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Learning how to build Lotus Seven replicas...together!
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PostPosted: April 9, 2007, 2:40 am 
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I was missing for a bit; went to CA to get a donor for a school project, then soon as I dropped it off, turned around and fetched a potential kit hauler--an '80 Toyota-powered motorhome with 9 wheels (2 in front, 4 on the drive axle, 2 idlers behind the drive axle, and a spare) of which 7 survived the trip north. Once the living quarters are gone I should end up with a big ol' flatbed with a 3500 pound payload and 20+ mpg.

Meanwhile, I've done some work on the sheetmetal parts but they're not ready for Prime Time 'till I figure out a locost way to bend them at home.

So here's this weekend's fender fab. You've likely noted that this process takes a long long time if you're counting days, but at an average of an hour a day or so, it's not too bad from an hourage standpoint. I favor slow cures to reduce heat and thus reduce shrinkage, but it does limit the amount of work one can do on any given part on any given day. Lucky there's lots of parts and lots to do.


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PostPosted: April 10, 2007, 1:04 am 
Hurry up already. I cant wait to see the finished part.


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PostPosted: April 11, 2007, 2:27 am 
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AlexPfeiffer wrote:
Hurry up already. I cant wait to see the finished part.
You and me both, but it's going to take a while anyway.

After tonight's episode, I'm going to drop out for a while, because there's lots of ordinary boring bodywork to do from here. I've tried to fill this patternmaking episode with tricks of the trade, and hope this has saved some time for folks with similar projects...but I'm no bodyman and don't have much to offer on the subject of finishing.

Next entry will relate to sheetmetal...if I figure out a way to make the 3/4" radius bend on the upper edge of the pontoons without a special fixture on a press brake. It's supposed to be locost, after all.

So here's how I skinned the fender pattern. From here I'll be puttying and sanding and repeat as needed until it looks like a fender.


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PostPosted: April 11, 2007, 2:56 am 
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Onward. Now we add the center skin, which is a 1/8" sheet of hardboard, long enough to fit the entire span of the fender (48" in this case--ain't CAD wonderful?) and wide enough to fit the widest gap. The rear of the skin is temporarily clamped to the back board...but I'm getting ahead of myself. Roll the tape.


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PostPosted: April 11, 2007, 3:19 am 
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And at last, it looks like a fender. Well, kinda; at least it's the right shape. I made this batch of puttyglue light on catalyst, so I'd have lots of time to work with it. Once mixed, I smeared some on the edges of the skin and some in the notches between the skin braces and the sides, then put the skin in place and clamped it down with the two tie straps you saw in photo #17. Since it was lightly catalysed, it didn't set quickly...not as quickly as the sun did, for example. But trust me, when the straps come off, the skin will stay...and then it's hours an hours of body putty and elbow grease, followed by a couple coats of water-base Kilz sealer, and then we'll make a mold.


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PostPosted: May 3, 2007, 11:16 am 
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Don't leave us hanging man!!!!

We need more!!!

Doc

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PostPosted: May 6, 2007, 2:17 am 
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Roger, Doc. It is taking a long time, isn't it?

I did the hours-and-hours of bodyputty and sanding, but the pattern came out all blurry. This eve I took it outside in the dark and spritzed it with some Satin Red Krylon so I could see where the really lousy places are...there are a few, but at least it isn't blurry any more.

I'm good at making patterns, shape-wise, and I'm good at making molds, but I sure suck as a bodyman, and the surface finishing is an essential step between the shapemaking and the moldmaking. So I have a proposal: anybody who is willing to do the finishing on any (or all) of these body parts (the job where you start with the unfinished pattern, make it smooth with body putty, primer it, and give it a 400 grit [or better] finish) can have the first part out of the mold for free. I'll pay FedEx shipping both ways for the pattern(s), plus shipping for your part(s). And maybe this string will get quicker entries than one every 26 days.


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PostPosted: May 9, 2007, 1:55 pm 
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I accept the challenge of the mold plug finish!!!

PM me on it. I am certainly game, and can certainly finish these with ease.

Doc

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PostPosted: May 25, 2007, 7:57 pm 
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Meanwhile, here's a look at the metalwork. The chronology is out of step, but it doesn't matter much which parts one makes first since they all have to be done.

Pontoons for the 2k7 prototype (and the school built GRM$2007 Challenger also) are 22 gauge steel; very strong (I'm literally having to reengineer my chassis torque test fixture because I can't detect <any> strain in torsion when using test equipment based on the Australian DMV test device) but perhaps moreso than they need be (unless you get hit in the side) and thus heavier than they need to be as well. Aluminum panels will be a whole lot easier to work, and testing the bending device on small samples of ali indicates the current bender dimensions (trough shape and forming tube diameter) will work fine on both metals.

Indeed the stiffness of the .030" mild steel made the development of a cheap bender for 3/4" radius quite a challenge. It took a month, we went through plenty of material (steel tube, steel pipe, PVC pipe, vinyl tube, sandwiches of steel tube/pipe in PVC tube/tubes, plywood, MDF, steel rollers, plastic rollers, steel rollers with rubber tires, ditto w/ urethane tires, 2" 3" 4" rollers, rollers with side plates, grooved rollers, various alignment devices, presses weights people etc) but--after having a local supplier accept our money and make us a punch and die set for his humongous hydraulic brake in a day--we eventually figured out a way homebuilders can do this on the cheap. As I think I've mentioned, I want the 2k7 body to be reproducable from plans, on a locost budget...but this one was tough, and a development project that was much easier to do for the kit version than for the plans version.

But the result is a sheetmetal bender that can be built in a day for about $30 if you're a decent scrounger, that produces a precise bend that matches the edges of the fiberglass parts.

Essentially it's a trolley made from an 8' long 2 by 4, with a grooved wheel in the center, two casters on the passenger end, a handle on the other end, and has guides on the passenger end for the trolley, and guides on both ends for the forming tube. The forming tube has alignment pins that fit into appropriately-placed holes in the sheet to be formed. The sheet is placed between the tube and the platform and the center roller is placed on the tube. The operator (wearing knee pads) pulls the trolley back and forth while putting pressure down on the handle, and the sheet gradually sinks into the trough. Once it hits bottom it stops bending, with +- 1 degree repeatability.


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PostPosted: May 25, 2007, 10:09 pm 
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Jack, you do realize that I am going to have to steal/steel that idea for my sides on mine.
Dale


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PostPosted: May 26, 2007, 1:41 am 
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Dale, your body design is too cool as is. The problem with the technique described above is it can only do simple bends, which means if you bend on one plane you can't bend on an intersecting plane...so you'd lose the smooth transition from the "door" area (where I presume there will be no door, but you know what I mean) to the flared area forward of that. I'm shooting for cheap and easy and let the looks fall where they may, where yours has some actual style to it. But if you can incorporate this technique to somehow make your job easier, I'll be flattered.

To get the 3/4" radius, the forming tube that did the job (cheap, easy, accurate, available anywhere in the USA) was a steel plumbing pipe slightly bigger than 1" diameter (I believe it's called 3/4") which I got from a building salvage lot, and a 1" Schedule 40 PVC pipe with a skill saw slit on one side so it would fit over the steel pipe. And by the way, in the upper photo of my last post, Sharon is not only holding a 55 pound anvil, she's sitting on an 80 pound sandbag, and I occasionally pushed down hard enough to lift her off the ground ...which means it took about 500 pounds load on the forming tube to get the job done.

The width/depth of the groove the sheet was pushed into (the "forming die" if you're telling your metalshop teacher why you deserve extra credit) is not what you'll want/need for yours, because I made mine to make the bend at less than 90 degrees so I could curve the outboard surface of the panel. In a few days i'll be back down south where this stuff is in storage, and I can measure it then...and I may be able to find my 90 degree tool, but for my application (where the pontoon is the primary torsional structure of the cockpit) the curved surface worked much better than a flat surface so I don't have any notes handy on the flat sided version.

The curved side is surprisingly easy to form...well, it is now, but I threw away a lot of bulkheads before I found out how easy it is. There's been a fair amount of, not failure exactly, but to paraphrase Thomas Edison, I've learned as many ways not to make a bulkhead as he learned ways not to make a lightbulb.

I'll pull out the bulkhead tool next week--I have to anyway 'cause I need to have the kids bang out a set--and get some measurements posted. It's a pair of matched 1" thick MDF patterns with two 1/4" holes matchdrilled through them both, which line up with two holes in each bulkhead. The bulkhead blank (also made of 22 gauge mild steel, like the pontoon sides) is clamped between the patterns (two 1/4" bolts through the holes, with washers and wingnuts) and the curved flanges are hammered down flush with the curved pattern.

Here's a photo of the bulkhead before it was installed in the pontoon (as sown in the photo above). Installation is easy; draw a felt pen line along the center of the flange, line up the pen marks with the holes predrilled in the side panel, drill through and rivit together.

The thing on the floor (upper left of photo) is a trolley guide.


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PostPosted: May 27, 2007, 11:58 pm 
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I have an aesthetic question for y'all. It would be easy to make the lower bend on the pontoon skin a 3/4" radius instead of a sharp corner, and the aerodynamic penalty wouldn't be significant on a street car (or at least not very significant, what with ride height unsuited to ground effect anyway). Also, I think it will be easier for homebuilders to do the 3/4" radius (for a number of reasons). What I'm wondering is, visually, would it be better with a curved corner on the bottom or a sharp corner?

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PostPosted: May 29, 2007, 7:08 pm 
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If easier to build then it will likely turn out better for the builder which in the end will look better. A minor imperfection on a straight edge will show up much more than on a 3/4 radius.
Dale


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PostPosted: May 30, 2007, 10:45 pm 
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dale wrote:
A minor imperfection on a straight edge will show up much more than on a 3/4 radius.
Good point. And I suppose it's easy to get minor imperfections on the street with a low car. A fairly insignificant ding on the bottom of that curve could be a significant owie when the side of the car goes all the way to down to a straight edge. Thanks for the input.

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PostPosted: June 10, 2007, 6:27 pm 
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Ne'er let it be said that I'm unresponsive to advice. I made a pontoon curved on both edges (I guess they're not edges now, since they're curved) and hung it on a chassis with a couple rivets, and by golly, it does look nicer. Also, in keeping with my philosophy of if-there's-no-clear-preference-choose-the-easy-way, although it's easier for me to do straight edge bends, not every builder will have a 4' pan brake in their shop, so it'll be easier for guys working from plans to do two curves per pontoon than one curve one straight.


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