mark chandler
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| posted on 3/7/05 at 09:05 PM |
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aluminium tube frame, has anyone done this ?
Hi, new to the forum and have started planning my first locost, £1000 budget for an bike engined effort so weight is key.
As I can weld aluminium I was wondering if anyone has built a frame using ali, then tigged the sheets to this ? (I hate rivits, hurt the wrist and
rattle loose after a while.....).
Also being that round tube is torsionally stronger than square is it okay to knock up a frame from this.
I plan to track day the product of my efforts, however second question is based around Camaraderie, do you arrange social track days ?
Regards Mark
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phelpsa
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| posted on 3/7/05 at 09:12 PM |
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I'm not sure this has been attempted, but im sure it could work with a lot of developement. Im not sure it could be done too well with a £1000
budget though.
Adam
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kb58
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| posted on 3/7/05 at 09:23 PM |
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Do a search here on that... it's been covered several times. There are two *very* opposing camps on it, one saying it should be fine, the other
saying it'll work-harden and crack. I believe the latter.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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mark chandler
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| posted on 3/7/05 at 09:31 PM |
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I can stretch the budget if required but a £1000 goal keeps thing interesting. I have priced up equivilent ali, not much in it when you add the costs
of rivits. I plan to build a reverse gear using a Landrover centre diff so save a lump of weight and money here, to my mind the most expensive bit
beyond the engine (R1/blade's go for around £600) will be the GAZ shocks. As I have a decent AC Tig welder and an understanding wife (at the
moment) the big cost to me will be time.
nb/ I noticed other posts about ali, however I will be welding all the panels/ floor etc to the frame so will effectively build a monocoque
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cymtriks
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| posted on 3/7/05 at 09:38 PM |
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You could do this but don't be confused by the aluminium "spaceframes" the certain exotics are now based on. Basically they are much
closer to ladder frames or multitube chassis!
A spaceframe is a triangulated structure that derives its structural worth from that triangulation. If you change the tubes in a spaceframe you will
end up with a change in chassis weight, strength and stiffness.
For aluminium a tube would be a third of the weight but only a third as stiff or as strong as a steel tube. To get back the stiffness you could triple
the wal thickness which restores the stiffness and strength but gives you the same weight as a steel chassis. No scope for improvement at all!
If you really want to make a stiff and light weight structure then you could try my mods as given in "kitcaranalysis" on the locost7.info
site but with the tubes in 18 gauge steel and the floor in 1mm steel. This will still be about 50% stiffer than the book chassis but should save 30 to
40 pounds.
Personally I think that the extra difficulties in welding 18 gauge as opposed to the standard and road proven 16 gauge might outweigh any advantages,
not so much because of the build, but because if a job's harder to do it's also harder to do right so you're taking a bigger risk
that the welds might be duff. Possibly brazing would be a better way to build an 18 gauge chassis than welding but it sounds as if you know more about
welding than I do anyway!
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Triton
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| posted on 3/7/05 at 10:01 PM |
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Go for 18swg erw or better still use T45(big quids tho!) and tig that rather than using ali.....like cymtriks mentioned you need to increase wall
thickness if using ali so no point as weight goes up.
I seem to remember Martin Keenan(MK eng) made an ali Locost a few years back.
Mark
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mark chandler
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| posted on 3/7/05 at 10:11 PM |
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I cannot find your notes 'kitcaranalysis" have you a url ? Lots of people have talked about Ali but it seems hardly anyone has tried I,ll
shelve that idea as I was worried about it work hardening and cracking around the suspension pickup points, was just looking for a bit of feedback.
The great thing about TIG welding is the precise control you get, its also very enjoyable (maybe I,m just sad) so a steel frame coming on with steel
sides and floor as light as I can make it !
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mangogrooveworkshop
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| posted on 3/7/05 at 10:36 PM |
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Make us lot ali tanks and sell em then you can buy subk2002 mk for cash.......
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mark chandler
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| posted on 3/7/05 at 10:44 PM |
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I do not mind welding someones tank for a drink, as long as the metal is folded so all I have to do is stick it togethe.
Probally more money in a budget reverse gear for a bike engined car I think I can sort out something with virtually no backlash for £100 would that be
more interesting (good for 200 BHP).
Anyway I thought the joy was the building, anyone with cash can go fast... its the going fast without money that the key.
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Volvorsport
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| posted on 3/7/05 at 11:00 PM |
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i dont think you can do it for £1000 - if its only trackdays , maybe , but youd have to trailer it, or go thro sva to drive , and it gets a bit more
complicated , what you going to do for bodywork etc ?
www.dbsmotorsport.co.uk
getting dirty under a bus
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bimbleuk
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| posted on 4/7/05 at 04:59 AM |
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I know of one Seven style kit car made from all aluminium and it weighs in at less than 400 kg!
However its track only and worse its been left standing in a garage since it was built 
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Dave Ashurst
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| posted on 4/7/05 at 07:25 AM |
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No I'm no expert in design with aluminium, but:
Unless you REALLY know what you are doing with your fatigue design calculations and practical fatigue detailing I suggest it would be safer NOT to use
aluminium for a car chassis.
Of course it's possible to MAKE an aluminium chassis. You might be good at TIG, enjoy it and (rightfully) take great pride in it. Depending on
design the aluminium frame you make might be strong enough based on a 3d spaceframe static analysis and it might be strong enough based on detailed
dynamic analysis.
The problem with Aluminium is FATIGUE:
- aluminium has a low cutoff stress threshold
- aluminium has a severely limited fatigue life in use under dynamic loading, compared to steel.
i.e. If you design for strength alone, your aluminium car chassis WILL break in use due to fatigue; and potentially quite soon.
So if you don't design for fatigue then it will break. The questions are :
Where will it break?
When will it break?
How will you spot the signs? and
Will you spot them early enough?
(in my opinion.)
Dave
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mark chandler
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| posted on 4/7/05 at 08:20 AM |
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Just picked up a fireblade engine for £400 on Ebay last night so commited.
Steel for the frame - £150, ali - £50
Shocks - £300 (GAZ)
Donor sierra - £50
Prop adaptor £75 (ebay)
Reverse gear modified LT230 transfer box.
I currently race a landrover so have a trailer and loads of useful bits like trackrod ends, lights indicators etc may even be able to flog the engine
and box off the sierra and recoup a bit.
Okay a nice set of wheels and an screen will be on top, but I am hopeful of getting a driveable car for my 1K.
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David Jenkins
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| posted on 4/7/05 at 08:44 AM |
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The other problem to add to Dave's list is that Ali doesn't just work-harden and develop stress cracks - it also age-hardens all by
itself. Anneal a piece of ali, leave it for a year or so, then try bending it.
I have some pieces of old ali sheet in my garage that have to be annealled before I can attempt a 90-degree bend, otherwise they just crack straight
along the bend.
Some grades of ali might be better than others (there are some aircraft grades that are alloyed with stuff like copper) but ordinary commercial grades
have to be treated with suspicion.
Anyway, in most cases where weight is an issue, the highest gains are usually found by reducing the mass of the soft, squishy thing holding the
steering wheel! 
...certainly in my case...
rgds,
David
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britishtrident
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| posted on 4/7/05 at 09:51 AM |
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Generally a steel spaceframe is the lightest method of construction, when I was racing in 1000cc specials sallons/GT I watched the weights tumble,
it was reckoned the best Maguire spaceframe Imps tipped the scales at little more than 600 pounds ready to race, this may have been paddock psyco
hype but I know they were a lot lighter than the Davrian monocoque cars.
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awinter
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| posted on 4/7/05 at 12:17 PM |
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Just out of interest, they have been building mountain bike out of Ali. These have the benifits of being lighter and alot stiffer than a simalar steel
bike. If the long term durability of ali was a problem why would a manufacturer choose to build an aluminium fame bike? Think of the loading imposed
on the front of the frame at the head set and bottom bracket where the chainset runs through the frame.
The frames do need to use oversize tube to retain strenght but are still lighter and stiffer than a steel frame. Is the increase in tube size the key
to getting durability and the fact that the aluminium age hardens over time then a benifit?
I don't know much about this but would be interested in how this progresses as this would have been something I would be interested in if I had
more time.
Ta
Allan
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andkilde
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| posted on 4/7/05 at 03:52 PM |
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quote:
Originally posted by awinter
If the long term durability of ali was a problem why would a manufacturer choose to build an aluminium fame bike?
Ali bicycles do suffer from fatgue cracking and failure Allan, particularly at the head tube join, and bicycles don't have to deal with the
vibration of an engine or the sort of mileage that can be racked up in a car.
You have hit the nail on the head though, in order to get the strength they need they go far bigger on the tube diameter.
There are all sorts of aluminium alloys, all with differing hardness and fatigue characteristics. If you poke around a bit on the net you'll be
able to find out about "age hardening", "artificial aging" "tempering" and a number of other things done to Ali to
improve it's strength and toughness.
The one thing steel has over Ali is that steel has vastly better fatigue resistance in its non-heat-treated form. So, from a Locoster's
standpoint, it's far more forgiving to the things we do to it, welding, forming etc.
If you have the engineering skills, access to proper heat treating facilities and the desire, I'm sure an acceptable Ali frame could be
built.
Cheers, Ted
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britishtrident
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| posted on 4/7/05 at 05:44 PM |
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One important difference is that a bike frame is of a size that can be heat treated as a whole unit after welding.
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rocket
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| posted on 4/7/05 at 09:24 PM |
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Ali frames
Alot of bikes use magnesium rich alloys. thats the key.
I'm building an 18g frame which will have ali underfloor. so it should be light.
All in all I would guess something like 20 kg. it's easy to weld ( I'm a fabricator) unless you have a really cheap mig that has to run
full up just to arc up, or you are using stick and are a novice.
But just to throw a spanner in the works look at delta box frame on super bikes?
These guys have been using 5% mag alloy for years no probs.
Lotus elise? even has alloy brake discs!!
the only argument against an alloy frame is impact.
When they tested the elise they found ali weld is strong until it cracks then it goes v. week and falls apart. When impact testing they found glueing
and riveting was better in a crash, this was because the joint moved and absorbed impact instead of cracking.
The best frame would be titamium but is too expensive.
Best idea is to save weight some where else!
But then again. . . by the time you have put wilwood calipers alloy hubs, magnesium bell housing light wieght racing wheels blah blah blah thats over
£1000.
So build a titanium frame then fit the normal stuff on!!
Or if you have abudget of around £8000 do both!!
Rgds
Roger www.shinybitz.co.uk
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cymtriks
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| posted on 4/7/05 at 10:00 PM |
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Mark, try
http://locost7.info/mirror/chassis.php
kitcaranalysis is in there!
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Volvorsport
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| posted on 4/7/05 at 10:54 PM |
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an ali frame will be better in an accident on a strength for strength basis .
www.dbsmotorsport.co.uk
getting dirty under a bus
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RallyHarry
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| posted on 5/7/05 at 05:17 AM |
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So how much for a Ti-frame then ?
How expensive is titanium ?, or is it the fabrication that's expensive ?
The good part will be that small dents will flex back to original shape !
And not least, is the main properties right ?
Cheers.
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RallyHarry
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| posted on 5/7/05 at 05:29 AM |
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To answer my own question:
Link to mountainbike frame materials
In short:
"Look at the chart again. You'll see that identical steel vs titanium frames would be about equal in strength, but that the titanium frame
would be about half the weight and half the stiffness.
Such a frame would likely have a whippy feel due to the reduced stiffness, especially in loaded touring applications. To compensate, builders of
titanium frames use somewhat larger diameter tubes to bring the stiffness more into line with what riders like. This tends to increase the weight a
bit, but by making the walls of the larger tubes a bit thinner, they can compensate to some extent, and come up with a frame that is still lighter
than a normal steel frame. "
Cheers
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rocket
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| posted on 5/7/05 at 09:14 AM |
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Titanium
It approx 3 times more expensive than 316 st/st ( if purchased in quantity)
rgds
Roger
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rocket
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| posted on 5/7/05 at 09:20 AM |
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ali frame
quote:
Originally posted by Volvorsport
an ali frame will be better in an accident on a strength for strength basis .
not if it's welded together.
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