57 Chevy Convertible Top Frame

More of an art than a science - discuss metalworking and welding here.



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Posts: 945
Joined: Mon Jun 20, 2011 3:58 pm
PostPosted: Sun Aug 02, 2020 9:51 am

I had some extra Tri 5 chevy convertible top metal frames and decided its time to do something with them.

Of course you can get reproduction top frames, but they are made in China using Chinese steel. The experience I have with imported steel has been with tri-5 body panels and I have found them to have less strength than original equipment, even though being the same gauge steel.

The highly respected parts vendor and restoration shop "East Coast Chevy", does not recommend the imported one piece full floor for tri-5 convertibles, they recommend the two piece floor pans made in USA, even though the imported is one piece, has all the braces, fits good, and its the same gauge steel.

All of the convertible top frames that I have messed with have had some kind of problem, quite often bent metal, and that's metal made in the USA over 60 years ago--the good stuff.

The conv top side rails get in a bind sometimes, but it never happened to me so I'm not sure what causes this. The rails are made of (.060) 16ga steel, and they are connected with 1/4" cast iron brackets, so if something has to give, its not going to be the cast iron.

You can see it in this picture, the rail on the right shows the damage from such a bind. The cast iron hinge is pulled away from the rail on the right which will make it sit higher in this photo, but lower as installed in the car.

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Some guys might think its an adjustment issue.

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I wanted to remove the cast iron hinge and straighten the sheet metal, but the factory welded it in a way that made that really difficult, so since I had extra parts with good ends, it was just a matter of cutting the bad end off of a nice rail and weld on another good end piece. So I really gave this a lot of thought, as far as how to make the cut so as to then be able to get it all back together in the right place.

With the shape of the top side rails, its impossible to lay one on top of another to make a cut line. I thought about making jigs to help line everything up, but that would be after the fact, then the right thought came to me---the metal chop saw. Some wood was placed in the bed of the chop saw for the flat area to rest on, and some space left for the hump to drop into, then slightly clamp it so its straight, and vice grips to hold it to the bed of the saw.

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Then it was just a matter of cutting the two rails to be spliced at the same spot, so I called Sherwin Williams to see if they had a (stop) that would work, and this is what they sent. Its simple and it works fine. 8)

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A spacer on one of the cuts compensated for the saw blade.

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That gave me a zero gap joint, and perfect alignment.

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Welding was done with a mig welder. Starting the first tack without gas. :rolleyes:

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This one was done the same way.

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The header bow on the top frame is held on to the side rails with two bolts on each side. One just goes through two holes and then takes a washer and nut, but the other one has a blind nut in a cage. If that bolt has any corrosion at all, the nut cage isn't strong enough to hold the nut. So the spot welds were all drilled out to get to the nut cage, then it was also drilled out.

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The welds were cleaned up, the cage straightened, and a new stainless steel bolt and nut replaced the original. I have some high temp paint to use on the inner areas before welding the parts back together that will with stand the power coat oven heat.

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To reassemble I have a Hobart HSW 15 portable spot welder, so I like to fill the holes and use it. I've read bad reviews on these small spot welders, but this one works awesome, I actually held the trigger too long here, it almost burned through this (.036)20ga clip.

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As well as even the (.060)16ga rail the clip was spot welded to. The hole next to the spot weld is for the weather strip, which may or may not line up with the new weather strip.

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To remove the factory spot welds in a way to put the same parts back together, I have found it a lot easier to drill a 1/16" hole exactly in the middle of the spot weld. It locks the pin of the cutter in to make a perfect 5/16" (or 10/32") hole, the same size as the cutter. I used a Roper Whitney punch to get an 11/32" disc of the same thickness, and drilled the hole 1/64" larger than the disc. The step drill bit gives me a nice round 11/32" hole, and the twist bit takes it the last 1/16" over.

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The disc fits perfect, and after flattening the peak with a hammer and dolly it will fit tight and lay flat. All the disc plugs are the same size, so I can punch them all out at one time, then the whole process goes fairly quickly.

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With a tig welder, it takes 5 seconds to go all the way around without filler rod. The weld sinks a little, but I'll be using a little filler in the rust pits else where anyway. I'm getting this powder coated so I have to use JB Weld as a filler because of the oven heat.

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Back side shows full penetration

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The hole is for the weather strip screw.

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Polished stainless steel bolts were made to replace the original rusty bolts, which had a coating mismatch of either chrome, zinc, or paint. The bolt heads are sanded, but not polished yet.

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Space is tight for some of the bolts, so they used smaller slotted heads, instead of the larger hex head.

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Just a small sampling of the different type bolts, and some originals. I didn't run the threads as far as the factory, because the bearings were running on half threaded part of the factory bolts.

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These dome hex head were the most difficult to make.

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The reproduction bolt kit uses zinc on the bolts, and they have brass flange bearings. My research didn't turn up any brass bearings anywhere on the net, they were all made of bronze, and bearing bronze was favored for low speed bearings. The holes for these bearings are somewhat worn after all these years, so I made all the flange bearings to fit the holes. Not one by one, I just made a bunch of them in various over sizes, then picked each one from there to fit the holes.

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All of the bolts also had a three wave washer that would allow parts some side movement, but the reproduction bolt kit wave washers are way too heavy for this application, and they are not even wave washers they are curved washers. I was finally able to find the correct ones on line.


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PostPosted: Sun Aug 02, 2020 11:17 am
Amazing workman ship, :worthy: fantastic editorial too I might add! :goodjob:

I used your idea with the Hole punch and a Step drill too repair all the Spot weld cutter holes I cut into my tail panel on my Fire Bird project works like Magic when combined with a Tig welder.
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



No Turning Back
Posts: 945
Joined: Mon Jun 20, 2011 3:58 pm
PostPosted: Sun Aug 02, 2020 4:21 pm
Thanks Dennis. Actually, I got that trick from a Ron Covell video, although I have refined it slightly. :bighug:



Top Contributor
Posts: 5245
Joined: Tue Sep 16, 2008 1:17 pm
Location: Pahrump NV.
Country:
USA
PostPosted: Mon Aug 03, 2020 5:00 pm
I have to get some of his videos!

I still haven't sat down and watched that one you suggested for the Lead, been kinda waiting till I start on the project that I plan to use the lead on. But its here!
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Tue Aug 04, 2020 7:32 am
Very nice repair, well thought out, well executed!

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PostPosted: Tue Aug 04, 2020 8:50 am
Thanks for posting. A great job and well documented.
1968 Coronet R/T


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