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Thread: Modern-day Miura

  1. #201
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    Typically, the side view of a front door cut (inward swinging workout) is the same as the SECTION at that point. Also the cut line will be at a 45% angle from the hinge line in top view.

  2. #202
    Senior Member C5GTO's Avatar
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    Post Door Engineering Challenges (cont.)

    I was first referring to this topic as door design but it is not. It is really door engineering. The next challenge area in my door engineering is to ensure the front edge of the door skin doesn’t contact the rear edge of the front fender as the door is opened. On the Miura, the doors are fairly thick due to the large amount of curve in the skin so this is a very real challenge. The door skins for this Miura will be 1 ¾” further outboard than where the door skins were on the donor C4 Corvette doors. This puts the door skin 4 ¾” outboard of the door hinge pins with the door hinges mounted on the front door posts as did the C4.



    Compare this to the very outboard placement of the door hinge pins on an original Miura.



    The net effect is that the front of the door skins will hit the front fender edge on the top portion of the door skin that has a horizontal orientation and is outboard of the door hinge pin location. Here is a top down view picture with a blue cross showing door hinge pin location.



    The door skin inboard of the door hinge pin moves outward as the door is opened. The door skin outboard of the hinge pin moves inward during door opening. Here’s the same top view with the door opened.



    The part of the door skin with a horizontal orientation that’s under the TIG filler rod that simulates the fender rear edge is an issue. It will never clear unless the door skin and fender are on different plains by at least 3/16” (width of the hem joint on fender rear edge) plus paint thickness and clearance. As on most cars, the Miura fender flows to the door skin so the surface heights are the same. The fix for the issue is to relocate the door hinges outboard so the hinge pins are in a location much more like the original Miura. It looks like the hinges can be moved about 1 ¾” outward and now I need to engineer a means to do so.
    Joel Heinke
    Be original; don't be afraid of being bold!

  3. #203
    The engineering in this build is amazing! Fantastic Updates! Keep them coming!

  4. #204
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    I had done a post back in 2012 on hinging geometry and here is a link. http://www.madmechanics.com/forum/te...ms-primer.html
    I believe this may help. Look at #23 especially. With a thorough understanding of the geometry, you should be able to get a good solution. You may want to make a good mockup with cardboard skins to check it out but the 45% angle principle and a bit of adjustability on the hinges will serve you well. Good luck.

  5. #205
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    A suggestion... I would recommend getting a carpenters lazer (the kind that projects a true vertical and horizontal line on the wall, etc.), if you don’t already have one. Then you can set up the car accurately and level according to a good reference system – a Centerline, Fore-aft zero line and Height zero line. The first two can be lines marked on the floor. Setting the car on tires is not good – jack stands or some kind of reliable fixturing is much better. I know a lot of people who don’t get an accurate setup and are forever struggling. You will probably want a way to measure any point in space on the car, in terms of the three axis (length or X, distance out from the centerline or Y and height from some “ground” reference or Z). Set your zero points OFF the car so all measurements are positive. I have my lazer on a camera tripod so it can be easily cranked up and down.
    Once a project is set up and measurements are accurately repeatable, you will have a much better chance of success – as well as saving a lot of time duplicating anything on the other side. It is good to use steel balls and conical fittings (or some similar accurate indexing) to enable the car to be pulled from the setup yet accurately put back later. These should be attached to both the floor and the vehicle.

    To do a door cut design, you can create 8 or 10 inches of the body side surface at the cut line, with wood sections and white cardboard for the surface. It’s good if the cardboard is about the same thickness as the ultimate body skin - easy to do for a metal body. Locate the lazer at a 45% angle to the side (in top view) so that the line projected on your surface is what you want. With a 45% angle, the side view of this line will be the same as the section. If you make little holes in the surface, the lazer will point through to the hinge line inside the surface.
    Ultimately, as you weld/bolt in any hinges, the cardboard surface can be reestablished and cut for a fender and door part to test the clearances during door swing. The very bottom and top of the cut line can vary from the lazer line but the mid section is important.

  6. #206
    Senior Member MacGyver's Avatar
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    When I built my 430 I had the same issue. To get the Fiero hinges closer to the door skin. I used solid blocks of aluminum between the body and the stock hinges along with longer bolts. I think they are around 2 3/4" thick. I also put a plastic panel over the aluminum blocks within the door jamb to cover them up. My doors open and close fine and I have an even 3/16" gap all around the doors. There are probably some photos posted on my build page if you hunt around.

  7. #207
    Senior Member MacGyver's Avatar
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    Page 37 on my build diary shows the aluminum blocks. They are 3.25 inches thick. My body is very wide. Obviously, yours will not need to be nearly that thick. The trick is to mount the hinge as close as possible to the door skin.

    http://www.madmechanics.com/forum/bu...430-build.html

  8. #208
    Senior Member C5GTO's Avatar
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    Aflo: thanks for your technical insights on this subject. I don't have any technical training in the area of door hinges and thus tend to engineer by trial and error. It's good to understand the technical concepts at play so I can minimize the quantity and severity of errors

    I do have the chassis on blocks and shimmed to level. My garage floor is not level with about 3/4" gradation side to side on the car. I make measurements to the floor only from the drivers side as it's the "high side". All measurements everywhere else are relative to the leveled chassis. I use a digital level (with double digit precision) to level the chassis so I'm confident it's actually level.
    Joel Heinke
    Be original; don't be afraid of being bold!

  9. #209
    Senior Member C5GTO's Avatar
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    Quote Originally Posted by MacGyver View Post
    Page 37 on my build diary shows the aluminum blocks. They are 3.25 inches thick. My body is very wide. Obviously, yours will not need to be nearly that thick. The trick is to mount the hinge as close as possible to the door skin.

    http://www.madmechanics.com/forum/bu...430-build.html
    MacGyver: thanks for the information. It's good to know the issue isn't unique to my car/situation and I'm on the right track to resolve. Yesterday, I mocked up a 2 1/4" outboard shift for the hinge location. I didn't get it quite finished so I don't know yet if it fully resolves the issue. I might be able to shift the hinges outboard another 1/4" if needed but I wanted to leave a little bit of space between hinge and door skin. I appreciate seeing the pictures for how you did the offset and bracing, etc. My mockup is very similar so at least that's some confirmation my engineering isn't totally out in left field.
    Joel Heinke
    Be original; don't be afraid of being bold!

  10. #210
    Senior Member MacGyver's Avatar
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    Quote Originally Posted by C5GTO View Post
    MacGyver: thanks for the information. It's good to know the issue isn't unique to my car/situation and I'm on the right track to resolve. Yesterday, I mocked up a 2 1/4" outboard shift for the hinge location. I didn't get it quite finished so I don't know yet if it fully resolves the issue. I might be able to shift the hinges outboard another 1/4" if needed but I wanted to leave a little bit of space between hinge and door skin. I appreciate seeing the pictures for how you did the offset and bracing, etc. My mockup is very similar so at least that's some confirmation my engineering isn't totally out in left field.
    Good to hear your getting it worked out.

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