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What Made You Happy today?


Hotplant
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Brace yourselves, I'm a mechanical engineer and this is going to seem dorky.

I have just finished designing a geared transmission shaft that is required to transmit 100 lbf +/-5% to two other gears with resistance torques of 300 lbf each. I designed it to have a 95% reliable infinite fatigue life with a fatigue safety factor of 3.02, and a desired safety factor for yielding of 2.00.

In essense, this part will never break, even after a lifetime of the specified load fluctuation (paperclips, for example, do not have infinite fatigue lifes as evident by them breaking after only a few bends back and forth).

You can even apply (statically) twice the rated loading, or 210 lbf, before this thing will yield/break. This is for your own safety. Think of a ladder that says it is rated for 250 lbs. Engineers know that a 350 lb person will no doubt use the ladder anyways, hence why we design with safety factors.

All this, while decreasing the shaft diameter from 1.38 inches to 1.179 inches. (Saves material. Material saved = higher profit)

In addition, I was able to write a Matlab program for a shaft of this type that will solve for the required shaft diameter needed (based on the max. shear stress & distortion energy theorms) for any desired safety factor. The program's required inputs include gear forces, gear diameters, desired safety factor, shaft length, etc.

There is no telling just how lame this must sound to all of you. I wouldn't be surprised if 60% of you haven't even made it to this point in my post before moving on to the next one. I guess this is the price I pay.

But there is no denying that this is what made me happy today.

Ah! I'm beginning to understand now, why I should have been born with six inch long rubber fingers. You guys design equipment as though it will "NEVER BREAK" LOL!

I've changed many a striped out gear shafts in the bottom of a barge in 104f temp.

after an impellar on the end of that gearbox locked up and the 671 Detroit Diesel with

a gear driven supercharger and 850ftlbs of torque sheared it like peanut butter without missing a beat! :lol:

A buddy of mine, his father was a mechanical engineer with a degree from Tulane and Loyola. One day he was installing winch motors on his boat that were to be used for hoisting wingnet frames (80ga aluminum) and he couldn't figure out why when he applied the switch that the motors wouln't run. So he calls me up and ofcourse I couldn't diagnose the problem over the phone so I head down to the dock to have a look.

Well as soon as I pull up I see the problem, he has 115v house wiring going up the A frame to the motors :lol:

I tell him that the wire is too small for a 12v system and he argues that the wire can handle 115v I said yes but it must have taken 15min for him to comprehend that he needed heavier gauge wire for the increase in amperage. The lower the voltage the higher the amps :lol:

Reminding me of this story is what made me happy today :lol:

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So far very nice. I loved the waterfalls yesterday and we gotta go back so i can get under it!!! Okay let's get going, i wanna try that Cuban cafe for lunch. Downtown Asheville is a great place! I'm trying to get Speed to post a pic of us...

Awww. Thank you ~tangerine~. Hope you enjoyed the guys at The Lobster Trap playing Led Zeps Tangerine for you. I know I sure did and the fresh lobster. Three cheers for 18hr Maine Lobster

:cheer: :cheer: :cheer:

Tomorrow will be Ghost Town and then Biltmore House. Today was Cherokee, Nantahala Gorge, Fontana Dam, Fontana Village and lake.....

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Ah! I'm beginning to understand now, why I should have been born with six inch long rubber fingers. You guys design equipment as though it will "NEVER BREAK" LOL!

I've changed many a striped out gear shafts in the bottom of a barge in 104f temp.

after an impellar on the end of that gearbox locked up and the 671 Detroit Diesel with

a gear driven supercharger and 850ftlbs of torque sheared it like peanut butter without missing a beat! :lol:

A buddy of mine, his father was a mechanical engineer with a degree from Tulane and Loyola. One day he was installing winch motors on his boat that were to be used for hoisting wingnet frames (80ga aluminum) and he couldn't figure out why when he applied the switch that the motors wouln't run. So he calls me up and ofcourse I couldn't diagnose the problem over the phone so I head down to the dock to have a look.

Well as soon as I pull up I see the problem, he has 115v house wiring going up the A frame to the motors :lol:

I tell him that the wire is too small for a 12v system and he argues that the wire can handle 115v I said yes but it must have taken 15min for him to comprehend that he needed heavier gauge wire for the increase in amperage. The lower the voltage the higher the amps :lol:

Reminding me of this story is what made me happy today :lol:

Mechanical engineers will be the first to tell you that they don't know shit about electrical. B)

As for the stripped out shafts - we design (with economic reason) to what people tell us the typical loading will be. Unless its life-threatening, it was probably almost better that the shaft sheared once the impellar locked up, because if it didn't, you could have incurred more costly damage to the engine, support bearings, etc. Designing a shaft that could withstand the things you speak of would be bad for resources as well - it would have a diameter of 2 feet, and it would cost and weigh a shitload. Aside for designing things that "never break", part of being an engineer is to decide what will break first.

It follows that you simply cannot please everybody all the time B)

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Mechanical engineers will be the first to tell you that they don't know shit about electrical. B)

As for the stripped out shafts - we design (with economic reason) to what people tell us the typical loading will be. Unless its life-threatening, it was probably almost better that the shaft sheared once the impellar locked up, because if it didn't, you could have incurred more costly damage to the engine, support bearings, etc. Designing a shaft that could withstand the things you speak of would be bad for resources as well - it would have a diameter of 2 feet, and it would cost and weigh a shitload. Aside for designing things that "never break", part of being an engineer is to decide what will break first.

It follows that you simply cannot please everybody all the time B)

:lol: I hear that brotha

Another thing made me happy today, I pre-ordered the TSRTS Vinyl set hope I'm one of the lucky 100 B)

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but the question i have is...why can't you design a paperclip with an infinite fatigue life?...

Many reasons.

The equation for bending stress is Mc/I, where M is the bending moment, c is the distance from the neutral axis of bending to the outermost surface of the material, and I is the area moment of inertia.

Because the diameter of wire that paperclips are made of is so small, the area moment of inertia (I) will be very small. Since this very small number is on the bottom of the fraction of the equation, the resulting internal stresses will no doubt be very high, eventually causing it to break.

You could fix this by using larger diameter wire, but then it would be heavy, and would not bend at all when you tried to paperclip a larger stack of papers together.

Another reason they fail due to fatigue is the cheap metal that paperclips are made of. Generally, the cheaper the material, the lower the yield strength.

A material will yield whenever the internal stress in a part (Mc/I) is greater than the material's yield strength.

Edited to add: You very well could design a paperclip with infinite fatigue life, but they would no longer be cheap, easy to produce, disposable, or economical.

I would rather forcus my efforts on something with a little more meaning B)

Edited by docron
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Many reasons.

The equation for bending stress is Mc/I, where M is the bending moment, c is the distance from the neutral axis of bending to the outermost surface of the material, and I is the area moment of inertia.

Because the diameter of wire that paperclips are made of is so small, the area moment of inertia (I) will be very small. Since this very small number is on the bottom of the fraction of the equation, the resulting internal stresses will no doubt be very high, eventually causing it to break.

You could fix this by using larger diameter wire, but then it would be heavy, and would not bend at all when you tried to paperclip a larger stack of papers together.

Another reason they fail due to fatigue is the cheap metal that paperclips are made of. Generally, the cheaper the material, the lower the yield strength.

A material will yield whenever the internal stress in a part (Mc/I) is greater than the material's yield strength.

Edited to add: You very well could design a paperclip with infinite fatigue life, but they would no longer be cheap, easy to produce, disposable, or economical.

I would rather forcus my efforts on something with a little more meaning B)

Makes sense to me. I used to bend them up just to feel the heat in them.

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My husband and I honeymooned in Asheville. I know the Cuban cafe you're speaking of.....SOOOOO good! Asheville is awesome!

Do you mean Havana? Didn't get there yet, wound up eating South American food which was delicious. There are so many great places to eat here.

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:lol: I hear that brotha

Another thing made me happy today, I pre-ordered the TSRTS Vinyl set hope I'm one of the lucky 100 B)

I will get those too. After all this CD crap I'm returning to vinyl. These CDs really aren't sturdy or sound as good as the old vinyl master discs. Why do I feel ripped off?

Good luck on the white wax's dzl...

Edited by Speed Racer
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Do you mean Havana? Didn't get there yet, wound up eating South American food which was delicious. There are so many great places to eat here.

I can't recall the name of the restaurant, but it's downtown, kinda right in the middle of everything. At the time it was the only cuban spot in Asheville that I was aware of anyway...If I remember correctly it was on a corner....Very small but always packed. You are right about the selection of places to eat though....sooo many to choose from.

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I can't recall the name of the restaurant, but it's downtown, kinda right in the middle of everything. At the time it was the only cuban spot in Asheville that I was aware of anyway...If I remember correctly it was on a corner....Very small but always packed. You are right about the selection of places to eat though....sooo many to choose from.

It's just across from The Grove Arcade with the Dragon Gargoyle statues out front :)

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my 7 yo just went to a birthday party. to some thats common, but its only the third for him. and he was well behaved and had a great time! he also got on so well with one of the other boys, that his mum and i exchanged numbers and will make a playdate. also a first! woo hoo . a great day. :D

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What made me happy yesterday, since today is a new day now:

Getting home safely after a long day of travel (after a very nice vacation)...

Getting the sweetest hug from my sweet child after missing her the past five days, and hearing about all the great fun she had on her fantastic week in Wildwood with my family...

at 1am getting ready to be happy hitting the pillow (or pretty soon)...and still have 2 more days off of work!

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I can't recall the name of the restaurant, but it's downtown, kinda right in the middle of everything. At the time it was the only cuban spot in Asheville that I was aware of anyway...If I remember correctly it was on a corner....Very small but always packed. You are right about the selection of places to eat though....sooo many to choose from.

That's Havana. We actually went in to eat lunch, but the menu was limited and i wasn't in the mood for any of the food. We wound up leaving and eating down the block at a fabulous italian restuarant. So many great choices in downtown Asheville.

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That's Havana. We actually went in to eat lunch, but the menu was limited and i wasn't in the mood for any of the food. We wound up leaving and eating down the block at a fabulous italian restuarant. So many great choices in downtown Asheville.

Asheville is currently doing Belle Chere. Years ago when all the stores moved out and went to the burbs. Someone had the idea to close off all the streets and have a huge international party and pray people would return to downtown and open up some abandoned shops. It worked, now thousands of people just walk about downtown and socialise, eat blah blah. Became very cosmopolitan.

The angel hair pasta/meatballs were to die for btw. With salad, hot bread and dipping sauce for $8 (lovely ambiance too)

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Starting off the day like most: being nagged endlessly by my child, lol. Well the happy part is debatable, but at least she's happy. Going to get some sunshine in a few. Feeling very relaxed after a great vacation this past week. That was just what i've need for a while now.

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Asheville is currently doing Belle Chere. Years ago when all the stores moved out and went to the burbs. Someone had the idea to close off all the streets and have a huge international party and pray people would return to downtown and open up some abandoned shops. It worked, now thousands of people just walk about downtown and socialise, eat blah blah. Became very cosmopolitan.

The angel hair pasta/meatballs were to die for btw. With salad, hot bread and dipping sauce for $8 (lovely ambiance too)

Who is the Headline music act this year?? Bele Chere is cool the first few times, after that the locals can't wait for the crowds to go away. It was cool when I lived downtown there though, we had only to step outside and be right in the midst of it all. ( College Street )

My youngest kids dad plays there some years. They're called Jimmy Baker and The Profits. B)

The best shows I saw there were Taj Mahal and then Bo Diddley.

Now they make you buy tickets to the headline, but it used to be all free.

ps: Jerusalem Garden has great sammies.

Edited by Hotplant
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