Every tried laser welding?
Mike
I have been critical (on various forums) of the way the Book Locost chassis and the Lotus chassis are assembled. The riveting of aluminum panels,
floor. bulkhead to steel tubes does not make good use of the stiffening property of sheet metal and also potentially limits the life span of the
chassis.
In my build I am considering replacing all sheet aluminium panels, floor, bulkheads with light gauge sheet steel.
My plan is to mig-weld the panels to the tubes in a sequential manner so that tube distortion will not take place. Before welding the panels to the
chassis I will roll bidirectional stiffening beads to the said panels, floor and bulkheads in order to enhance their rigidity.
My questions are these.
1) Does any one of you who work with CAD files have the total aluminium area of the Book Locost handy... and would you mind telling me what it is so
that I could calculate the amount of additional dead weight the above strategy will cause and make a final decision?
2)What do you think of my suggestion to use steel?
Philippe.
_________________
Loads of people use steel floors instead of ali ones.
When i did some calculations a 2mm ali floor was around 5-6kg lighter than a 1.2mm steel one.
Ali panels weigh only 1/3rd as much as steel ones. So even if you halve the thickness for steel panels an ali one will still be lighter.
I am not sure if its been suggested to you to use strutcural adhesives (3M VHB tape is good stuff) to bond the ali panels to the chassis, along with a
few rivets, you will end up with a similar stiffening effect to that of welding in steel panels.
The use of structural rivets to hold the floor and other panels on is well known, and if its good enough for the aerospace industry, it's sure as
hell good enough for a Locost. The next best thing to use are closed end rivets.
The other problem is distortion in welding thin sheet steel. Try it, and you will see. However careful you are, you will always get distortion with
thin sheet, its an inherent parts of the welding process (i.e. loads of heat!)
In short, for the amount of miles your average locost will do, theres no need to worry about failure of riveted ali panels. (To my knowledge there
havent been any)
You can use steel but it will be significantly heavier.
All IMO, but there we go.
my chassis uses grp/kevlar to replace the aluminium , no distortion , good strength to weight ratio, and can be done at home . I also made the tunnel
completely in kevlar , so ive saved on tube also .
have you looked at an AC chassis ? complete sheet metal with tube subfames .
you still have to skin the outer layers , to make em look nice .
I what why does the Ali pannels limit the life if the chassis? If properly constructed it should not (i.e sealed, and carfull choice of rivet to aviod
galvanic corrosion). The whole point of a space frame is that it takes the loads via compression and tension in the tubes... The pannels are not load
bearing it should not fatigue...
[Edited on 10/1/06 by Bluemoon]
quote:
Originally posted by flak monkey
Loads of people use steel floors instead of ali ones.
When i did some calculations a 2mm ali floor was around 5-6kg lighter than a 1.2mm steel one.
Ali panels weigh only 1/3rd as much as steel ones. So even if you halve the thickness for steel panels an ali one will still be lighter.
I am not sure if its been suggested to you to use strutcural adhesives (3M VHB tape is good stuff) to bond the ali panels to the chassis, along with a few rivets, you will end up with a similar stiffening effect to that of welding in steel panels.
The use of structural rivets to hold the floor and other panels on is well known, and if its good enough for the aerospace industry, it's sure as hell good enough for a Locost. The next best thing to use are closed end rivets.
The other problem is distortion in welding thin sheet steel. Try it, and you will see. However careful you are, you will always get distortion with thin sheet, its an inherent parts of the welding process (i.e. loads of heat!)
In short, for the amount of miles your average locost will do, theres no need to worry about failure of riveted ali panels. (To my knowledge there havent been any)
You can use steel but it will be significantly heavier.
All IMO, but there we go.
Wouldn't bother with the steel to be honest it sounds like a bit of over-engineering to me! I'm not saying that you wouldn't notice any difference but function over form and all that - Ali is lighter, and as mentioned I've not heard of any failures yet! I'm going with the if its good enough for everyone else, its good enough for me plan! Obviously my opinion but hey in this world that's all you got right?! Oli.
quote:
Originally posted by Volvorsport
my chassis uses grp/kevlar to replace the aluminium , no distortion , good strength to weight ratio, and can be done at home . I also made the tunnel completely in kevlar , so ive saved on tube also .
have you looked at an AC chassis ? complete sheet metal with tube subfames .
you still have to skin the outer layers , to make em look nice .
yeah , the less resin you use , the lighter it will be , but you have to try and keep with the recomended resin/glass ratio - which is 1:1 for most
cloths and weaves .
altho ive not weighed it before and after - ive used 4 -5kgs of mat so about 5 kgs of resin , so about 10 kgs altogether , but i have no central top
tubes and no diagaonals in the footwell/tub area .
Also those 10 kg comprise the full enclosed tub - so the panel on the top of the footwell is closed off , and of course the trans tunnel is done
aswell .
quote:
Originally posted by Bluemoon
I what why does the Ali pannels limit the life if the chassis? If properly constructed it should not (i.e sealed, and carfull choice of rivet to aviod galvanic corrosion). The whole point of a space frame is that it takes the loads via compression and tension in the tubes... The pannels are not load bearing it should not fatigue...
[Edited on 10/1/06 by Bluemoon]
If you use a steel panel of 1/3 the thickness of the ali you replace then you will have the same weight. You will have to make the steel a bit
thinner to counter the weight of the paint or powder coat that you will have to use to stop the steel rusting. If you think that this painted thin
steel is better then go for it. Ali is not the answer to the world's problems but it does have its uses.
My ali floor is bonded on to the chassis with PU adhesive and is also riveted at frequent intervals. The adhesive and rivets together will make the
ali add to the strength of the steel tubes.
There isn't a problem with ali or with steel. Use what you think best.
some pics to clarify my chassis - its a 442 ish size so it will be heavier
http://www.dbsmotorsport.co.uk/Html/index3.html
[Edited on 10/1/06 by Volvorsport]
The problem will be that using 0.5mm steel (as opposed to 1.2mm ally) will mean that the steel will wrinkle when welded, almost impossible to stop this happening with very thin section sheet steel.
About the riveted aluminum-paneled car not lasting as long, that may be be. But the *real* question is, will the aluminum-paneled car last longer then you wish to own it... If so the whole issue goes away.
I cant see anyway of getting a weld of high enough quality to bring any benefits over rivetting and / or bonding, when joining very thin gauge steel plate to box section or tubes with considerably greater wall thickness. IMHO I think you would actually make the structure considearbly weaker for the same given weight.
Just not issue ----
Early Lotus car were constructed almost exactly the same way as the Locost and there are still a high % number of survivors around that are going on
for 50+ years old. I might add Lotus used tube 1.2mm thick.
Re-skinning a Seven style car is no big deal, the alloy gets minor damage with everyday wear and tear.
quote:
Originally posted by NS Dev
The problem will be that using 0.5mm steel (as opposed to 1.2mm ally) will mean that the steel will wrinkle when welded, almost impossible to stop this happening with very thin section sheet steel.
Plus you would have to have the welding current turned down so low for welding the thin mild steel sheet with mig that it would not fuse to the
thicker box section tubes.
Every tried laser welding?
Mike
is it not possible to spot weld the thin sheet to the square tubes or the difference in thcknesses too great?
using steel has anther disadvantage - rust! so you need rust treatment and paint = more weight!
the question is how much rigidity you gain by a more solid join of sheet to the frame, if you knew that, then maybe you could use lighter tube so shed
some weight there.
quote:
Originally posted by cossey
the pannels in a seven are stressed and have a considerable effect on the stiffness of the chassis.
quote:
Originally posted by 02GF74
is it not possible to spot weld the thin sheet to the square tubes or the difference in thcknesses too great?
using steel has anther disadvantage - rust! so you need rust treatment and paint = more weight!
the question is how much rigidity you gain by a more solid join of sheet to the frame, if you knew that, then maybe you could use lighter tube so shed some weight there.
quote:
Originally posted by Prez
I cant see anyway of getting a weld of high enough quality to bring any benefits over rivetting and / or bonding, when joining very thin gauge steel plate to box section or tubes with considerably greater wall thickness. IMHO I think you would actually make the structure considearbly weaker for the same given weight.
quote:
Originally posted by britishtrident
quote:
Originally posted by NS Dev
The problem will be that using 0.5mm steel (as opposed to 1.2mm ally) will mean that the steel will wrinkle when welded, almost impossible to stop this happening with very thin section sheet steel.
R-I was refering to sequential spot welding. This is the way the industry stitches car bodied together. Punch holes all around the perimeter of your panels, turn the amp at the lowest on your mig welder, weld one second hole at the time, etc.... No distorsion, no buckling, perfect.
Philippe.
Yes ;-) it buckles or to put it anotherway because of the greater thickness an aluminium panel is stiffer in bending than a comparable steel panel -- which is why aluminium and magnesium alloys are such excellent materials for making road wheels.
impressive eh !! wooo .
it could be a lot better - that entails makig another chassis to make the GRP/kevlar bit even better/easier to do , it was quite fiddly but rewarding
when i stood in the tub and jumped up and down !!! .
by my rule of thumb , if i can remove most of the tube work within the tub apart from the perimeter frame, and using a rear gearbox UN1 style , i can
get one below 500kgs , which aint bad for the volvo turbo lump up front .
quote:
Originally posted by Bluemoon
The whole point of a space frame is that it takes the loads via compression and tension in the tubes... The pannels are not load bearing it should not fatigue...
[Edited on 10/1/06 by Bluemoon]
quote:
Originally posted by Philippe
R-Could you elaborate? I would join the plates to the tubes in a common mig or tig welded spot by spot fashion, the way car bodies are built in the industry. There is nothing weak about that?
Philippe.
My floor is 16g steel as is trans tunnel and bulkhead. Won`t make no difference to my car as I hope to lose three stone before it`s SVAd. My wife
will be riding shotgun and if she happens to drop that purse of hers on an ally floor..
Alex
Pretty well all cars here are just spot welded together. Stronger/lighter than rivets but weaker than bonding.
Ive never seen a spot welded car come apart at the seam and I have twisted the hell out of a few of them .
Had a camaro that tore the quarter panel, tore out the door striker, and twisted the car enough the dome light stayed on but there was no damage to
the spot welds. Little too much power/traction for the stock body.
Spot welded steel will be just fine. having said that, I intend to use SS structural rivets and also bond the aluminum to the chassis. I want to
leave the sides bare aluminum. Havent decided what to do on the tunnel though. The thought of using aluminum there and having a u-joint fail scares
me. Not a V8 car though so less likely than I am used to I guess.
Cheers.
Cymtriks recommends welding a steel panel under the nose as part of the torsional rigidity improvements.
I've been considering using the roof off my donor Suzuki van for the floor (as suggested by Uncle Ron) - it has stamped ribs running down
it's length, so would be nice and stiff. 
The original 7 was a little on the flexible side - I'd like mine to be a little stronger around my vital bits (and don't mind a bit of extra
weight closer to the ground) 
... and I'll save some weight by going for an axle, gearbox and all-alloy engine that are heaps lighter than Ford's 
quote:
Originally posted by C10CoryM
Pretty well all cars here are just spot welded together. Stronger/lighter than rivets but weaker than bonding.
Ive never seen a spot welded car come apart at the seam and I have twisted the hell out of a few of them
Had a camaro that tore the quarter panel, tore out the door striker, and twisted the car enough the dome light stayed on but there was no damage to the spot welds. Little too much power/traction for the stock body.
Spot welded steel will be just fine. having said that, I intend to use SS structural rivets and also bond the aluminum to the chassis. I want to leave the sides bare aluminum. Havent decided what to do on the tunnel though. The thought of using aluminum there and having a u-joint fail scares me. Not a V8 car though so less likely than I am used to I guess.
Cheers.
quote:
Originally posted by Philippe
Indeed spot welds need dynamite to be separated.
[Edited on 11/1/06 by Philippe]
Get one of these they're good for splitting panels. I've used them or just drilled through the welds and peeled them with grips or split them with a chisel but that tears the metal so you need to be careful if you are reusing it. You can reweld in a different place to recycle panels though.
quote:
Originally posted by Philippe
quote:
Originally posted by britishtrident
quote:
Originally posted by NS Dev
The problem will be that using 0.5mm steel (as opposed to 1.2mm ally) will mean that the steel will wrinkle when welded, almost impossible to stop this happening with very thin section sheet steel.
R-I was refering to sequential spot welding. This is the way the industry stitches car bodied together. Punch holes all around the perimeter of your panels, turn the amp at the lowest on your mig welder, weld one second hole at the time, etc.... No distorsion, no buckling, perfect.
Philippe.
Yes ;-) it buckles or to put it anotherway because of the greater thickness an aluminium panel is stiffer in bending than a comparable steel panel -- which is why aluminium and magnesium alloys are such excellent materials for making road wheels.
quote:
Originally posted by britishtrident
quote:
Originally posted by 02GF74
is it not possible to spot weld the thin sheet to the square tubes or the difference in thcknesses too great?
using steel has anther disadvantage - rust! so you need rust treatment and paint = more weight!
the question is how much rigidity you gain by a more solid join of sheet to the frame, if you knew that, then maybe you could use lighter tube so shed some weight there.
Lotus or at least Arch Motors used 1.2 mm round tube for the spaceframes. 1.6 RHS is easier work with.
Early Lotus space frames were a lot sparser than the Locost --- somewhere on the net is a picture of chunky Chapman holding up an Eleven chassis-- just try that with book chassis.
With the Seven Series 2 Chapman tried to take even more weight out cutting out nearly all of the diagonals -- the result was a lot of broken chassis (mainly fatigued brazed joints), with the late Series 2 and Series 3 the missing members were re-instated. Locost are about twice the weight of a Lotus Seven S2 chassis.
Chasing grams on the chassis isn't worth it, the chassis dosen't way a lot compared to the bits bolted on to it.
quote:
Originally posted by NS Dev
quote:
Originally posted by Philippe
quote:
Originally posted by britishtrident
quote:
Originally posted by NS Dev
The problem will be that using 0.5mm steel (as opposed to 1.2mm ally) will mean that the steel will wrinkle when welded, almost impossible to stop this happening with very thin section sheet steel.
R-I was refering to sequential spot welding. This is the way the industry stitches car bodied together. Punch holes all around the perimeter of your panels, turn the amp at the lowest on your mig welder, weld one second hole at the time, etc.... No distorsion, no buckling, perfect.
Philippe.
Yes ;-) it buckles or to put it anotherway because of the greater thickness an aluminium panel is stiffer in bending than a comparable steel panel -- which is why aluminium and magnesium alloys are such excellent materials for making road wheels.
You mean what I would call plug welding, i.e. puddle welding through punched holes with the MIG.
I use this technique a lot, but it still wrinkles 0.5mm steel sheet, in fact it still wrinkles 0.8mm sheet, even when pretensioned.
quote:
Originally posted by NS Dev
quote:
.......Chasing grams on the chassis isn't worth it, the chassis dosen't way a lot compared to the bits bolted on to it.
The last line of the above is one of the best observations made on here for a while!
For me, I must lighten the nut holding the wheel (yes, I know I've said it before... quite recently in fact!)
David
Surely that one Nyloc doesn't weigh THAT much does it?????
"Chasing grams on the chassis isn't worth it, the chassis dosen't w[eigh] a lot compared to the bits bolted on to it."
But only if that is followed through - I find it's actually the opposite. I think instead the thought "it's just a few ounces, it
won't hurt", happens to just about every part of the car.
It's just like dieting where people cheat, "it's just a little bit." That thinking, carried to its logical end, results in
overweight people - and cars. I realize we don't have the buget for carbon this or titanium that, but it's still important to always be
asking, can I make this (and every) part lighter.
It's well worth reading "Driving Ambition" by Doug Nye (and Gordon Murray & Ron Dennis) about the design and manufacture of the
McLaren F1. Murray set a 1000kg weight target and was fanatical about chasing every spare gram. In the end the road-ready car weighed (from memory)
1100kg, amazing for a 3-seat 5 litre V12 autobahn weapon! Murray said that only setting the (probably unachievable) 1000kg target had kept the
design/development team focused enough to reach the (still impressive) 1100kg end result.
Now, none of us are building 300km/h+ supercars (well, I'm not - anyone else want to claim otherwise?) but, as Kurt points out, it's
possible to let a "Near enough is good enough" attitude compromise the end result significantly. So, I say, think about those extra grams,
even if you decide in the end that it's not worth saving them. At least then it's an informed decision rather than a "swept aside, too
small to bother about" dismissal.
Will my car be heavier than it could be. Absolutely! Will I cry tears of blood over that? No because, wherever possible, I have considered the
factors and made a decision. In a lot of cases, that decision was that I would accept a (probable) weight penalty in exchange for ease of
construction or availability of materials or peace of mind about strength or any of a hundred other reasons.
To try and drag this polemic back on topic, my car will have bonded (sikaflex or equivalent) and riveted aluminium skins. I'm not too concerned
about corrosion since I intend not to park the car underwater any more than neccesary. Living on the dryest continent on Earth helps but, that
said, we've had 75mm/3" of rain this year and it's only the 12th of January.
Anyway, enough rambling from me. I'm back to the garage to make some more informed, considered decisions about engine bay tube sizes. I think I
see a way to save about 4kg!
Dominic
That would be a button weld
I'm tired so a short reply!
Yep, in order to achieve the ultimate we need to do everything to the
ultimate................................................................................................................................but then we
must not over complicate things!
Keep It Simple Stupid, as they say!
Look at the Ultima GTR (to current demo car spec)......vastly quicker in a straight line than the McLaren, quicker around a track, less than 1/10 the
cost, nearly 200kg lighter, 100 times simpler and uses an ancient engine design that still makes more power!!!! There is no stressed carbon fibre on
the car, a steel spaceframe chassis, pop-rivetted alloy panels etc etc.................................................................... Simple is
Quick, Colin Chapman taught all of us that but nearly all have forgotten it completely.
Simplicity is the reason that to save weight in my 7, I am simply not bothering with things that I don't need! Maybe I can save a few grammes on
the chassis, but having no instruments saves a lot and why do I need them???? What does trim do exactly???? Don't need that. No windscreen, no
heater, no wipers, no washers............nothing that I don't need in order to use the car for what it was meant for...FUN!!
quote:
Originally posted by NS Dev
No windscreen, no heater, no wipers, no washers............nothing that I don't need in order to use the car for what it was meant for...FUN!!
quote:
Originally posted by Peteff
That would be a button weld
quote:
Originally posted by Mark Allanson
quote:
Originally posted by Peteff
That would be a button weld
Or even a plug weld!
It had already been called a spot, plug and puddle weld, I just thought I'd throw another one in there
lol
quote:
I think instead the thought "it's just a few ounces, it won't hurt", happens to just about every part of the car.
I realize we don't have the buget for carbon this or titanium that, but it's still important to always be asking, can I make this (and every) part lighter.
has anyone tried epoxying the floor on rather than using pu glue which isnt rigid so wont kelp with the stiffness of the chassis?
no but epoxying it on is a much better idea!
Would have done but for the expense of the epoxy!!
Epoxy can be a bit brittle and doesn't stick to its full potential unless the surfaces are impossibly clean.
PU is very sticky and is flexible. it is less likely to brake or come loose even though it is perhaps less strong.