - http://www.shapeways.com/rrstatic/material_docs/mds-strongfl ex.pdf - as there's probably no one who has the exact same model as you're envisaging for an answer to your questions.

Re: Building Large Stuff [message #52428 is a reply to message #52401 ] Thu, 09 August 2012 19:31 UTC
 rusalkin wrote on Wed, 08 August 2012 23:34 I've been doing some research into this and the shukhov tower seems like the best candidate.

I think both your hollow cone and a Shukhov tower will fail by buckling if loaded vertically - and that is a much more difficult calculation than straight tension/compression. You need to build models and experiment.

Bill Bedford
Re: Building Large Stuff [message #52437 is a reply to message #52428 ] Thu, 09 August 2012 23:21 UTC
i agree its just thats its an expensive undertaking and i am trying to gather as much data as possible before experimentation.

For instance i could make a pole in the middle of the shukhov tower and connect it with multiple wires to the outer shell every 10 cm of height to prevent buckling.

I still have to figure out how i am supposed to use the data from the material specifications on all of this, i am unfortunately not a static expert and my math is weak at best.

But thanks to everyone for their input.

If anybody could tell me at least how much weight i could hang on a 1mm thick wire without it ripping, it would give me a good estimate of its properties without complex math. So if anybody from shapeways is reading this, maybe if you have some spare time in maybe you could do this experiment, you know in the name of science

[Updated on: Thu, 09 August 2012 23:24 UTC]

Re: Building Large Stuff [message #52438 is a reply to message #52437 ] Fri, 10 August 2012 00:23 UTC
From the MSDS above.. it says that PA220 has a tensile strength of 6962 psi (lb/in) - that translates to 10.8 lb/mm2

The problem here is that you're not "stretching" the item, but rather compressing it... the weight comes from above, and the compressive strength is not listed on the MSDS.

You may be able to get a better number from the Flexural Strength which is 8412 psi or 13 lb/mm2

As to the tower "strength".. In over-simplified terms, if the side angle of the tower is 20 degrees, then the force to cause a bend is reduced by 20/90. In otherwords, a tilted beam would only support 13*(1-20/90) or 10.1 lb/mm2. This discounts (slightly) the effect of having the rings at each level of the tower.. those rings cause the number to go back up a bit.

[Updated on: Fri, 10 August 2012 00:31 UTC]

Patience, Persistance, Politeness - the 3Ps will help us get us to Perfect Printed Products
Re: Building Large Stuff [message #52461 is a reply to message #52438 ] Fri, 10 August 2012 13:07 UTC
so roughly 4,5 kg per mm2 ?

that sounds like a lot, if that is true then thats an impressive material, of course this only tells us the weight under which it would break / rip and not as you mentioned the whole compression / bending thing, still impressive.

I can work with that, thanks.
Re: Building Large Stuff [message #52531 is a reply to message #52428 ] Mon, 13 August 2012 04:18 UTC
Bill, I see you are confident is using your 3-Link & Instanta couplings in situations under tension for 4mm scale. What deliberate failure points have you pressed them to? Noel

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