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  #151  
Old 07-22-2017, 08:44 PM
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heinke heinke is offline
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Quote:
Originally Posted by Charlie Myres View Post
Yes it will! Any two dissimilar metals in contact when wet, will start electrolysis.

If you put a thin film of silicone rubber between the two when they are joined, it will prevent any electrolysis.

Nice work on the car; it is one of my favourite reads!

Cheers Charlie
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Originally Posted by AllyBill View Post
If you put a thin film of silicone rubber between the two when they are joined, it will prevent any electrolysis.

Better still, use an aerospace-grade polysulphide and you'll never have to look at it again.

Will
Charlie and Bill: Thanks for info! I stand corrected and will make sure I put some material between these metals to prevent problems.
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  #152  
Old 07-22-2017, 09:03 PM
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Post Making GTO trunk lid (cont.)

I’ve made more progress on the trunk lid by completing the AL 3003 frame for attaching the trunk skin. The first step prior to starting on it is to adjust the square tube SS frame to the proper height. I adjusted to make sure there was at least 3/16” gap between this frame and where the top of the trunk skin would be. I’m using .063 sheet for both the skin and the mounting frame so these together gives 1/8”. The extra 1/16” is to make sure the skin would only contact the mounting frame at the very outside edge.

Checking frame spacing with 3/16” round rod and ruler simulating where the top of the skin will be.



Next was to mock up mounting for the trunk latch. I built a bracket from SS sheet that will add extra support under the trunk skin and hopefully keep the trunk skin from warping if someone presses on the latch to close it. I also made up a latch catch from piece of rectangular tube. I’ll cut this catch down and make it look nice later.



Now for the skin frame itself. I started with the longest section which is at the bottom of the trunk lid. This was cut to fit the trunk opening and have ¾” to fold down on inside of the mounting frame.



Next was the top of skin frame. I had to first eliminate all the “C” clamps temporarily holding the frame to the hinges. I made some screw plates, cut slots in the square tube to insert them, and mounted the frame to the hinges with some ¼” screws. Notice the bottom skin frame now has the inside edge cut and folded. The fold line is curved so I did the fold on a combination of bead roller tipping wheel and power hammer flanging dies. I also had to shrink the folded edge so it would fit the curved horizontal plane for the trunk lid. I’m purposely keeping the join/weld lines away from the corners as I want these in low stress areas.



The right-side piece joining top and bottom is welded in and now I’m making a cardboard template for curved portion of skin frame. I decide the best approach for this piece was welding in the flange around the curve.



Here’s the sheet for curved portion ready to tack in place. I’m able to tack the pieces in place using the SS frame to hold them for a close fit.



And now here’s the skin frame all welded, trimmed for fit to SS frame and metal finished.

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  #153  
Old 08-01-2017, 02:09 PM
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Post Making GTO trunk lid (cont.)

A progress update on making of GTO trunk lid. Now that the frame is fabricated, it needs some small adjustments prior to fitting the skin. First is it needs to be leveled such that the outside edge is 1/16” below the surrounding body surface. The skin is 1/16” thick. I do the leveling by hand and use a piece of .063 thick scrap as a guide.

Once the edge height is set, the edge gap needs to be set. I’ve decided to shoot for a 1/8” final gap around the trunk so a 3/16” gap is needed for the frame. I use the sharp points on a caliper to scribe a mark for 3/16” gap prior to cutting with aviation snips.



The last bit of preparation prior to starting on the skin is to polish the frame. The car’s interior is polished aluminum so this lead me to do the underside of the trunk lid as polished as well. Truth be told, I hate polishing metal. It’s a laborious, dirty task that takes a lot of time. But I do like the look when it’s done.



Now on to making the trunk skin. I started by making some surface templates from ¾” wide 20-gauge steel as guides for the crown and arrangement. This is a technique I had learned from Lazze.

I cut the Al alloy 5052 sheet and added a low crown using the Ewheel. When I bent the skin into arrangement and looked across the surface, I could immediately see issues in the form of 3 good sized high spots. Not good.



I first tried removing the high spots using a leather faced flat wood slapper over a sandbag. This didn’t work due to the large size of the high spots and the skin had already work hardened. Next I tried hammer and dolly using off dolly technique. It worked some but it was clear the metal needed to be annealed before it was going to move much using that technique. So, I decided to try a shrinking disk. This put a good amount of heat into the metal but galled the surface badly. It didn’t remove the high spots either and was doing more damage than good. I decided that a shrinking disk is not good for use on aluminum.

After thinking about it and recalling the physics at play as described by Lazze when I took his metal shaping class years ago, I came on another approach to remove the high spots. It’s not intuitive as it involves using the ewheel and metal stretch. The concept is that metal with a compound curve consists of metal surrounding the compound curve that forms a “frame”. The sheet metal inside the “frame” is raised up to form a curve because it is constrained by this “frame”. If the metal forming the “frame” is altered this will affect the shape of the metal inside the “frame”. For example, if the metal in the “frame” is stretched, the curve of the metal inside the frame will be reduced because there is less constraint holding in the shape.

Now to test the concepts on my warped skin. I carefully wheeled the metal around the high spots making sure to not also wheel on the high spots. The high spots disappeared. It worked! With careful, low pressure wheeling the skin was starting to look good again and I could clearly see that it could be rescued.

I however decided to start over with a fresh sheet given the galling/gouges left from the shrinking disk.



For my second attempt, I decided to use a different approach to this very low crown skin. I decided to bend it into arrangement first and then add the shape. This is reverse order from my first attempt. This seemed to work better as I could frequently check the shape with the templates and focus the wheeling to only where it was needed.







I got the skin shaped to match the templates on my second attempt and gave a sigh of relief. It was time for final trimming before attaching the skin. I had left an extra ½” around the edge that needed to be trimmed off. Just to be sure, I re-checked the shape with the templates after trimming. The arrangement was still there but a good part of the crown was gone. Ah, the ½” that I had cut off was acting as part of the “frame” and I had altered it. Oh well, more wheeling and I had the desired crown back in the skin.

Bottom side of skin with flange turned, ready to attach.



That’s it for now.
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  #154  
Old 08-01-2017, 05:25 PM
Charlie Myres Charlie Myres is offline
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A brilliant explanation about the high-spots Joel!

Thank you for sharing,

Cheers Charlie
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  #155  
Old 08-01-2017, 08:33 PM
crystallographic crystallographic is offline
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Staying on your toes, Joel, and dealing with the curveballs as they come across the plate - good going!
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  #156  
Old 08-02-2017, 08:20 AM
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Great details on your process.
Did you find any change in crown after you turned the edge?
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  #157  
Old 08-04-2017, 07:10 PM
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Quote:
Originally Posted by blue62 View Post
Great details on your process.
Did you find any change in crown after you turned the edge?
Dave: good question. I didn't experience any change in the crown from turning the flange on the edge. There was however some change in arrangement until I used the shrinker on the flange to put the arrangement back. This was expected and what happens when a flanging a curved piece.
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  #158  
Old 08-04-2017, 09:57 PM
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Post Making GTO trunk lid (cont.)

The GTO trunk lid is now complete. I got it 90% complete and then had to step away for a few days to help at Boy Scout camp for my son’s troop. I’m back, recuperated and finished up the trunk lid.

Here’s the detail. First, let me give some context. This trunk skin is a very low crown panel. I already talked about the challenges in shaping the skin to achieve this crown. What I didn’t talk about is that there were several things along the way giving me doubt about how well this would end up.

Firstly, as I was annealing the edge prior to flanging, the skin would oil can and loose the crown just from heating an edge section. After the heated section was quenched, a small press on the skin backside would “pop” the crown back in place. While I understand the physics at play, having a piece of metal continually pop out of shape doesn’t instill confidence.

Secondly, while installing the skin, it oil canned many times losing the crown. Again, a small press on the backside and it popped right back in place. I finally set a sandbag on the backside middle to keep the crown from oil canning while I was installing the skin. Again, the fact I needed to do this did not instill confidence.

Hammering the flange over to close the hem was mostly straightforward. I started in the middle of the long sides and worked out to the corners so I wouldn’t trap any metal. The inward curved section that goes around the fuel opening was different though. I couldn’t just flange it to 90 degrees, anneal, and then close the hem. It would have required a big shrink and then re-stretch to do it that way given the inward curve in this section. I decided to do it in a continuous/flowing roll to keep the arrangement as close as possible.





Then the hem was closed out at the bottom corners.



The trunk lid fits great and the gap came out nice. I had to do some hammer and dolly work for edge height adjustments but I was able to match the surfaces all around.



The skin came out smooth with the desired crown. Once the trunk latch was installed, the underside latch support bracket prevents the crown from oil canning out. I didn’t have a lot of confidence but it seems to have turned out fine in that regards.



I do like how the trunk lid underside turned out as well.



There were some challenges with this one, but all’s well that ends well
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  #159  
Old 08-05-2017, 05:41 AM
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Looks great Joel.
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  #160  
Old 08-05-2017, 08:28 AM
blue62 blue62 is offline
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your doing some amazing work there Joel.
Keep it up and keep the posts coming.
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