machine shop theory.

Discussion in 'The Garage' started by colbystephens, Jan 23, 2006.

1. colbystephens1 ton statusGMOTM Winner

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so i've been thinking about expansion of metal under heat, and i came up with a question. here's the scenario: you're creating a force fit with a shaft and a clearance hole, and you heat up the object, and freeze the shaft to do this. pretty basic. so clearly when you heat up the object with the clearance hole to make it bigger, why does the metal expand unilaterally, and not bilaterally causing the hole to shrink as the entire shape of the object expands?

Last edited: Jan 23, 2006
2. Leper1/2 ton status

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I have wondered that myself.

3. spearchucker1/2 ton status

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Take a metal ring and cut it so that you have coincentric circles that are one molecule thick. Take the outermost ring and cut it and role it out flat so it looks like a bar. When you heat it up the molecules want to move away from each other and the only way for that to happen is if the bar gets longer. Just imagine standing in a line shoulder to shoulder and then everyone stretches their arms out so they're now finger tip to finger tip. Now if you take that metal bar and put it back into the shape of a circle it will have a larger diameter than what you started with. Do the same for the next coincentric ring until and you can see what will eventually will happen. Hope that makes sense.

4. theperfectgarage1/2 ton status

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I spend enough time wondering when things DONT work, When things do work, I stop thinking.You should prob. do some upgrade to your truck or take your lovely avatar mate to bachlor for the weekend. This will help stop your thinking. But seriously, it seems to me that if heat a chunk of steel with a hole in it, the steel will expand ( leaving the hole now larger ). But I am a simple man.

5. southernspeed1/2 ton statusGMOTM Winner

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I concur....good analogy!

6. colbystephens1 ton statusGMOTM Winner

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yeah, that makes sense. so essentially, the ring is not expanding radially out from the center, but rather it is expanding in circumference. thus, the added "length" of the circle forces the circumference to increase, thereby increasing the dia. of the hole. good info.

7. colbystephens1 ton statusGMOTM Winner

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she is pretty cute, huh? she happens to like me thinking tho. by the way, have you ever done ostrich racing at the ostrich farms between tucson and phoenix? when i lived in phoenix, i always wanted to do that. now i'd like to take my avatar mate to do that. very original.

8. tiny20851/2 ton status

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If you have a solid bar and you heat it, it will expand from a center point outward, take that center point out and it will still expand from the center point.

Does that make sense to anyone but me ?

9. theperfectgarage1/2 ton status

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That works for me.

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