Ah the almightly dome

[Elliot]

What GreyCoyote said... about the edge of the crimp. The instant I saw the dies, I wanted to take a file or grinder to it, and round those edges. What you have there now is called a stress riser. The first place it will break -- and this will happen much sooner -- is along the sharp crease. Rounding and polishing the edges of the depressions in the dies should do it. If in doubt, you could ask advice from LeChatNoir on this board. He's a tool-and-die maker.

[LionsNzebras]

Elliot,

I dont know what a stress riser is hehe.
Which diagram are we talking about here? Sorry I am still learning.

Stress Riser.jpg

OR are we talking about this?

Stress Riser 2.jpg

OR This?

Stress Riser 3.jpg

Wow I just think I answered my own question.
The red arrows on stress riser.jpg and stress riser 3.jpg point to the same place. One just happens to be on the die, the other on the strut.

But just for clarification.
We are talking about increasing the slope on the strut itself, by adjusting the die to allow more metal to be squished in the finger nail shape?
This should reduce the stress on the rise from the flat to the round?

[Elliot]

Yes, you answered it yourself. You want to avoid the abrupt transition. Though I'm not sure what you mean by more metal to be squeezed. You want a little less squeeze around the edges of the fingernail. A rounded transition.

[LionsNzebras]

Now there is a small curve there, I can try and zoom in on it if you wish, or take some high quality pictures.
I could email you the original pictures, they are much larger and higher res.

It might not be quite enough of a curve if I understand what you guys are saying.

This die and all the parts are now in my possession, is it a major issue if I dont have it done on this dome, but possibly have it done for future domes?
I do have about 3-4 weeks before I am going to press the ends anyway. I could take it back and ask for a few adjustments.

[Elliot]

I added a sentence to my previous post.
The pictures are fine.
Imagine that your dies were made to clip off the end of the conduit, instead of just flattening it. Then you would wind up with a "fingertip" made of conduit. That's what you don't want to happen to your dome, from flexing under load.
Stress riser means weak point.

[Elliot]

As for whether a change must be made, is hard to say. Probably not. I'm talking primarily about a principle, and I have no idea of your engineering numbers. (I confess, I have not read the whole thread. Too technical. For example, I have no idea what "frequency" means in this context. But I know a bit about basic mechanics.)
GreyCoyote can probably make a better judgement.

Your crimping design has a tremendous advantage over a straight line. If you just stuck each tube in a vice and flattened it straight across, it would be horribly weak. The fingernail shape spreads the load-flexing-area ( i just invented that term ) over a considerable length of the tube, making it much stronger. But you can improve it further by increasing the radius of the transition.

As it is, the radius of the transition is something like the thickness of the metal. You might want to increase that radius to... oh... maybe something like five times the thickness of the metal.

[LionsNzebras]

Elliot,

Yes that is one of the reasons we went with the finger nail shape vs the straight approach. I talked with a different engineer who said the stress point is still at the top of the finger nail shape, but the stress on the strut are much much more absorbent he said, than a straight press.

To be quite honest, I dont want to do more changes to the current design, purely out of excitement of building the actual dome!
I am such a nerd hehe.

I have all the stuff in the back of my jeep, just have to wait to sneek it into the garage so my wife does not see the GIANT stack of money, I mean EMT hehe.

[Elliot]

"A good plan carried out today always beats a perfect plan carried out tomorrow." -General George Patton.

[LionsNzebras]

I did talk with zebra today, I might just get my press for christmas

[LionsNzebras]

Well we finally got around to getting a press. Having a hell of a time finding a hydraulic\pneumatic one in town. Will have to order a good one.
I fully expect this one to fail, due to its leaking. Were using 9.5 tons of pressure maximum.
The die fits in it very nicely, and as long as the steel is warm, it does not squish out one side abnormally.

IMG_3242.JPG

We are also warming the steel with a garage heater, its -5c here and going down now, so production will stop for a while.
We did manage to press 33 struts this weekend, only 120 or so more to go

We have also been talking a lot about what to cover the dome with, and due to time restraints and budget it may not get its magical canvas cover this year. Only time will tell though.
If anyone has some cover ideas please feel free to share them.

We were thinking of sewing some t-shirts together to build more of a circus tent cover, just to fit with the theme this year, sheets perhaps, something along that line.