Frogger is absolutely correct; when you get out of "vertical alignment" for whatever reason, the load it will carry goes down really fast. The fact that both base and chimney, independently, held 15kg, and the combined didn't get to 3 says it all. Worth digging back thru earlier posts on how to check alignment. With reasonably simple tools, being able to measure within a millimeter for position of top end of legs is doable. That relative to the surface you're measuring from, of course. If the test surface is other than level, you can have a very precise build, and the lean from a non-level surface will bite you. You can control this variable in your own testing, but you can't, of course at competition. For towers going to the 70cm height range, that suggests building in some sort of safety factor may be wise. Having a little plumb bob device for checking levelness of test surface surface at competition would be smart, too, and if you make one leg a bit stronger, and put it to the "downwind side", that could help.Frogger4907 wrote:Even the slightest lean will really affect the distribution of weight to one side of the tower causing it to snap much quicker. and unlevel testing surface could provide a similar affect.thsom wrote:Hey guys, I just tested a tower and it held merely 2.57 kg . However, when I tested the base and chimney at home, both held over 15 kg. The tower broke at the connection. No wood actually snapped causing it to break, the chimney just literally quickly fell of of the base. Was it because of a small lean and improper/inadequate connection of the two because if I can fix this issue, I could have a nice tower.
Your description of the failure mode also makes me wonder about alignment and glue; how closely do bottom ends of chimney legs line up with top ends of base legs? To not have major issues (the sort of result you ran into) this alignment has got to be really good- certainly within 1/2 a mm; ideally, better than that. I assume you're running ladders at/very near the top of the base legs; with the lean-in angle, these will be under significant compression load (the tops of the base legs pushing in toward the center). If they're not adequately braced against that, there will be a shear load at where the chimney and base legs meet. Plenty of glue, and/or little gusset plates could help handle that.