How to Reduce Tower Weight Without Sacrificing Strength?

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Ray Li
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How to Reduce Tower Weight Without Sacrificing Strength?

Postby Ray Li » May 5th, 2012, 1:39 pm

I'm part of the Central High School team that will be representing Arkansas at the national competition this year. The tower that I built for the state competition is strong, but it is too heavy. I am looking for ideas/designs that will make my tower lighter, but not sacrifice its strength.

Wood used:

Balsa
Basswood
Hardwood from Home Depot (did not specify what kind of hardwood)

Glue:

Titebond III

Tower height:

70 cm

Load held:

Held all 15 kg

Tower weight:

182 g

Wood size used:

1/4 x 1/4 in.
3/16 x 3/16 in.


Here are pictures of my tower:

http://gallery.scioly.org/details.php?image_id=3715

http://gallery.scioly.org/details.php?image_id=3714

http://gallery.scioly.org/details.php?image_id=3713


I would also appreciate methods/tools for cutting hardwood like basswood. I'm currently using a razor saw.

http://www.google.com/imgres?q=razor+sa ... x=35&ty=28

It can cut through the hardwood sticks that I'm using, but it takes considerable pressure to completely cut through. This causes the cuts to be uneven and not straight sometimes. Some of the pieces of wood on my tower did not fit together and as an result and I had to use glue as a filler. I'm pretty sure that I'm not cutting against the grain, but I may be wrong. Additionally, has anyone tried using a power saw like a Miter saw to cut through small sticks of wood like the ones I used for my tower?
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Balsa Man » May 5th, 2012, 7:47 pm

Congrats on going to Nats.
You don't have much time, so a quick, straight answer

First thing, take the time to read through this year's tower building posts. That is the value of this board- the accumulated knowledge.
Then look at the pictures of the towers. Think about what you have read and seen.

Right now, you you're weighing 20 times what competitive towers at Nationals will. Ten times what ~40th place will

Wood you're using is WAY to big, and heavy- as you read, you will understand what others are using.

In the base particularly,about 3/4 of the pieces are doing nothing structurally; they're just extra weight. Glad to talk more when you've done your basic homework
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Frogger4907 » May 5th, 2012, 9:49 pm

Build the same thing, but out of balsa... I bet with the same thicknesses you will still hold it all.
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Ray Li » May 6th, 2012, 7:36 am

With thin pieces of wood, should I still use lap joints? I've never used any wood with a thickness less than 3/16 in. and so I don't know how strong thinner pieces are. Also, I am completely re-thinking the design for my national tower. Circles are the strongest geometric shape if I am not mistaken, so would having a triangular prism frame (with bracing) wedged between two circles be a good idea for the chimney of the tower?
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby SLM » May 6th, 2012, 8:09 am

With thin pieces of wood, should I still use lap joints? I've never used any wood with a thickness less than 3/16 in. and so I don't know how strong thinner pieces are. Also, I am completely re-thinking the design for my national tower. Circles are the strongest geometric shape if I am not mistaken, so would having a triangular prism frame (with bracing) wedged between two circles be a good idea for the chimney of the tower?
Lap joints would work.

As BalsaMan said, you don't have much time. At this point, it would not be wise to start experimenting with different geometric configurations, especially a triangular prism which could easily twist under load. Your best bet is to use a rectangular chimney with either a rectangular or square base. The design of your chimney is fine, you just need to reduce the size of the members. Again, the base of your tower has too many extra members. Take a look at the image gallery for ideas about the shape of the base. More importantly, spend couple of hours reading through the posts in this forum, you will find the information you need for building a relatively competitive tower for the Nationals.

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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Ray Li » May 6th, 2012, 8:43 am

Should I still use Titebond III glue? It is very strong, but I'm starting to think that it is too heavy and not necessary. Also, should I dilute all glues that I use with 70% being glue and 30% being water?
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Balsa Man » May 6th, 2012, 8:54 am

Yup (to what SLM says),
Couple more thoughts/comments.
If you were to do your chimney as shown, but in 1/8th bass legs, with 1/16th balsa bracing (if you're buying wood from a hobby store, try to pick heavier/stiffer ones), you would save a lot of weight. Built with any reasonable level of precision, it will hold 15 kg- actually should hold significantly more, but trying to get you quickly to something a lot better than what you have now.

That same combination will be more than enough in the base. Look at the pictures of C-Div bases in the Gallery to better understand how simple it can/should be, compared to what you have now. 4 legs, 4 "ladders" joining the tops- the tops of the base legs line up with the bottoms of the 4 chimney legs. 4 ladders joining the mid-points of the base legs. X- braces (using the 1/16th balsa), joining the upper ladders and leg mid-point ladders, and from the leg mid-point ladders down to the bottoms of the base legs. You probably won't need it, but for a safety factor, with minimal weight, run a "strap" around the bottom of the base, using 1/16th balsa.

Consider using slow CA glue - it will save you a lot of waiting for glue to dry time. For the problem of joints not fitting/filling, and filling with glue, sand, or use a little file to get a good fit.

Make sure the bottom ends of your base legs are sanded/filed so they are flat and in full contact with the...ground. Then make sure the tops are flat, and provide a LEVEL base for the chimney to sit on. Before putting chimney on the base, make sure the bottoms of the chimney legs are sanded/filed so it sits straight up and down. This is really important- lean will kill you
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Ray Li
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Ray Li » May 6th, 2012, 9:10 am

I have Gorilla Super Glue. Would that work? Should I dilute the glue to reduce its weight?
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Balsa Man » May 6th, 2012, 9:15 am

Yes, it will work.
NO on dillution- nothing to dilute it with- it doesn't "dry", it reacts/"goes off." Weight saving comes from not using too much. It takes very little. Practice/play with it on scrap pieces before trying to use on a tower; get the feel of how it works
Len Joeris
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Re: How to Reduce Tower Weight Without Sacrificing Strength?

Postby Ray Li » May 6th, 2012, 9:24 am

I've looked through the gallery and it seems that most people who use x braces tend to have one strip of wood running diagonally on the front of the two legs and then another strip running diagonally in the other direction that is also on top of the legs. In the middle, where the two pieces meet, one of the pieces is forced to bend upwards. Shouldn't that be a bad thing? So should i have one piece on top of the legs and the other on bottom and then use a little piece of wood to fill in the space where they cross?
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