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Learning how to build Lotus Seven replicas...together!
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PostPosted: Wed Feb 01, 2012 5:12 pm 
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Mid-Engined Maniac

Joined: Sun Apr 23, 2006 8:26 pm
Posts: 4858
Location: SoCal
The sad thing is that I do in fact have several friends who would say something like that. You could it yell it at me if you see me on the street... we don't live far apart.

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Kimini book: Designing mid-engine cars using FWD drivetrains, http://www.kimini.com/book_info/


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PostPosted: Wed Feb 01, 2012 7:10 pm 
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Joined: Sat Jul 29, 2006 9:10 pm
Posts: 2349
Location: Oregon, usually
carguy123 wrote:
And then there's the impossibility to build your chassis 100% flat, true and accurate...build your chassis and then attach your suspension based not upon the chassis, but upon what it needs to be...
Sound observation and advice, carguy. The chassis is a meta-bracket that keeps all the components flying in formation, but the only components where precision position really matters are the suspension brackets. I favor welding the suspension brackets on the chassis without clamping the chassis to the table--if you have to clamp it to the table to get it flat, it's going to sproing back when you unclamp it, and the brackets will sproing out of alignment in sympathy.

So, build yourself a nice chassis, and if you use the tips on the previous pages, it'll be more true than the chassis the robots weld in Detroit, but it won't be perfect. Then add the suspension brackets; either way would do, but I start with the rear brackets, and then position the front brackets in reference to the rears.

If I were making mass quantities of chassis, I'd make a fixture out of I-beams that would hold all the suspension brackets at once. Then I'd drop an otherwise finished chassis into the fixture, and weld the brackets to the chassis.

BTW, the reason the Kinetic standard suspension brackets have their 1/2" hole .050" off center is so a builder can make a subtle hole position adjustment ( .100" +/- relative to the other brackets) by flipping a bracket over.

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Locost builder and adventurer, and owner/operator of http://www.kineticvehicles.com


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PostPosted: Thu Feb 02, 2012 5:00 am 
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Joined: Sun Jul 22, 2007 10:58 pm
Posts: 387
Location: Zagreb, Croatia
I'd just like to add a few things..

for my build table I used two rails made of twin 3.5x2.5 inch rectagular profiles welded togeather... It is quite a sturdy structure, yet, when I welded in the last section of the frame, the frame itself managed to bend the build table.. :)


I also made the frame in the worst possible way, making the suspension pickups an integral part of the frame from the start... yet, I got really good accuracy.. My "secret" was building the frame in sections, making sure to fully weld each section, then weld those togeather.. That way I could pay more attention to each section accuracy and when I got to the point of welding them togeather, there was much less weld joints to distort + I got a second chance to realign everything..

Image

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Building a single seater middy BEC with GSXR 1000 power :)
build log: http://locostusa.com/forums/viewtopic.php?f=36&t=5899

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PostPosted: Thu Feb 02, 2012 11:23 am 
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Joined: Fri Oct 24, 2008 2:13 pm
Posts: 1653
Location: Carlsbad, California, USA
kikiturbo wrote:
. . . <snip> . . . My "secret" was building the frame in sections, making sure to fully weld each section, then weld those togeather.. That way I could pay more attention to each section accuracy and when I got to the point of welding them togeather, there was much less weld joints to distort + I got a second chance to realign everything..
. . . <snip> . . .


Very interesting. I had just imagined in my mind that approach (fully welding subsections in separate jigs and then joining them together), but wasn't sure how much benefit it would yield. In part, it was based on what I observed being done by an old time builder who was very precise and beautiful cars.

For my humble little one-off it is hard to justify all that work, though. And, I really don't have the physical space either. You've obviously taken great care with your own build, which is considerably more unique in both design and construction than my own project. I'm going to review your build log in detail very soon. There's lots of great stuff in there both in the text and photos.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Thu Feb 02, 2012 11:53 am 
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Joined: Sun Jul 22, 2007 10:58 pm
Posts: 387
Location: Zagreb, Croatia
thanks, first of all.

if I could give advice, based on what I know now, I would suggest following the well established mantra of adding the suspension pickups last...

however, I stand by my method of using fully welded subsections... In my case, with many tubes and difficult joints, it is much easier turning around a 20-40 pound subsection, then whole 120 pound frame, and access is much better..

of course, this depends on the design..

If I had to do this again, I'd spend much more time on setting up some fixed markers, frame centerline, etc, to facilitate easier measurement later.... In fact, this is the single biggest issue for homebuilders... precise measurement.. however, I really do not have the space.. :)

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Building a single seater middy BEC with GSXR 1000 power :)
build log: http://locostusa.com/forums/viewtopic.php?f=36&t=5899

day job: http://smg.photobucket.com/albums/v723/turbolimac/portfolio/


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PostPosted: Fri Feb 03, 2012 8:03 pm 
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Joined: Mon Oct 19, 2009 9:36 pm
Posts: 1549
Location: meadview arizona
imust admit to building the sides of the chassis layed flat on the table then the sloping bit can be done whith out having to find a point in space.

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drag racers lament

oh to go down to the strip again where the blacktop meets the sky
all i ask is a small block and some fuel to make her fly
with slicks a smokin pushrods pokin next round i'll get a bye

she's up on song the shift was strong in the finals to boot
it's back to the pits and take it to bits and don't forget the shute
the final round was good and sound so come on give me the loot


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PostPosted: Fri Feb 03, 2012 8:15 pm 
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Joined: Mon Oct 19, 2009 9:36 pm
Posts: 1549
Location: meadview arizona
with regard to straightening the chassis after i dropped it

i just worked out how to drop it at the right angle and did it again

but i did use ratchet straps to pull it and also made some cuts in one face of the tube and welded it back up to pull it towards the weld.

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drag racers lament

oh to go down to the strip again where the blacktop meets the sky
all i ask is a small block and some fuel to make her fly
with slicks a smokin pushrods pokin next round i'll get a bye

she's up on song the shift was strong in the finals to boot
it's back to the pits and take it to bits and don't forget the shute
the final round was good and sound so come on give me the loot


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