Base failures

jinhusong
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Re: Base failures

Postby jinhusong » February 7th, 2019, 8:42 pm

Anonymous15 wrote:How would you slot your tension members through the base? How would you put holes through the base? And what size base are you using for this (as I can imagine my 1/2 by 3/32 basswood is too thin for this method. Also, how do you increase surface area with this method?


We use 1/4X1/2 basswood block, so, you can slot. Drill hole or groove on the side then sandwich.

Someone else: 1/2 X 3/32 basswood just glue it between the tension members, then sandwich them with sheet. I forgot the thickness, guess 1/16 basswood sheet.

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Re: Base failures

Postby waffletree » February 8th, 2019, 8:00 am

jinhusong wrote:
Anonymous15 wrote:How would you slot your tension members through the base? How would you put holes through the base? And what size base are you using for this (as I can imagine my 1/2 by 3/32 basswood is too thin for this method. Also, how do you increase surface area with this method?


We use 1/4X1/2 basswood block, so, you can slot. Drill hole or groove on the side then sandwich.

Someone else: 1/2 X 3/32 basswood just glue it between the tension members, then sandwich them with sheet. I forgot the thickness, guess 1/16 basswood sheet.

Jinhu

yea i glue strips cut from a sheet of basswood on top of and underneath the tension members with superglue or gorilla glue.
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Re: Base failures

Postby S4BB » February 10th, 2019, 6:38 am

Anonymous15 wrote:How would you slot your tension members through the base? How would you put holes through the base? And what size base are you using for this (as I can imagine my 1/2 by 3/32 basswood is too thin for this method. Also, how do you increase surface area with this method?

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Re: Base failures

Postby Anonymous15 » February 10th, 2019, 8:46 pm

Thanks for the replies! I'll probably just sandwich my tension members with a bass stick/sheet.

Also, I just tested another boomilever. I have pictures attached.

https://www.dropbox.com/s/jck3o0ez1jho50r/IMG-9446.JPG?dl=0
https://www.dropbox.com/s/roy9mi4zgzlb4yl/IMG-9445.JPG?dl=0
https://www.dropbox.com/s/77u37dp66ts98av/IMG-9444.JPG?dl=0

There were two main failure points: one at the base (where that crater was) and one at the compression member, where one compression member split right in half. I understand the base failure-I attached some light-density balsa last minute to correct for some slight misalignment (which was a bad idea), but the compression failure still has me confused. I used no tension-compression bracing, and my compression members were 1/8 by 1/2 light density balsa. I used rectangular balsa compression to counteract the forces in the tension-compression plane rather than using bracings. Is this where the problem is (is 1/2 too thin?)

Thank you, as always, for your help!

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Re: Base failures

Postby Anonymous15 » February 10th, 2019, 8:47 pm

Also, as we were testing, the crater at the base was slowly growing, which caused the boomilever to tip downwards, which probably increased the compression force. The boom broke at around 8kg. Could the downwards tipping have caused the premature compressive failure?

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Re: Base failures

Postby MadCow2357 » February 10th, 2019, 8:52 pm

Anonymous15 wrote:Thanks for the replies! I'll probably just sandwich my tension members with a bass stick/sheet.

Also, I just tested another boomilever. I have pictures attached.

https://www.dropbox.com/s/jck3o0ez1jho50r/IMG-9446.JPG?dl=0
https://www.dropbox.com/s/roy9mi4zgzlb4yl/IMG-9445.JPG?dl=0
https://www.dropbox.com/s/77u37dp66ts98av/IMG-9444.JPG?dl=0

There were two main failure points: one at the base (where that crater was) and one at the compression member, where one compression member split right in half. I understand the base failure-I attached some light-density balsa last minute to correct for some slight misalignment (which was a bad idea), but the compression failure still has me confused. I used no tension-compression bracing, and my compression members were 1/8 by 1/2 light density balsa. I used rectangular balsa compression to counteract the forces in the tension-compression plane rather than using bracings. Is this where the problem is (is 1/2 too thin?)

Thank you, as always, for your help!

You need tension compression bracing to prevent buckling, which is what happened in your boom. I'd do that at intervals of around 10 cm, with 1/8 by 1/16 wood.
Anonymous15 wrote:Also, as we were testing, the crater at the base was slowly growing, which caused the boomilever to tip downwards, which probably increased the compression force. The boom broke at around 8kg. Could the downwards tipping have caused the premature compressive failure?

Yes, the compression member would be at an angle and therefore more susceptible to cracking, which is what happened. Use all basswood for the bsae, if you can. Try minimizing the length of your base so you can make it thicker.
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Re: Base failures

Postby Anonymous15 » February 12th, 2019, 1:55 pm

Hi everyone,
I just tested another boom. It held 5.6kg and failed at the base. Here are pictures:
https://www.dropbox.com/s/la9tf6np6c4csxl/IMG-9461.JPG?dl=0
https://www.dropbox.com/s/9rhz145s3gjrs3z/IMG-9460.JPG?dl=0
https://www.dropbox.com/s/796cm94y6uw56ky/IMG-9459.JPG?dl=0
https://www.dropbox.com/s/yji5qn940grq2oc/IMG-9458.JPG?dl=0
https://www.dropbox.com/s/t1epy43ofeu4kpm/IMG-9457.JPG?dl=0

I used 1/16 square basswood for the tension members, and 1/2 by 3/32 basswood for the base. I also added reinforcements around the base. The tension member actually ripped off from the base (there is still part of the tension member on the base), so is it a surface area problem?

Also, the compression part was completely intact, it was really just the base that came off. For next time, I probably will use a 3/8 square bass for the base, with 1/16 square tension members. Has anyone tried this, and could it work?

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Re: Base failures

Postby Anonymous15 » February 12th, 2019, 6:45 pm

To add, I just built a new base:
https://www.dropbox.com/s/vnaodcol2adg82f/IMG-9468.JPG?dl=0
https://www.dropbox.com/s/41lijoa80i9zmrd/IMG-9466.JPG?dl=0
https://www.dropbox.com/s/bfe3m9qdrsotsep/IMG-9465.JPG?dl=0
I drilled 5/64" holes into the base, which is 3/8 square bass. Then, I inserted 1/16 square basswood into the holes. I used CA and gorilla glue(still drying) to keep it in place). I know people have used this drilling method with 1/16 square bass tension to good results, but does anyone know if 3/8 square bass for the base will work?

Also, I made a different base as well:
https://www.dropbox.com/s/t7udb7w5pfprzxw/IMG-9464.JPG?dl=0
https://www.dropbox.com/s/i4pnlh8qy6ryoas/IMG-9463.JPG?dl=0
https://www.dropbox.com/s/cc8kcj6vdb1cyjr/IMG-9462.JPG?dl=0
For this one, I used 3/32 square bass and put a 3/32 by 1/2 bass stick in between it. Then, I put 3/32 by 1/2 bass sticks on top and below this, sandwiching the tension members. With these sizes, could this base hold full weight?

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Re: Base failures

Postby Anonymous15 » February 12th, 2019, 7:04 pm

Also just realized that I connected the tension members too far behind the distal end, which made the compression members bend, which may have led to premature failure?

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Re: Base failures

Postby Anonymous15 » February 12th, 2019, 9:05 pm

Though the main failure point was probably at the base.

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Re: Base failures

Postby Anonymous15 » February 13th, 2019, 2:48 pm

Sorry for posting so many times! Just wanted to make sure the above doesn't get lost.

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Re: Base failures

Postby Anonymous15 » February 13th, 2019, 7:25 pm

Just wondering, does anyone know if a 1/4 square dowel would work with 3/32 square tension members that are drilled into the dowel? I'm really worried about surface area, as I am having trouble with finding the base setup that works the best. I tried 3/8 square bass with 1/16 square tension members drilled into it, but that broke early for me (I have trouble getting the alignment right). I also tried sandwiching 3/32 square tension members in between bass sheets, and though that held much more, one member still broke clean off. Does anyone know if this setup with the 1/4 dowel will work?

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Re: Base failures

Postby Anonymous15 » February 17th, 2019, 4:53 pm

Hey guys!

Just tested another boom. I used tension-compression bracings and kept the compression bracings the same. It held around 10 kgs. The failure was in the base, which just flew off. There are literally 0 signs of damage anywhere else on the boomilever lol. I used 3/32 square tension members, put a 1/2 by 3/32 basswood piece in between them, and then covered both tension-base joints with a small piece of basswood that was the same size as the bass. Then, I glued balsa wood (1/2 by 1/8) over the tension member and the basswood reinforcements. This setup enclosed the tension members on all four sides.

I'm not completely sure why the base broke--is the 3/32 thickness for the base too thin to allow enough surface area? I didn't think adding balsa wood to reinforce one of the sides could cause problems; could I be wrong about that? The distance between the two tension members was around the distance between the compression members, which was 5 cm. Is that gap too large?


I also tried gluing 1/16 square tension members into a 3/8 square basswood block (I drilled 5/64 in holes). However, when I pulled on it, it could not hold much weight (as per reading on luggage scale). I tried to make the base as symmetrical as possible around the luggage scale when pulling, but it is possible that it slipped as I pulled. Is 3/8 square not big enough or could that be an error that was caused by me not being careful enough when pulling on the luggage scale?


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