Towers B/C

[Balsa Man]

Thanks Balsa Man. You won't believe how much that picture helped me. I have one question. The legs of the tower won't be flat against the jig. Right? Will that be a problem?

You're welcome. As they say, a picture is (can be) worth a thousand words......
You're right, leg won't be flat against the edges of the jig plates. That's what the first paragraph under "Improvements from last year" is about. Re-read, and think about what the words are saying.

The edge strips, which get glued along the outside edges of the jig plates hold/align the legs. These strips, looking at one end-on, have a cross section that looks like an underlined capital letter M. The width between the vertical lines of the letter is the same as the thickness of the jig plates. The angle of the V between the letter legs is 90 degrees. The legs ride in that V groove, so one diagonal edge of each leg is up against the bottom of the V. If you looked down on the top of the jig with the strips and legs in place, you'd see a cross with diamonds (the ends of the legs) at the ends of the cross. The underline is the bottom/inside edge of the leg holding strip; it is that edge that is glued to the jig plates. The distance between the bottom/apex of the V-groove and the bottom edge of the strip is about 1mm.

So, in the end, the legs are tight up against the jig plates, actually tight up against the strips which form the outer edge of the plates. With the diagonal edges of the legs pointing at the vertical centerline of the tower, looking at one side of the tower - two adjacent legs, the outside faces of the legs are precisely parallel/in the same plane, the same as what they would be if you built one side of the tower on a template/drawing (by putting the legs down flat on the template, and then joining them with bracing pieces (Xs) glued to the faces of the legs. So, not a problem, but rather the solution to a problem; how to align/position the legs very precisely and symmetrically in 3-d space.....

[Balsa Man]

Definitely a candidate for laser cutting.

Yup; just not something you could practically do/cut by hand cutting, but a piece of cake with a laser cutter. Last year, with straight legs, with good skills, and a lot of care and time, hand cutting of 4 plates (and using a center post to put them onto), you could get to a reasonably decent jig.

Its really impressive, if you stack up a number of the cut plates, and feel/see along the edges how...identical they come out. And the slot cuts give you a nice, snug slip fit. You could probably get similar precision with a large computer controlled end mill at a machine shop, but it would cost...oh, a hundred times what it costs for laser cutting. We paid about $50 for the plastic and the cutting (two jig plates, a 12" square base plate, and two 6" (perfect) squares, and two 3" squares for aligning the panels perpendicular to each other......
Not bad for a solution to what is arguably the biggest barrier to a high-performing tower; getting precise 3-d symmetry of the leg positions.

[Gr8tor]

Balsa Man, you said you 3-D printed your edge strips. Would it be possible to laser cut those too?

[Balsa Man]

Balsa Man, you said you 3-D printed your edge strips. Would it be possible to laser cut those too?

Don't think so with just a laser cutter. In all the laser cutters/engravers I'm aware of, there's a bed the material to be cut lays on, and a... mechanical system to move the laser head in x and y directions above the bed. The laser head points down vertically, and cuts as the system moves it. Can only make a vertical cut. No way to do a V notch.

The only way I can think of, I don't think would be practical; you could conceivably machine a set of parallel V grooves in a sheet of material (if you have access to a CNC router or milling machine), and then use a laser cutter to cut along the edges of the V grooves to produce V-grooved strips....

[Gr8tor]

Balsa Man, What glue do you use for your jig?
Does super glue work for cast acrylic and 3-D printed stuff?

[Gr8tor]

Balsa Man, What glue do you use for your jig?
Does super glue work for cast acrylic and 3-D printed stuff?

[Gr8tor]

Sorry for the double post. I didn't realize I posted the first time

[Balsa Man]

Balsa Man, What glue do you use for your jig?
Does super glue work for cast acrylic and 3-D printed stuff?

This stuff:

https://www.amazon.com/dp/B00JFPF0UQ/re ... 3982566764

With the applicator bottle w/ needle tip.
You do not want to use it except under a lab hood, or a VERY well ventilated space, or with an organic vapor respirator (serious inhalation hazard). It is just solvents; dissolves the plastic, then pretty quickly vaporizes away, so the joint created is... like welding
There's a thicker, a bit slower version in a tube (similar inhalation hazard) (see in the other things at the bottom of the page). The thin just works better. You have to practice a bit with scrap pieces to get the hang of using it, but when you do, its awesome; hold one piece against another, let a bit run out against the seam/joint, it flows into the joint, and in a minute or two things are held/locked in place, with full strength reached in ~12hr. A reasonable alternative is plastic model cement from a hobby shop. CA does not work very well; its quick, of course, but it doesn't dissolve the plastic and is somewhat brittle, so joints in a plastic assembly can come apart.

[IvySpear]

So I spent some time reading through the thread and this is basically what I got out of it (Excluding the mathematic formulas):

1) This year must be a double part tower, with a wide base truncated pyramid as the base and a perfectly vertical chimney as the upper portion

2) It would be prudent to shoot for the bonus this year, since it offers too much value to be ignored

3) It's very hard to build a tower whose base and chimney matches up perfectly, but using a jig would help with this. I have a question, if I don't have the means to build an accurate jig, are there are steps I can take to try to build as accurately as possible without one? Tips, order in which I should build etc.

4) You should build the chimney and the base separately then connect them? Not sure on this one

5) All X bracings are superior to including a ladder, but this year you do want ladders on your upper chimney portion? Then we don't need them for the lower base portion I assume? Also the ladders should be in between the two main beams correct? Not on the outside.

6) The beams for X bracings should not be square? Or is it fine if they are. How would you cut them out from sheets anyway? Will I have to buy balsa sheets from an online website?

7) The meta position for the X bracings is on the outside of the tower. Wouldn't that warp one or both of the X bracings in that scenario though? Can someone attach a picture since a picture is worth a thousand words

Additionally, how thick should the main, longer legs be? Is 1/8" too much already? Will 1/16" braces work in general, or are there some exceptions?

Also, I'm not very satisfied with the current cutter I have (It's an X-ACTO Knife), so are there any alternatives?

Thanks and sorry for asking so much, I just wanted to clear some things up

[Gr8tor]

Balsa Man, Would you need a mask and gloves for that? Also, a little off topic, how do you create and send your design to the people who laser cut? What software do you use? AutoCad?