roll bar build
#21
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so for all you thread bashers, who have nothing better to do than say stupid ****. shed some light and tell me exactly what is wrong with this hoop. I would like to be enlightend by the pros, who know piping, on how "unsafe" my hoop is. Y8s can you tell me why this is crap? where exactly is the weak point in this bar?. Also why is this bar much more inferior than the ones that are made on a jig and are dom? as far as im concerned. this tubing is far more thicker and stronger than what miatacage has.
#22
In engineering terminology:
You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).
Make the main hoop out of one piece. Yours wiiillll bend.
You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).
Make the main hoop out of one piece. Yours wiiillll bend.
#23
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In engineering terminology:
You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).
Make the main hoop out of one piece. Yours wiiillll bend.
You are creating stress concentrations. Whether you sleeve it or not, your main hoop endures bending loads. Sleeves are designed for axial and torsion loads. (EDIT: Sleeves are a BAND-AID used to cover unavoidable joints that endure axial and torsion loads).
Make the main hoop out of one piece. Yours wiiillll bend.
#24
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another question about roll bars/ cages. i dont really know how to explain this. or ask the question, but, comparing my seam which is solid on the inside and sleeved, and comparing another portion of miatacage's cage (where the overhead bars,(the bars that go through the dash and up the a pillar), weld to the main hoop) how strong is that seam? granted it is connected by the area of the dead pedal and connected to the main bar, how strong exactly is it that thoes welds just dont break off and you have this bar come crashing down on your face?
#25
The problem is where the outside bar (sleeve) ends....you are creating a moment about that point (on both sides of sleeve) which will cause failure. It is "stronger" in some directions, but could fail -in dramatic fashion- under the right circumstance.
Consider the outside points of that hoop (which bolt to car) as the end of a lever. You have created a leverage point at that joint which would not be there if it were a seamless piece.
The bends at the sides of the hoop are the failure method for a roll bar. A gradual, mandrel bend with predictable failure which can take a lot of energy and do not break violently until WELL beyond their design range.
That sleeve joint in not only a THIRD failure point, but one which has a poor failure mode. It will take a good deal of force to break, but will not deform in a predictable fashion like the bends. It may bend as little as 10* before it shears in fast fracture failure. This would be bad.
In reality it may not happen, but it's a poor design.
#26
another question about roll bars/ cages. i dont really know how to explain this. or ask the question, but, comparing my seam which is solid on the inside and sleeved, and comparing another portion of miatacage's cage (where the overhead bars,(the bars that go through the dash and up the a pillar), weld to the main hoop) how strong is that seam? granted it is connected by the area of the dead pedal and connected to the main bar, how strong exactly is it that thoes welds just dont break off and you have this bar come crashing down on your face?
Different stresses, different application.
Those bars tie in two members to form a complete frame, and only see axial loads. There are normally not moments created about those until the frame as a whole has already failed it's designed purpose.
Those sleeves are also necessary for assembly....yours are avoidable...and should be avoided.
Just because you can doesn't mean you should.
#28
It's one thing to have a bad idea, it's another thing entirely to not listen to the advice of others on how bad that idea is.
Stick around...keep learning...all those guys bashing you on page 1 can help you learn a LOT about making a fast Miata.
#31
that's a little better, and honestly would work...but it's bad practice, and easier to buy a longer bar and bend it.
You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.
What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.
You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.
What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.
#33
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that's a little better, and honestly would work...but it's bad practice, and easier to buy a longer bar and bend it.
You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.
What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.
You have just moved the stress concentrations further out in the main hoop. They will see a smaller moment there, and be less likely to fail...but they are still and will always be BAD.
What is worse if if those points get too close to the bends in you hoop...then you are compounding stress there, and could very easily "rip a corner" off that bar as you're sliding down the highway shiny side down.
#35
Also consider that all this sleeve-jointing and inside-barring is adding a lot of weight at your roofline, which raises the CG of your car, and will have an effect on handling.
If you think that effect is small then you probably shouldn't own a Miata, or atleast not one modified enough to need a rollbar. I just swapped my carpet, and drove a few weeks sans rollbar and passenger seat, almost every day with the soft top down.
It was a whole different car.
If you think that effect is small then you probably shouldn't own a Miata, or atleast not one modified enough to need a rollbar. I just swapped my carpet, and drove a few weeks sans rollbar and passenger seat, almost every day with the soft top down.
It was a whole different car.
#39
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i will probally end up doing that. or if for some odd reason, i am compelled and feel that this is stronger, then it might stay. Being bashed on or not bashed on, i dont really mind. like i said. its just kinda a way for others to see how to make their own. Depends on them if they do one continous bar, or reinforced to the max bar. but like i said. twice as thick as miata cages tubing. we'll see how it goes, should i ever roll, ill be sure to make a post ,if im still alive.