Tower Design

[JZhang1]

Lets have a topic on successful designs, design related issues, and all things design related.

[hearthstone224]

Personally for me, I am planning something in the shape of a thin square at the top which angles out to meet the requirement for 21.5 cm at the bottom, going for the bonus and all.

[Llamastwaimzjf]

Hey, I like your idea . I was wondering on what to do with the four supports that connect at the square on top, do you have any ideas?

[SPP SciO]

Here's an issue we've had trouble with - ensuring all 4 legs sit flush on the table.

We've been using 1/8" square legs, and the best efforts of the students to measure and cut the proper angle into the legs hasn't worked perfectly. They've also tried post-construction sanding, and it's maddening when 3 legs are making solid contact while the 4th is not, etc.

Is the trick to this simply practice + patience? Or is there an effective way? We thought about applying gentle pressure to the top of the tower and rubbing the legs all at once across a large piece of fine sandpaper, but it seemed too risky with possible twisting/breaking. A jig, much like the one described in the other thread, is in the works, and I imagine that will help also.

[Balsa Man]

Here's an issue we've had trouble with - ensuring all 4 legs sit flush on the table.

We've been using 1/8" square legs, and the best efforts of the students to measure and cut the proper angle into the legs hasn't worked perfectly. They've also tried post-construction sanding, and it's maddening when 3 legs are making solid contact while the 4th is not, etc.

Is the trick to this simply practice + patience? Or is there an effective way? We thought about applying gentle pressure to the top of the tower and rubbing the legs all at once across a large piece of fine sandpaper, but it seemed too risky with possible twisting/breaking. A jig, much like the one described in the other thread, is in the works, and I imagine that will help also.

Practice and patience will certainly help. It is really important to have the ends of all 4 legs in parallel planes. Getting 4 points into a plane can be a bear..... As discussed, a good jig (as I've described in detail)provides a number of benefits. One important one is making it much easier to do this.

The approach we use (when you have a jig) is making a 'go-by' stick for the legs. Using 1/8 bass (a little bit longer than the legs):
a) cut one end at close to the proper angle. Put it on the jig, with the angled cut end down, on the base plate. Make/use a sanding strip- like from 1/16 sheet balsa, like 1" x 3". Glue a piece of sandpaper on it. Put the sanding strip underneath the leg end, sandpaper side up. Holding the leg in place, move the strip back and forth, with gentle down pressure on the leg piece. With patience, you'll get to/have the proper angle.

Then (with sanding strip removed) tape the leg piece firmly on the jig, with the angle cut end firmly down on the base plate. Now you want to carefully cut the top end to the proper angle. A fine-tooth razor saw works . You want to do a cut t that is a) close to the proper angle, and b) leaves the leg piece just a little long. Then using the sanding strip, or a little file, file/sand the top end down till angle and length are correct.

Then using thin CA glue, soak both ends. This is to harden them. Carefully mark your bracing points on the stick.

Use this 'go-by' stick to cut legs. Take a leg stick. Get the bottom end cut/finished correctly by doing what you did on the first cut on the go-by stick (put on jig, sand bottom end). Tape the go-by stick and leg stick together, with one end....'lined up. Then make an approximate cut of the other end, so leg is just a hair longer than the go-by stick. Sand/file till the ends 'match'; till the leg is the same as the go-by stick.

This way, the legs will be very close to the same. Taped onto the jig, the bottom ends will all be in the base plane. However, no matter how carefully you do the matching, it is likely the top ends will not be perfect (as in all 4 in the same plane). When you've put in the bracing, you'll be ready to finish the top. Use a sanding block (a little wider than 5cm, maybe 10-15cm long) to sand the leg tops into a common plane. By having the sanding block.... somewhat long, you can level the top, so the top plane is parallel to the bottom/base plane. Put a ruler, or something straight on top of the sanding block. Set it so ends are at the same distance from the center. Measure distance to the bottom/base. Sand till equal at both ends. Rotate the block 90 degrees. Use the sanding block to get equal distance to ground in that direction. You end up with 4 leg ends in the same plane, parallel to the base.

Have fun!

[Llamastwaimzjf]

Can you explain that because I think it's a great concept but in a simpler manner, I'm having trouble comprehending?

[Random Human]

Can you explain that because I think it's a great concept but in a simpler manner, I'm having trouble comprehending?

This is about as simple as it gets, try doing some research on what we are saying and maybe that'll help.

[JZhang1]

Question - Are there any advantages to building a tower that spans the gap so it is 5 x 21 or so centimeters (30 if going for the bonus), over a 16 x 16 cm tower?

[Unome]

Question - Are there any advantages to building a tower that spans the gap so it is 5 x 21 or so centimeters (30 if going for the bonus), over a 16 x 16 cm tower?

Advantages - possibly weight, not sure
Disadvantages - higher forces on each axial compression member, since they're at a wider angle than if the base were square. Also, imperfections in the Test Base (see 2012 subforums) are more likely to cause the tower to tip over, since it's narrower.

[Balsa Man]

Question - Are there any advantages to building a tower that spans the gap so it is 5 x 21 or so centimeters (30 if going for the bonus), over a 16 x 16 cm tower?

I think that's ....an open question. There certainly are folk out there who are thinking its the way to go. My personal take is disadvantages outweigh advantages. Apparent advantage is a bit less total length of ladder braces (adding all 4 sides up, for however many bracing intervals).. Less length = less weight, IF density of ladders is the same in both cases. However, particularly down toward the bottom, the ladders on the long sides have to be significantly longer. That means higher density, to have enough strength = more weight. I believe that increase offsets the decrease in total ladder length. The bigger issue, I think, is a tower 5cm wide. straight up two sides will have major stability, as in fall over issues.
Just my take.