Connecting tower base with top

[darp]

I've tested my tower several times but every time, the top vertical portion of my tower tips over and the tower breaks prematurely. The glue between the base and the vertical top detaches every time.

For my tower, there are only 4 1/8" cu locations where the base meets the top. According to a leveler, the top of my tower was 0-1 degree below the horizontal (not perfectly stable but very close).

This leads to me think that one or more of the following caused the top of the tower to tip over:

1) The base is unstable which forced the top to tip.
2) the glue on one of the four meeting locations (where the base is glued to the top) was not as strong as the others - therefore, it tipped.
3) 4 1/8 cubic inches is not enough surface area to connect the two parts.

I believe that 3) is the most likely reason for this since the bucket's instability may sometimes cause the tower to tip even if the tower is stable.

How do you connect your tower base to its top?

Any other opinions and suggestions will be highly appreciated! Please help!

[Random Human]

I've tested my tower several times but every time, the top vertical portion of my tower tips over and the tower breaks prematurely. The glue between the base and the vertical top detaches every time.

For my tower, there are only 4 1/8" cu locations where the base meets the top. According to a leveler, the top of my tower was 0-1 degree below the horizontal (not perfectly stable but very close).

This leads to me think that one or more of the following caused the top of the tower to tip over:

1) The base is unstable which forced the top to tip.
2) the glue on one of the four meeting locations (where the base is glued to the top) was not as strong as the others - therefore, it tipped.
3) 4 1/8 cubic inches is not enough surface area to connect the two parts.

I believe that 3) is the most likely reason for this since the bucket's instability may sometimes cause the tower to tip even if the tower is stable.

How do you connect your tower base to its top?

Any other opinions and suggestions will be highly appreciated! Please help!

3 Is wrong. Likely your gonna want to hit on 1 and 2. Mine works perfectly. The key is to have the top and bottom connection areas fully contacting so that all weight is properly transfered. Before connecting top to bottom, sand it so that weight will not be on one leg and cause tipping. As well as this, its a good idea to drench the connection points with glue, before and after.

[darp]

3 Is wrong. Likely your gonna want to hit on 1 and 2. Mine works perfectly. The key is to have the top and bottom connection areas fully contacting so that all weight is properly transfered. Before connecting top to bottom, sand it so that weight will not be on one leg and cause tipping. As well as this, its a good idea to drench the connection points with glue, before and after.

Thank you! But how do you ensure that it is perfectly leveled? Also, is it the four pieces of the base or the top that are connected to the other? or do you place a flat strip of wood in between? (I usually sand the 4 ends of the base and place 2 strips of 1/8"x 1/16" on top and glue the top to that. However, this time, the glue detached between the flat 1/8" x 1/16" strip and the base.
I will drench the piece with glue both times from now on.

[Unome]

3 Is wrong. Likely your gonna want to hit on 1 and 2. Mine works perfectly. The key is to have the top and bottom connection areas fully contacting so that all weight is properly transfered. Before connecting top to bottom, sand it so that weight will not be on one leg and cause tipping. As well as this, its a good idea to drench the connection points with glue, before and after.

Thank you! But how do you ensure that it is perfectly leveled? Also, is it the four pieces of the base or the top that are connected to the other? or do you place a flat strip of wood in between? (I usually sand the 4 ends of the base and place 2 strips of 1/8"x 1/16" on top and glue the top to that. However, this time, the glue detached between the flat 1/8" x 1/16" strip and the base.
I will drench the piece with glue both times from now on.

There's no way drenching the glue is necessary to make a sufficiently strong connection. @Random Human - wondering, why do you recommend this?

[DarthBuilder]

I might be wrong here but I did do that before. I did drench the towers joints with glue and it held all. But I’m not sure what to recommend (I did this last year for towers for my first few towers)

[dholdgreve]

Be careful that you do not violate rule 3.a.i... Some judges will not differentiate between paint and adhesive. Totally saturating the joint may violate this rule if taken to the extreme.

A couple other thoughts: Possibly a few small gussets that extend from the upper columns at a 45 degree angle down to the compression members at the top of the base section may help hold your upper columns in line with the lower ones. If you are X bracing the upper section, are your X braces extended all the way to the bottoms of the upper columns? If not, they should be. Are your compression members at the top of the lower columns? If not they need to be.

[Balsa Man]

A few thoughts/comments on this subject-

Early-on this season, I discussed a) how critical it is to get base/chimney leg joints right, and b) how difficult /darn near impossible that is to do if you’re building base and chimney separately, and then mating them up to complete the tower. To review and elaborate:

There are multiple aspects to getting this joint right:
One, as noted by Random Human, is to have top (of base legs) and bottom (of chimney legs) connection areas ‘fully contacting.’ That means when the two leg segments are in….design position/alignment, the faces of both the leg ends are in the same plane, and they’re flat from edge to edge.
The next aspect is that the shape and surface area of the cut ends needs to be the same. If, as many folk try at the start, you cut the top of the base legs so the ends are all in a plane parallel to the test base- to create a “flat” top of base section, because of the lean-in angle of the base legs, the cut ends at the top of base section end up in the shape of a rhomboid – a diamond shape. It has a ‘long axis’ joining the diagonal corners that face toward and away from the vertical centerline of the tower, and a ‘short axis’ joining the other two diagonal corners. Now if you cut the bottom ends of the chimney legs to ‘fully contact’ with the tops of the base legs, because the chimney legs have only a very slight lean-in angle, the (bottom) cut ends end up being very close to being square- the long axis is only a very tiny bit longer than the short axis.

When you mate the two ends, the face of the bottom of the chimney leg is significantly smaller in area than the area of the base leg top end. You can easily see how the long axis of the base leg ends sticks out beyond that of the chimney leg ends. If you manage (on all 4 legs) to perfectly align the short axis of the chimney leg faces with the short axis of the base leg faces (the short axes of both being the same length), then the two leg segments will be ‘axially aligned’- the short axis of both segments will meet in the joint. The force coming down the axis of the chimney leg will go/flow down the axis of the base leg. However, if that ‘axial alignment’ is not perfect, then the base leg segment will not be “axially loaded – the load coming down the axis of the chimney leg will be “off axis” going onto the base leg. Having spent a lot of time (back in 2011/2012- last time we had rules driving a ‘2 part/base/chimney sections’ design requirement) trying to create base and chimney jigging that would perfectly align all 4 legs so that the base legs would be seeing axial loading, I can tell you it is very unlikely you will be able to pull that off. First, the positioning of bottom of chimney legs and top of base legs has to be perfectly matched- in the exact same square (or if not perfect square, the exact same….quadralateral), and along with that the short axes of the end cross sections have to line up on all 4 legs.

Our buckling strength measurements for figuring out how strong and how braced a base leg segment needs to be to carry full/design load assume axial loading- that’s one of the base assumptions in Euler’s buckling equation. If the loading a column/a leg segment sees is off axis, its buckling strength will be significantly less than if its axially loaded. Off-axis loading will immediately, as load starts to develop, induce a bending moment into the column being loaded. Very little load (far short of the load required to buckle an axially loaded column) will start bending- i.e., buckling. The math to calculate the reduction in buckling strength as a function of the amount/degree of non-axial loading, is very complicated. But the important part to understand is that a very small amount of off-axis loading – like less than you can see just looking at the joint – will result in a significant bending moment being produced. Non-axially loaded base legs will fail at significantly lower loading than axially loaded ones.

More importantly, in terms of overall tower performance, is what this means in terms of the …. vertical stability of the chimney section. Because of its narrow width, compared to its height/length, the chimney, as a whole, is very sensitive to off-axis loading. In the perfect case, the legs are oriented in a perfect square, and the load is evenly distributed among the 4 legs – i.e., it is being applied, vertically down the vertical centerline between the 4 legs. If, looking just at the chimney, you get the leg bottoms sanded just right, so the chimney is sitting absolutely vertical, and all 4 leg bottoms are in full/even contact, let’s say if you were to test just this hypothetical chimney, and find it carries 15kg. What would happen if a) the load block was not quite centered, or b) it wasn’t quite vertical, or both a) and b)? With very small mis-alignment of loading or very small mis-alignment from vertical, it would fail (or fall over) at significantly less than 15kg loading.

If our perfect/hypothetical chimney is sitting on a tower base section (let’s say a base that has been independently built and tested to hold 15kg loading), and the leg tops in that base section are perfectly ‘in-plane’, so, as in the test of the chimney by itself on a testing base, it is really sitting vertically, and the load is symmetrically distributed to the 4 legs, what happens if, because of non-axial loading onto one or two of the base leg segments, just a little bit of bending of one/two of the base legs starts? One corner/one side of the level platform the chimney is sitting on is lowered- the chimney will immediately start to lean toward the lowered leg/side. All it takes to start this is… like one or two thousandths of an inch. That lean causes a quick and significant transfer of additional loading to leg(s) its leaning toward- that increases the loading onto the non-axially loaded base leg(s), increasing chimney lean, and in an instant chimney is leaning enough we see the…’classic’ failure mode- chimney falling to one side, chimney/base leg joint failing- the exact situation being discussed.

It is because of these factors- and the way they work together to turn/cascade a set of very minor mis-alignments into tower failure – that I have been recommending a) a single jig approach - a jig that carries/aligns “assembled legs”- where chimney and base legs, glued together at the joint are mounted on the jig, and then the bracing is put on, and b) cutting of the leg ends (both bottom of chimney legs, and top of base legs) so that they are cut at the same angle – that angle being ½ of the angle formed between the base legs and chimney legs. With both leg ends cut at this same angle, the faces that get joined are the exact same cross sectional shape and area – when you mate them up, all corners and faces of the sticks line up perfectly – you have full contact, and loading onto the base legs is axial. In addition to getting the cut at the top of base legs correct, it is important to use some sort of tool/jig to make the bottom of base leg cuts so a) that angle is correct – the bottoms of the base legs sit flat on/in full contact with the test base, and the length is exactly the same. It is also important to carefully fit ladders at top of base- that are strong enough, and while it is not necessary to ....slather the joint with lots of glue, it is not a joint to push the limits on how little glue can you get away with....

There may well be…. clever folk out there who have figured out other ways to get the precise alignment needed for high performance of the base/chimney leg joints. The way I’ve described is one way, and the best I know of at this point. Hope the discussion above helps to understand what’s going on, and what needs to be controlled/managed to get to high performance.

[Random Human]

3 Is wrong. Likely your gonna want to hit on 1 and 2. Mine works perfectly. The key is to have the top and bottom connection areas fully contacting so that all weight is properly transfered. Before connecting top to bottom, sand it so that weight will not be on one leg and cause tipping. As well as this, its a good idea to drench the connection points with glue, before and after.

Thank you! But how do you ensure that it is perfectly leveled? Also, is it the four pieces of the base or the top that are connected to the other? or do you place a flat strip of wood in between? (I usually sand the 4 ends of the base and place 2 strips of 1/8"x 1/16" on top and glue the top to that. However, this time, the glue detached between the flat 1/8" x 1/16" strip and the base.
I will drench the piece with glue both times from now on.

There's no way drenching the glue is necessary to make a sufficiently strong connection. @Random Human - wondering, why do you recommend this?

It's a bit hard to visualize. But after you connect two pieces of wood, ones that are critical to your towers strength. You'd find that some bad sanding job or connection job leaves a small gap in between the two wood. I'd like to put a bit of glue just around the connection point. It comes at a small cost, and can mitigate large risks, explained by darp.

[Raleway]

I think this question has been needlessly discussed over and over again (we really need a simple redirect to the main towers forum)

Without a jig, getting precise alignment is near impossible to achieve and even then, replicate. Adding a ladder between them only makes freehand alignment easier, but still terribly difficult and near impossible to do right. The addition of another piece of wood to me is not necessary if you have a jig as adding another piece introduces more variability and possibility of premature failure. The only known solution is to align it with a support (whatever you choose to use). Drenching the joint in glue could help, but it will never give you a competitive tower (2.5k-3.5k).

Folks, please just realize that you will need a jig this year. You will be hard pressed to consistently break even 2000 without it. There is nothing more to really say in my opinion.

[Unome]

Thank you! But how do you ensure that it is perfectly leveled? Also, is it the four pieces of the base or the top that are connected to the other? or do you place a flat strip of wood in between? (I usually sand the 4 ends of the base and place 2 strips of 1/8"x 1/16" on top and glue the top to that. However, this time, the glue detached between the flat 1/8" x 1/16" strip and the base.
I will drench the piece with glue both times from now on.

There's no way drenching the glue is necessary to make a sufficiently strong connection. @Random Human - wondering, why do you recommend this?

It's a bit hard to visualize. But after you connect two pieces of wood, ones that are critical to your towers strength. You'd find that some bad sanding job or connection job leaves a small gap in between the two wood. I'd like to put a bit of glue just around the connection point. It comes at a small cost, and can mitigate large risks, explained by darp.

I see what you mean - to account for any imperfections and avoid bombing, at the cost of a relatively small drop in score in most cases from the added weight.