Welding on Big box store bikes?

Birddog1148 said:
So I took a used hub in to get it laced onto my Cranbrook rim so I can add disc brakes to the MB. The guy at the shop say welding to a bike is like welding to a spring. How true is that on the cheep bikes like Cranbrook? I am a good welder and have no doubts about my skills, but will I do more harm than good metaurgecly speaking?
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You bike is already welded. That dude might not be to smart. I have tried to mig weld a bike frame, but I burned through it. I am not a good welder yet either. I took it to a guy I know and he smoothed out some of my mess with a mig, no problems. I'm sure it depends on the frame. If the metal sparks when you hit it with a grinder, then it is steel-ish. If it simply turns to dust, it's probably aluminum.
 
sojudave said:
You bike is already welded. That dude might not be to smart. I have tried to mig weld a bike frame, but I burned through it. I am not a good welder yet either. I took it to a guy I know and he smoothed out some of my mess with a mig, no problems. I'm sure it depends on the frame. If the metal sparks when you hit it with a grinder, then it is steel-ish. If it simply turns to dust, it's probably aluminum.
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Or use a magnet, besides ferrous welds wont stick to alluminum Thats how I get broken steel studs out alluminum heads, I just put a nut over the broken stud and weld it on, weld only sticks to steel
 
Retmachinist said:
The guy at the bike shop doesn't know what he is talking about. There is no heat treat to the cheap steel tubing they use on dept. store bikes. My only concern would be that you would blow holes in the thin steel tubing, and I mean "thin".

John
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Been there, done that. lolz
Had to rebuild a little patch that burned through, but my bike is holding up great.
 
If your blowing holes your using to much heat! dial it down and your feed. If you use to low of heat though, it heats up the surrounding base metal alot more than short concentrated welds. I also wouldnt use flux when welding so no smaw. But mig and definatly tig will be just fine.

I think the guy at the bike store was trying to sell ya something, or he was thinking about aluminum. Some aluminum alloys are heat treated, and you want to preheat those before you weld them and postheat after. Others are not and do not require it.

Heat treatable series: 2000, 6000, 7000.
Non-heat treatable: 1000, 3000, 4000, 5000.
 
I am hearing cheap, thin, not heat treated steel.

Maybe not the best choice for a disk brake mount.

Welding the cheap, thin, not heat treated tubing will not make it stronger and there could be huge stress on the welded mount depending on how hard you hit the brake.

I would change out that fork with a nice one set up for a disk brake.
 
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kicking said:
do you think an mount for an drum brake may work as well for the disk somehow ? Drum Brake Springer Fork Leg Clip for Schwinn Whizzer - eBay (item 300446284120 end time Jul-20-10 18:53:55 PDT) I was thinking about putting brakes on my bike . so i will be looking at this thread , and an few other threads
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All that clip does is hold the drum brake in position so it doesn't rotate. If you were to put the load of a caliper on that thin piece of metal the twisting reaction would distort it immediately.

That machined adapter looks like it might do the job though. I'm thinking of replacing the band brake with a disk and that looks like the way to go.
 
xct2
caduceus said:
All that clip does is hold the drum brake in position so it doesn't rotate. If you were to put the load of a caliper on that thin piece of metal the twisting reaction would distort it immediately.

That machined adapter looks like it might do the job though. I'm thinking of replacing the band brake with a disk and that looks like the way to go.
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let us know how it gos with the machined adapter . and give some links if you can , and pictures if you have time ' ; Latter still kicking
 
To the OP..

Just welded a couple brackets for a different gas tank today. I found the bike (Cranbrook) easier to weld then the sheet metal I used.

Beat on them with a hammer a few times before I hooked everything up (nobody likes a flying gas tank), and it holds perfectly fine. And I'm what you would call a below amateur welder.
 
Welding on an aluminum frame or fork is probably a bad idea, as the welding heat softens the aluminum permanently (unless you have it heat-treated again, that is).

Welding on steel is possible, but bronze-brazing it would be safer.
Thin steel will tend to carburize a lot on the back side and flake off, weakening the metal around the weld. Brazing is done at a much lower temperature, and totally avoids this problem.

Venice Motor Bikes said:
I would mount the caliper on the back of the fork leg so the stopping force pushes on the back of the fork instead of trying to tear it off the front of the fork! ;)
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This is not a good idea.
Normally the caliper on the front side gets pulled forward, and the wheel axle gets pushed UP into the dropouts.

If you mount the caliper on the rear of the fork blade, then the caliper gets pushed into the fork blade (no problem there) but the caliper's stopping power pulls DOWN on the axle. A few people who tried this have had their front wheels come out while riding because of this when they stopped hard. The couple times I saw pics, the dropout itself cracked in half.

Motorcycles can do this (mount the front calipers behind the fork blades) because they do not have slots in their fork ends--they have holes, and a thru-bolt.
~
 
42blue15 said:
Welding on an aluminum frame or fork is probably a bad idea, as the welding heat softens the aluminum permanently (unless you have it heat-treated again, that is).

Welding on steel is possible, but bronze-brazing it would be safer.
Thin steel will tend to carburize a lot on the back side and flake off, weakening the metal around the weld. Brazing is done at a much lower temperature, and totally avoids this problem.


This is not a good idea.
Normally the caliper on the front side gets pulled forward, and the wheel axle gets pushed UP into the dropouts.

If you mount the caliper on the rear of the fork blade, then the caliper gets pushed into the fork blade (no problem there) but the caliper's stopping power pulls DOWN on the axle. A few people who tried this have had their front wheels come out while riding because of this when they stopped hard. The couple times I saw pics, the dropout itself cracked in half.

Motorcycles can do this (mount the front calipers behind the fork blades) because they do not have slots in their fork ends--they have holes, and a thru-bolt.
~
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Makes you wonder why they are factory built this way.
 
If you have oxy-acetelyne to weld with try the silver brazing rods with the blue flux on them. You can buy them at Home Depot or most any hardware store. Brazing makes it easier to get a nice fillet to your weld and the silver rods are MONDO hard, VERY high tensile strength. Also, you'll never get the temp hot enough to burn through whatever you're brazing to. I use them all the time and have yet to have anything break off.
 
Any experiences welding on the hubcenters of the rear wheel on big-box stroe bikes? Building a full-custom MB, and I have to weld a new sprocket and spacer onto the rear wheel. Any input would help.
 
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