Modern-day Miura

[heinke]

I started fabricating the rear part of the front clip sub-structure, the part that runs transverse to the chassis. The main consideration was to provide good mounting surfaces for the two latch pins and provide good support for the vertical members to be located behind the front wheel openings. Given these considerations, I went with a forked design so that a vertical member could be placed just behind the wheel opening and another at the front clip rear edge.



To maximize cowl clearance, the transverse sub-structure members were bent to the adjacent body shape using a bottle jack pipe bender. I was able to check the shape for these against the station buck. An additional tube was located below the top longitudinal member to provide triangulation support.



Using the buck station for the front edge of the door, I created a cardboard template to verify the sub-structure is located within the body skin envelope.



Latch pin mounts are started but still require some tubes to be cut and welded to sub-structure prior to being complete.





I’m using the dual hood latches, cables, and hood release lever from the C4 Corvette. I might need to outfit the latch pins with lighter release springs as I want to be able to close the front clip by simply dropping it versus pressing down on the body skin. I won’t know if the Corvette release springs are too heavy until I get further along to find out how much front clip weight will be coming down on the latches.

There’s not much clearance between the sub-structure and the windshield wipers arms.



I purposely designed the sub-structure with this close fit as it needs to provide support for the body skin all the way across the windshield width. One of the next steps is to add a way for the front skin to be attached to sub-structure across the windshield bottom in a way that provides good support across this wide opening.

[heinke]

I finished the front grill opening hammer form and now the front clip station buck is complete.









More details are posted in the Miura buck thread here: http://www.allmetalshaping.com/showp...7&postcount=44

[cliffrod]

The shape looks great, especially the contours visible in the side view. Very cool.

[heinke]

I’m working on the area where the front clip intersects with the windshield. My high level plan is to use a hem joint to attach the hood skin to the sub-structure. This is the first time I’ve built out something like this, so my question is if a hem joint is the best way to attach a front clip skin to the sub-structure over an area that’s about 65” long in a continuous sweeping curve? In addition, any tips and tricks for building this type of sub-structure are welcome.





As you can see, the windshield wipers are hidden under the front clip when they park. This differs from original Miura in that it had exposed wipers mounted to an exposed cowl section. The cardboard taped to the windshield represents the gap I think will be needed for the windshield wipers to clear the front clip when in operation. I mocked this up with some buck stations for the door skins so I could visualize what the rear edge of front clip might look like if I built out the substructure up to that piece of cardboard and then hemmed the front clip skin over it.

Is there a better way? Or am I on track with best practices here? I’ve been scratching my head over this for about a week now and thought I’d seek some input.

[heinke]

Build out of the front clip substructure continues. I extended the framework with ¾” square tube as close to the windshield as possible and provide clearance for windshield wipers to sweep.



At least I thought my design would provide the needed clearance. Prior to welding it in place, I decided to do a clearance test.



Passenger side is good with about 3/16” clearance with wiper at windshield edge. Drivers side didn’t pass though as it contacted the new framework prior to completing its sweep.



Ah, windshield wiper pivot points are not quite symmetrical in location. I redesigned the framework on drivers side and it now has needed clearance.





Next step is to further extend substructure toward windshield with aluminum sheet to form shape for rear edge of front clip.

[Steve Hamilton]

Looking good Joel

Thanks for sharing your progress with us!

Steve

[Gojeep]

Thanks for posting Joel. Love following along.

[heinke]

I’m now extending the rear part of substructure with a flange made of .063” 5052 AL sheet to provide a flange to hem the hood skin over. The first step is to make cardboard templates to capture the sheet cut out shapes. I decided to construct this part of the flange from 3 pieces to be welded together.



The mount side edge was folded over on a break, pieces welded together and holes are being drilled for fasteners. Rivnuts are used in the aluminum frame and button head screws then fasten the flange in place.







The flange meets up nicely with the cardboard spacer taped to windshield. There should be plenty of space for the windshield wipers to sweep under the hood skin but I plan to verify it to make sure. Additional pieces will be welded onto the flange to extend it to where the front clip rear edge meets up with the doors. I’ll add these once the front clip substructure is fully built out along the front of door openings.

[heinke]

I decided to continue fabricating the front clip rear mounting flange toward the driver side door. In order to do this, it became apparent I’d need to determine the exact location for the front edge of the door. One of my lessons learned from my prior GTO project is that doors are complicated and thus really hard. And specifically the pocket located in front of the door needs to be placed and sized appropriately or bad things happen to the front part of the door when opened all the way.

The first step is door pocket lateral placement such that the door skin will have sufficient clearance to avoid contact with the rear edge of front fender when the door is fully open. The second step is to ensure the width and depth of the door pocket is sufficiently large enough that the front edge of the door skin won’t contact anything as it moves inward during door opening.

I had estimated the position for rear edge of front fender while fabricating the front clip framework. I planned to run a vertical tube straight downward from the rear part of the framework. So I needed to do a lot of mockup to verify the door pocket placement. A piece of TIG filler rod was used to simulate the rear edge of front fender. Steel rulers were taped to buck stations to simulate the door skin.



Sure enough, the door only opened about ¾ and the door skin was hitting the front fender. I had to move the door pocket forward by an inch to get the needed clearance.



With the lateral position of the door pocket now established, the next issue became apparent. The upper front part of the door hits a framework tube during door opening. My original plan was to run a vertical tube down from the framework tube that now needs to be cut out. I had to establish where a vertical tube could be placed and still have adequate space in the door pocket.



Re-work time. Time to break out the Sawsall and make some room in the door pocket.





I first mocked up the vertical down tubes as straight tubes. I could minimize the forward shift on the vertical tube in the door pocket by curving it. I decided to curve the front one as well to make more room for the wheelhouse. A final door full open test. The door skin clears and no obstructions in the door pocket.

I now have the door design past the first two challenge areas. There’s still lots more door challenges to overcome.

[heinke]

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.