How to Reduce Tower Weight Without Sacrificing Strength?

[Balsa Man]

Yes, Xs from square cross section stock bowing is a problem.
In your chimney, if you just go with 1/8 bass legs, and 1/16 balsa Z-bracing like you have, you don't have to worry about it; with those sizes, and the bracing interval you're at, you'll be plenty strong.

In the (simplified) base, using ladders and xs, as I've suggested one direction on the outsides, and the other (running the opposite direction) on the inside will solve the problem. No, you do not want to glue the intersection together.

[Ray Li]

As for the frame on the bottom of the base, should I glue the legs on top of the frame or should i glue the frame pieces around the legs?

[Balsa Man]

Around the outside; ends of the legs sitting on the test surface

[thsom]

I would strongly encourage looking at the wiki towers design. What you should do is this, a design that worked with me with special density balsa, but would be absolutely strong enough with regular density balsa: base braced 4 times with x's, 16 cm to 4.5 cm at the top. The x's each span 4.5 cm of main legs making a base that is 16 cm tall. Then, make a chimney/top that is 55 cm tall braced with diagonals every 3.5 cm (if you are unsure with it, go with every 3 cm which should hold all 15 kg), but no lateral pieces are required. The main pieces of the skeleton are 1/8 squared balsa and for cross bracings it is 1/16th square balsa. It should look like this:
http://gallery.scioly.org/details.php?image_id=3643
for the base, but the top portion should be braced twice instead of once, making there be 4 x's

It should look like this:
http://gallery.scioly.org/details.php?image_id=3664
for the top, braced every 3.5 or 3 cm with no laterals:
/\/\/\/\/\/\/\
With this design, the tower should hold all 15 kg and be about 10-11 grams, 12-15 grams compensating for excessive glue use (especially when joining the base and top, don't use too much, but use enough).
My state tower was 8.88 grams and it held all 15 kg at my school, broke early at comp. because of transport issues, but you should be fine.

EDIT: for your cutting device, I recommend that you use a smaller blade, yet still the same sharpness. About 1-2 inches in length. This way you have more control over the cuts and you can be accurate and precise.

[Ray Li]

Should I construct my tower completely out of balsa wood or use a combination of balsa and basswood with basswood/hardwood in places that need to be the strongest?

[Balsa Man]

As you've seen if you've reviewed this year's tower posts, there are lots of ways to get to a competitive tower, and a range of opinions, both on basic approach and various details. What thsom is suggesting would work. What I suggested would work. They'll both come out in the 15, certainly less than 18gr range. What I suggested will be slightly heavier than what thsom is suggesting; it will also be more tolerant of a less than precise build.

Both should get you an order of magnitude farther along than what you have. Hardwood has no place; there is just no need. There is no need for anything bigger than 1/8th.

The wiki has some good info, also some less than good info; you probably don't have the experience base to tell the difference.

As I said at the outset, time is not your friend. You need to settle on an approach, and then build it as carefully as you can

[thsom]

I agree my design takes a steady hand, however if constructed to plan, you can get away with it being ~10-11 grams, something that could very well win a less competitive state competition and place in the top ten at a very competitive one. Depending on your experience,(seeing the design, I'd say basic) I also agree with a slow CA glue, if you can handle it, i suggest medium CA glue, The only places where I used Thin CA glue was in Joints that I wanted to bond instantly so that they would be exact.

[LKN]

I'm going to have to go with balsaman with this, you are definitely looking in the neighborhood of 15grams if built reasonably. You are looking at about 1.5grams of base leg weight,3 grams of base bracing, 5ish grams in the chimney legs, and another 4ish grams in bracing the chimney. Tack on wight to attach the chimney and base and inexperience add a gram. You are looking at 15 grams or so at 70cm. Balsa 1/8 varies a lot, but denser stuff for what you want you look at about 2.0-2.4grams per 36" stick and if you pick out stiffer 1/16 balsa you are looking at .5-.6grams per 36" stick. Go the full 70cm centimeters as well, especially following either build design suggested. Find yourself a good blade, I use a window scraper with a razor blade. It makes a good punch-cut action and is quick and convenient. It might take a little bit of muscle to get through 1/8balsa wood, but you should be fine once you get a feel for it.

[Ray Li]

I am almost finished with my tower. It weighs 13 grams right now, but it will probably be heavier when I glue the base and chimney together. All together, it should weigh around 15 grams. Are there any ways to reduce the weight at this stage? Also what are some good methods to transport towers? I am planning to transport it in two pieces. My team is going by air and I don't think I can take it as a carry on item. I will try and post a picture of the finished tower as soon as possible.

[J-Fish123]

Chicken