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  #191  
Old 10-01-2019, 12:18 PM
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heinke heinke is offline
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Post Door frame alterations

I switched tracks a bit to working on the doors. Before I can continue building the front clip sub-structure I need to know the size and location measurements for the vents located on top of hood. I need these measurements as I plan to run sub-structure members around the vent edges and thus provide mount points in the middle of the front clip skin. It’s going to be a couple of weeks before I can get the needed vent measurements so I went to the next item on my build list which is the doors.



The doors relate to the front clip in that they are adjacent panels but on the Miura there is also a common rocker panel, silver in the rendering above, that extends from the front wheel opening under the door all the way to the rear wheel opening. So it will be important to know the exact rocker panel height and thus where the top edge of this rocker panel will be under the front clip. The door bottom is the main constraint on rocker panel height and the door bottom is constrained by door hinge location and side window lift location.

As a reminder, I’m using the door frames, hinges, and side windows from a 1991 C4 Corvette. The Corvette doors are taller by 5 ½” than what I need for the Miura. So I need to remove the bottom 5 ½” from the donor doors and bring the bottom, rear corner forward by 6 ½”. The two main impediments to doing this is that the electric window lift mechanism needs to be shortened and the bottom hinge moved upward. Here’s a door with the new size marked in masking tape and a mock-up of the shortened window lift.



So now I needed to move the bottom door hinge upward by 1 ¾” as it is located too low in the donor door. The main limitation for a new hinge location is the wire harness routing to the door via a rubber boot. By relocating the bottom hinge to snug up under the oval boot hole, it will be real close to providing space for the 5 ½” door chop. Even if I can’t get the full 5 ½”, I decided it was better to have the rocker top edge a fraction of an inch lower than to completely re-do the door pillars.

The door hinges use 3 bolts that screw to the door pillars via a cage nut plate. The cage nut plate is located on top of a heavy L shaped reinforcement plate spot welded inside the door pillar. By drilling out the spot welds, I was able to save and reuse all the hardware.



The bottom 3 square holes are the original hinge location and the top 3 square holes were cut out for the new hinge location. The reinforcement plate was rosette welded into the new position via the open holes and a sheet of steel placed behind the remaining holes and rosette welded to seal everything up.



The door frame was easier as I was able to just drill some new holes through it for the new hinge location.



Here it is with hinges and wiring harness boot back in place. It’s tight but should work fine. I can now start cutting away at the lower door frame.
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  #192  
Old 10-08-2019, 09:31 PM
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heinke heinke is offline
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Post Door frame transformation

The next step in the door frame transformation was to bring the bottom rear corner inward by at least 6 ½”. C4 Corvette doors are composed of a spot welded sheet metal frame that’s bonded to and sandwiched between a plastic inner door panel and a composite door skin. I’ve already peeled away the outer door skin so only the inner panel and door frame remain. This close-up shows the Miura door skin edge outlined in masking tape over the door frame to indicate places requiring modification or removal. I don’t plan to use any of the plastic inner panel in the final Miura door so I will be cutting it away in pieces when access is needed to the metal door frame for modifications.



I first drilled out the spot welds between side impact channel and rear of door frame. I then made a pie cut below the door latch mount point to straighten an angled section, sliced off about 6 inches of the plastic inner panel and bent the rear edge of the door frame forward. At this point everything inside the door is now in close quarters. I had to remove some gusset material inside the door frame rear edge to provide clearance for the side window to be lowered. After a few rounds of trial fitting the door and side window in place and measuring everything multiple times, I put in a few tack welds to hold the door frame together in the desired shape.



The long end of the side impact channel will get cut off once I’m sure about the modifications and it’s ready for final welding. Part of the verification process is making sure the side window glass won’t be touching metal when it’s fully retracted and when being raised. I thought the angled corner shown in the following picture had insufficient clearance and wanted to do something about it.



I’ve been told that tempered glass cannot be cut and side window glass is tempered. I could compromise by taking away some of the door rear edge angle and thus free up some space inside the door frame. Alternatively, if I could just remove about ¾” from that corner of the glass I could get the needed clearance and keep the Miura signature door rear edge swooping angle.

My son does lapidary (stone cutting, shaping and polishing) for a hobby. He has some nice industrial diamond tooling for shaping stones which turn out to be just about the same hardness as tempered glass. Specifically, he has a motorized grinder/polisher somewhat like a bench grinder but it has diamond encrusted wheels the coarsest being 80 grit. I figured what the heck; let’s give it a go, the worst that could happen is we’d end up with a bunch of shattered glass. Well it turns out you can fairly quickly grind away tempered glass with the right tooling.

This same window corner was also making for a clearance challenge when the window is partially retracted with that corner in the door latch area. My first thought was to use a narrow “bear claw” latch to avoid the clearance issue. This would work but I’d much rather used the wider OEM Corvette door latch because it provides for external and internal door lock to latch interfaces. It turns out that with the window corner ground away; the door glass now just clears the Corvette door latch. It’s tight enough that I think some thin nylon shielding might be needed to ensure no glass to metal contact but I think it will work.



My final check was to mockup the door rear edge in cardboard.



It’s looking good! I need to have at least a ½” flange on the door frame in order to clamp an aluminum door skin to it. I plan to encase the door frame in aluminum sheet and the flange will be part of that. So here’s my final check to see if there’s adequate space for the flange. It looks like it.



More to come on door frame transformation…
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  #193  
Old 10-09-2019, 03:59 AM
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Gojeep Gojeep is offline
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That is great Joel and glad the door glass could be ground as well. Was it kept cool with water while doing it as have heard that helps a lot to stop it shattering?
You had good luck with keeping the original latches afterwards too there.
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  #194  
Old 10-09-2019, 06:10 AM
cliffrod cliffrod is offline
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Very impressive, Joel. I appreciate seeing the unseen & all that's done to make it functional.

I'm also curious about more info about grinding glass. I understood the grinding wasn't as much of a problem as the creation of minute scratches/fractures minute stress risers during the grinding, which will likely lead to larger fractures & overall failure at a later time. Did you polish the ground edge after grinding to help address this possibility?
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  #195  
Old 10-09-2019, 10:13 AM
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heinke heinke is offline
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Quote:
Originally Posted by Gojeep View Post
That is great Joel and glad the door glass could be ground as well. Was it kept cool with water while doing it as have heard that helps a lot to stop it shattering?
You had good luck with keeping the original latches afterwards too there.
Hi Marcus: yes, the lapidary machine has a water cooling system and we used it while grinding the glass. I'm very glad the original door latch can be used as well. I found the locking mechanism on the last set of bear claw latches I used to be overly simplistic and still required quite a bit of engineering on my part to make it work.
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  #196  
Old 10-09-2019, 10:20 AM
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heinke heinke is offline
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Quote:
Originally Posted by cliffrod View Post
Very impressive, Joel. I appreciate seeing the unseen & all that's done to make it functional.

I'm also curious about more info about grinding glass. I understood the grinding wasn't as much of a problem as the creation of minute scratches/fractures minute stress risers during the grinding, which will likely lead to larger fractures & overall failure at a later time. Did you polish the ground edge after grinding to help address this possibility?
Hi AC: I haven't polished to ground edge yet but plan to once I've completely verified that more clearance grinding won't be needed. Yes, the 80 grit diamond wheel does leave a small bit of chipping on the very edges of the ground surface. I seem to recall that Jack used a DA sander with fairly common sandpaper to polish the edges on his cut down windshield. I'll probably try that first and if the tempered glass is too hard for that then it would be back to the lapidary machine with a finer polishing wheel.
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  #197  
Old 10-09-2019, 11:15 AM
cliffrod cliffrod is offline
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Quote:
Originally Posted by heinke View Post
Hi AC: I haven't polished to ground edge yet but plan to once I've completely verified that more clearance grinding won't be needed. Yes, the 80 grit diamond wheel does leave a small bit of chipping on the very edges of the ground surface. I seem to recall that Jack used a DA sander with fairly common sandpaper to polish the edges on his cut down windshield. I'll probably try that first and if the tempered glass is too hard for that then it would be back to the lapidary machine with a finer polishing wheel.
As a substitute for wet/dry fine grit sandpaper, I use DMT 6" diamond whet stones like these- https://www.sharpeningsupplies.com/D...iABEgJ9j_D_BwE.
I got three (I believe the equivalent of this set) in a larger lot of tools years ago. They are very handy for appropriate finishing jobs- as easy to keep wet as traditional paper, they eliminate the paper/backer issue and being rigid helps avoid stray scracthes like flexible sandpaper can sometime do. Not as cheap as a few sheets of paper, but they last very well. I've had mine for at least a decade and am very happy with them.

Good for your knives, too. I restored the proper bevels on my Beverly Shear blades with them- slow going but excellent results.
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  #198  
Old 10-12-2019, 10:52 PM
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heinke heinke is offline
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Post Too much of a good thing

So I was taking another look at the clearance between the now trimmed side window glass and the door latch. A thought occurred to me that if I just removed another 1/8” it would provide a good safety margin of clearance space. So I pulled out the side glass and took it over to the lapidary grinder/polisher. I’m grinding away and … I think you can see where this is going and should have left good enough alone.

Well, I can now speak from firsthand knowledge that tempered glass is very stable until it isn’t. It can be instantaneously explosive! One second you have a full pane of glass in your hands, the next second your hands are holding air and the tempered glass is now thousands of shards spread across the work area blast zone. I guess the good news is that I didn’t get cut by all that flying glass.

I do know what I did wrong, I think. I think the grind contact zone got too close to the edge of the diamond wheel. My son says he stays away from the wheel edges as the diamonds there can “grab” a stone out of your hands and basically trash it. I think either the sharper diamonds or maybe the wheel edge itself started a chain reaction fracture that blew-up my glass.

The other good news is that I was able to find a matching set of C4 Corvette side windows on eBay for $160 shipped. So this learning opportunity cost me something, but it’s really not that expensive of a lesson, yet. Cross my fingers that I can grind that corner off the new glass without an explosive outcome
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  #199  
Old 10-13-2019, 04:08 AM
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That is a shame but all been there many times before. So many 'just a little bit more' ends up far worse than if you have left it. Very character building that is for sure!
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  #200  
Old 10-13-2019, 12:19 PM
cliffrod cliffrod is offline
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Glad you're ok Joel with no injury from flying glass. Good luck with the next one.
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