Saddletramp1200
Custom MB Buiilder
I will have to tell My Point Beach to start cracking. I have ridden it daily with a DAX 66 for over four years. 
Frame: Steel vs. Aluminum?
- Thread starter youknouno
- Start date
bigbutterbean
Active Member
Is the point beach made of aluminum? I have had a cranbrook for two years now, and its held up just fine. No cracks or visible signs of stress at all, and that's with a bgf 68.5cc high comp engine and my 6 ft 2, 280 lb butt on it lol.
scotto-
Custom 4-Stroke Bike Builder
BarelyAWake
New Member
That - while somewhat true, is an exaggerated simplification yank...
Just about any metal that's used in bicycle frames should be heat treated/annealed/tempered/case hardened/through hardened after welding to optimize the alloy's properties... as an example 4130 chrome moly is particularly susceptible to embrittlement as a result of welding, requiring both pre-heating and post-weld stress relief and the heat control only TIG is capable of, yet I don't see anyone saying "chrome moly is bad" - and I suspect none of the box store bikes are treated in any way whatsoever save paint, regardless of the material used.
Generally speaking these post weld treatments are side stepped in both mass-production and shop fabrication by simply using additional gussets, more weld filler and thicker material than could be utilized in the ideal treated state, the hydroformed/extruded 6000 series aluminum commonly used for the lower cost bicycles no exception.
The applications these heat treatment welding protocols are adhered to stringently are primarily in the most extreme cases of minimalistic construction, aerospace engineering for example - or for our application, the very best of the "high-end" bicycles, where every ounce of excess material is considered a liability... but those bicycles should not be modified in any case, not just for welding/treatment concerns but also the focus on minimalist weight conservation engineering.
It all boils down to common sense, if you start with an overbuilt platform (such as a mountain bike) of even average acceptable quality (wall thickness & factory welds) and are familiar with basic construction & engineering concepts - welding/modifying any material is simply a matter of considering "acceptable risk" and compensating as necessary...
...yet if you are not familiar with such basic construction & engineering concepts and/or utilize only the lowest quality/most inexpensive platforms to modify in any way (including simply motorizing something not designed for such) - no material is "safe" and it all entails some amount of risk. If you have even some fabrication & modification experience, using aluminum has no greater risk then steel - yet if you have little to no experience in fabrication and welding, the material alone won't make any difference.
Again, it's not so much about the material used - it's the design that material is used in that needs be considered, the care & quality in which it's constructed... and that's so variable with our hobby, there's no clear cut rules, no easy answers - for every post warning against aluminum there's an equal or greater number of reported steel frame failures. Every motorized bicycle on this forum has been modified well beyond it's initial operating parameters, every one a risk to some degree - simply focusing on the material used without considering it's design is the fundamental mistake here, most focusing on price and/or aesthetics alone.
Just about any metal that's used in bicycle frames should be heat treated/annealed/tempered/case hardened/through hardened after welding to optimize the alloy's properties... as an example 4130 chrome moly is particularly susceptible to embrittlement as a result of welding, requiring both pre-heating and post-weld stress relief and the heat control only TIG is capable of, yet I don't see anyone saying "chrome moly is bad" - and I suspect none of the box store bikes are treated in any way whatsoever save paint, regardless of the material used.
Generally speaking these post weld treatments are side stepped in both mass-production and shop fabrication by simply using additional gussets, more weld filler and thicker material than could be utilized in the ideal treated state, the hydroformed/extruded 6000 series aluminum commonly used for the lower cost bicycles no exception.
The applications these heat treatment welding protocols are adhered to stringently are primarily in the most extreme cases of minimalistic construction, aerospace engineering for example - or for our application, the very best of the "high-end" bicycles, where every ounce of excess material is considered a liability... but those bicycles should not be modified in any case, not just for welding/treatment concerns but also the focus on minimalist weight conservation engineering.
It all boils down to common sense, if you start with an overbuilt platform (such as a mountain bike) of even average acceptable quality (wall thickness & factory welds) and are familiar with basic construction & engineering concepts - welding/modifying any material is simply a matter of considering "acceptable risk" and compensating as necessary...
...yet if you are not familiar with such basic construction & engineering concepts and/or utilize only the lowest quality/most inexpensive platforms to modify in any way (including simply motorizing something not designed for such) - no material is "safe" and it all entails some amount of risk. If you have even some fabrication & modification experience, using aluminum has no greater risk then steel - yet if you have little to no experience in fabrication and welding, the material alone won't make any difference.
Again, it's not so much about the material used - it's the design that material is used in that needs be considered, the care & quality in which it's constructed... and that's so variable with our hobby, there's no clear cut rules, no easy answers - for every post warning against aluminum there's an equal or greater number of reported steel frame failures. Every motorized bicycle on this forum has been modified well beyond it's initial operating parameters, every one a risk to some degree - simply focusing on the material used without considering it's design is the fundamental mistake here, most focusing on price and/or aesthetics alone.
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scotto-
Custom 4-Stroke Bike Builder
TIG a lugged frame......you're killing me John, I almost choked on my own saliva laughing.......seriously!
BarelyAWake
New Member
Lugged? Brazing & silver soldering? Perfect examples of "Again, it's not so much about the material used - it's the design that material is used in that needs be considered, the care & quality in which it's constructed... and that's so variable with our hobby, there's no clear cut rules, no easy answers..."
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happyvalley
New Member
Short and to the point.
Aluminum is subject to fatigue with repeated stress and why many of the box store aluminum bikes are made of frame members so thick they end up being heavier that a bike made from quality, drawn steel tubing.
culvercityclassic
Well-Known Member
I built this frame out of steel and all the joints were tig welded with Silicon Bronze filler rod. I will add a couple gussets in certain areas and that's it. I have built a few frames and did some good research with the supplier of the filler rod. That’s why I chose it.
http://motorbicycling.com/showthread.php?t=39900
Another venture I am on is an aluminum frame with some steel areas mixed in; the main part of the frame will be aluminum. We shall see how that turns out.
The bottom line is I favor steel, but like working with aluminum due to the ease of fabrication.
Now ask me what frame I would chose for a Motorbike build if I had to chose one to purchase...I think Scotto has the answer...
http://motorbicycling.com/showthread.php?t=39900
Another venture I am on is an aluminum frame with some steel areas mixed in; the main part of the frame will be aluminum. We shall see how that turns out.
The bottom line is I favor steel, but like working with aluminum due to the ease of fabrication.
Now ask me what frame I would chose for a Motorbike build if I had to chose one to purchase...I think Scotto has the answer...
bigbutterbean
Active Member
I chose my Cranbrook due to the limited budget I was working with. Sometimes,, people have no choice but to buy something inexpensive. I didn't have $300 to spend on an expensive bike, nor did I have the equipment or knowledge to build my own frame. Sometimes, the walmart bikes do break. I still worry sometimes if my frame will break. I do know that I have had it for two years, and it shows no signs of stress. Perhaps I got lucky. All I know is that I paid $75 for this bike, and it may last a few more years. All in all, I say $75 wasn't a bad deal. If I had a choice, would I have chosen a better frame mde of quality american steel? You bet. But I didn't at the time.
happyvalley
New Member
There are too many variables to make blanket statements or say 'one size fits all' when much depends on a case by case basis of what a bike is used for plus rider weight, drive train weight and applied power, tour of duty and miles covered.......Some folks are happy with a bike where the wheels stay more or less round and use it joyriding the neighborhood or running errands to the store. Others might want something that can handle more regular commuting. Some might want a bike that can cross a continent. Race bikes, another category, etc etc.
'Preciate that fellas. The insight is helpful. I know it get a little technical. The ol' school is steel and the new boy Felt's aluminum. My first china will go onto the Colombia (nicknamed the UFO) and one day all of my motorbike dreams will come true when I get ahold of that italiano monster... she'll go onto the Felt.
Ibedayank
New Member
being you can't weld steel and aluminum togather I would like you to explain how you plan on doing this besides using bolts or rivets and control the Galvanic corrosion that is caused by using 2 dissimilar metals togather
Galvanic corrosion also happens when using carbon fiber without adding another layer between it and aluminum parts
I guess what I haven't the capacity to understand yet is: What advantage or for what purpose would someone mx n match metals?
locell
Member
bigbutterbean
Active Member
I would imagine the reason behind it would be to try to find a good balance between strength and flexibility.
Ibedayank
New Member
then explain this....
Welding
6061 is highly weldable, for example using tungsten inert gas welding (TIG) or metal inert gas welding (MIG). Typically, after welding, the properties near the weld are those of 6061-O, a loss of strength of around 80%. The material can be re-heat-treated to restore -T4 or -T6 temper for the whole piece. After welding, the material can naturally age and restore some of its strength as well. Nevertheless, the Alcoa Structural Handbook recommends the design strength of the material adjacent to the weld to be taken as 11,000 psi without proper heat treatment after the weld. Typical filler material is 4043 or 5356.
http://en.wikipedia.org/wiki/6061_aluminium_alloy
as I have said welding aluminum weakens the metal around the weld and requires heattreating to get its strength back