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Learning how to build Lotus Seven replicas...together!
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PostPosted: July 4, 2009, 9:17 am 
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Joined: June 27, 2009, 9:58 am
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Location: Savannah, GA
I first stumbled across this site while originally looking for AC cobra replica build logs and was instantly hooked. I remember seeing lots of these on the road a few years back ( I lived in the UK for most of my life ) but i was so determined to do the cobra that i never really paid much attention to them. After looking through what goes into getting one of these 7 replica's completed, there was no doubt i wanted a go myself. I'm thinking of going +442E with a ford 5.0. I wanted to go with the 4.6 modular but it was way to big and the frame would have looked ridiculous. Rear will be IRS. I have no fabrication experience whatsoever, so this will be a monumental challenge for me. So, i have the space of a double garage, i have plenty of hand tools from being a mechanic for many years, but i need a lot more.

Ordered my welder 2 day's ago, A Hobart Handler 140 MIG. No gas yet, i need to get a bottle sorted out. There are a couple of Steel yards in Savannah near where i live, so framework shouldn't be too much of an issue. I know i'll need plenty of G clamps and magnets, gloves, steel cleaner etc, but what do you experienced guys wish you had with yours, or did have and never regretted it? I need a saw for the steel, but wasn't sure what to buy. I read a couple of posts with people using regular compound mitre saws with metal cutting blades. Is this recommended? I thought i would need a dedicated metal chop saw, or a bandsaw? Any other special tools? What about the suspension wishbones, is MIG ok, or should i get them done with a TIG?

For my build table, i'm going to go with 3/4 MDF with steel studs, and then make a lower frame and put it on locking wheels. I already have a regular workshop bench with a vice. I'm looking for any advice experience has brought to others. I can't wait to get started :D


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PostPosted: July 4, 2009, 9:35 am 
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Joined: June 27, 2009, 9:58 am
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Location: Savannah, GA
Also, can i stick with the 1" square or will i have to go to 1 1/4" like i've seen on other builds?


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PostPosted: July 4, 2009, 10:08 am 
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Joined: June 21, 2009, 11:33 pm
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Buy a tank, don't rent.

Don't learn to weld on your frame, build shop fixtures, tables, etc until you can make a nice looking STRONG weld. I have seen some nice looking 'cold laps'. The main thing beginners do wrong is not enough heat. Keep turning up the power and wire speed until you are blowing through the metal. Then either weld faster or turn down the heat and wire speed.

There is a very small range of wire speed that works with each power setting. Changing the wire dia will change this wire speed. When you figure out the wire speed write it all down on a business card and leave this card in where the wire spool goes so you will have the info readily available. Welding overhead you will need to slightly increase the wire speed.

If the wire seems to be pushing the torch away from the bead then your wire speed is too high. If the weld seems to be zzzzt zzzzt zzzzzt zzzzt then your wire speed is too low.


.023/.024/.025" wire for thinner metal and .030 for the thicker stuff should get you by on a locost although on a V8 car you might have some thicker bits where .035 would be correct.

In a pinch you can use the thinner wire for thicker metal, just have to turn up the power and wire speed to suit the amperage requirements. It's wasteful of wire. Using the thicker wire for thinner metal does not work as well so change the wire.

It is best to get a really good welder to show you how and get you started.


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PostPosted: July 4, 2009, 10:14 am 
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Joined: June 21, 2009, 11:33 pm
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shelby427uk wrote:
Also, can i stick with the 1" square or will i have to go to 1 1/4" like i've seen on other builds?


Personally, I would use 1x2 or even 2x3 for the lower rails and main crossmembers. You are building a relatively heavy [ compared to a book car ], VERY fast car. Don't scrimp on the frame. 1.750 x .120 DOM for the roll bar and braces.


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PostPosted: July 4, 2009, 10:23 am 
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Location: Savannah, GA
Regarding the welding, i have friends that can weld well to help me, and i may even go and take a class on it. I do intend to build some things first to get the hang of it, like a welder cart and a steel top bench. I don't want to have to contract anything out on the build apart from the custom drive shaft i will need and maybe the suspension wishbones if the MIG will not cut it for strength. There is no way i will touch the frame with the welder until i am confident that it's going to be good.


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PostPosted: July 4, 2009, 10:37 am 
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I am about a tenth of the way through my build but I'll tell you a couple of things I think are important.

#1. If you haven't bought your saw yet, pick up a cheap band saw. Way less noise so you don't disturb the family and your neighbors. If you are working in a fairly enclosed space a chop blade STINKS!!!! And I think the band saw makes a little nicer cut. I have a 14 inch chop saw that I quit using after the first few cuts. My 10 inch Ryobi miter saw has done a good job but when the project is through, the saw will be also.

#2. Make sure you have adequate stout storage racks for parts and things. It's very easy to misplace things if you don't have a cental area to keep them.

#3. Wear gloves and googles. That's the safety guy coming out in me. I hate having grinding or burn sores on my hands and I hate having little slivers of steel taken out of my eyes.

#4. Use the experience and knowledge on here. For the most part these guys know what they are talking about and can steer you in the right direction or away from the wrong one. If you have a cool idea, bounce it off of one of these engineers, they're free. And don't hesitate to copy someones else's idea. You probably won't ever meet them and you can pass their idea off as yours. :lol:

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PostPosted: July 4, 2009, 11:06 am 
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Joined: June 21, 2009, 11:33 pm
Posts: 60
Also, KISS !!!!!!!!!!!! Simplicity is usually best.

My pet peeve is inboard, pushrod/rocker arm coilovers up front. You move the coilover from it's natural place between the lower control arm and the upper frame rail and you move it inside the frame or above the frame where it is in the way or requires the relocation of some other component or makes changing the spring a chore or otherwise compromises the maintainability of the car. Plus it makes the car heavier and adds several highly loading bearings that will require more maintenance/expense.

Properly layout of the mounting points of the std coilover setup will yield a small amount of rising rate. I bet many of the people building pushrod/rocker arm setups don't have any idea what sort of leverage ratio the shock sees. Could easily be falling rate.


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PostPosted: July 4, 2009, 12:03 pm 
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rayjay wrote:
Properly layout of the mounting points of the std coilover setup will yield a small amount of rising rate.
Cool! Where does one put the mounting points to yield rising rate? I put my upper shock mounts on little extensions coming out from the chassis but the extension length is limited by upper control arm clearance (the shock spring gets too close to the point of the "V").

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PostPosted: July 4, 2009, 12:22 pm 
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IIRC Carroll Smith discussed this in his books. It was common for some builders to place the upper shock mount inline with the pivot for the upper control arm. This typically gave a falling rate. By moving the shock mount upwards and outwards you end up with rising rate.

With the suspension bottomed out you want the angle of the shock and lower control arm to be close to 90 degrees. When the suspension is at full droop there will be a greater angle between the shock and the lca. This greater angle means that the lca has more leverage against the shock. As the suspension compresses the angle is getting closer to 90 degrees meaning the lca has less leverage against the shock, hence rising rate.

There should be some possible combination of upper and lower shock mount positioning to allow at the very least a linear rate and hopefully a rising rate.

This same idea was used in the early days of long travel rear suspension on motocross bikes. With the two shocks properly placed on the swingarm and frame they gained rising rate. Due to poor design, the first Kawasaki single shock MX bikes had falling rate.

ETA: I just noticed the locost in the picture at the top of the page has the coilovers mounted to give falling rate. You can see the severe angle formed between the lca and the shock. This angle will only get more severe as the suspension compresses thereby giving falling rate. The more the suspension compresses the less the spring resists the compression. What you actually want is the more the suspension compresses the stiffer the spring gets [ a gross oversimplification to be sure ].


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PostPosted: July 4, 2009, 12:31 pm 
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Joined: June 27, 2009, 9:58 am
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Location: Savannah, GA
Some good info so far, thanks guys. I do not have any books to help me with the build and was going to order Ron Champions book. Are there any others that i will find helpful or better than this?


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PostPosted: July 4, 2009, 12:40 pm 
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Get all of Carroll Smiths books. Read them over and over until the info is burned into your brain.


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PostPosted: July 5, 2009, 12:14 am 
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Joined: October 26, 2008, 8:17 pm
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Location: Baton Rouge
rayjay wrote:
Get all of Carroll Smiths books. Read them over and over until the info is burned into your brain.


Ditto.. particularly the one on fasteners. not the most entertaining, but its stuff anyone building a car needs to know.

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PostPosted: July 5, 2009, 1:00 am 
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JackMcCornack wrote:
Where does one put the mounting points to yield rising rate? I put my upper shock mounts on little extensions coming out from the chassis but the extension length is limited by upper control arm clearance (the shock spring gets too close to the point of the "V").


Make it so in full droop the angle between the lower A-arm and shock is less than 90 degrees and approaches 90 degrees as the suspension is compressed, but does not pass that value. Picture a sin wave; it reaches maximum value at 90 degrees - simple as that.

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PostPosted: July 5, 2009, 7:25 am 
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Joined: June 21, 2009, 11:33 pm
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When you go to assemble the car for the LAST time use nylock nuts everywhere. On blind threaded holes use some sort of threadlocker.


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PostPosted: July 5, 2009, 12:36 pm 
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Quote:
Picture a sin wave; it reaches maximum value at 90 degrees - simple as that.


Note also that a sine wave is flat at it's peak and doesn't change much near there. Unless you get far away from the center I don't think the small amounts of rising or falling rate amount to much. Spending time worrying about little things can cause you to ignore other bigger things.

On a Locost I think it would be hard to arrange much rising rate on the front. Other issues could be introduced that would make things worse. So this may not be a great issue to push in a thread for an initial or newbie build.

I think the Keith Tanner book would also be useful for a newbie more then the Carrol Smith books.

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