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Learning how to build Lotus Seven replicas...together!
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 Post subject: Re: sprite into locost
PostPosted: July 13, 2015, 12:10 pm 
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Joined: January 31, 2008, 5:34 pm
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Location: SW Wes Consin
It has been a while. My computer's wi-fi died which resulted in a new box :( And many hours trying to get everything transferred over. A real trick without wi-fi. Makes the cloud pretty worthless. I finally resorted to a thumb drive. Slow but effective.

Progress on the buck repair has been attaching a wire skin over the wood stations. This consisted of adding a #2 sweep bend to the side trim tube and attaching it to the fender crown front and rear. This gives the buck a lot more flow. I also wired around the cockpit. This was pretty tricky as the cat walk (valley between the front fender and the bonnet) needs to fade to flat at the fire wall. If it doesn't you end up with an ugly gap under the wind screen. This didn't work out as well at the cockpit rear because all the lines are tapering down from the fire wall but it doesn't look bad so I guess it flies.

I hope with the pics this makes some sense. Any suggestions appreciated.


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File comment: Body side at #2
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File comment: rear cockpit corner
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File comment: front cockpit corner
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IMG_0972.jpg [ 795.46 KiB | Viewed 1164 times ]
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 Post subject: Re: sprite into locost
PostPosted: July 13, 2015, 12:50 pm 
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Joined: June 12, 2012, 8:40 pm
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Location: York,Pa
vroom wrote:
I hope with the pics this makes some sense.

Yup, it does.
vroom wrote:
Any suggestions appreciated.

Keep the pictures coming. I'll be back to work on mine when the weather cools off a bit.

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 Post subject: Re: sprite into locost
PostPosted: July 25, 2015, 4:41 pm 
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Joined: January 31, 2008, 5:34 pm
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Location: SW Wes Consin
It is hotter than the hinges (by my standard) and I have been spending too many hours trying to figure out my panels.
So time for a break. I have had this mind worm for quite a while. Ever since some guy suggested that it would make more sense to build the body over the chassis. In this way I wouldn't make any mistakes about how the wheel wells worked out. I knew this but that isn't how this project has come together. But it did give me this mind worm. I have been worrying about it ever since. So today for a break from learning to make panels (scrap) I pulled my axle out of the attic and stuck it under the buck. This wasn't entirely successful the buck frame interfered with the wheel causing it to stick out about 2". But, it does line up with the to be built body pretty well. The mind worm is dead! :cheers:


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 Post subject: Re: sprite into locost
PostPosted: July 25, 2015, 6:14 pm 
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Location: Summerville, SC
That's coming along nicely

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 Post subject: Re: sprite into locost
PostPosted: August 8, 2015, 12:04 pm 
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Location: SW Wes Consin
Haven't posted for a while just trying to master the hammer. The panel I am suffering with right now is the bum. This panel wraps over the top and bottom edges and around the side and takes either a big shrink or a big stretch or both. Mark Gerisch has a video that shows a similar panel from a Cobra which he he made by stretching. I am not that good.


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File comment: The Grand kid at RA with an example of Mark's Art
IMG_0985.jpg
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File comment: One of many not good enough panels
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 Post subject: Re: sprite into locost
PostPosted: December 9, 2015, 6:56 pm 
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Joined: January 31, 2008, 5:34 pm
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Location: SW Wes Consin
Once again it has been awhile. Not that I have not been busy. Back in July SWMBO suggested that we weren't having enough fun. To make a long story short we ended up buying a '90 Miata for use until the locost is finished. Well of course the car turned out to be almost rust free so no outside winter storage and no cutting it up for parts. She likes the car and it needs indoor storage :x . So once again I dragged out the woodworking tools poured a slab and added 14' to existing building #5. Well, after 3 months of walking past the buck and thinking about it I am pretty much convinced I need to finish wiring over the buck. Photos to follow.


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 Post subject: Re: sprite into locost
PostPosted: December 9, 2015, 11:30 pm 
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Joined: October 19, 2010, 11:57 am
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Location: Waterloo, WI
Always enjoy the updates, Vroom. At least we've had a very mild Fall to get things done! :cheers:

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 Post subject: Re: sprite into locost
PostPosted: December 28, 2015, 6:16 pm 
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Attention serious smart guy technical types. A question but first some comments. Sevens used space frame bays with flat sheet aluminum bonded and riveted to the tubes. Folks I know who raced such things have told me that Sevens were seriously unstiff and the rivets frequently got loose. Forghieri says Ferrari used the sheet aluminum wrapped around and bonded to tubes in place of diagonals until into the composite age. It is apparent that many of the cars that used this construction were conceived as throw aways post racing season. Many design books including Seward's mention this method. So here is the question: can I ditch the diagonals? How is it possible to calculate what sheet to use? OK it's two questions. Are space frames with diagonals not just a PITA to weld but belt and suspenders? Right, three questions. It is now winter in Wes consin and time to ponder such things.


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 Post subject: Re: sprite into locost
PostPosted: December 28, 2015, 7:27 pm 
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Location: SoCal
Agree that a flat panel riveted to a flat tube frame bay does not need diagonals - the panel serves that purpose just fine. In your case however it's not quite so straightforward since many (most?) of your bays aren't flat/two-dimensional. I never done what you're doing, but if I did, I'd make a traditional triangulated frame and add the body panels for looks and aero. I don't think it's realistic to count on curved aluminum panels to serve as structural strengthening elements, but that's just me.

As far as rivets coming undone, I think that's more a reflection of Lotus cutting things really close for every last ounce of weight savings. Using steel rivets or aluminum rivets that retain their stem are probably superior to what Lotus used. Also, as is widely known, Lotus had a bad habit of leaving out tubes that were later found to be structurally necessary. Yes they'd last for a couple seasons, but that was about it. My point is that if you build a proper chassis to start with, I don't think you'll have any issue with the paneling coming loose.

(I've always wanted to get into making proper panels via beating, shrinking, and stretching. Seeing your comments would fit me to a tee, creating large pieces of yard art, with a free helping of much cursing and pounding noises.

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 Post subject: Re: sprite into locost
PostPosted: December 28, 2015, 7:59 pm 
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To put your mind at ease about the durability of light weight structures that are riveted together think airplanes. Think old airplanes, like DC-3s and many others. Lots of rivets installed correctly seem to last forever, no matter the stresses on the airframe.

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 Post subject: Re: sprite into locost
PostPosted: December 29, 2015, 12:51 pm 
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Location: SW Wes Consin
A little misunderstanding, I wasn't referring to body panels I meant any space frame bays that are two dimensional. My suspicion is that the adhesive should be doing most of the holding so if that is the case why would the rivets come loose? Another concern I have, not having a math model to work with, is how thick a sheet and what alloy and temper? Some of the FSAE guys might understand this. Or they did what I suspect Ferrari did and built it and tested.
I would be inclined to try building a chassis this way but if a sheet goes all wrinkley it would be a PITA to redo. A sample bay built both with a diagonal and another with a glued and riveted sheet and then both tested to destruction would make an interesting experiment but I don't have a good way to do it. Any ideas?


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 Post subject: Re: sprite into locost
PostPosted: December 29, 2015, 1:28 pm 
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Location: Halifax, Nova Scotia
Build a smallish rectangular frame (actually two: one with a diagonal and another with a bonded skin) with hefty brackets on opposing corners and either pull on the brackets or, lacking a suitable foundation, jack between the two brackets. You will be approximating the distortion caused by the shear loads that the diagonal or skin is trying to resist. The load is different but the racking distortion is the same.

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Build Log: viewtopic.php?f=35&t=11601


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 Post subject: Re: sprite into locost
PostPosted: December 29, 2015, 1:51 pm 
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My problem Warren is what do I attach the whole thing to that will hold it in place while applying the force? I could use my floor jack for force but I don't have anything heavy enough to hold the assembly down that is in the range of what might be needed. I thought about a reduced scale test samples but then I would be stuck with the problem of what the plate should be (thickness, alloy etc.).


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 Post subject: Re: sprite into locost
PostPosted: December 29, 2015, 5:01 pm 
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If using a jack between the brackets the test frame can't go anywhere. Just lie it down or prop it up and the jack is pushing against the opposite sides of the frame. Another, easier approach if you had a good (say 20 ton) shop press, would be to simply compress the frame diagonally and just forget about the brackets. I you could measure and record hydraulic pressures you would have some relative measure of strengths.

If using a come-along you will need two good foundations and you might end up doing more damage to your garage than the test frame. :oops:

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 Post subject: Re: sprite into locost
PostPosted: December 29, 2015, 5:18 pm 
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We are definitely thinking on the same lines. I don't have a nice hydraulic press and I'm not sure I want to tear up the garage. Somebody out there must have done a test along these lines.


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