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Mini truss

G'day people
Time to show me if Instructables lives up to its name

I need to come up with a very easy and fast way to build a minituare truss (picture of truss attached). It basically consists of two aluminum face sheets, that sandwich a network of drinking straws. The drinking straws are arranged in such a way that they form little pyramids (take a look at the picture for it to be clearer).
My issue is that I'm working with very tight dimensional restrictions. The 2nd picture shows the dimensions of the top and bottom face sheets. The drinking straws are 3mm in diameter. The edges of the "pyramids"  must form an angle of 30, 45 or 60 degrees with the horizontal plane.

The current method I'm using to make these trusses takes about 5 - 6 hours.  I need something that could take less than an hour. Also, the straws are glued to the face sheets with a small glue gun, but this leaves a lot of "glue residue" around the straws. If you have any better ideas....

what say you?!!

edit: I forgot to mention that money is not really much of an issue, so if you suggest I need some equipment or something of the sort that would be rather expensive, I will seriosuly consider it!

Picture of Mini truss
untitled.JPG
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Instead of makeing the fingers to put inside of another leg, which to me has to be really time consuming.  Why not just cut it longer so your makeing 2 legs and 2 feet at the same time.  It could still be connected at the finger cut area and your actually cutting in half, at the least, the amount of time and effort in connecting it all together.  As Kiteman said a jig would be the best way to cut more than one leg at a time which I think would speed up your process a bit too.

As for glue, try putting the hot glue inside the straws and heat it up again right before placement.  Might help make it look cleaner without all the glue on the outside of the straws.  Not sure if it will work but it's worth a shot.
texasratt12 (author)  RedneckEngineer7 years ago
Thats actually a BRILLIANT IDEA
I'll try that out tomorrow

The jig idea....I've already tried this, but the problem is that it messes up the mechanical properties of the truss...
Well keep me posted how it works out.  I am wondering how useing a jig to make a single repetitive cut messes up the properties of the truss.  If all the leg cuts need to be cut at the same degree angle then useing a jig should produce the same cut over and over.  Unless you need a better designed jig or your trying to cut too many at once and things are moveing.  Which are entirely differant problems that could be solved.  Don't forget to give best answer award :)
Either way glad it helped. 
texasratt12 (author)  RedneckEngineer7 years ago
I made a mistake in my previous post... It's the boss connection idea that messes up the mechanical properties of the truss...

However, your suggestion  actually turned out better than I predicted. It took me about 1 hour 15 minutes to make one truss today. The only issue was that there was less structural stability than desired, so I'm going to have to either improve on this idea, or think of new ones.

I'm experimenting with using a flat clay base with little clay pyramids on it, so I can just place the bottom aluminum sheet on the base and then put the straws on the corners of the pyramid.
Also looking into investing in a metal stamping machine to make a metal pre-form to construct the truss on

I'll keep ya'll updated!
lemonie7 years ago
Jigging covered already, it might help to use bosses instead of the finger-arm connection.
www.indigo.com/models/minit-molecular-model-components.html
It's just an Idea.

L
Kiteman7 years ago
"The current method I'm using to make these trusses takes about 5 - 6 hours."

What is the current method you are using?  Maybe we could suggest a way of speeding up what you already do?

(Such as a jig for cutting dozens of straws at once, cutting through several layers of aluminium to make more than one plate at a time etc)
texasratt12 (author)  Kiteman7 years ago

It takes about 5 minutes to cut the aluminum sheets so thats not much of a problem.
The time consuming part is cutting the straws into the right dimensions.

What I do is cut up a drinking straw into small pieces. Each straw is then divided into 3 regions: the finger, the arm, the leg (See attached picture).
I cut the straw so that the finger part is just barely still attached to the arm. The leg is cut at such an angle so that, when the arm is placed on the bottom sheet, it will have full contact with it (i.e. the cut is made horizontally).
I make four of these "arm straws". I then arrange the straws such that the finger of one straw is inserted into the arm of another. This makes a pyramidal shape that is somewhat stable. I then glue this pyramid onto the aluminum sheet.

It may not seem like much but, it takes a long time.

straw strut.JPG
If all your straws are to be cut identically, why not make a jig?

Two pieces of wood to hold the straw in place, saw-cuts in the wood to allow you to swipe through with a sharp blade?

Or go mass-production - make the same cut, over and over, then make the second cut etc.
texasratt12 (author)  Kiteman7 years ago
Due to the nature of some of the cuts to be made, I don't think using a jig would be very helpful (partial cuts and angled cuts...)
And I'm currently using "mass production" but, again, it takes a while. The straw lengths are very very small (i.e. the arm of the straw is usually between 10 and 15 mm) making this difficult.
Sorry, then, that's me out of ideas.

I hope you can get something more useful from other members.