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Learning how to build Lotus Seven replicas...together!
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PostPosted: Sat Jan 28, 2012 12:21 pm 
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For about $300-$400 you can build a seriously sturdy I-beam table. I know its not low-cost, but I bet its one of those items that would be fairly sought after in the classified section once you were finished with it. Spend the $$$ and when you are finished, sell it for a hundred or so less and let the next guy have at it. Kinda like "pay it forward". Just a thought.

I've had a table for many years and its something that I find may uses for. It was built with I-beam sections from a local steel supplier. Everything was sourced from "drops" or the cut-off sections from other orders and bought for 1/2 or the normal cost. Some planning, drilling and welding and you'll have an awesome platform. The last thing you'll need to worry about is if the chassis is flat. You'll get all of your distortion from the welding process not from the table being bowed.

Just my .02

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PostPosted: Sat Jan 28, 2012 3:02 pm 
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w650gb500 wrote:
For about $300-$400 you can build a seriously sturdy I-beam table. I know its not low-cost, but I bet its one of those items that would be fairly sought after in the classified section once you were finished with it. Spend the $$$ and when you are finished, sell it for a hundred or so less and let the next guy have at it. Kinda like "pay it forward". Just a thought.

I've had a table for many years and its something that I find may uses for. It was built with I-beam sections from a local steel supplier. Everything was sourced from "drops" or the cut-off sections from other orders and bought for 1/2 or the normal cost. Some planning, drilling and welding and you'll have an awesome platform. The last thing you'll need to worry about is if the chassis is flat. You'll get all of your distortion from the welding process not from the table being bowed.

Just my .02


Totally cool table, Dan.

I take you level each leg with (what appears to be) a leveler at the bottom. It looks like you use the smaller I-beams as cross stations along the way and clamp them in place where needed along the two major I-beams. Had you removed some cross beams when this photo was taken?

If that's the way it works, I could see using a cross I-beam under the front frame, firewall, seat back and so on, as required for early chassis building. When you get the major rails in place do just what the lower photos show. That is, block it up and you have complete access to the drive line, suspension, etc. Very nice!

Thanks for posting,

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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: Sat Jan 28, 2012 3:29 pm 
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Yes, I have 6 smaller "cross beams" that clamp on. Each leg is leveled with a 5/8" bolt and a lock-down nut. I can evenly space out the cross-beams and lay a sheet of MDF on and clamp it down. Its very versitile and took one weekend to grab everything, cut, weld and bolt it all together. It breaks-down in an hour and can be stored against a wall and in a corner.

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PostPosted: Sun Jan 29, 2012 11:24 am 
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That is nice! Is there such a thing as table ENVY.
Dave W


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PostPosted: Mon Jan 30, 2012 5:02 pm 
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Lonnie,

The short answer is "Don't worry about it, it doesn't really matter." Keep in mind that the original Champion book shows building the frame using chalk marks on a concrete floor. A lot of Locosts were built that way. You know mine was built on saw horses with some 2x6's supporting a sheet of MDF. I've never had a single thought that maybe I should have done it differently. You are a much more meticulous builder than I was, but I'm still quite certain that: a) No one can build a perfect chassis, b) Yours will close as they get because that's just the way you are :wink: , and c) Even if it's perfect on the table, it isn't once you load it up with a motor, fuel tank and passengers.

So don't sweat the small stuff!

John


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PostPosted: Mon Jan 30, 2012 6:11 pm 
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Locost_Johnh wrote:
Lonnie,

The short answer is "Don't worry about it, it doesn't really matter." Keep in mind that the original Champion book shows building the frame using chalk marks on a concrete floor. A lot of Locosts were built that way. You know mine was built on saw horses with some 2x6's supporting a sheet of MDF. I've never had a single thought that maybe I should have done it differently. You are a much more meticulous builder than I was, but I'm still quite certain that: a) No one can build a perfect chassis, b) Yours will close as they get because that's just the way you are :wink: , and c) Even if it's perfect on the table, it isn't once you load it up with a motor, fuel tank and passengers.

So don't sweat the small stuff!

John


Hey, John. Thanks for the encouragement. I do tend to get fussy about these things, don't I? I keep thinking maybe there's a secret German side to my family that I don't know about :lol: Anyway, I'm busy laying out the chassis members on my build table so, I'm on my way now crown or no crown.

I was thinking of you yesterday and wondering how your new barn is coming along.

Cheers,

Lonnie

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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: Tue Jan 31, 2012 1:51 pm 
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its not the table you need to get flat, its the chassis,
i say flat because level is not requisite,

ask yourself is the tube straight when you buy it,

the book says fully weld the bottom, grind down the welds and then flip it over and build the rest from there, well i ask you how flat is that,

after i tacked my chassis, i removed it from the build table and in the process dropped it! so i put it back on the table and tweeked it till it was straight and true, then with 4 people removed it for fully welding, i put it back on the table about 4 times during the fully welding process and had to tweek it every time,

being flat on the table only deals with one axis, i found that the diagonals, both front to back and up and down were what was moving,

of course, when the drive train was installed the whole thing moved in all directions,

close riviting of the sheet to the frame stiffens it up quite a bit,

when you make the hood, be sure that the drive train is in and its standing on its wheels on level ground!

all that is really critical is that you pick a datum tube and a center line and go from there,

make all your diagonal measurements from their axis and a known vertical fixture at 90 deg. to the face of the table.

i used to build morgans from a chassis, they were a 'z' rail, the new chassis had only two holes drilled in it for the fixed end of the rear springs, you had to work off those two holes for everything else with a tape measure.

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PostPosted: Tue Jan 31, 2012 10:19 pm 
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john hennessy wrote:
. . . <snip> . . .
after i tacked my chassis, i removed it from the build table and in the process dropped it! so i put it back on the table and tweeked it till it was straight and true, then with 4 people removed it for fully welding, i put it back on the table about 4 times during the fully welding process and had to tweek it every time,

being flat on the table only deals with one axis, i found that the diagonals, both front to back and up and down were what was moving,
. . . <snip> . . .


John,

Thanks for posting this. It was all very interesting.

Of course, I know what you mean by "tweeking", but what actual, physical process did you use to true up the chassis as welding proceeded and the chassis moved out of position?

Thanks,

Lonnie

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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: Wed Feb 01, 2012 10:17 am 
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Lonnie-S wrote:
...what actual, physical process did you use to true up the chassis as welding proceeded and the chassis moved out of position?

What ever it takes. One time I had to lay down the chassis floor frame in the driveway and park my truck on it to bend it back straight again. When welding, the metal heats, expands, then melts. When it cools, it first solidifies, then strinks as it cools. This explains why welds pull in the direction of the weld.

The forces can be enormous. If you fully weld a T-junction, the top of the "T" will no longer be straight. It's not a small amount either, and it's made much worse due to us using fairly long tubes in places. That is, even one degree distortion ends up being 1" at 57" down that tube. That's why welding has to be done in a back-and-forth side-to-side alternating style. As each weld cools it pulls the chassis in that direction, so if you keep switching sides, the distortion will average out to be fairly small.

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PostPosted: Wed Feb 01, 2012 11:10 am 
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You're scaring me now, Kurt. The experiences I'm reading about from you guys plus the results on my build table have got me thinking there must be a better way. Amateur airplane guys use even thinner, longer tubes yet appear to get better, more accurate results without all the distortion problems. Why is that? What do they do differently?

One of the old time race car builders in my home town had a very different approach and did beautiful work. He had a big build table with a very flat, thick piece of sheet steel as the working surface. He built the bulkheads first using layout jigs on the steel sheet, so they were built on a flat surface and controlled very carefully. Then he would erect the bulkheads on edge as they sit in the finished car, positioning everything with a surveyors transit. Last he'd weld in the side rails, connecting all the bulkheads to make the completed chassis.

I don't know what kind of accuracy he achieved, but it sure looked good and he had a reputation for being very precise. He also had a pretty good side business fixing the bad work of other builders and even some big name chassis makers from Europe.

Well, the Locost process is what it is and I'll keep working through it and do my best to get a good result.

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: Wed Feb 01, 2012 11:43 am 
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You might learn something just by looking at the legs on your build table with a straight edge. If you consider something like welding a T shape with the leg vertical, I can imagine rigidly clamping it down would make the distortion worse. If you have a little extra scrap that might be an experiment to try. I've also heard say here to clamp it down while tacking to get the shape true and then just welding it symmetrically without the clamps.

People often weld the cockpit sides first.

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PostPosted: Wed Feb 01, 2012 11:50 am 
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You can use weld distortion to your advantage, knowing the direction it'll pull in. That is, if a tube is bent due to welding heat, you can melt a bead on the backside and it'll help draw the tube back straight.

You just have to expect stuff to move around and you'll be fine. Just don't expect perfection.

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PostPosted: Wed Feb 01, 2012 12:42 pm 
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KB58 wrote:
One time I had to lay down the chassis floor frame in the driveway and park my truck on it to bend it back straight again.


Yup, common.

KB58 wrote:
You can use weld distortion to your advantage, knowing the direction it'll pull in.


Yup, common.


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PostPosted: Wed Feb 01, 2012 2:27 pm 
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It's only "common" to people who've done a build and therefore know about it. It's mentioned specifically because it isn't common to new builders, so specific examples are helpful.

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PostPosted: Wed Feb 01, 2012 4:49 pm 
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And when you're all done and a "friend" tells you "your chassis looks like a truck ran over it" you'll have a reason for him. :P

John


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