flak monkey
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| posted on 24/11/06 at 08:48 AM |
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Some aluminiums are very strong indeed, but are not weldable (many aluminium alloys infact cannot be welded!).
Some alumnium can be heat treated and hardened by solution hardening, and some of these alloys are also weldable. However, they need to be retreated
after welding!
Designing in aluminium is different to designing with steel. You have to worry about fatigue in everythig you design in ali, also in general ali is 3x
lighter and also 3x less stiff than steel, so the actual fundamental design considerations are completely different if you want a stiff ali structure.
Sera
http://www.motosera.com
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Lippoman
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| posted on 25/11/06 at 05:21 PM |
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Aluminium vs Steel
The rule of thumb I was thaught is that Al is 1/3 the strength and 1/3 the weight of steel.
So, theoretically, a skinned honeycomb panel could be as light and as stiff if steel 1/3 of the thickness was used as compared to Al, but it would be
much more sensitive to deformation in the skin as the section of the skin itself would be so thin.
(Moment of inertia is cubed by the thickness of section.(simplification))
This is one of the reasons why you can create parts that are stronger in Al compared by weight to steel, especially in parts where expected life is
limited. Add fatigue into the equation and you've opened a new can of worms...
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Peteff
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| posted on 25/11/06 at 06:19 PM |
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Al is 1/3 the strength and 1/3 the weight of steel.
So for the same strength you would need 3 times as much material which would bring you back up to the same weight and cost you how much more as well?
This seems like an exercise in futility as the whole idea in the first place is to save weight isn't it? Stick to using aluminium for the
bodywork and wheels I think is the message.
quote:
both F1 and bicycles used aluminium for this exact reason, before switching to carbon fiber.
I've seen aluminium and carbon frame bicycles break but all the steel ones I've seen in similar cases have bent, admitted they
are lighter in other materials but you can straighten the steel and don't need to replace or tig to repair. F1 will have a limited life
expectancy anyway so they are not really relevant as they are only engineered to do the job for a season at most, not to last for years.
[Edited on 25/11/06 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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dnmalc
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| posted on 25/11/06 at 10:07 PM |
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strong Al alloys can be welded the Fox armoured car is made from Al armour plate. Many years ago I used to examine the welders test pieces. These were
14 run welds and were only allowd 1 inclusion or void per half meter length of plate.
Much Much Respect
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Lippoman
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| posted on 26/11/06 at 10:16 AM |
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Peteff: Not "an exercise in futility"
Loads may buckle very thin steel, so using 2 times thicker Al there increases the stiffness 2,6x while still having a weight of 0,67x...
It is still weaker than the steel in tension but "stronger" in compression as it doesn't buckle. This is especially important in the
web of beams or in skins...
Manufacturing issues (especially in casting) may also make the Al version much lighter, you simply cannot always create steel parts as thin as needed
to make them lighter than the Al parts that are strong enough.
Chosing the correct material is much more than just looking at the strength in material specifications, you have to factor in manufacturing, design
and all the loads the part will encounter. Also the fail mode is important, it is often preferrable that the part yields rather than breaking of
suddenly...
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Syd Bridge
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| posted on 26/11/06 at 01:58 PM |
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And as I've put far too may times, the problem with ali castings is crystallisation, and designing for proper cyclical fatigue loading problems.
Proper heat treatment is all important, and many small manufacturers seem to omit this vital part of the process, or shortcut it.
Failure mode is critical.
To be safe, an ali part for an upright will be as heavy as a properly designed steel item.
I've seen the result of this type of design far too often. The parts I deal with in my work are lifed. On gravel roads this can as little as
50~80kms!! If things are really rough, steel is the material of choice every time, to avoid failures.
Cheers,
Syd. 
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JB
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| posted on 26/11/06 at 04:40 PM |
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Uprights
So there is mass discussion about materials. I will offer some input on the actual design.
For a front upright I prefer to see automotive balljoints used. It is difficult to get reasonable suspension travel and steering lock with spherical
bearings. Plus quality bearings will cost at least £30 each.
The same upright will be used on the left and right. The steering arm will bolt on and be a double shear arrangement to take a spherical bearing as a
track rod end. Or you could bolt on a steering arm that uses an automotive track rod end. a bolt on arm gives you the choice.
A standard centre section is required but the upper and lower should be easy to alter so you can optimise the ball joint position for different
suspension designs.
I am unsure if a live stub (as in Sierra) or a dead stub (like Escort) is preferential. With a live stub machining accuracy of the upright is
critical. With a bolt in stub you do not have to be so critical on the machining of the upright. Regarding structural considerations perhaps somebody
else can advise.
Rear upright design can wait until another time!
John
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andyd
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| posted on 27/11/06 at 08:04 AM |
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quote:
Originally posted by JB
The steering arm will... be a double shear arrangement
Can you explain how you would make it double shear please?
quote:
A standard centre section is required but the upper and lower should be easy to alter so you can optimise the ball joint position for different
suspension designs.
How would you allow the positions to be adjusted if not part of the machined whole? Bolt on in some way as the steering
arm?
quote:
live stub (as in Sierra) or a dead stub (like Escort)
Can you explain the differences?
Andy
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Syd Bridge
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| posted on 27/11/06 at 08:56 AM |
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You can get much better geometry with the 'live' stub axle. As in the Sierra.
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NS Dev
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| posted on 27/11/06 at 09:49 AM |
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Live stub certainly gives you the choice to put things where you want them, and if making uprights with thread-in stubs anyway, the live stub is no
harder to make either.
PS to answer the question about what is the difference, live stub is where the stub is "with" the hub and rotates with the wheel in
bearings in the hub carrier like on the sierra design. Dead stub is where the stub is fixed to the carrier and the hub rotates on it like the cortina
design.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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NS Dev
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| posted on 27/11/06 at 09:51 AM |
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quote:
Originally posted by JB
So there is mass discussion about materials. I will offer some input on the actual design.
For a front upright I prefer to see automotive balljoints used. It is difficult to get reasonable suspension travel and steering lock with spherical
bearings. Plus quality bearings will cost at least £30 each.
The same upright will be used on the left and right. The steering arm will bolt on and be a double shear arrangement to take a spherical bearing as a
track rod end. Or you could bolt on a steering arm that uses an automotive track rod end. a bolt on arm gives you the choice.
A standard centre section is required but the upper and lower should be easy to alter so you can optimise the ball joint position for different
suspension designs.
I am unsure if a live stub (as in Sierra) or a dead stub (like Escort) is preferential. With a live stub machining accuracy of the upright is
critical. With a bolt in stub you do not have to be so critical on the machining of the upright. Regarding structural considerations perhaps somebody
else can advise.
Rear upright design can wait until another time!
John
Totally agree particularly with the use of automotive balljoints. They are a much better solution than rose joints on the budgets that are discussed
on this site.
You can get good rose joints, but not for the same sort of money that will buy transit tie rod ends!!!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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Peteff
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| posted on 27/11/06 at 11:54 AM |
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Manufacturing issues (especially in casting) may also make the Al version much lighter, you simply cannot always create steel parts as thin as needed to make them lighter than the Al parts that are strong enough.
I've worked in foundries making valves for the oil industry and rotors for the power industry and anything you can cast in aluminium can be cast
in steel with a lot less waste and shrinkage, can you explain why the thickness (or thinness?) can't be achieved in steel? (Quote from
Lippoman)
[Edited on 27/11/06 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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NS Dev
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| posted on 27/11/06 at 12:10 PM |
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Ahh! wasn't specifically referring to uprights, and WAS referring to a DIY situation.
What I meant was that in a lot of cases, steel parts are only heavy because they were vastly overspecced for the job, largely because the steel that
was available was too thick for the job.
For example, think of making a steel bike frame. The amount of steel actually required to perform the job is TINY, but physically forming tube thin
enough is very expensive, so heavier tube is used, then people say it is heavier than aluminium. Practicality of manufacture comes into this argument
a lot more than people will acknowledge!
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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JB
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| posted on 27/11/06 at 05:28 PM |
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Answers
To make a steering arm double shear you use 2 plates. This could be a bolt on “U” shape that goes on the front or back side of the upright. Or 2
plates that go across the back of the upright. As in the picture of my car.
(I know it needs a clean but I was too busy driving it and I will clean it over Christmas)
The advantage of these double shear plates is that it is easy to alter the ackerman and or steering ratio and they are structurally more efficient
than single shear.
This upright uses a push in lower ball joint and Jag upper ball joint. Apart from the hassle I had getting the steering arm on they are OK.
quote:
"A standard centre section is required but the upper and lower should be easy to alter so you can optimise the ball joint position for
different suspension designs.
How would you allow the positions to be adjusted if not part of the machined whole? Bolt on in some way as the steering arm? "
This is where it does get more difficult. If it is a steel fabrication then you just alter the size of the patterns you use to cut the steel. On a
casting you could have a pattern in 3 pieces, a standard centre section then various top and bottom parts. You could use bolt on parts but then you
are making it structurally less efficient.
John
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nealg
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| posted on 27/11/06 at 09:16 PM |
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would something like this be suitable as
used on the dp1 car but using a fixed stub axel
 
Rescued attachment dp1_upright.jpg
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Lippoman
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| posted on 28/11/06 at 12:20 PM |
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Casting Steel vs Al
If cast to the same dimensions (same mold) the Al part will be 1/3 the weight of the steel part. So every section you have to make thicker due to
casting or mold making reasons than needed for mechanical strength/stiffness will make the Al part lighter in comparison.
Weaker, but lighter.
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scotmac
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| posted on 29/11/06 at 02:39 AM |
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quote:
Originally posted by dnmalc
strong Al alloys can be welded the Fox armoured car is made from Al armour plate. Many years ago I used to examine the welders test pieces. These were
14 run welds and were only allowd 1 inclusion or void per half meter length of plate.
Much Much Respect
Aluminum is 1/3 the weight of steel and 1/3 the *stiffness* of steel, but *80%* the "strength". Hence it has a much better
"strength" to weight ratio of steel. But yes, it is also a question of the application, and how it's other features fit w/ the use
(fastening for example).
In terms of bicycles and racing chassis, it is definitely a win. Here is a good article on the different bicycle frame components:
http://www.calfeedesign.com/whitepaper4.htm
[Edited on 29/11/06 by scotmac]
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Lippoman
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| posted on 29/11/06 at 05:27 PM |
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Scotmac: 80% strength Al?
Which cast aluminium alloy/steel are you referring to?
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scotmac
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| posted on 1/12/06 at 11:22 PM |
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6000 series or 7000 series...eg, 6061-t6 used extensively in bicycle frames.
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