Hot Rods The Belly Button Bucket Build Thread

Note to self:
Buy more Tylenol.

 

After all that we need a little of this

 

Lol. Wow.


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Thanks @Tim_with_a_T for my daily nerdgazim

I needed that!

 

That explanation made me a little dizzy....... I always wondered why engineers seemed to be in their own little world.....Guess they are just busy calculating all that stuff in their head instead of just guessing whether they should use 1/8" or 3/16" wall 2" tube for that hitch cross arm.

 

That figures !!
Thanks for the explanation in understandable terms for us normal people!
Very well explained

 

So.... all that math means, thicker metal and deep penetrating welds? Got it.

 

RE: THIS thread;
In the future, please refrain from asking "Hey, do you think it's strong enough?".

 

And that is exactly why I was an English major...

 

You guys should have sat through 4 years of that $#!T.... every single class you're wondering wtf you were thinking. BUT... many, many times I was told by older engineers to just deal with it, get it over with, and I'd never use it again anyway....well, I can't say they were right.

 

Career day at the local high school.

 

And yet another class at career day.

 

Long, long time ago, when I was a fresh out of school engineer, my boss told me that of the three major professions, (doctors, lawyers, engineers), I had chosen the worst one. Asked him why and he replied....Doctors bury their mistakes, lawyers lock theirs away out of sight...but engineers build monuments to theirs.

 

So very true. People rarely remember when you get it right, but when you screw it up, they never forget!

 

Tim

After all the engineering is done don't forget to pull it out of the garage and get a lawn chair and move back twenty or thirty feet and look at the profile for a few hours to see how it looks. Then change what you have done wrong.

Gary

 

But Gary come now engineers never make mistakes and get things wrong.
What works on paper or in their heads always works out in the real world

 

That is what I am afraid of Larry. Tim is using only one side of his brain. Lets just hope he has a little use of the artistic side of his head. Some engineers don't understand the importance of making their machines look good.

Gary

 

And some artists don't understand the importance of making their machines safe, functional and reliable.

 

Gary;
Maybe you should review this whole thread & note the progression & changes (Tim's been rather careful to get proportions correct). Esp the last few pages. I doubt you'll see much "real-life traditional"-looking 'joining' going on here. (If you define traditional : as what was actually done by the vast majority of people, in the time frame considered, not the rarified handful of folks that that most everyone aspired to duplicate), which = no bird-shit or booger welds, no "clean accurate" cuts w/the torch, no left-as-cast that's been modified-n-hacked. His chassis is one of the nicest I've seen pic of. & the proportion(s) are spot-on, as well. It's light years beyond near anything I've ever seen from the 50s->60s. W/the exception of most Indy cars, & rail chassis (starting in the mid->late 60s) from the few top names. IMHO.

&, BTW Tim, thanks for the math lesson & graphic demo. Was a bit above my head, but I still liked reading through it. It's all just an Opportunity to Learn. .

Marcus...

 

^^ No one was disputing or being too critical of any of that, just taking the opportunity to poke a little good natured fun ^^
I know that in this format that can be a little hard to understand, but if you knew us in person you would get it.

 

Tim is doing a wonderful job. I didn't realize that he had the mechanical skills he has. It is as high quality as I've seen. Larry yours is equal. But in doing that some ascetics can be overlooked. I know I had to, over the years changed some ugly things on my roadster. Remember the "UGLY GAP" between the engine and firewall that Chip mentioned. Had to move the body forward maybe three inches. Changed "THE LOOK" dramatically. (Have I mentioned lately how much I love spellcheck.) Just remember great engineering can go hand in hand with a beautiful look.

Gary

 

Wouldn't hurt to remember ...'beauty is in the eye of the beholder ' either....

 

And in my eye, there is a lot of beauty in the bucket Tim is building!

 

Totally agree....

 

Starting year 3 of it in Oct., Tim. At least YOU were smart enough not to wait till your 50's to start it! Balancing it and a full time job has been fun.....not! Taking Statics and Strengths of Materials for the second time (had to leave mid class last time to go fix a nuclear submarine in Maine last time) in August.

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The tensile strength, deformation strength, and deflected strength of the u-bolts are the only things that matter. Any of those in any degree will encourage failure. Cause they are not being inacted upon only staticly. They are being inacted on dynamicly in two planes of motion. Yes, I am an ignorant red neck. And again your trailer hitch is only as strong as your spring mount bolts. I don't think your equations are realistic dynamically.

 

I just looked at this thread tonight. I can now see how to make a "repair bracket" for my highboy A Tudor panhard bar, to correct an arc problem I "redneck engineered" in.
Thank you, and damn beautiful job! Some of my parts I've fabbed have more industrial look to them, and I'm not an angle iron hacker.

 

Hang in there! SoM is a fun class. Statics.... not so much LOL. I know working full time and school on top of it is no fun at all, but in my opinion, it's way better than racking up piles of student loans to pay off. You'll get done soon enough and be damn proud you did it. No one can ever take away your education.... Although my school tried to do that... but that's another story for another day not on this forum...

Thank you, sir! I found a few pictures of your chassis on a couple of your posts, but I didn't see any redneck engineering... Ha!

 

I'll expand on my design one more time, then I'm moving on - I'll address these statements by topic in an effort to cover maximum ground....

"The tensile strength, deformation strength, and deflected strength of the u-bolts are the only things that matter."
"And again your trailer hitch is only as strong as your spring mount bolts."

Not at all true. The trailer hitch is only as strong as the weakest link in the assembly. In this case, the weakest link is not the mounting bolts. Each 1/2" diameter mounting bolt can withstand in excess of 17,000 lbs until failure if loaded in shear and greater than 58,000 lbs until failure if loaded in tension, and as my design calculations show, I am nowhere near these numbers.

Millions of pickups and utility vehicles have come from the factory with a bumper hitch and a rated towing capacity far exceeding what I intend to tow. Hitch bolts to bumper, bumper bolts to chassis.

There are also millions of vehicles out there with aftermarket hitch assemblies that are bolted to the chassis. An extreme example of which is the lifted pickups you see driving around with an 18" drop hitch, again bolted to the chassis, and again, towing something far exceeding what I intend to tow.

"Any of those (forces) in any degree will encourage failure. Cause they are not being inacted upon only staticly. They are being inacted on dynamicly in two planes of motion."
"I don't think your equations are realistic dynamically."

I know you're referring to the bolts again here, so I'll use them for an upcoming example covering fatigue strength. To clarify something: when an object (in this case the bolts) has forces acting on it in two directions, you must analyze each force in magnitude and direction to see which causes the object (the bolts) to fail first. In the case of the bolts, they will fail in shear before they are pulled apart (fail in tension), so shear controls their design. That is why there's 6 pages of calculations - I am looking at the magnitude and direction of each force component in relation to the part they are acting on.

Each component of the hitch assembly must be strong enough to take the applied force of the trailer. The applied force acts on the same point of the hitch assembly each time - the magnitude and direction of the force may change, but the location does not. Because of this, we can use STATICS - an engineering method of analyzing a problem - to draw a free body diagram of our assembly. The free body diagram is used to determine the reaction forces of the applied load, again using STATICS, assuming the ASSEMBLY is in STATIC EQUILIBRIUM. The reaction forces are then used to analyze the strength of the chosen materials.

The maximum applied load was determined by calculating the force of deceleration of a trailer double the weight I intend to tow, which is my safety factor of two in this scenario. This uses DYNAMICS - another engineering method to analyze a problem (and in this example it's not much different than a high school Physics problem). The maximum load is only seen on extreme deceleration. In other words, the trailer hitch assembly sees a load less than that at all other times. In fact, most of the time (i.e. at idle and at cruise), the hitch will see a load very close to zero. As you can imagine, the acceleration, cruising, and deceleration of the vehicle will apply some sort of load on the hitch assembly a whole bunch of times. This is called cyclic loading. Using what's called an S-n curve, you can determine the fatigue strength of a part you have designed, or in other words, determine how many times it can be loaded before failure.

There are many different acceptable models of the S-n curve out there depending on material, and many different acceptable methods of determining the fatigue strength of your part... I touched on fatigue strength in my calculations on Page 3. While I did not show this calculation, and I will not due to complexity, I will quote a couple relevant sections on Wikipedia and GREEN a few key statements for fatigue strength.
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Definitions
The ASTM defines fatigue strength, SNf, as the value of stress at which failure occurs after Nf cycles, and fatigue limit, Sf, as the limiting value of stress at which failure occurs as Nf becomes very large. ASTM does not define endurance limit, the stress value below which the material will withstand many load cycles, but implies that it is similar to fatigue limit.
Some authors use endurance limit, Se, for the stress below which failure never occurs, even for an indefinitely large number of loading cycles, as in the case of steel; and fatigue limit or fatigue strength, Sf, for the stress at which failure occurs after a specified number of loading cycles, such as 500 million, as in the case of aluminum. Other authors do not differentiate between the expressions even if they do differentiate between the two types of materials.
Typical values
Typical values of the limit (Se) for steels are 1/2 the ultimate tensile strength, to a maximum of 290 MPa (42 ksi). For iron, aluminium, and copper alloys, Se is typically 0.4 times the ultimate tensile strength. Maximum typical values for irons are 170 MPa (24 ksi), aluminums 130 MPa (19 ksi), and coppers 97 MPa (14 ksi). Note that these values are for smooth "un-notched" test specimens. The endurance limit for notched specimens (and thus for many practical design situations) is significantly lower.



(you can read more here: https://en.wikipedia.org/wiki/Fatigue_limit)
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Long story short, if your stress values are low enough (below roughly 30ksi for steel), your part will never fail, no matter how many cycles. I used an online calculator to estimate the endurance limit for the bolts loaded cyclically in shear (which the calculations adjust for), and as expected, the stress is low enough the part will not see failure. And when I say low enough, I don't mean just below the endurance limit at 29ksi, I mean 1.66ksi...so again, I say, the bolts are plenty strong enough.

I'm really not sure where the hang-up is in communicating my design, but I think what is being overlooked each time is that I do not intend to tow something greater than 900 lbs. I used 1800 lbs in my calculations to give myself a buffer for safety. The calculations clearly show the materials chosen are up to this task. If I was trying to tow the space shuttle like that Toyota commercial awhile back, I could see reasons for your concerns...but we're talking about a teardrop trailer here...

Queue more Dilbert comics and hopefully no more trailer calculations......