Hi all, I have a need to weld some frameworks in Aluminum 6061 & 6063
extrusions and plate, up to 1/4" and some extrusion to 1/2" plate. There's
almost enough of it to consider getting the equipment to weld it myself.
This is hobby stuff not commercial so part of the deal is to be able to do
it myself.

Here's the problem. Never done it before. Years ago did a reasonable amount
of gas welding in steel, mostly tube work race car and bike chassis, and
some general buzz box stick stuff.

What's the best method to weld this stuff? Mig? I've been looking at a
lincoln 135 or 175 with an AL mod. would an average welder get a good
result with either of these machines? Would a mig machine of this scale
give a decent structural weld? Is there something else I should look at?

Is anything from ( big intake of breath) HF able to do the job?

thanks...

In article , Mike
wrote:

Hi all, I have a need to weld some frameworks in Aluminum 6061 & 6063
extrusions and plate, up to 1/4" and some extrusion to 1/2" plate. There's
almost enough of it to consider getting the equipment to weld it myself.
This is hobby stuff not commercial so part of the deal is to be able to do
it myself.

Here's the problem. Never done it before. Years ago did a reasonable amount
of gas welding in steel, mostly tube work race car and bike chassis, and
some general buzz box stick stuff.

What's the best method to weld this stuff? Mig? I've been looking at a
lincoln 135 or 175 with an AL mod. would an average welder get a good
result with either of these machines? Would a mig machine of this scale
give a decent structural weld? Is there something else I should look at?

Is anything from ( big intake of breath) HF able to do the job?

thanks...


The most cost effective solution would be a 250 - 300 amp DC Stick
welder and a Readywelder spoolgun.

http://www.readywelder.com/

They may look like toys, but believe me they work very well.

You will also need a bottle of Argon or argon-helium mix.

On Sun, 21 Nov 2004 03:39:24 GMT, Mike wrote:

Hi all, I have a need to weld some frameworks in Aluminum 6061 & 6063
extrusions and plate, up to 1/4" and some extrusion to 1/2" plate. There's
almost enough of it to consider getting the equipment to weld it myself.
This is hobby stuff not commercial so part of the deal is to be able to do
it myself.

Here's the problem. Never done it before. Years ago did a reasonable amount
of gas welding in steel, mostly tube work race car and bike chassis, and
some general buzz box stick stuff.

What's the best method to weld this stuff? Mig? I've been looking at a
lincoln 135 or 175 with an AL mod. would an average welder get a good
result with either of these machines? Would a mig machine of this scale
give a decent structural weld? Is there something else I should look at?

Is anything from ( big intake of breath) HF able to do the job?

thanks...


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

So, for a "decent" weld, I like TIG. For one you trust your life to?
Rivet.

wrote in message
...


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he modified
the 7 chassis so it could be made out of angle.

Ed Huntress

On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:

wrote in message
.. .


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he modified
the 7 chassis so it could be made out of angle.

Ed Huntress

Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

wrote in message
...
On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:

wrote in message
.. .


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he
modified
the 7 chassis so it could be made out of angle.

Ed Huntress

Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

It sounds interesting. If he puts any photos of it online, let us know.

Ed Huntress

On Sun, 21 Nov 2004 20:08:30 GMT, "Ed Huntress"
wrote:

wrote in message
.. .
On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:

wrote in message
.. .


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he
modified
the 7 chassis so it could be made out of angle.

Ed Huntress

Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

It sounds interesting. If he puts any photos of it online, let us know.

Ed Huntress

He won't, but I might.

wrote in message
...
On Sun, 21 Nov 2004 20:08:30 GMT, "Ed Huntress"
wrote:

wrote in message
.. .
On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:

wrote in message
.. .


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is
building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a
do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he
modified
the 7 chassis so it could be made out of angle.

Ed Huntress

Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

It sounds interesting. If he puts any photos of it online, let us know.

Ed Huntress

He won't, but I might.

The idea of making a space frame with L-channel raises all sorts of
engineering questions, but the bottom line will be how well it actually
performs -- and what it winds up weighing.

As a matter of interest, the radius of gyration for L-channels sucks in a
major way, compared to tubes, which means that it's unlikely to resist
buckling nearly as well as a tube-based space frame. That's the major rub, I
would think. But there are more issues that this design raises as well.

However, a finished Lotus 7 is actually a hybrid chassis, with shear-panel
design combined with space frame. And the torsional weakness in a 7 (Mk. II
or Mk. III; I don't recall how the Mk. IV stresses out, but almost all
replicas are Mk. IIIs) is in the cockpit bay, anyway, which can generously
be called parallel girders with a shear-panel floor. That's true of many
open space-frame cars.

So a good, tightly riveted cockpit bay, made of L-channels, could make the
car stiffer than the original. I don't know. It would take a complete FEA
analysis, or a model analysis, to tell.

In any case, if the car is raced, they'll find out a lot about it from the
way it performs on the track. And I'd find it very interesting, as I'm sure
many other people who follow chassis design will find it interesting.

Also for the record, a true space frame is the design concept, among all
design concepts for car chassis, which benefits LEAST from use a low-density
material: aluminum over steel. There have been aluminum-tube space frames
(1960s Bobsy sports-racer; Porsche 917; a special made by the Locost folks),
but, in general, the slight weight savings have never been worth pursuing.
In theory, if not in practice, a steel space frame versus an aluminum one
should come out weighing exactly the same, for equal stiffness and strength.

But there are issues other than the pure, simplified engineering theory
involved, and aluminum may provide a fairly large advantage with channel. It
will help the column stiffness and help prevent buckling in compressed
members.

We'll find out when they get it on the track.

Ed Huntress

On Sun, 21 Nov 2004 03:39:24 GMT, Mike wrote:
Hi all, I have a need to weld some frameworks in Aluminum 6061 & 6063
extrusions and plate, up to 1/4" and some extrusion to 1/2" plate. There's
almost enough of it to consider getting the equipment to weld it myself.
This is hobby stuff not commercial so part of the deal is to be able to do
it myself.

Woooo! Half inch!

Here's the problem. Never done it before. Years ago did a reasonable amount
of gas welding in steel, mostly tube work race car and bike chassis, and
some general buzz box stick stuff.

What's the best method to weld this stuff? Mig? I've been looking at a
lincoln 135 or 175 with an AL mod. would an average welder get a good
result with either of these machines? Would a mig machine of this scale
give a decent structural weld? Is there something else I should look at?

Way too small. You need a MIG machine that can do 500 amps to weld
half inch aluminum. Rule of thumb, 1 amp per 0.001 inch thickness.

More practical would be to Vee prep the hell out of the joint, preheat
the hell out of it, and do it multipass with a 250-300 amp TIG machine.

Is anything from ( big intake of breath) HF able to do the job?

WAY out of their league.

Gary

On Mon, 22 Nov 2004 02:43:25 GMT, "Ed Huntress"
wrote:

wrote in message
.. .
On Sun, 21 Nov 2004 20:08:30 GMT, "Ed Huntress"
wrote:

wrote in message
.. .
On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:

wrote in message
.. .


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is
building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a
do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he
modified
the 7 chassis so it could be made out of angle.

Ed Huntress

Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

It sounds interesting. If he puts any photos of it online, let us know.

Ed Huntress

He won't, but I might.

The idea of making a space frame with L-channel raises all sorts of
engineering questions, but the bottom line will be how well it actually
performs -- and what it winds up weighing.

As a matter of interest, the radius of gyration for L-channels sucks in a
major way, compared to tubes, which means that it's unlikely to resist
buckling nearly as well as a tube-based space frame. That's the major rub, I
would think. But there are more issues that this design raises as well.

However, a finished Lotus 7 is actually a hybrid chassis, with shear-panel
design combined with space frame. And the torsional weakness in a 7 (Mk. II
or Mk. III; I don't recall how the Mk. IV stresses out, but almost all
replicas are Mk. IIIs) is in the cockpit bay, anyway, which can generously
be called parallel girders with a shear-panel floor. That's true of many
open space-frame cars.

So a good, tightly riveted cockpit bay, made of L-channels, could make the
car stiffer than the original. I don't know. It would take a complete FEA
analysis, or a model analysis, to tell.

In any case, if the car is raced, they'll find out a lot about it from the
way it performs on the track. And I'd find it very interesting, as I'm sure
many other people who follow chassis design will find it interesting.

Also for the record, a true space frame is the design concept, among all
design concepts for car chassis, which benefits LEAST from use a low-density
material: aluminum over steel. There have been aluminum-tube space frames
(1960s Bobsy sports-racer; Porsche 917; a special made by the Locost folks),
but, in general, the slight weight savings have never been worth pursuing.
In theory, if not in practice, a steel space frame versus an aluminum one
should come out weighing exactly the same, for equal stiffness and strength.

But there are issues other than the pure, simplified engineering theory
involved, and aluminum may provide a fairly large advantage with channel. It
will help the column stiffness and help prevent buckling in compressed
members.

We'll find out when they get it on the track.

Ed Huntress


The car is supposed to weigh in at around 700 lbs. 1.5" angle
replacing 1" square tube for most of the chassis, and 3X6 more or less
for the bottom "frame rail" that a real lotus does not have (OK, it
has a 1X1 tube) and he figures it will be roughly as stiff as the real
seven.

He (the father) has built and raced numerous sevens over the last
several decades and is intimately familiar with its features and
shortcomings..

He has also built several planes,(and has been working on several
"texas parasol" type planes - of rivetted aluminum angle construction
) so is also familiar with riveted aluminum construction

As you say - it will be interesting to see it actually perform on the
track.

Stainless 'pop' rivets in a structural application? Yuck!

wrote:
On Sun, 21 Nov 2004 05:54:15 GMT, "Ed Huntress"
wrote:


wrote in message
. ..


I like the job my buddy does with the tig welder.
Another friend of mine has built a lot of race cars - and is building
one now with an aluminum chassis (a "clone" of a Lotus 7 - not an
abomination like a Locost, but actually to accurate lotus 7
dimensions, modified to make out of aluminum angle, and running a V
twin bike engine.) It is ALL being rivetted, as he says with welded
6061T6, unless you can re-heat-treat it (which is NOT a do-it-yourself
job) you have no idea WHAT you have after welding. So, he's building
it according to "aircraft standards" - all joints rivetted and
gussetted.

Does he have anything online about this? I'm curious about how he modified
the 7 chassis so it could be made out of angle.

Ed Huntress


Nothing online, and it has not been proven yet - but this guy has
repaired, rebuilt, and reproduced more sevens over the years than
likely anyone else in Canada. He's got all the jigs.

The "angle seven" is being built by his son, actually, (with Dad's
help) for one of the "formula grassroots" type races - something like
Formula 2005? where you get to spend up to $2005 US to build a car and
then race it.
He expects to also drive it on the street.

The seven is built mostly of square steel tubing (mild steel at that)
- much of it 1" square.

The "Angle Seven" is made of 6061T6 or 6061T651 1 1/2 inch (I think)
angle and will have the driveshaft tube fully triagulated into the
front bulkhead.

He estimates the material cost for the chassis, with some carefull
scrounging, to be about $200 Canadian plus rivets. Mostly stainless
steel Pop rivets

I suggest you get a copy of "Design of Weldments", Blodgett. Read,
especially, his discussions on columns, buckling and torsional
rigidity. Particularly note the comparison of open (e.g. angle) vs
closed (e.g. tube) sections in torsion.

Through your reading, keep in mind that aluminum is 1/3 the weight of
steel but also has 1/3 the elastic modulus.

Ted

"Tim Williams" wrote in message
...
"Ted Edwards" wrote in message
...
Through your reading, keep in mind that aluminum is 1/3 the weight of
steel but also has 1/3 the elastic modulus.

The nice thing about it though, is if you can give up stiffness in one
dimension, you gain 3 times the stiffness in the other (think edgewise).

It doesn't apply with space frames, Tim. A "pure" space frame loads its
members only in tension and in compression. Thus, aluminum versus steel is a
wash. Aluminum offers no weight advantage, neither for stiffness nor for
strength.

In practice, the reality is not far from that, if the space frame is
properly triangulated throughout. Most space frame cars are good at the
front and rear bays, but they depart from a true space frame in the cockpit
bay.

There are several issues here, which Ted has alluded to. First, there is
some torsional loading in actual space-frame members. In the cockpit bay,
there often is a *lot* of torsional loading. With round or square tubes,
once again, aluminum offers no advantage here. But it can offer an advantage
with other structure shapes, such as the L-channels (angle aluminum) that
were being discussed. There, the PLATE stiffness and strength, which is what
you're talking about, comes into play. The stiffness and strength in a plate
vary with the cube of the thickness. An L-channel subject to bending or
torsion presents a complex resistance, and plate stiffness is one part of
it.

Again, that isn't true with tubes. If the limiting factor in a space-frame
design is resistance to columnar buckling, aluminum's advantage in plate
stiffness is a help, because thicker-wall or larger-diameter tubes have more
resistance to buckling. This is something that designers try to avoid today.
But the Lotus 7, like other Chapman designs before the early '60s, tend to
have long, thin tubes loaded in compression. Aluminum could help,
theoretically.

But a better answer is to produce a better design, in which the frame is
less likely to fail by buckling. The Caterham folks, who build the Lotus 7
under license, have done just that. They re-designed the frame with the aid
of finite-element analysis.

Ed Huntress

Ed Huntress wrote:

have long, thin tubes loaded in compression. Aluminum could help,
theoretically.

How, Ed? Long thin tubes approach the Euler formula in which only
elastic modulus and radius of gyration matter. For example

2{pick}S_r I_tube 2 .05 {rem} radius of gyration for 2"OD, .05"
wall
0.6896557112
2{pick}S_r I_tube 2 .15 {rem} radius of gyration for 2"OD, .15"
wall
0.6562202374

Not much change there but the equal weight .05" wall steel tube would
have three times the elastic modulus of the .15" aluminum tube and, in
fact, a slightly larger radius of gyration.

Ted

"Ted Edwards" wrote in message
...
Ed Huntress wrote:

have long, thin tubes loaded in compression. Aluminum could help,
theoretically.

How, Ed? Long thin tubes approach the Euler formula in which only
elastic modulus and radius of gyration matter. For example

2{pick}S_r I_tube 2 .05 {rem} radius of gyration for 2"OD, .05"
wall
0.6896557112
2{pick}S_r I_tube 2 .15 {rem} radius of gyration for 2"OD, .15"
wall
0.6562202374

Not much change there but the equal weight .05" wall steel tube would
have three times the elastic modulus of the .15" aluminum tube and, in
fact, a slightly larger radius of gyration.

Ted

Because the tubes could be of larger diameter and *also* have thicker walls,
for the same weight -- thus producing a higher value "r."

In fact, that's how the Bobsy was designed, with aluminum tube space frames,
back in the '60s.

Ed Huntress

Ed Huntress wrote:

Because the tubes could be of larger diameter and *also* have thicker walls,
for the same weight -- thus producing a higher value "r."

I picked 2" as an example but the same comparison applies to any OD
until the walls become so thin that other factors become involved.

In fact, that's how the Bobsy was designed, with aluminum tube space frames,
back in the '60s.

That doesn't neccessarily make it right.

Ted

"Ted Edwards" wrote in message
...
Ed Huntress wrote:

Because the tubes could be of larger diameter and *also* have thicker
walls,
for the same weight -- thus producing a higher value "r."

I picked 2" as an example but the same comparison applies to any OD
until the walls become so thin that other factors become involved.

In fact, that's how the Bobsy was designed, with aluminum tube space
frames,
back in the '60s.

That doesn't neccessarily make it right.

Correct me if I'm wrong, Ted (and this is stuff I'm 'way rusty about), but
the larger diameter tube made possible by lower density of aluminum will
have a higher value for the radius of gyration than will a steel tube of the
same weight, and of smaller diameter.

Correct?

Ed Huntress

Ed Huntress wrote:

Correct me if I'm wrong, Ted (and this is stuff I'm 'way rusty about), but
the larger diameter tube made possible by lower density of aluminum will
have a higher value for the radius of gyration than will a steel tube of the
same weight, and of smaller diameter.

Correct?

Correct but misleading. Of course the radius of gyration increases with
increasing diameter but the increase in diameter is not simply "made
possible by lower density of aluminum". One could instead choose to
make the wall thinner for steel but keep the same diameter. You might
want to take a look at "Design of Weldments", Blodgett, Sec. 2.5. I'd
be surprised if you didn't have *that* book.

Ted

"Ted Edwards" wrote in message
...
Ed Huntress wrote:

Correct me if I'm wrong, Ted (and this is stuff I'm 'way rusty about),
but
the larger diameter tube made possible by lower density of aluminum will
have a higher value for the radius of gyration than will a steel tube of
the
same weight, and of smaller diameter.

Correct?

Correct but misleading. Of course the radius of gyration increases with
increasing diameter but the increase in diameter is not simply "made
possible by lower density of aluminum". One could instead choose to
make the wall thinner for steel but keep the same diameter. You might
want to take a look at "Design of Weldments", Blodgett, Sec. 2.5. I'd
be surprised if you didn't have *that* book.

I don't, but I still have a couple of Mechanics and Statics-and-Dynamics
books from college, as old as I am. The formulas for moment of inertia and
radius of gyration are the same but the Earth rotated the opposite way in
those days, which makes it confusing. g

About those tubes, Euler's formula and much of the rest are long lost in my
memory, but my non-mathematical recollection of the situation is this.
Increasing resistance to buckling for a given *weight* of of a given tubular
material, by increasing tube diameter and thinning the walls, is
self-limiting. You reach a degree of wall thinness at which the diameter
(and the curvature) of the tube becomes a lesser factor and the thin walls
begin to behave more like a plate loaded in compression, on edge. In other
words, plate stiffness in compression-induced bending begins to cross curves
with the sectional stiffness of the large-diameter tube.

Aluminum in the form of a tube, having 1/3 the density of steel and also 1/3
the stiffness (roughly), can be made larger in diameter (for the same
material weight and length) because the relative wall thickness remains
greater, even when the tube is somewhat larger in diameter. In other words,
you can take advantage of aluminum's far greater plate stiffness, per pound
of material, and, in doing so, you can increase the diameter of the tube
somewhat. You can increase diameter and still have considerably thicker
walls than you'd have with steel tubes of the same weight. The total effect
is an increase in the radius of gyration for the aluminum tubes over the
steel tubes, because of the greater diameter, before you start to cross
curves with the plate stiffness of the walls.

To get back to the space frames for cars, and what I originally said about
there being no theoretical advantage in performance for an aluminum-tube
space frame, the things I've just said above don't change that. The
performance of a space-frame car chassis is limited by stiffness, not by
strength, and the actual resistance to buckling should never come into play
at all, in a properly designed, fully triangulated space-frame chassis --
until you crash. g

Ed Huntress

On Tue, 30 Nov 2004 21:05:34 GMT, Ted Edwards
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Well all I can say is that reading these posts, my radius of gyration
is becoming increasingly small, but my speed is being maintained. In
the end my brain will probably exceed Yield Stress! G

Ed Huntress wrote:

Correct me if I'm wrong, Ted (and this is stuff I'm 'way rusty about), but
the larger diameter tube made possible by lower density of aluminum will
have a higher value for the radius of gyration than will a steel tube of the
same weight, and of smaller diameter.

Correct?

Correct but misleading. Of course the radius of gyration increases with
increasing diameter but the increase in diameter is not simply "made
possible by lower density of aluminum". One could instead choose to
make the wall thinner for steel but keep the same diameter. You might
want to take a look at "Design of Weldments", Blodgett, Sec. 2.5. I'd
be surprised if you didn't have *that* book.

I do have to say that you guys may be arguing at cross purposes. I
_thought_ that Ed was saying that tube stiffness is not the only
thing. Wall thickness is important as well, because that will prevent
buckling under certain circumstances.

I am trying to learn here, from minds that scare my dilettante little
brain! G

AFAICS the argument revolves around the fact that you can keep the
same wall thickness or even nincrease it, using aluminium, and use a
larger diameter tube to achieve the stiffness. You in fact need to do
this.

Having a smaller diameter tube would presumably make a given wall
thickness less likely to buckle. That feels right to me.

But would a steel tube of small diameter, having the _same weight_ as
a larger tube of aluminium, have as strong a _wall_ as the alum one?

If you thinned the walls of the steel pipe, in order to allow a larger
diameter for the same weight, the walls would _not_ be as strong as an
aluminium tube of the same weight as the thin-walled steel one, with
wall thickness strengthening as a cube of the thickness (?) while
weight is linear. Looking at the wall as a bar of steel, aluminium
would be stiffer than the same _weight_ bar of steel. (?????)

Hope I am saying this in a way that can be understood. trying to avoid
having to learn a whole dgree's worth of engineering terms and
conditions, by using gut feeling and laymen's terms.

"Old Nick" wrote in message
news
On Tue, 30 Nov 2004 21:05:34 GMT, Ted Edwards
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

Well all I can say is that reading these posts, my radius of gyration
is becoming increasingly small, but my speed is being maintained. In
the end my brain will probably exceed Yield Stress! G

Here's the lab demo: Take a soda straw. Push on both ends. Watch what
happens and write a description of it in your lab notes.

Then take an aluminum beer can. Place it on end on the floor, or on your
forehead, whichever you prefer. Stomp on it. Watch what happens and write a
description of it in your lab notes.

You now have completed the course in Failure Modes of Tubes of Widely
Varying Proportions in Compression, and you're ready to design the Lotus 8.

Actually, Chapman already designed the Lotus 8, and wished that he hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed life
as we know it.

Ed Huntress

On Wed, 1 Dec 2004 01:20:10 -0500, "Ed Huntress"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

"Old Nick" wrote in message
news
On Tue, 30 Nov 2004 21:05:34 GMT, Ted Edwards
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

Well all I can say is that reading these posts, my radius of gyration
is becoming increasingly small, but my speed is being maintained. In
the end my brain will probably exceed Yield Stress! G

Here's the lab demo: Take a soda straw. Push on both ends. Watch what
happens and write a description of it in your lab notes.

Then take an aluminum beer can. Place it on end on the floor, or on your
forehead, whichever you prefer. Stomp on it. Watch what happens and write a
description of it in your lab notes.

You now have completed the course in Failure Modes of Tubes of Widely
Varying Proportions in Compression, and you're ready to design the Lotus 8.


Peuh! Boring!

Used the straw to drink the beer. As I wanted to ensure that the test
was repeatable I tried this severla tims. Now the strwa is alread bnet
cause I staempd on it. I reul...re...know this nillu... nuli... makes
the test not vrey god.

msorry. Faliuer mode of a diffrent sot altogether.

Sory. That's...... shoobee _differen_ sot.

Actually, Chapman already designed the Lotus 8, and wished that he hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed life
as we know it.

no kid!??

On Wed, 1 Dec 2004 01:20:10 -0500, "Ed Huntress"
wrote:


Actually, Chapman already designed the Lotus 8, and wished that he hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed life
as we know it.

Ed Huntress

My life is forever changed because of it.

Whats a Lotus 9?

Gunner

"I mean, when's the last time you heard of a college where the Young
Republicans staged a "Sit In" to close down the Humanities building?
On the flip side, how many sit in's were staged to close the ROTC building back in the '60's?
Liberals stage protests, do civil disobedience, etc.
Conservatives talk politely and try to work out a solution to problems
through discourse until they believe that talking won't work... they they go home and open the gun cabinets.
Pray things never get to the point where the conservatives decide that
"civil disobedience" is the next step, because that's a very short route to "voting from the rooftops"
Jeffrey Swartz, Misc.Survivalism

Gunner wrote:

Whats a Lotus 9?

AFAIK, it's a flower that grows in CHina and Japan.

Ted

Ed Huntress wrote:

want to take a look at "Design of Weldments", Blodgett, Sec. 2.5. I'd
be surprised if you didn't have *that* book.

I don't, but I still have a couple of Mechanics and Statics-and-Dynamics

You might want to get it. It's put out by Lincolm (the welder people)
and, like most of their books, is both good and cheap. As well as
unusually readable theoretical stuff, there's a lot of charts, tables,
worked problems and comparisons of designs.


About those tubes, Euler's formula and much of the rest are long lost in my
memory, but my non-mathematical recollection of the situation is this.
Increasing resistance to buckling for a given *weight* of of a given tubular
material, by increasing tube diameter and thinning the walls, is
self-limiting.

Correct. As with most things, if you go to extremes, you get into
trouble. Just where that point occurs requires working through a
particular case. My point is that it is not clear that going to
aluminum will improve stiffness - you need to do the calculations for a
particular case.

BTW, similar considerations apply to torsion.

Ted

"Old Nick" wrote in message
...

Sory. That's...... shoobee _differen_ sot.

Actually, Chapman already designed the Lotus 8, and wished that he
hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed
life
as we know it.

no kid!??

Would I kid you? The 9-1/2 was *really* brilliant. It didn't make much of a
car, because, in his never-ending quest to add lightness, he left off the
wheels and seats. But it had a great sound system. It became the iPod.

Ed Huntress

"Gunner" wrote in message
...
On Wed, 1 Dec 2004 01:20:10 -0500, "Ed Huntress"
wrote:


Actually, Chapman already designed the Lotus 8, and wished that he
hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed
life
as we know it.

Ed Huntress

My life is forever changed because of it.

Whats a Lotus 9?

I don't know. It probably never made it off the drawing board. Or maybe it
was one of the small open-wheelers.

The 8 was a one-off, a design exercise toward the purest possible space
frame. It turned out to be a backfire, construction-wise, because it
required a lot of add-on assemblies to be a practical car. But it raced, and
it was a good one.

The 10, IIRC, was a tiny front-engined car like the 11. The Lotus 11 was a
major design, one of the last of the little front-engined racing sports cars
made for the 1100 cc class. Somebody is building replicas. It's a wild
little thing.

Ed Huntress

On Wed, 1 Dec 2004 22:47:51 -0500, "Ed Huntress"
wrote:

"Gunner" wrote in message
.. .
On Wed, 1 Dec 2004 01:20:10 -0500, "Ed Huntress"
wrote:


Actually, Chapman already designed the Lotus 8, and wished that he
hadn't.
The Lotus 9 was developed into the Budweiser beer can and has changed
life
as we know it.

Ed Huntress

My life is forever changed because of it.

Whats a Lotus 9?

I don't know. It probably never made it off the drawing board. Or maybe it
was one of the small open-wheelers.

The 8 was a one-off, a design exercise toward the purest possible space
frame. It turned out to be a backfire, construction-wise, because it
required a lot of add-on assemblies to be a practical car. But it raced, and
it was a good one.

The 10, IIRC, was a tiny front-engined car like the 11. The Lotus 11 was a
major design, one of the last of the little front-engined racing sports cars
made for the 1100 cc class. Somebody is building replicas. It's a wild
little thing.

Ed Huntress

Cars? Cars????? Homebrew racing cars?????

Who the hell cares about them?????

This whole thing has been about freaking cars??????????????

Christos on a crutch...airplanes, firearms, even sail boats...but
cars????????

Your kidding me...right?

****..they havent made a decent car since my Rambler.

Gunner

"I mean, when's the last time you heard of a college where the Young
Republicans staged a "Sit In" to close down the Humanities building?
On the flip side, how many sit in's were staged to close the ROTC building back in the '60's?
Liberals stage protests, do civil disobedience, etc.
Conservatives talk politely and try to work out a solution to problems
through discourse until they believe that talking won't work... they they go home and open the gun cabinets.
Pray things never get to the point where the conservatives decide that
"civil disobedience" is the next step, because that's a very short route to "voting from the rooftops"
Jeffrey Swartz, Misc.Survivalism

"Gunner" wrote in message
...

Cars? Cars????? Homebrew racing cars?????

Who the hell cares about them?????

Well, in terms of attendance, car racing is the world's most popular
professional sport.


This whole thing has been about freaking cars??????????????

Mostly Lotus cars.


Christos on a crutch...airplanes, firearms, even sail boats...but
cars????????

Your kidding me...right?

Cars. Cars that weigh from around 800 pounds to 1,300 pounds. Really little
cars. Fast little cars.


****..they havent made a decent car since my Rambler.

I think you mean "descent." That's how you get a Rambler started, right?
It's all downhill. d8-)

Ed Huntress