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customizing an aluminum frame

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customizing an aluminum frame

Old 08-07-11, 08:50 AM
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Big Lew
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customizing an aluminum frame

Are there any concerns about welding small aluminum flat metal bar extensions to the ends of the rear forks of an aluminum-framed bike in order to provide more attachments for sturdy racks or for trailer rigging? Are most aluminum frames actually aluminum, or alloy, and would welding pure aluminum bar be compatible and a good bond?
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Old 08-07-11, 09:03 AM
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Originally Posted by Big Lew View Post
Are there any concerns about welding small aluminum flat metal bar extensions to the ends of the rear forks of an aluminum-framed bike in order to provide more attachments for sturdy racks or for trailer rigging? Are most aluminum frames actually aluminum, or alloy, and would welding pure aluminum bar be compatible and a good bond?
Most aluminum frames are alloy typically 6061 or something similar. Pure aluminum is very soft. I bet the bars are a 2000 or 3000 series. If the person welding really knows what they are doing it should be fine.

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Old 08-07-11, 09:13 AM
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Big Lew, If you're considering tacking something on to the dropouts, you might be okay. Anywhere else and I wouldn't suggest it. What are you considering?

Brad
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Old 08-07-11, 09:22 AM
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1) Aluminum is very difficult to weld. I can TIG weld well enough that I've built my own (steel) bicycle frame, but aluminum is still crazy difficult. Guys who can weld aluminum well often charge a premium for their services.

2) There are a zillion different alloys of aluminum. Welding aluminum requires knowing exactly which alloys are being welded, so you can pick a "filler" alloy that will bond with both sides of the weld. Pick the wrong filler and the weld won't hold... though it may look fine initially.

3) Most aluminum frames are heat-treated after welding to increase strength.

4) My welding instructor claimed that some aluminum filler alloys don't respond well to anodizing. The welds end up a distinctly different color than the rest of the piece, according to him. Not an issue if you paint or powdercoat, obviously.

My guess is you'll find that attempting to modify an aluminum frame probably isn't worth the cost...
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Old 08-07-11, 09:31 AM
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Originally Posted by bradtx View Post
Big Lew, If you're considering tacking something on to the dropouts, you might be okay. Anywhere else and I wouldn't suggest it. What are you considering?

Brad
I have a Devinci Monaco hybrid touring bike. The flat end of the rear forks where the rear wheel is attached is quite wide and substantial. I am considering having an additional flat piece welded to the back of it in order to add pins for a homemade "Extra Wheel" style trailer attachment.
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Old 08-07-11, 11:45 AM
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BoB's and Xtrawheels just use an alternate skewer thru the QR ,
so trailer does the Up/Down float around that axis

simpler perhaps? BoB skewers are available as a spare part..

Last edited by fietsbob; 08-07-11 at 12:15 PM.
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Old 08-07-11, 01:16 PM
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Originally Posted by sstorkel View Post
1) Aluminum is very difficult to weld. I can TIG weld well enough that I've built my own (steel) bicycle frame, but aluminum is still crazy difficult. Guys who can weld aluminum well often charge a premium for their services.

2) There are a zillion different alloys of aluminum. Welding aluminum requires knowing exactly which alloys are being welded, so you can pick a "filler" alloy that will bond with both sides of the weld. Pick the wrong filler and the weld won't hold... though it may look fine initially.

3) Most aluminum frames are heat-treated after welding to increase strength.

4) My welding instructor claimed that some aluminum filler alloys don't respond well to anodizing. The welds end up a distinctly different color than the rest of the piece, according to him. Not an issue if you paint or powdercoat, obviously.

My guess is you'll find that attempting to modify an aluminum frame probably isn't worth the cost...
Thanks, that's what I was suspicious about, I think I'll forget that notion, not worth compromising my bike frame. Although I have regular welders, I'm not set up for aluminum welding, nor would I attempt the job myself. I had planned to have an aluminum welding shop do the job.
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Old 08-07-11, 01:26 PM
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Frames get Solution heat treatment, to normalize the stresses of joints working against each other..
after all the welding is completed..

then Re - heat treaded again .. bike factories can do that Home shops cannot.

Anodizing requires immersion, in a big enough tank.. ..
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Old 08-07-11, 03:50 PM
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I've been told by a few welders (who regularly weld aluminum) that since bike frames are almost always heat treated after welding, any attempt to weld on the frame will remove the heat treatment and significantly weaken the frame.
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Old 08-07-11, 04:01 PM
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Thanks everyone, I'll not attempt it, and look into the alternate skewer.
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