Glue Types and Techniques

[Balsa Man]

Of the couple towers I've tested in this season so far, I've only managed to get a score of just over 1000. I've followed a pretty basic design of a square ~16x16 base with a vertical portion on the top. Here's a pic of one I tested at invitational yesterday: https://goo.gl/photos/WTiRL1WLv1vUYHzM6 So far, it seems like my problems have arose from not the actual sticks breaking, but a glue joint breaking, followed by the rest of the tower. So, it leads me to the following questions:

1. What type of glue is most effective in making a solid joint? So far, I've been using the BSI CA glue in the purple bottle, which had served me pretty well in bridges in the past, but not so much now. I've also experimented with adding wood glue around the joint after gluing with CA glue, but I'm not really sure how effective it is. Perhaps the glue I am using IS effective, but I am just not gluing with the correct technique, but are there any glues that are better in terms of bonding strength? Is epoxy an effective adhesive to look into? If so, how do you clamp it (due to the long cure time) without damaging the wood?

2. Butt joints or lap joints? So far, I've used butt joints almost exclusively because 1. slightly less wood and 2. having joints only of the outside might be bad if the vertical beams end up twisting. Thinking about it now, having lap joints does make a lot more sense because you do not suffer from non-precise cuts and there is more surface area to glue, but it also brings up another question: if you have a tower that has 4 sides that are non-vertical (like the base part of the tower that I made), how do you make a lap joint? The surfaces of the main beams will NOT be flat on the same axis, but rather at a slight angle away from each other, so any trusses that are added will not be able to make a perfectly flat contact. Should you sand away the beams to make them on the same axis, or will simply gluing it on at that angle be enough?

Thank! I look forward to incorporating your responses into my next design.

Your main problem is that you're building your tower as though we are still living under the 2012 rules; you don't need a separate base and chimney, a single pyramid is legal (and will do much better).

I don't want to argue with you, but I have a lot of perspective why a 2 part design (chimney base) is better. Tell me if I'm wrong. Yes, 2 part design adds more leg stick length, but it does allow the chimney leg sticks to be closer togheter, saving bracing sticks, and making it stronger, and you can use less heavy sticks on the top, distrubuting the weight to the weaker bottom, where u can use bracing at lower intervals incrasing the strength. Any thoughts, maybe why im wrong, and why pyramids are better than mine?

Likewise, not trying to argue, just provide perspective from coaching, hmmm 6 or 7 years of towers. As I've said in a number of posts, and explained the reasons for saying so, I don't think a two-piece design (like you describe, like what was needed under 2011/2012 rules, but isn't under this year's rules) can compete with a one-piece/truncated pyramid design. The fact that you're only at score of 1000, and folk are building (1-piece) towers scoring 2000 and above....needs to be considered as the first reason. Even if you get a 50% improvement (solving your butt-joints trying to work in tension problem- which, from your description, is what's happening- if you look at those "failed glue joints", you will see bits/a layer of wood on the exposed glue face- its the end grain of the wood failing), you're only half way there.. Other factors, include: with the higher leg angle in the bottom section, higher leg loads, which means denser legs and/or more bracing; with those higher leg loads, the bottom ends have more force pushing them out,. which means some kind tension bracing...around the bottom, connecting the legs (more weight- with lower angle legs, you have a shot of holding them in with X-strips/pieces coming down from the first ladder above the base; true, the legs close together in the chimney mean the ladders can be really light, but you can only go so light (bottom end of the density range balsa ...exists in- savings possible in tower weight isn't all that much; its really tricky to get a 2-piece...mated up to where everything is really symmetrical, and the chimney is really vertical and centered, and it doesn't take very much mis-alignment (a couple millimeters off top to bottom) to put significantly disproportional loading on one leg, so it fails... prematurely. That's what my years of experience tell me.....even if you assume... near perfect construction, when you run the numbers with right densities/strengths, 2-piecer will be heavier.

[dhdarren]

Your main problem is that you're building your tower as though we are still living under the 2012 rules; you don't need a separate base and chimney, a single pyramid is legal (and will do much better).

I don't want to argue with you, but I have a lot of perspective why a 2 part design (chimney base) is better. Tell me if I'm wrong. Yes, 2 part design adds more leg stick length, but it does allow the chimney leg sticks to be closer togheter, saving bracing sticks, and making it stronger, and you can use less heavy sticks on the top, distrubuting the weight to the weaker bottom, where u can use bracing at lower intervals incrasing the strength. Any thoughts, maybe why im wrong, and why pyramids are better than mine?

Likewise, not trying to argue, just provide perspective from coaching, hmmm 6 or 7 years of towers. As I've said in a number of posts, and explained the reasons for saying so, I don't think a two-piece design (like you describe, like what was needed under 2011/2012 rules, but isn't under this year's rules) can compete with a one-piece/truncated pyramid design. The fact that you're only at score of 1000, and folk are building (1-piece) towers scoring 2000 and above....needs to be considered as the first reason. Even if you get a 50% improvement (solving your butt-joints trying to work in tension problem- which, from your description, is what's happening- if you look at those "failed glue joints", you will see bits/a layer of wood on the exposed glue face- its the end grain of the wood failing), you're only half way there.. Other factors, include: with the higher leg angle in the bottom section, higher leg loads, which means denser legs and/or more bracing; with those higher leg loads, the bottom ends have more force pushing them out,. which means some kind tension bracing...around the bottom, connecting the legs (more weight- with lower angle legs, you have a shot of holding them in with X-strips/pieces coming down from the first ladder above the base; true, the legs close together in the chimney mean the ladders can be really light, but you can only go so light (bottom end of the density range balsa ...exists in- savings possible in tower weight isn't all that much; its really tricky to get a 2-piece...mated up to where everything is really symmetrical, and the chimney is really vertical and centered, and it doesn't take very much mis-alignment (a couple millimeters off top to bottom) to put significantly disproportional loading on one leg, so it fails... prematurely. That's what my years of experience tell me.....even if you assume... near perfect construction, when you run the numbers with right densities/strengths, 2-piecer will be heavier.

I've read plenty of your posts on this year's forum thread (and other years'), and I definitely appreciate your help and contribution! Based on yours and others' posts, I'll be moving to a one-piece design next. I just didn't have time to come up with a new design in time for the invitational my school attended yesterday, so I built the two-piece tower as shown just to have one for competition. When you refer to ladders, does this just refer to horizontal bracing that connects the to main members, paired with X or Z bracing between these ladders? Also, I've seen some post mentioning "bracing intervals," with 1/5 being the near optimum; I've done a lot of reading posts, but still haven't really figured out what this means. Could you explain to me what these numbers mean? And is CA glue sufficient, assuming that I use one-piece tower that doesn't have the very steep angles of a two-piece tower? Thanks for the help!

[Balsa Man]

Understand your time bind.
Glad info/discussion I've provided has been of help- that's why I do it... Try/tried to cover both the underlying science, and the 'how the heck do you make that happen, how do you do that' issues.

Take a look at the long post I put up on Towers B/C thread earlier this evening (its getting hard to keep up with all lines of discussion with all the threads being created...). Goes into ...a lot of detail addressing some of your questions (and other aspects of bracing); worth digesting.
Briefly-
Yes, ladders are the horizontal pieces in an "Xs and ladders" system, Xs are the crossed, diagonal pieces between ladders.
Bracing intervals = the equal intervals you break a leg into with bracing points; 1/2, 1/3, 1/4, etc. To brace legs at 1/2 interval, one ladder, half way along the legs btw bottom and top, 1/3 interval, one ladder at 1/3 of the legs, another at 2/3 of the legs, etc. Go way back (page 2, 3, 4?, or so) for introductory discussion of how buckling works, and how bracing turns a long leg into 'stacked', shorter segments, with increased buckling strength. You want the bracing intervals even, all the same length, because if one interval is longer, the buckling strength of the legs in that longer interval will be lower, and that's where the leg will fail.

CA glue works fine. You'll find description of how to use thin CA for ladder (butt) joints, and medium CA for (lap-jointed) X-strips.

Hope this helps!

[dhdarren]

Understand your time bind.
Glad info/discussion I've provided has been of help- that's why I do it... Try/tried to cover both the underlying science, and the 'how the heck do you make that happen, how do you do that' issues.

Take a look at the long post I put up on Towers B/C thread earlier this evening (its getting hard to keep up with all lines of discussion with all the threads being created...). Goes into ...a lot of detail addressing some of your questions (and other aspects of bracing); worth digesting.
Briefly-
Yes, ladders are the horizontal pieces in an "Xs and ladders" system, Xs are the crossed, diagonal pieces between ladders.
Bracing intervals = the equal intervals you break a leg into with bracing points; 1/2, 1/3, 1/4, etc. To brace legs at 1/2 interval, one ladder, half way along the legs btw bottom and top, 1/3 interval, one ladder at 1/3 of the legs, another at 2/3 of the legs, etc. Go way back (page 2, 3, 4?, or so) for introductory discussion of how buckling works, and how bracing turns a long leg into 'stacked', shorter segments, with increased buckling strength. You want the bracing intervals even, all the same length, because if one interval is longer, the buckling strength of the legs in that longer interval will be lower, and that's where the leg will fail.

CA glue works fine. You'll find description of how to use thin CA for ladder (butt) joints, and medium CA for (lap-jointed) X-strips.

Hope this helps!

Sure does, I really think I have a better understanding of where to go next with my tower. Looking up your long post right now, thanks so much!

[dhdarren]

Understand your time bind.
Glad info/discussion I've provided has been of help- that's why I do it... Try/tried to cover both the underlying science, and the 'how the heck do you make that happen, how do you do that' issues.

Take a look at the long post I put up on Towers B/C thread earlier this evening (its getting hard to keep up with all lines of discussion with all the threads being created...). Goes into ...a lot of detail addressing some of your questions (and other aspects of bracing); worth digesting.
Briefly-
Yes, ladders are the horizontal pieces in an "Xs and ladders" system, Xs are the crossed, diagonal pieces between ladders.
Bracing intervals = the equal intervals you break a leg into with bracing points; 1/2, 1/3, 1/4, etc. To brace legs at 1/2 interval, one ladder, half way along the legs btw bottom and top, 1/3 interval, one ladder at 1/3 of the legs, another at 2/3 of the legs, etc. Go way back (page 2, 3, 4?, or so) for introductory discussion of how buckling works, and how bracing turns a long leg into 'stacked', shorter segments, with increased buckling strength. You want the bracing intervals even, all the same length, because if one interval is longer, the buckling strength of the legs in that longer interval will be lower, and that's where the leg will fail.

CA glue works fine. You'll find description of how to use thin CA for ladder (butt) joints, and medium CA for (lap-jointed) X-strips.

Hope this helps!

Just to confirm, does this crude, not-to-scale MS Paint drawing accurate depict a 1/6 bracing interval? https://goo.gl/photos/PPXjcrCQLhDR5myp6

[dholdgreve]

Understand your time bind.
Glad info/discussion I've provided has been of help- that's why I do it... Try/tried to cover both the underlying science, and the 'how the heck do you make that happen, how do you do that' issues.

Take a look at the long post I put up on Towers B/C thread earlier this evening (its getting hard to keep up with all lines of discussion with all the threads being created...). Goes into ...a lot of detail addressing some of your questions (and other aspects of bracing); worth digesting.
Briefly-
Yes, ladders are the horizontal pieces in an "Xs and ladders" system, Xs are the crossed, diagonal pieces between ladders.
Bracing intervals = the equal intervals you break a leg into with bracing points; 1/2, 1/3, 1/4, etc. To brace legs at 1/2 interval, one ladder, half way along the legs btw bottom and top, 1/3 interval, one ladder at 1/3 of the legs, another at 2/3 of the legs, etc. Go way back (page 2, 3, 4?, or so) for introductory discussion of how buckling works, and how bracing turns a long leg into 'stacked', shorter segments, with increased buckling strength. You want the bracing intervals even, all the same length, because if one interval is longer, the buckling strength of the legs in that longer interval will be lower, and that's where the leg will fail.

CA glue works fine. You'll find description of how to use thin CA for ladder (butt) joints, and medium CA for (lap-jointed) X-strips.

Hope this helps!

Just to confirm, does this crude, not-to-scale MS Paint drawing accurate depict a 1/6 bracing interval? https://goo.gl/photos/PPXjcrCQLhDR5myp6

Yes... Your sketch would diagram a 1/6th (6-tier) tower with ladders

[dhdarren]

Understand your time bind.
Glad info/discussion I've provided has been of help- that's why I do it... Try/tried to cover both the underlying science, and the 'how the heck do you make that happen, how do you do that' issues.

Take a look at the long post I put up on Towers B/C thread earlier this evening (its getting hard to keep up with all lines of discussion with all the threads being created...). Goes into ...a lot of detail addressing some of your questions (and other aspects of bracing); worth digesting.
Briefly-
Yes, ladders are the horizontal pieces in an "Xs and ladders" system, Xs are the crossed, diagonal pieces between ladders.
Bracing intervals = the equal intervals you break a leg into with bracing points; 1/2, 1/3, 1/4, etc. To brace legs at 1/2 interval, one ladder, half way along the legs btw bottom and top, 1/3 interval, one ladder at 1/3 of the legs, another at 2/3 of the legs, etc. Go way back (page 2, 3, 4?, or so) for introductory discussion of how buckling works, and how bracing turns a long leg into 'stacked', shorter segments, with increased buckling strength. You want the bracing intervals even, all the same length, because if one interval is longer, the buckling strength of the legs in that longer interval will be lower, and that's where the leg will fail.

CA glue works fine. You'll find description of how to use thin CA for ladder (butt) joints, and medium CA for (lap-jointed) X-strips.

Hope this helps!

Just to confirm, does this crude, not-to-scale MS Paint drawing accurate depict a 1/6 bracing interval? https://goo.gl/photos/PPXjcrCQLhDR5myp6

Yes... Your sketch would diagram a 1/6th (6-tier) tower with ladders

Ok, thanks!