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Old 02-01-05, 04:39 PM   #1
KingFoo
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So how can somebody with little or no experience (me!) in frame materials identify whether an old frame (found at a garage sale, swap meet, etc) is steel or aluminum? Can you tell just by looking at the welds, or tapping on a tube? Yeah I know sometimes there are decals that tell the whole story, but what if there aren't any decals? What if the frame was repainted or something? I wouldn't know what a lug was if it jumped up and bit my a$$. Thanks. I hope some noob-tolerant guru can enlighten me.

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Old 02-01-05, 05:10 PM   #2
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Does a magnet stick to it? If yes, it's steel. If no, it's something else.
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Old 02-01-05, 05:20 PM   #3
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http://www.oldmountainbikes.com/frames/

Steel frames. Alu tubing is gererally larger diameter, will have wider weld bead.

Lugs can be very ornate, often represent craftmanship in building. Inspect the quality of the dropouts, joining.

Tube internal wall thickness changes (butting) and tube can be ovalized and even rectangular..

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Old 02-01-05, 06:10 PM   #4
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I'm learning! (that magnet test is genius, BTW - why didn't I think of that?) So, a steel frame can be fillet brazed, TIG welded, or lugged - but can aluminum tubes also be joined this way? There are no lugged aluminum frames, right? I should assume inspection of the welds themselves won't tell me the frame material, except in the case of lugs. I have an old aluminum Cannondale frame, but it has a lugged fork. I should assume the fork is steel, I guess.
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Old 02-01-05, 06:34 PM   #5
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I've seen a filleted Alu frame. Heavy duty mtb.

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Old 02-01-05, 09:35 PM   #6
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My aluminum Vitus Futural has internal lugs, also known as screwed 'n' glued. It also has 'standard' diameter tubes, like a steel road bike.
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Old 02-01-05, 09:52 PM   #7
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My first 'serious' ten-speed circa 1973, was Reynolds 531. It was lugged, pinned and silver-soldered. BTW, 531 is alu/steel and is very weakly attracted to magnets.
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Old 02-01-05, 11:25 PM   #8
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Originally Posted by BlazingPedals
My first 'serious' ten-speed circa 1973, was Reynolds 531. It was lugged, pinned and silver-soldered. BTW, 531 is alu/steel and is very weakly attracted to magnets.
531 is Manganese Molybdenum alloyed steel. Magnets stick fine.
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Old 02-02-05, 07:40 AM   #9
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531 is Manganese Molybdenum alloyed steel. Magnets stick fine.
Really! All these years I've believed what that !@#$%^ bike shop told me. I knew there was some manganese in the mix somewhere, but NO aluminum? Oh well, I still liked the bike.
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Old 02-02-05, 02:22 PM   #10
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Originally Posted by BlazingPedals
I knew there was some manganese in the mix somewhere, but NO aluminum?
Actually, it's not all common to find aluminium alloyed with steel. Chromium, nickel, manganese, molybdenum, tungsten or silicon are common, but not aluminium. (But tungsten tends to be used in tool steels, not bike frame steels.)

Tubes made from steel alloys and aluminium alloys are very different beasties. Steel alloys are characterised by narrow diameter, thin walled tubes, which tend to be springy. Aluminium alloys are characterised by larger diameter, thick walled tubes which tend to be very stiff.

If a bike frame has round, somewhat "fat" looking tubes, it is probably made from an aluminium alloy. If it has thin tubes, it is probably a steel alloy.
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