General Discussion

[LKN]

I really have had something along similar lines as a question for debate too.. Thanks for bringing it up fishman100. First off, never heard about the alcohol mixing with CA. I have heard of the baking soda technique, but merely heard, not from a credible source. Thanks for throwing up the link as a reference.

Mrsteven, why was accelerator a mistake for you? Just want to hear your reasoning.

I believe that accelerator adds nothing to your tower weight because it evaporates. I am not sure though, I wonder what others think. But, I do believe that glue must be the strongest when allowed to set on its own time. How much stronger? I do not know. I do believe if you use accelerator correctly than it can save a little building time.

Here are some guidelines I follow while using accelerator:

1. Do not use the spray pump, it uses way more accelerator than necessary. Instead, unscrew the bottle and "dab on" the accelerator to the specific glue area you want to quicken. Watch out for the unscrewed bottle, you don't want to spill it.

2. Make sure the joint is tight with as little space between the glued surface areas as possible. You are causing the glue to near instantly cure, and you do not want glue globs between surfaces. The glue can technically, and I mean technically, be next to infinitely strong assuming that there is absolutely no distance between surface areas. Since this is basically impossible, we can only get close. Having cured glue over the distance of a gap drastically destroys the integrity of a joints. This is what makes using accelerator difficult and possibly a liability for your tower. You must make sure everything is tight when you instantly cure the CA with accelerator.

Now for my question. I have been using the Gorilla Glue CA Brand. I believe it came out within the last few years, and I seem to be having success with it. Has anyone else tried this or is currently using it? What are your thoughts? The only real difference it appears to have between regular CA glue is that the gorilla glue has "rubber particles" to be "impact tough". Does that mean it could be heavier or more durable?

Link: http://www.amazon.com/Gorilla-Glue-7805 ... _hi_text_b

[mrsteven]

My reasoning? Simple, and you covered it in your reply

I find the instant curing detrimental because it gives the glue less time to naturally absorb into the wood which gives a weaker bond. The 2 towers I made with it both broke at the glue (no wood damage, a joint popped) that was attributed to that. I know it was the accelerator b/c I made roughly the same tower that held ~5 kg more and ended with a literal beam snapping.

I've also read through the towers, and other modeling based events forums for the last few years and in terms of towers, many many-a-posts concur with the result of a weaker tower due to accelerator (but yes, there were a couple posts countering it, but nothing that was terribly factually based if I recall correctly).

I haven't noticed a weight different with accelerator, maybe extremely minimal

[jander14indoor]

I thought the question of accelerator effect on CA was interesting, so I turned to google.
Here's one technical paper on CA strength, nothing about effects of accelerator.
http://www.masterbond.com/sites/default ... rylate.pdf
Here's an interesting dicussion about CA you may find useful. It state "over-application of the accelerator may reduce the ultimate bond strength significantly". And that matches my experience. Use only a little accelerator and little effect, flood it and the joint is brittle. And here in the dry midwest in winter, in can take a while to cure due to moisture in the atmosphere (the usual mechanism).
http://www.woodturningvideosplus.com/cy ... lates.html

Didn't find any more hard data in the time I spent looking (though I found a lot of info about different KINDS of CA, some of which might suit our applictions better than others). See what you can find.

Jeff Anderson
Livonia, MI

[TYG]

Would there be any benefit in putting a gusset plate on the chimney to base connection?

[SLM]

Would there be any benefit in putting a gusset plate on the chimney to base connection?

If there is one place in the entire tower where gusset plates are needed, it would be at the connection(s) between the chimney and the base.

The primary purpose of a gusset plate is to help with the transfer of force between the members at a connection; the plate provided an additional path for the force transfer.

The connection between the chimney and the base is the most critical one in the tower as it undergoes the most amount of stress. The internal force in the chimney (the compression force) has to pass through that connection to get to the legs. If the connection is not properly constructed, if it is weaker than intended, then it could fail. A properly placed gusset plate at the connection offers the compression force an additional (or alternative) path to travel from the chimney to the base thereby strengthening the connection.

[flyingwatermelon]

Hi all!

After examining my design again and again, I've been thinking whether it is necessary for a tower to have the long connecting member at the bottom of the base, creating a "hoop" around the base and preventing the legs from jutting laterally. Apparently, adding the final member increases the strength dramatically, but I also notice that such a long member adds some weight to the base. Is there any of way of bypassing this?

[Balsa Man]

Hi all!

After examining my design again and again, I've been thinking whether it is necessary for a tower to have the long connecting member at the bottom of the base, creating a "hoop" around the base and preventing the legs from jutting laterally. Apparently, adding the final member increases the strength dramatically, but I also notice that such a long member adds some weight to the base. Is there any of way of bypassing this?

Depends on a couple things. There is indeed a significant force outward from the center at the bottom of the legs. Order of magnitude, a couple kilos at full load. A properly constructed"hoop" will control/prevent leg end kickout. So will a pair of diagonal (as in X) braces coming from above, acting in tension to hold the end in-place. If there's any stretch under tension in these braces, the chimney will go out of vertical, and down she comes. Low density balsa stretches more under tension than higher density. The tension force on members of a hoop will be less than on diagonals, because of the angle (parallel to the force as opposed to carrying it at an angle).
So, if diagonal bracing to the leg ends is strong enough to hold them in place, a hoop would be redundant. If diagonals are allowing essentially any outward movement, then either they need to go up in density (which will elongate less), or it needs to be hooped. I gather from your earlier posts you're using 1/16th x 1/6th for diagonal bracing (and it sounds like for hooping). If the density is high enough to prevent elongation (in either diagonals or hoops), (probably 0.7 gr/36", + or - 0.1) then you have some excess wood. Most of the tension is being carried along the face of the brace against the legs, the rest of the cross section is "along for the ride." I can tell you that 1/64th by a bit over 1/16th wide, cut from a 3"x36" sheet at 8.5gr is enough without hooping.
So, maybe a test- put hoop on. When under load, cut it and see if it holds. Maybe at opposite ends of a hoop segment, do the diagonals in 1/16th, and at the other in 1/64th...

[flyingwatermelon]

Hi!

I know this isn't part of the official Tower building/design help issues, but does anyone know a good resource for ordering z87+ goggles? We happen to be short on some and need to order more. Thanks!

Also: Thanks Balsa Man for responding to my previous quesiton.

[mrsteven]

Hi!

I know this isn't part of the official Tower building/design help issues, but does anyone know a good resource for ordering z87+ goggles? We happen to be short on some and need to order more. Thanks!

Also: Thanks Balsa Man for responding to my previous quesiton.

your high school chem lab....

[flyingwatermelon]

Hi!

I know this isn't part of the official Tower building/design help issues, but does anyone know a good resource for ordering z87+ goggles? We happen to be short on some and need to order more. Thanks!

Also: Thanks Balsa Man for responding to my previous quesiton.

your high school chem lab....

Good point...well it was for the Div. B team I'm tutoring.