Engineering/Structure – How I Solved…

How I solved Breaking DI News

2010 marks by 15th year of participation on a DI Team and 11th year of solving the structure challenge.  I also graduated from the University of Texas at Dallas (“Whoosh” ).  I did not have much time to work on this year’s structure.  I built one for State and then tested 2 complete structures before building my structure for Global Finals.  I would have loved to have had more time to work on the challenge but with class finals and graduation and looking for a job I just couldn’t carve out any more time.   I ended up with a 15.26 ratio at Global Finals.  I certainly would have liked to have had a better ratio but hey..  I’m the Balsa Goddess.. NOT the Newspaper Goddess.

My brother had a 27.78 ratio in SL Breaking DI News.  He has written up an explanation of how he constructed his structure at:  http://tooltime.texasdi.org/2010breakingdinews .

Because of my experience in CardDIology I believed that the best solution would involve rolling up newspaper to make columns.

Most of you who solved this challenge probably figured out that newsprint has grain.  If you didn’t discover this then try this experiment.  Try to tear a piece of newspaper from top to bottom and then try to tear it from side to side.  It should tear very cleanly when you tear it from top to bottom but you will have trouble tearing it from side to side.  Since the grain of the newsprint runs from top to bottom I knew that I would need to roll my columns with the grain (with the printing running perpendicular to the length of the column).

I also discovered that there are several grades of newprint.  Almost every day in our daily newpaper there was an advertising supplement that was printed on slightly heavier newprint than the main body of the newspaper.  Sometimes it was a single sheet and some times it was a double width.  It was still newsprint but it was much sturdier than regular newsprint.  It weighed almost twice as much as regular newsprint and according to my micrometer it was almost 3 times as thick.  I decided that I would save these and use these sheets to construct my structure.

Because I was so short of time I did some incremental testing.  First wanted to determine if there was an ideal column diameter for the newsprint that I was using.  I cut several pieces of 8″ x 12″ (the width of a single piece of newspaper) from the heavier newsprint and rolled it around various sizes of steel rods starting with a clothes hangar wire and ending up with a 1/2″ piece of copper tubing.  I used a column tester (plans available from specializedbalsa.com) and determined that I was able to get the most consistent results by rolling my paper around a 1/8″ steel rod (your results may vary).   I cut the paper 8″ for height so that I would have room to clean up the ends of the columns.  No matter how careful I was I was never able to roll up a column exactly and had to trim both ends (using a small craft saw and miter box) to get a smooth end for the columns.   The only glue used in the column was a tiny amount of wood glue run along the edge of the trailing edge of newprint as it rolled around the column.

 

BRACING

Next I turned my attention to bracing.  I knew that the very thin CA glues would quickly absorb into newsprint and set almost immediately to create a very stiff piece of paper.  After some experimentation I ended up rolling small pieces (2″ x 2-1/2″) of regular newspaper into tubes around a pieces of clothes hangar wire.  My braces were going to end up being about 2-1/4″ long so this left me some room for adjustments.  I thin used tweezers to carefully dip each brace into a medicine bottle containing then CA glue.  I had to use two pair of tweezers because I had to switch the brace back and  forth between the tweezers to keep the tweezers from getting glue to the brace.   After letting it drain for a few seconds I placed the brace over two pieces of clothes hangar wire running parallel over a piece of glass to allow the brace to continue drying.  I had to move the braces periodically during this process to keep them from sticking to the hangar wires.  This produced very stiff braces that would provide stability to my structure.  After the braces were dried I used a toothpick and medium viscosity CA glue to glue the ends shut.   I took a small amount of CA glue on a toothpick and inserted it into the end of the brace and then used a pair of pliers to crimp the end of the brace and hold it for 15 seconds while the glue set.  This gave me a flat surface for glueing my braces to my columns.

CAUTION

If you try this you need to be very careful.   The CA glue sets very fast and gives off heat (enough to slighly burn you if you touch it).  It also gives off fumes that are very irritating to the eyes.  It is also very easy to spill the glue (learned that lesson myself).  A paper towel will help pickup some of the spilled glue from the table but it also starts to set and if your fingers are in the wrong place you end up glued to the paper towel and possibly slightly burned (learned that lesson also).   Find someway to stabilize the bottle with the glue so that it sets safely on the table.

COLUMNS

I then returned to thinking about my columns.  I wondered if I could do the same thing with my columns that I did with my braces.  I constructed a column with 8″ x 12″ of newsprint and then dipped the entire column into super glue.  I used an 8″ x 1/2″ pipe with a cap on one end and filled it about 1/3 of the way full with the thin CA glue.  I then dropped the column into the tube and filled it up the remainder of the way.  Using tweezers I would then pull it out and let it drain before placing it on pieces of hangar wire to dry as I did with the braces.  What I discovered is that the CA glue did not penetrate much past the first layer of the paper and only provided marginal improvement to the columns ability to hold weight.

I then experimented with different ways to construct my columns.   I took my 4 pieces of 8″ x 12″ newsprint and cut them into 2, 3, 4 and 5 equal sections 8″ long.  I used these pieces to make 4 different test columns.  Using the example of the newsprint cut into 3 sections I first took a 4″ x 8″ long piece of newsprint and rolled it around the 1/8″ rod and glued the edge down.  After waiting about 20 minute for the glue to dry I then dipped the entire column into the thin CA glue and set it aside to dry.  After it dried I took some 600 grit sandpaper and lighly sanded the column to remove any rough pieces.  Then I used wood glue to glue one edge of 4″ x 8″ newsprint to the in progress column (length wise) and let the wood glue dry.  I then rolled the newsprint around the “in process” column and glued the edges down and waited for it to dry.  I then once again dipped it into the CA glue and allowed it to dry and then repeated the entire process one more time.  This gave me a layered column using 3 pieces of 4″ x 8″ newsprint with each layer having been dipped into the CA glue.  I did this for each of the 4 columns (using 2 ea 6″ x 8″ pieces of newsprint, 3 each 4″ x 8″ pieces of newsprint, 4 ea 3″ x 8″ pieces of newsprint and 5 ea 2.4″ x8″ pieces of newsprint respectively).

After all of the test columns were complete I used a hobby saw and cut pieces of each column into lengths that would match the column section length if I was using 4, 5 or 6 sets of braces.  I used another tester to test the short pieces of column (plans available from specializedbalsa.com).  I determined that the column constructed from 5 sections of newsprint with 4 sets of braces would give me the best ratio.   I tested two structures using this method and then built my structure for finals.

As a final touch to the columns after they were completed and cut down to length, I dipped each end of each column into the thin CA glue to help seal the ends of the colums where I had used the saw to cut the newsprint.

Here are pictures of tested structures.  Click the thumbnail for a larger image.

 

 

This is a side view of the second structure I tested before building my structure for Global Finals.  Note that this structure failed the way you want all of your structures to fail… with the material just crushing at the top.  This means that the column material itself failed and that the bracing was adequte for the material being used.  Additional bracing would not improve this structures load bearing capacity because braces will not make a column stronger than it is.
Another view  
 Another View  
View of the top of the structure.  If you look closely you can see how the braces were constructed and also the hard end of the column where I dipped the end into thin CA glue.  
 Another top view.  
 A picture showing the braces.  
My global final structure.  Obviously I had some quality/consistency issues because the structure did not fail as the last test structure that I built.  
 A view of the top of my Global Final structure.  
 Another view.  

* Copied from: “Diary of a Balsa Goddess” http://structure.txdi.org/2010news  ©2009 Heather Compton

Diary of a Balsa Goddess by Heather Compton is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.

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