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Frogger4907 wrote:

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.

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.

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.

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.

Balsa Man wrote:

Frogger4907 wrote:

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.

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.

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.

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.

The connection between the base and chimney was uneven. How do you measure the evenness/levelness of that? Is there any device because I have jigs for the base and the chimney but I don't have one for connection (and how would you make one for the connection of them?) Lastly, none of the wood actually broke causing the failure, the chimney literally slid off of the base and then it broke. So would more glue need to be used or should I use a 1/16*1/8 balsa piece to connect the base to the chimney on each side?

thsom wrote:The connection between the base and chimney was uneven. How do you measure the evenness/levelness of that? Is there any device because I have jigs for the base and the chimney but I don't have one for connection (and how would you make one for the connection of them?) Lastly, none of the wood actually broke causing the failure, the chimney literally slid off of the base and then it broke. So would more glue need to be used or should I use a 1/16*1/8 balsa piece to connect the base to the chimney on each side?

You want to get the bottom of the chimney so that chimney is standing up straight, then you want to get the top of the base so that its as level as you can- in both cases, careful filing or sanding. for leveling the top of the base, putting a plate- like a piece of plexi, or aluminum, and laying a ruler or something straight- measure how far the ends are above the ground, as you rotate around to check all legs. Get them all even.
With no broken wood, that says not enough glue. More glue may solve. Lightest way to get gusseting would be pieces of 1/64th, like 3/32nds x 1/4- won't take much; tweezers work to put them on

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.

In addition, most people create the base, then create the tower, then attach the two together. unless you are EXTREMELY precise, you run the risk of making an uneven connection with the base, which often is the factor.

I always build the tower from the base UPWARD to the top. Basically, I build the tower on top of the base, not as two separate entities.

Balsa Man wrote:

thsom wrote:The connection between the base and chimney was uneven. How do you measure the evenness/levelness of that? Is there any device because I have jigs for the base and the chimney but I don't have one for connection (and how would you make one for the connection of them?) Lastly, none of the wood actually broke causing the failure, the chimney literally slid off of the base and then it broke. So would more glue need to be used or should I use a 1/16*1/8 balsa piece to connect the base to the chimney on each side?

You want to get the bottom of the chimney so that chimney is standing up straight, then you want to get the top of the base so that its as level as you can- in both cases, careful filing or sanding. for leveling the top of the base, putting a plate- like a piece of plexi, or aluminum, and laying a ruler or something straight- measure how far the ends are above the ground, as you rotate around to check all legs. Get them all even.
With no broken wood, that says not enough glue. More glue may solve. Lightest way to get gusseting would be pieces of 1/64th, like 3/32nds x 1/4- won't take much; tweezers work to put them on

For gussets I like to use very light 1/32 by 1/8 and connect the top to the bottom laterally and vertically on all four sides. It certaintly adds mass, but it is worth it to not have your tower give up and flop over on the test platform. Also, use a 8-oz plumbob to make sure that the top is perfectly sraight up and down. This is by far the easiest way to check levelness. Check the levelness of the floor first, then insert the plumbob attached to a loading block through the chimney. If the string attached to the plumbob hangs perfectly down the center of the tower, you are all set to test. However, if it does not hang perfectly, then sand the legs, not the top, of the tower first. Then after you have that done, you should lightly sand the top, hopefully keeping the plumbob centered. Be aware, this process may take half an hour or more, but not doing it can have tragic consequences. Hope this will be slightly helpful and sorry if it's confusing.

This is a bit off topic, but it's been weighing on my mind nonetheless. (sorry for the bad pun)

Since this is the second year of towers, does that automatically mean boomilever will be back in the rotation next year? If so, how similar do you envision boomilever to be relative to the 2008 rules? 2007/2008 was the last time this event was active.

Aia wrote:This is a bit off topic, but it's been weighing on my mind nonetheless. (sorry for the bad pun)

Since this is the second year of towers, does that automatically mean boomilever will be back in the rotation next year? If so, how similar do you envision boomilever to be relative to the 2008 rules? 2007/2008 was the last time this event was active.

automatically? no.
Very likely, yes
I envision them being fairly consistent. Like from one year to another of towers or bridges there is a minor addition or deletion of a rule or two, but the same overall theme.
For example, they'll always (I predict) keep the dimensions for towers base to be over the hole the same, b/c people have them around the nation for invites and such its a pain to make everyone change. same thing with the loading block dimensions.

Soo some things different, but you can guess pretty well whats the same

Aia wrote:This is a bit off topic, but it's been weighing on my mind nonetheless. (sorry for the bad pun)

Since this is the second year of towers, does that automatically mean boomilever will be back in the rotation next year? If so, how similar do you envision boomilever to be relative to the 2008 rules? 2007/2008 was the last time this event was active.

The current plan is indeed to have Boomilever (and it's very unlikely to change, but you never know). We actually are just about to start committee discussions about changes to the rules for next year, so I'll throw out my standard offer: make suggestions as to what you want to see in the rules and I'll be sure they get passed on to the committee as part of the discussion.

Does anyone know if the following tips are true?

• Mixing one part alcohol with one part CA glue will make the glue stronger (or something like that; I don't remember exactly)
• Also, according to this website, sprinkling baking soda on glue accelerates the drying time.

Finally, if you buy the Accelerator (a liquid that speeds up the drying time almost instantly) and spray it on your tower/structure, do you think it will add a considerable amount of weight?

fishman100 wrote:Does anyone know if the following tips are true?

• Mixing one part alcohol with one part CA glue will make the glue stronger (or something like that; I don't remember exactly)
• Also, according to this website, sprinkling baking soda on glue accelerates the drying time.

Finally, if you buy the Accelerator (a liquid that speeds up the drying time almost instantly) and spray it on your tower/structure, do you think it will add a considerable amount of weight?

dont use accelerator for towers. I made that mistake before. BAAAD