aluminum frames
#1
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aluminum frames
hello people: Has anyone just made an unpainted AF? With this new to me, Hardrock had some ugly-looking scratches in areas so I filled the paint and just left the plane alum. I kinda like it. Also then if you scratch it up you could take down the flaw with sandpaper or a file.
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There have been lots of raw aluminum frames over the years, especially BMX and mountain bikes. In the 90s, GT made the Avalanche in raw aluminum. Might have ben polished, though.
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Raw untreated aluminum will corrode. How much will depend on environmental conditions. I owned a Mercury Zephyr(Ford Fairmont clone) that had 1\4" thick cast aluminum bumpers. they were very strong. One time I was hit from behind at a stoplight, a pretty good whack and no damage was done. However, after about 5 years the bumpers had holes from corrosion at the points where the bumpers were bolted to the steel mounting points. Aluminum may be rustproof, but it isn't corrosion proof
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Clear coated aluminum looks very nice depending on who did the preparation and painting. Plus clear coat will protect raw aluminum form corrosion.
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#6
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hello people: I have raw alum. on my motorcycle and I just hit it scotch bright if I want it to look nice. It sits in my shed over the winter and come spring all I have to do is what I say and it's all good.
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hello people: Didn't Merlin frames come raw? Maybe just not painted? I think they were made in Somerville Mass. at one time
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Raw aluminum oxidizes pretty quickly. The trick is to passivate the surface so that the atoms are happier to not react with any other passing elements.
Various grades of Chromium Phosphate are used throughout the aerospace industry. This creates a very strong bond with the aluminum atoms such that even oxygen does very little to convince them to recombine.
The difficulty is proper preparation. But it's totally do-able & Chromium Phosphate is readily available online. Bond-Rite is one such brand name. As with all chemicals, it will cause cancer in California.
Various grades of Chromium Phosphate are used throughout the aerospace industry. This creates a very strong bond with the aluminum atoms such that even oxygen does very little to convince them to recombine.
The difficulty is proper preparation. But it's totally do-able & Chromium Phosphate is readily available online. Bond-Rite is one such brand name. As with all chemicals, it will cause cancer in California.
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There have been more than a few bikes available with polished (unpainted) aluminum frames; notably 1990’s bikes like the aforementioned GT’s, and similar vintage Cannondale models. A handful of the SoftRide Power-V ‘wing’ bikes were polished as well.
Factory polished frames are usually clear-coated, but for DIY, you may be better off leaving it unsealed. If the clearcoat has any ‘thin spots’ or gets scratches in it, moisture or other contaminants can get between it and the polished surfaces, leading to cloudiness or “chrome worm”. The only way to fix it is to strip the clearcoat off.
A lot of hot-rodders will wax polished parts after polishing, as it’s a lot easier to touch-up the shine over time
Factory polished frames are usually clear-coated, but for DIY, you may be better off leaving it unsealed. If the clearcoat has any ‘thin spots’ or gets scratches in it, moisture or other contaminants can get between it and the polished surfaces, leading to cloudiness or “chrome worm”. The only way to fix it is to strip the clearcoat off.
A lot of hot-rodders will wax polished parts after polishing, as it’s a lot easier to touch-up the shine over time
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He was 60 at the time and was the overall strongest rider in our group of 13.
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Raw untreated aluminum will corrode. How much will depend on environmental conditions. I owned a Mercury Zephyr(Ford Fairmont clone) that had 1\4" thick cast aluminum bumpers. they were very strong. One time I was hit from behind at a stoplight, a pretty good whack and no damage was done. However, after about 5 years the bumpers had holes from corrosion at the points where the bumpers were bolted to the steel mounting points. Aluminum may be rustproof, but it isn't corrosion proof
Add chloride ions from various road salts (not just sodium chloride) into the mix with a bit of water, and even the anodization can be plucked off. Add in a contact between steel and aluminum along with the chloride and you have a recipe for accelerated corrosion.
But, bare aluminum used in a dry environment or even a wet environment without much salt should be fairly impervious to corrosion.
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I think I mentioned this a long time ago, but my red anodized CK headset spacers “became one” with the steel steerer tube of my Colnago carbon fork thanks to my caustic sweat, riding in the rain and poor maintenance habits. After days of experimenting with ways to free them, the shop finally had to cut through them with a Dremel and pry them off. Wish I had saved the spacers for visual effect.
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They need to be substantially thicker than steel or titanium tubes, to avoid the "beer can dent" buckling. Also, aluminum needs to be thicker to avoid fatigue failure.
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( I believe this was the subject of the project / thesis Gary Klein worked on back in his days at MIT )
https://en.wikipedia.org/wiki/Klein_Bicycle_Corporation
I had an early 90's Cannondale 2.8 frame that had large diameter butted tubing with thin walls - in some areas I believe the wall thickness was .6 mm
this frame was defective - we cut to inspect - but this was in the mid-90's so I cannot be certain on the dimensions
a relatively strong hand could get a little 'oil can' effect from the middle of the top tube on that frame
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Any commercially produced "raw" aluminum frames you see are painted with clear coat. I do like the looks - my wife had that kind of a Cannondale cross frame that I built up for her first "gravel" bike and I really liked the looks of it. It didn't really show minor grease grime, was easy to clean and looked brand new with no visible scuffs and scrapes. I bought her a new gravel bike, Litespeed titanium Watia and i sincerely believe I could have "snuck" it into the garage with her thinking it was another clear coated aluminum frame. But since she pays the credit card bills, I didn't bother.
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Just buy a ti frame and color it with Cerakote.
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0.6 mm thick aluminum seems extremely thin. That's about 20 mils, and the thinnest commonly available Al tubing is ~25 mils. A thin steel tube is about 28 mils.
BTW, I had a Klein Navigator, which weighed in at about 25 lbs. V-brakes, bar end sifters, triple chainrings, 3 water bottle cages.
I rode the cols of France on it, during the 2003 Tour. Here I am, proving that I have some upper body strength:
Water stop somewhere in the Pyrenees.
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