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Discussion Starter · #1 · (Edited)
I know this doesn't specifically relate to Turner, but you guys are the "go to" guys when it comes to needing information.

I'm looking at 20" kid geared bikes. The main difference between the two that I'm looking at is the aluminum that the frame is made out of.

Is one stronger than the other? Lighter? Doesn't make a difference, just pick one?

Thanks for any help,

crazyhouse
 

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Trampelpfadbenutzer
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Probably someone like DT or Knolly can explain this more accurate but the main difference is that the 6000 series alu is easier to weld but need headthreading to give the material its strenght back wich it looses during welding.This needs some time and the propper tools (oven).

The 7000 series alu (especially 7005,not all 7000 series alloys are weldable)is relative easy to weld too and will not need to be headthreated after welding but needs to be aged.
This means after a period of time(a month or so) the material got back to its former preweld strenght after some time from alone.
This is a mayor plus for overseas producers,they can weld the frames,paint them and then ship them to us at the same day.
During the time the frame reaches the customer it is back to its strenght.

At the other hand the local custombuilder can weld a 6061 (or similar quality in the 60xx series) frame today, headthreat it overnight and give it to you tomorrow.
This is roughly the difference, but I am no engineer.

Here is a link where you can check some applications about weldability,anodizability,strenght and so on.
This chart is a bit incomplete not showing all possible alloys but should give you an idea.

If I remember correct Turner uses (or have used?) a 6013 alloy wich needs a way more complex headthreating process but will give you a about 30% increased strength over 6061.

For a kids bike it should not be a huge difference between the 6061 and 7005 in a technical way.The difference will be the price for the product IMHO.

Hope this helps
RaD
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Not a huge amount of difference in the end product to be honest.

As RaD posted, the main "functional" difference between the two materials is how they are heat treated after welding. While I'm not a metalurgical engineer, my understanding of "why" the materials are heat treated after welding differs for both 6000 and 7000 materials.

The main advantage of 7000 material is that is requires only an artificial age after welding. The material loses only minimal strength after welding. However, it is very subseptable to stress corrosion cracking. If it is not properly aged after welding, the frame's long term durability will be significantly reduced. Almost all aluminum alloys age somewhat at room temperature. However, I'm pretty sure that you MUST artificially age 7005 aluminim post weld to maximize its resistance to stress corrosion cracking.

Because the frame only needs to be "baked" after welding, it makes for a much easier manufacturing process. Any builder can invest a small (relatively) amount of money and build a heat treat oven. Typically, only two different temperatures are required, and they are fairly low (the high 300's and mid-high 200's F).

So, a welder can weld the frame, straighten it, then stick it in an oven and take it out 11 hours later (or what ever the time is).

7005 is one of a few 7xxx alloys that can be easily tig welded. My understanding is it was invented precisely for this purpose (i.e. easy welding and lack of a solution / quench process - explained below). I'm not 100% sure about this, but otherwise, there's no real advantage of 7005 as it is typically much weaker than other 7xxx high strength alloys such as 7050 and 7075.

One last problem with 7005 is its severe lack of availability in North America, especially as of earlier this year as Easton stopped tube production in the USA and moved it overseas. So, if you're just buying the basic pre-made pieces for a road bike, then you're going to be ok. However, getting material for for CNC'd parts and such is now very difficult (and the material is very expensive).

6000 series alloys (6061 is the most poppular) is a very common alloy and typically called "air craft" grade aluminum (there there are many different types of aluminum used in aircraft).

It welds easily and material is very very common and generally easy to find, which makes it easy to design and manufacture complex CNC'd parts. It is very soft when annealed which makes it easy to form into complex structures like monocoque shells.

It's slightly less strong than 7005, but has a much higher durability because of greater elasticity. It also has better corrosion resistance. However, it requires a two stage heat treating process that is much more complicated than what 7005 requires.

When welded, 6000 alloys lose significant strength (i.e. annealed 6000 is about 10-20% of the strenght of a T6 heat treat grade of the same material). So, the 6000 frame must be heat treated, otherwise, you'd bend it just by pedalling it.

The first stage involves a solution bath typically around 800* F for typically 30-60 minutes. Then, the frame must be rapidily quenced: almost down to room temperature within less than a minute I think. This locks the alloy's molecular structure in place. Afterwards, the frame is re-aligned, then it goes for an artificial age.

The solution process redistributs the alloying elements in the frame, the quench looks them in place. Afterwards, the aging gives the material it's high strength.

Functionally, very good bikes can be made from both materials - the 6000 or 7000 decision is typically a manufacturing decision and has very little to do with performance characteristics. The ONE exception is Scandium material for XC and Road bikes. This material achieves the same stiffness as 7005 aluminum, but allows for thinner wall sections (I think) resulting in a weight reduction of the frame. However, it's not suitable (or practical) for heavier duty frames.

Hope that helps and I hope that I have everything more or less correct.

Edit: RaD - that link is cool - thanks for posting it! Another cool link is www.matweb.com if you're interested.

Cheers,
 

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"El Whatever"
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Wow... very technical, yet my 11mo old kid could understand it.

Questions for both DT and Knolly if you don't mind...


1.- Do you see any future for steel on bikes??

Some alloys might had been developed since we dropped the use of steel and some light yet strong frameset (or parts) could be made out of steel.

I understand that most of the problems with steel are kind of the same that with 6XXX Al series. Post welding/forming Heat Treatment. Another factor is it's higher strenght that usually requires more powerful machines (or energy in the form of heat) to make some shapes easily obtainable with Al. Riding characteristics (read: mechanical properties) are another point to consider.

2.- How is the sequence in which a frame is made??? What do you guys start with first?? Which tube is the more critical, let's say on the front triangle? I mean especially welding wise. I know you just can't start welding anywhere you please.

And lastly... only to congratulate you both for making such terrific bikes! Welds (and finishes) on your frames are simply gorgeous. Your welders have to be terrific guys with the torch to make such a beautiful job right at the first time (I suppose all weding on a typical bike frame is a single pass, maybe two for much).

Thanks for any insight.
 

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turnerbikes said:
That is one heck of a lot of words. Thanks from many on the general differences.

DT
Hey DT!

Grade 9 typing class - most useful course I have EVER taken in grade school or university - I am 100% serious on this!

I hope all is well in California - sorry to poach the Turner forum :)

Cheers,
 

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Natl. Champ DH Poser/Hack
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its a hijack!

anyone know of a domestic builder who is willing to repair 7005? i have 4 frames in need of some light grade love. ive found a tube and rod suplyer courtesy of a pal in az and a local welder but id much prefer someone who knows bikes to a trailer jockey. my search of builders and repair stations on google provided me with jack. any info or offers to do the work will be met with much thanx and reasonable compensation.
 

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cactuscorn said:
anyone know of a domestic builder who is willing to repair 7005? i have 4 frames in need of some light grade love. ive found a tube and rod suplyer courtesy of a pal in az and a local welder but id much prefer someone who knows bikes to a trailer jockey. my search of builders and repair stations on google provided me with jack. any info or offers to do the work will be met with much thanx and reasonable compensation.
Linky
 

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Warp2003 said:
Wow... very technical, yet my 11mo old kid could understand it.

Questions for both DT and Knolly if you don't mind...

1.- Do you see any future for steel on bikes??

Some alloys might had been developed since we dropped the use of steel and some light yet strong frameset (or parts) could be made out of steel.

I understand that most of the problems with steel are kind of the same that with 6XXX Al series. Post welding/forming Heat Treatment. Another factor is it's higher strenght that usually requires more powerful machines (or energy in the form of heat) to make some shapes easily obtainable with Al. Riding characteristics (read: mechanical properties) are another point to consider.

2.- How is the sequence in which a frame is made??? What do you guys start with first?? Which tube is the more critical, let's say on the front triangle? I mean especially welding wise. I know you just can't start welding anywhere you please.

And lastly... only to congratulate you both for making such terrific bikes! Welds (and finishes) on your frames are simply gorgeous. Your welders have to be terrific guys with the torch to make such a beautiful job right at the first time (I suppose all weding on a typical bike frame is a single pass, maybe two for much).

Thanks for any insight.
Some quick answers:

1.

Personally, I don't see much use for steel in full supsension bikes simply because it can not touch the stiffness to weight ration of aluminum. The same is true for titanium as well. Full suspension frames already have issues with flex due to long unsupported linkage members and pivots and I don't see why the frame should be made any flexier. Sure, steel will have more durability, but it will also be significantly heavier to achieve the same stiffness as an aluminum frame.

My personal philosophy with full suspension frames is that the suspension design should do the work, not the individual parts of the frame. I.e., I don't think that the front triangle should provide any "lively" feel any more than the chain stay should. The front triangle is just there to be as strong and rigid as possible and hold the fork, cranks, seat post and the rest of the bike. The frame's performance should come from the suspension alone. This is a very different philosophy from many builders, especially those who build hard tail frames.

2.

Sorry, but that is something that I won't get into - I would prefer to keep our manufacturing techniques to ourselves. Don't worry - no offense taken on the question, it's just not something that I wish to discuss in a public forum.

Regards,
 

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Jerk_Chicken said:
It's good to see mutual respect between bike manufacturers. There is plenty of business to go around without resorting to dirty tricks.

Cheers, Noel!
I totally agree. And for the record, if I didn't manufacture frames, the following list would be the bikes that I would ride:

www.turnerbikes.com
www.canfieldbrothers.com
www.chromagbikes.com

So, props to these cool frame companies!
 

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Natl. Champ DH Poser/Hack
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knollybikes.com said:
Some quick answers:

1.

Personally, I don't see much use for steel in full supsension bikes simply because it can not touch the stiffness to weight ration of aluminum. The same is true for titanium as well. Full suspension frames already have issues with flex due to long unsupported linkage members and pivots and I don't see why the frame should be made any flexier. Sure, steel will have more durability, but it will also be significantly heavier to achieve the same stiffness as an aluminum frame.

My personal philosophy with full suspension frames is that the suspension design should do the work, not the individual parts of the frame. I.e., I don't think that the front triangle should provide any "lively" feel any more than the chain stay should. The front triangle is just there to be as strong and rigid as possible and hold the fork, cranks, seat post and the rest of the bike. The frame's performance should come from the suspension alone. This is a very different philosophy from many builders, especially those who build hard tail frames.

Regards,
amen! ive had that argument a few times myself. its nice to know im not a total moron. great posts man. thanx for the info and personally im glad to have ya join us. im sure ya know yer stuff is talked about plenty in here. its cool to see more domestic folks tryin hard to make nice stuff like it was back in the day.
 

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"El Whatever"
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knollybikes.com said:
Some quick answers:
1.
Personally, I don't see much use for steel in full supsension bikes simply because it can not touch the stiffness to weight ration of aluminum.
I see it. I kinda was aware of it and thought some allows would have been developed to address those "weak" spots of steel, but I see it's very little possible due to the nature of the material.

knollybikes.com said:
2.
Don't worry - no offense taken on the question, it's just not something that I wish to discuss in a public forum.
Regards,
Thanks Noel... again. No offense or bad feelings on this side either... I'm kinda getting used to these kind of answers :D I might be asking too much!

In any case I respect that... no problem.

Cheers!
Warp
 
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