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Author Topic:  aluminum expansion rate
Joe Delaronde


From:
Selkirk, Manitoba, Canada
Post Posted 1 Dec 2002 8:18 am     Reply with quote

Re: Machinery's Handbook, Revised 21st Edition, page 2270, states;

"Specific Gravity and Properties of Metals."

Aluminum;
Quote "Linear expansion per unit length, per Deg. F. is 0.00001244", Unquote

Does this mean that if I have a piece of aluminum 12" long, and raised the temp by 10 Deg F., it will expand by 0.0014928" ?

Thanks
Joe

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Donny Hinson


From:
Glen Burnie, Md. U.S.A.
Post Posted 1 Dec 2002 11:00 am     Reply with quote

Yes, that's exactly what it means Joe! In most applications, this small amount of expansion would not be noticed, but it does have a bearing on pedal steels, most of which use aluminum. This factor is offset, somewhat, by the expansion of the strings, though. (Being made of steel, they don't expand quite as much as the alumnium.) But, as any instrumentalist will tell you, significant variations in temperature do wreak havoc on their instruments.

Interestingly enough, the effect is really magnified on large structures made of aluminum, such that factories where airframes are constructed must now be temperature-controlled, or most of the holes wouldn't line up close enough to install the rivets and other fasteners.
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Joe Delaronde


From:
Selkirk, Manitoba, Canada
Post Posted 1 Dec 2002 12:51 pm     Reply with quote

Don

Very interesting.

My friend worked in the aircraft industry drilling holes in fusilages for the aluminum sheeting. I recal he mentioned the inspectors would check the holes to make sure they had a .010 clearance. I thought this would make a very loose hole, but now I know why. Thanks.

After reading the threads pertaining to temerature changes and detuning to steel guitars with aluminum necks, etc., I thought it might be interesting to try an experiment.

The steels I used for the experiment are non-pedal models. My beaver log, which is exactly that, a log, and my all aluminum cabinet double 10 console model.

The log and the aluminum model both use a B6th tuning so they had identical readings on my tuning meter. The second neck on the aluminum model uses E13.

I placed a large fan 8 feet in front of both steels and allowed the cool air to blow over them for 3 hours, after which I took another meter reading. Both B6th tunings had the same reading and were slightly higher than
the original reading. However the E13th tuning read slightly higher again by 1/2 cent.

I played both steels to a rhythm track and found they were off fret so slightly it didn't bother me.

I went farther with the experiment and placed a 500 watt halogen lamp the same distance in front of the both steels for the same time. The results were the same, but in opposite directions.

I looked in the Machinist handbook to find out how much wood expands. I couldn't anything on this.

I decided that IF the wood never expanded, then the aluminum never expanded enough (key word "enough")to make a difference, BECAUSE they both had the same readings after each test.

So what caused the slightly higher & lower readings? The only thing left in the equation are the strings.

I have more to add to this, but would like know if my train of thought is on the right track.

Thanks
Joe

[This message was edited by Joe Delaronde on 01 December 2002 at 12:54 PM.]

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ed packard


From:
Show Low AZ
Post Posted 1 Dec 2002 1:31 pm     Reply with quote

If you use THE STANDARD HANDBOOK for MECHANICAL ENGINEERS you will find the TCE for Woods, Alum's, Steels, Ceramics, etc..

If you search the Forum re TCE or Thermal, you will find some other info/experiments, and just plain statements (commercials?) re material strength, temperature effects, etc..

Most pickers do not speak this language and could hardly care less about what all the jargon and math means re the final instruments performance. Those folk that have a product to sell usually do not provide material data nor experimental results.

The same materials employed via a different process will give different results so just material data is only part of the story ,..so terms like "better", "harder", "more", "less" "smoother", cause some (me for instance) to mentally quote the line that BIG E sings in one of his jazz pieces..."compared to what?".

Thermal changes on steel strings causes several things to happen: the material expands in all directions; this means the they get thicker = increased mass => lower pitch for the same length, and if the nut to bridge distance does not change the tension reduces => lower pitch. One would like the string holding structure (body + metals) to expand in such a manner as to "nearly" retain the same tension on the strings as the temperature changes.

All the above assumes that only linear expansion in the direction of the strings is what occurs that is of interest re pitch changes, ..the body may actually bow with thermal changes thus introducing another variable causing the string holding mechanisms to tilt.

You might also use a search engine to get the material properties for the materials of interest.

[This message was edited by ed packard on 01 December 2002 at 01:31 PM.]

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Tom Olson


From:
Spokane, WA
Post Posted 4 Dec 2002 8:53 pm     Reply with quote

The density of a string may change as a function of temperature, but not it's mass.
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ed packard


From:
Show Low AZ
Post Posted 5 Dec 2002 6:37 am     Reply with quote

Tom; You are right; Read diameter change instead of mass, so I would guess that any pitch change from this would be little if any. Good catch.
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Erv Niehaus


From:
Litchfield, MN, USA
Post Posted 5 Dec 2002 7:56 am     Reply with quote

This coefficient of expansion thing is the reason that reinforced concrete works. The coefficient of expansion for concrete is the same as that for the reinforcing steel.
Erv
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