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iwonder wrote:Here's another question, I was thinking about trying a tube boom this year, and I fully understand how they could've been made last year, but I could never figure out how to handle a base this year. The only thing I could think of is a dowel and you would have to have two tension members the went into the distal end as one member, but split and attached to either side of the base. Is there some other method I'm not thinking of?

That's a good question. Let me throw out a few things to think about. I'm not coaching a team this year, so these thoughts are not from actually building/testing. This is coming from thinking about how to translate something that worked last year (with bolt and washer), to the J-hook of this year.

What we used last year was a "lock block" on the underside of the tension member. It provided a way to "hook" the T-member on the top of the washer. T-memb was 3/16ths" er 1/4" wide by about 1/32nd thick. Lock block 1/4" wide x thick x 1/2" long. The face of the block contacting the washer is cut at an angle, so that when the T-member is sloping down toward the distal end, the face is vertical. That means it's in full contact with the backside of the washer. The washer is held vertical by a 1/2" thick, end grain, light balsa. Tightening the bolt against the washer and block be clamped the washer vertically in place. A sloped 1/4" wide slot in the top of the balsa block allowed the tension member to sit down in the block so that the top edge of the washer was almost in contact with the underside of the tension member. Tension member done in hickory, lock block in oak. Two 1/32" diameter oak pins through the tension member and lock block.

The factors you have right for a joint like this to work are the shear strength- parallel to the grain - of T-member and block and glue area. It's all about force per unit area, e.g.pounds per square inch; the larger the glue area, the lower the
shear strengths can be. These woods and glue area worked for a C-boom; tension load about 90 pounds; about 3/4 of that for a B- boom. The reason for a flat/strip T-member was to increase glue area.

So, finally, to how might one adapt this to a J-hook??
What have you got to lock against?
The most obvious thing is the inside of the J.
Hmm. to do that, you would have to turn the T-member on edge- where the 1/4" dimension is vertical, rather than horizontal. I don't see a reason that can't be done; might just be worth checking out. The face of the lock block against the inside of the J would have to be curved to match the radius of the J curve; that's not a problem. Probably would have to file a 1/8th" radius groove; to keep the block from slipping sideways.... that's not a problem.

A nice thing is it's pretty easy to test T-member+lock block and joint- hang it vertically.... don't need to do whole structure testing.

Hi i know this may sound stupid but how essential is a strong truss to a tension boomilever?

A truss for what part of the boom?

rmp509 wrote:Hi i know this may sound stupid but how essential is a strong truss to a tension boomilever?

No, not stupid; maybe uninformed is the right word; you're smart to be asking questions to try to figure out how to do well.

The greatest value of this board is that it compiles knowledge; it is a library. There is a lot of discussion; this year and last year- from really basic stuff, right up through some very advanced topics. There's nomenclature/terminology, that makes it a lot easier to understand what part/component someone might be talking/asking about. The same holds true for your other events; lots of information and understanding sitting there waiting for you to come looking for it.

When you say "the truss", I'm guessing you are asking about the compression member(s).
Having all the.....components "strong" is "essential." The structure will fail at the weakest place. How strong, how essential; depends on how well you're trying to do.

After some research, you'll have some more specific questions, and you'll be able to get some ideas/feedback that will really help you.
Enjoy; learn; do well

I've been building a couple of box beams this year, and one thing I've noticed is how much weight the glue adds. I am using a thin, continuous line of fast Ca+ (zap-a-gap), which doesn't seem to add too much, but it usually adds up to .7 grams, making each individual beam go from 1.9 to 2.6-2.7. It would be very nice if I could cut that down to .2-.3 grams per beam.

Is anyone else experiencing this problem? Does anyone have any tips?

I've got the same issue, I haven't tried it but I'm looking at switching to a needle to apply the glue, should be a thinner line. (and it'll get me weird looks from store people... )

I also thought about using a needle, but won't the CA glue clog up the needle and dry, thereby rendering the needle useless? Or does CA glue stick to the needle at all?

Yes, I tried using a syringe but it gets clogged up very quickly. I think if you were super careful with it, maybe it wouldn't clog up. Or maybe before every use, filling it with CA de-bonder to break up the glue? I would just say to use less glue as a simpler solution.....

Using less glue really isn't as easy as it sounds and yeah, I was planning on having to buy a new one each time :/

Are you aware of the plastic "extra-fine"/micro - tips that Hobbytown sells? They slip over the glue bottle nozzle. If they sit for a while, you'll get a hardened plug right at the tip, but you just slice maybe a 16th of an inch off w/ a razor blade and you have flow again. Lots cheaper than syringes.