Boomilever B/C

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Re: Boomilever B/C

Postby iwonder » March 13th, 2013, 7:59 am

One thing I've noticed is that in wood a 1/4" hole and a 1/4" bolt don't quite fit together, I end up having to turn the bolt and kinda thread it in to the hole. So that may be the issue? A 5/16" bolt probably wouldn't fit through a 1/4" hole without putting noticeable cracks in the balsa.
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Re: Boomilever B/C

Postby jander14indoor » March 13th, 2013, 8:26 am

Actually, a 1/4 inch hole in wood will slide over a 1/4 inch bolt without problem.

The problem is, a 1/4 inch twist drill (which most people have) doesn't drill a 1/4 inch hole in wood, first pass. See, twist drills aren't really optimised to cut wood, they are designed for metal. As a result, they tend to push the wood fibers at the edge of the hole out of the way instead of cutting them and when the drill is withdrawn these fibers spring back into the hole leaving it undersize.

So, what to do.
One trick is to run the drill into and out of the wood multiple times. Sort of works. If you are on a drill press generally nothing bad happens, but you are a little undersize still. If hand drilling, you are likely to get an ovalized, non-straight hole.
Alternatively, you can use SLIGHTLY larger twist drills, say 9/64 or a number 30 (0.1285 in) or 29 (0.136 in).
Best is to use a drill designed for wood. These cut the sides of the hole BEFORE the center ensuring it is true to size. Brad point bits, auger bits and forstner bits all do this.

Hope that helps.

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Re: Boomilever B/C

Postby iwonder » March 13th, 2013, 10:37 am

I think you mean something more like a 17/64" or maybe an F(.257) or G(.266) ;)

And thanks for the correction, I guess I've been doing to much metal work to realize the woods deformation is significant :D
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Re: Boomilever B/C

Postby Balsa Man » March 13th, 2013, 11:02 am

I think you mean something more like a 17/64" or maybe an F(.257) or G(.266) ;)

And thanks for the correction, I guess I've been doing to much metal work to realize the woods deformation is significant :D
Aside from the dimensions, Jeff's advice is right-on (of course). Right tools/techniques matter. One other option is a 1/4" rat tail file
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Re: Boomilever B/C

Postby jander14indoor » March 13th, 2013, 11:14 am

I think you mean something more like a 17/64" or maybe an F(.257) or G(.266) ;)

And thanks for the correction, I guess I've been doing to much metal work to realize the woods deformation is significant :D
Dang, probably too late to go back and edit the note to correct 1/4 inch dimensions instead of 1/8 inch.

Wait, I'm a super user with super powers. All I have to do is delete iwonder's note, edit mine, edit Balsa Man's and NO ONE WILL EVER KNOW about my mental slip!!

Right, like that'll work.

Wait, what was I talking about...

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Re: Boomilever B/C

Postby S4BB » March 14th, 2013, 11:03 am

One thing I have noticed, is that prior to final glueing (CA), the fit of the bolt through the hole works fine, but after the glue is applied it seems to wick through the grain and we have to go back in and sand/file the hole again.

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Re: Boomilever B/C

Postby Unbihexium » March 16th, 2013, 10:43 am

Just wondering, what do you guys think of bass tension members? I've been using balsa ones for ages, but been thinking about it, are bass tension members in terms of equal strength usually better or worse? I know Aia used them, but what bothers me is lack of glue surface area. Also, does anyone have suggestions for a pretty weird break i have? My boomi always breaks straight down the middle through the lateral bracing, leaving everything else untouched...Also, anyone have any opinions on end grain balsa vs alternating grain balsa play attachment bases? Which one saves more weight? I've got a design that holds it all at 10.3 grams, but I'm trying to shave down weight now...
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Re: Boomilever B/C

Postby sjwon3789 » March 16th, 2013, 10:51 am

I just started using bass 3/32" but I haven't tested it yet. As long as you do the triangle wedge Aia's been using, I don't think surface area is an issue. Also, I've never experienced the break you had because my boomilever's tension glue comes off, instead of breaking anything. If any tension breaks, it was because I used much less dense tension members. I'm guessing get denser materials?
I don't understand "end grain balsa vs alternating grain balsa" your referring to.
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Re: Boomilever B/C

Postby iwonder » March 16th, 2013, 11:28 am

We've been discussing the different bases for quite some time on this thread, so I assume he's referring to that. End Grain is lighter in my experience(my base is below 1g and hold the full load, being a piece of end grain) the ply seems pointless to me, as the vertical grain direction is just pointless, it's not giving you any strength that you need(that I can think of), so it's really a question of end grain vs horizontal grain.

As to your break, is it suddenly snapping in half, or does it slowly deform and then break? Also, does the loading block fall through the middle and tip it apart, or did I read your description wrong? :D
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Re: Boomilever B/C

Postby flyingwatermelon » March 16th, 2013, 2:43 pm

We've been discussing the different bases for quite some time on this thread, so I assume he's referring to that. End Grain is lighter in my experience(my base is below 1g and hold the full load, being a piece of end grain) the ply seems pointless to me, as the vertical grain direction is just pointless, it's not giving you any strength that you need(that I can think of), so it's really a question of end grain vs horizontal grain.

As to your break, is it suddenly snapping in half, or does it slowly deform and then break? Also, does the loading block fall through the middle and tip it apart, or did I read your description wrong? :D
I never paid attention to whether it deformed or not, because I had not expected it to break there. I do know that it appeared to suddenly snap in half and based on post-analysis, the break was not due to another failure in the structure.

I think just expanding the hole slightly or using different drill bits as mentioned, as well as revising the construction of my base would resolve this issue. Thanks everyone!

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Re: Boomilever B/C

Postby Unbihexium » March 16th, 2013, 4:50 pm

I have a balsa 5 ply i glue together thats never broken for bases and is about .4-.6 grams, I was just wondering about ways to improve thats all. And yeah I get this weird failure where all the lateral bracing fails down the middle instead of tension or compression members failing, basically whole thing splits into 2 sides... just instantly breaks apart. What sort of tension member weight can you get from 3/32 bass? My balsa tensions are around 2 grams each, as are my compression members of around 2.5 grams balsa I'm just trying to figure out where to shave off weight...
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Re: Boomilever B/C

Postby sjwon3789 » March 16th, 2013, 8:48 pm

I was also wondering about the bass tension members. In Aia's guide, any bass 3/32 would be enough to carry a full load. Would compression-tension connectors help in lessening the chance of tension breaking? If so, wouldn't using bass wood a bad idea when I'm trying to decrease the weight of my booms?
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Re: Boomilever B/C

Postby iwonder » March 16th, 2013, 9:59 pm

Compression-Tension connections do not effect the tensile strength of the tension member, this is an inherent property of the wood. If anything they lessen it, because the add extra sideways forces and things into the members(these are typically insignificant).
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Re: Boomilever B/C

Postby Balsa Man » March 17th, 2013, 9:23 am

Just wondering, what do you guys think of bass tension members? I've been using balsa ones for ages, but been thinking about it, are bass tension members in terms of equal strength usually better or worse? I know Aia used them, but what bothers me is lack of glue surface area. Also, does anyone have suggestions for a pretty weird break i have? My boomi always breaks straight down the middle through the lateral bracing, leaving everything else untouched...Also, anyone have any opinions on end grain balsa vs alternating grain balsa play attachment bases? Which one saves more weight? I've got a design that holds it all at 10.3 grams, but I'm trying to shave down weight now...
Well, if you're running a design with 2 compression members 5-ish cm apart, and you're running 2 tension members to separate bolts (10cm apart), that's where the 'ripping apart' is coming from. The tension forces run along the tension members- they're pulling both upward, and outward (to left and right as you look toward the wall. That means out where they join the compression members, they're pulling the ends of the compression members apart- ~2,3,4 kg of tension. That means some 'tension control' is needed piece or pieces joining the compression members, strong enough to handle the separating forces.

On end-grain in the wall block(s). Grain oientation has nothing to do with weight; that's purely a function of density. So, you can use really low density when you align it "end grain"- with the grain perpendicular to wall. If you make it ~1/2" thick, and put a thin 'skin' on both sides, you get a very light block that is very stiff. The crushing strength is much stronger parallel to the grain. If you put that same 1/2" thickness in with grain running parallel to the wall, its really soft- when the tension members pull, the bolts/washers can crush into it
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Re: Boomilever B/C

Postby Unbihexium » March 17th, 2013, 1:25 pm

Just wondering, what do you guys think of bass tension members? I've been using balsa ones for ages, but been thinking about it, are bass tension members in terms of equal strength usually better or worse? I know Aia used them, but what bothers me is lack of glue surface area. Also, does anyone have suggestions for a pretty weird break i have? My boomi always breaks straight down the middle through the lateral bracing, leaving everything else untouched...Also, anyone have any opinions on end grain balsa vs alternating grain balsa play attachment bases? Which one saves more weight? I've got a design that holds it all at 10.3 grams, but I'm trying to shave down weight now...
Well, if you're running a design with 2 compression members 5-ish cm apart, and you're running 2 tension members to separate bolts (10cm apart), that's where the 'ripping apart' is coming from. The tension forces run along the tension members- they're pulling both upward, and outward (to left and right as you look toward the wall. That means out where they join the compression members, they're pulling the ends of the compression members apart- ~2,3,4 kg of tension. That means some 'tension control' is needed piece or pieces joining the compression members, strong enough to handle the separating forces.

On end-grain in the wall block(s). Grain oientation has nothing to do with weight; that's purely a function of density. So, you can use really low density when you align it "end grain"- with the grain perpendicular to wall. If you make it ~1/2" thick, and put a thin 'skin' on both sides, you get a very light block that is very stiff. The crushing strength is much stronger parallel to the grain. If you put that same 1/2" thickness in with grain running parallel to the wall, its really soft- when the tension members pull, the bolts/washers can crush into it

Firstly you misunderstand, I'm running to one bolt not two, with the tensions being the width of the washer apart at the wall, and the still split outwards. My question was if you can use lower density end grain instead of say a balsa ply which has weight from glue and has a relatively high density. Ultimately my questions are as such: How much weight can you make a end grain wall block assuming washer width, and is that less than .4 grams, and also whether basswood tensions can be under 2.5 grams, considering that's what I have for balsa ones currently.
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