tia
Hello, welding theory question. Rather than try and describe it, which is better out of these two options; red or blue?
tia
IMHO Red for better load spread !
That's what I would guess, but lots of welding tidbits have come up on here that are contrary to what I would have guessed as common sense.. hmmm
Yes, red...in theory because it allows all the tube centrelines to converge.
In reality it doesn't matter that much.
I would go for blue because the weld is longer/stronger in one plane.
The centerlines of the tubes imerge when the diagonal is under 45° wich is only the case when a square is braced.
Imagine 3 tubes layed out in a "Z" form and think for yourself what would be the strongest way to connect the 3 tubes,the "blue"
or "red" option.
The red one is the better option.
At a mulitiple tube junction all the tube centrelines should converge at the centreline of the main tube.
With the blue option the force from the diagonal (ie the blue member) is all going into the horizontal piece. The weld to the main member is then
loaded in compression and tension. Welds should not be loaded in tension, welds should be loaded in shear.
The red option loads the welds in shear and distributes the load between two members.
JB
How do you manage to converge all centerlines of the tubes on the main tube without changing the geometry of the rectangle?It seems to me that sooner
or later you gonna end up with the blue option.
No critisism here,just want to learn.
If you've already made the outer frame before you put the diagonals in you can't change the geometry of the rectangles. You will have to
make them to fit in the spaces already there. I use the blue option as it's easier.
I'm doing my typical thing of worrying about the tiny details before doing anything.. so we haven't actually started on the chassis yet.
so I can choose to do what I like 
I think the red option wins, unless mark allanson wants to come along and show me I know nothing again.
ta
The main tube is the vertical one. Draw a centre line on this tube, and then draw a line on the horizontal tube.
These 2 cetntre lines will meet (at the centre of the vertical tube).
Any diagonals (which will be added after the previous two tubes) should be position so their centre line meets on the above point.
Another point: When designing a chassis the aim is to load all tubes in tension or compression (NOT BENDING). The blue option will put a bending load
into the horizontal member.
For further reading on this : Prepare to Win by Carroll Smith.
Race Car Chassis Design and Construction by Aird
JB
Blueshift,if you think the red option is the best solution can you please explain me how you gonna achieve the converging of the centerlines in a
given,or any rectangle?
It sure looks ugly to change from one option to another in the same frame
i just made a small test drawing in autocad.
A rectangle 1m x .30m in .25m RHS
The red option is....nearly gone up into the...blue option with all centerlines converged!!!!
You almost have to come to a square to get a noticable diff between the red en blue option.
most of the chassis, once panelled - especially if you do the inside as well - is so covered you wouldnt notice style differences!
atb
steve
If the inside and outside of the frame is covered with sheet than you maby can leave the diagonals out!
Problem solved
quote:
Originally posted by Cita
Blueshift,if you think the red option is the best solution can you please explain me how you gonna achieve the converging of the centerlines in a given,or any rectangle?
The problem is that when you want those centerlines converge in one center you will end up most likely with one small side and one large side and the
diff between those two sides will be so great that you...just as well could be gone for the blue option in first place
This would have been even easier but how would it perform compared to the others?
Rescued attachment barjoint.jpg
I'm with JB on this one, the idea of triangulation is to focus all the loads at specific nodes. If the nodes are not fully bisected, you get
leverage, and then stress fatiguing
OK the chassis would be minutely less rigid, probably not measurable for a locust, but in something a bit more highly stressed, it could be a factor.
I made an overhead crane for the CEGB at Hinkley Point, they were fussy!
It will please me to know that our chassis is put together in the best way possible, even if it means fiddlier fitting and filing. Thanks for comments all.
Good thread, I like the points brought up. I too would have to agree that the red tube will be better in loading, so would shoot for it on most my bracing (or did as the case may be) but I often used the blue style on lightly loaded or non-structural sections. Cheers!
IMHO for a locost it's a waste of time and energy to go for the red option.The loads in the locost frame are so light that the gain would be
inperceptable.
The pick up points for the suspension are "floating" so why go through the hastle of difficult, time consuming bracing of the frame.
The most important thing however is that the builder feels good about what he has built wether it be the red or blue option.
quote:
Originally posted by Cita
IMHO for a locost it's a waste of time and energy to go for the red option.The loads in the locost frame are so light that the gain would be inperceptable.
The pick up points for the suspension are "floating" so why go through the hastle of difficult, time consuming bracing of the frame.
The most important thing however is that the builder feels good about what he has built wether it be the red or blue option.
Thanks for the reply.it is not my intention to encourage unsafe or dangerous methods if that appears to be the case than i'm sorry for this
'cause it would be wrong to do so.
All i'm saying is that, first the drawings in this thread give a somewhat wrong impression in that all the diagonals are set at an angle of 45°
witch only occurs within a square.How many true squares are there to brace in a locost?
Everybody who's jumping on my neck(no offence taken)doesn't seem to have taken the time to actually draw an example and see how strange
things can turn out and even if it look like the blue option was used, it actually was the red option.
When you think about it very carefully for a chassis made of RHS there are grounds for suspecting the eaiier blue option of actually being stronger.
There are always grounds for thinking in all sorts of ways about this stuff, as Mark Allanson says, you can be fussy or not, the choice is yours. If
you have bought a locost chassis, odds are this is irrelevant because this kind of analytical thinking will most probably not have gone into it,
that's why you can buy it for £450 or so! To take it on a stage, with either option, if you MIG weld it, unless you are an exceptionally good mig
user (and Mark Allanson, you may well be if maiking cranes for the CEGB, as you say they are fussy!) you will not notice any difference simple because
a MIG is not controllable enough.
If on the other hand you use a TIG for pretty much everything like JB does, you may see the difference (i.e. there may be a difference)
NSDev could you please explain the "weld thing" Mig/Tig and the relation to both options?
I know the diff between Mig and Tig but i'm afraid that my English is not good enough to understand what you mean.
Thanks.
Blueshift,
For what it's worth I did mine using the Red option as I wanted to take as much stress away from my welding as possible. I used to build balsa
aircraft kits and always did them this way too. It just seems to "make sense" and looks "right" to me and my instincts don't
usually let me down. That's all the analysis that I need!
Now stop messing about and start building your chassis or are you planning to drive around in a V8 powered Black & Decker workmate for ever?
Cheers,
Craig.
Cita, the difference between MIG and TIG is just down to controllability and prescision. With TIG you can put the weld pool exactly where you want it,
with prescision of fractions of a millimetre rather than millimetres. You can also control the heat much better than with MIG, getting a near perfect
weld every time.
The best MIG users can achieve this but it is not easy. TIG is not that easy either but it does not flatter crap welds in the way which MIG can.
quote:
Originally posted by craig1410
Now stop messing about and start building your chassis or are you planning to drive around in a V8 powered Black & Decker workmate for ever?
Start with 7 lengths of 1" 16g and go from there.. Right, get on with it.
Yes I'd even go for 8 (7m lengths) as I think I only got 5 to begin with and then got another two or three later on. I've still got the
better part of one left which comes in handy at times for bits and pieces of construction. You'll also need the 3/4" stuff and I think I got
two 7m lengths of it IIRC.
I think the main reason I needed extra 1" square ERW is because I used it in place of the round stuff for the chassis triangulation to provide
more strength at the front for the V8 engine. I also have more triangulation than normal to accommodate my engine "cradle".
Blueshift, just remember the old chinese proverb about a journey of 1000 miles beginning with a single step. In the context of the Locost it is more
like a build of 1000 hours beginning with a single book!!! Oh well, at least it's only going to cost £250(0+) 
Craig.
I liked the saying
'building a car is like eating an elephant one peice at a time'
mine seems to be a lard assed overweight elephant
atb
steve
It's those f******g toenails........
sooooooooooooooo hard to chew...
Heh. I thought it would be optimal to figure out what steel I'd need for everything, then order it all in one go and get best bulk discount and
save on delivery and all that.
however, taking 6 months doing nothing but planning how to save £30 is fairly suboptimal too.
Blueshift,
If you can predict every bit of steel you will need in advance and never need to buy any more right through until you pass your SVA then you are a
better man than I !! I don't think you will even save £30 by getting it all in one go either to be honest.
As long as you buy stock length's of steel from a local "no-frills" stockholder then you'll be fine. Ask if they have an offcuts
bucket when you are there and offer the guy £10 or so for a bunch of offcuts. Try to get odd bits of heavier gauge (4mm to 6mm) steel plate and rods
as these come in very handy later and are costly to buy in short lengths.
Seriously though, just try to get your ERW tubing for the main chassis initially and buy the rest more or less as you need it. Here are the main sizes
which I bought:
For main chassis:
25mm x 25mm x 2mm(or 1.6mm) ERW
20mm x 20mm x 2mm(or 1.6mm) ERW
19mm x 1.6mm ERW round section for luggage section (1 stock length)
For turrets, suspension brackets and other chassis appendages:
100mm x 3mm flat bar (1 stock length)
40mm x 3mm flat bar (1 stock length)
25mm x 3mm flat bar (1 stock length)
13mm x 3mm flat bar (1 stock length)
For various brackets and mounts:
25mm x 5mm flat bar (2 or 3 meters)
50mm x 5mm flat bar (2 meters)
Miscellaneous:
1.6mm sheet for the floor
48mm x 3mm black pipe for the rollbar
I purchased my wishbones and built my panhard rod and trailing links using the Rally Design tubing and inserts for the rod-ends.
Hope this helps,
Craig.
Phoned two steel stockists today for 18g sheet, first one £33 second £21, why the difference?
The first guy thought you were a Muppet!
I was once quoted £132 by some tubing company up in Falkirk (IIRC) for enough CDS tubing to do my wishbones, panhard rod and trailing arms. The guy
was none too pleased when I asked if it was 18 carrat or 24 carrat gold they were made from... Some people just try it on and the only way to combat
this is to know your stock sizes, sound like you know what you need and avoid saying "what do you think?" at all costs!!!
Cheers,
Craig.
I've just noticed that I'm now a "posting freak" just like you Peteff! When did that happen? Is it 1000+ posts?
[Edited on 24/5/2004 by craig1410]
I think we should get an email from the management asking if we want to be promoted. If I could choose my title now I would be a marklar.