1949 Cadillac Roadster Build

[lots2learn]

What filler rod are you using, 308L? Tig or Mig.

[kcoffield]

Originally Posted by Jack 1957

.....Next, I made 4 foam patterns for the grommets that hold the rear backup sensors. These will be cast in aluminum and polished but I'm not going to have them done right away. The last pieces I'll need cast are two pedestals or perches for the side view mirrors. I'll mess with those when I've finished the bumper.

Those should be easy. (famous last words)


Will look forward to seeing those Jack. Keep up the good work.

Best,
Kelly

[Jack 1957]

Along with being a battle of wills, welding this bumper up will be an exercize in patience. I decided to start with the outer corners because there is more shape in these areas than in the center. crown and bends will help minimize warping and distortion.
I am going to weld a variation of a flare bevel and a lap joint (more of a lap joint) along the edge of the sheet where it meets with the tubing. The lap needs to be built up large so that when I grind it smooth, I don't have to start grinding into the sheet.
I picked up some heat sink paste to further swing the odds into my favor. I am really impressed with this stuff. I was laying down oversized beads about 4" long at a time and there was no heat warpage... NONE.
It is reusable but I wasn't taking the used stuff off and putting it on the next stretch. I was using fresh paste on each stretch. I don't think the paste itself does much to disipate the heat. I think it's more about the amount of water this stuff can hold. While welding I can hear it sizzling off and I can see a little steam but nothing to worry about. I didn't see any smoke that might contaminate the weld.
When I used all the fresh paste, I put it all back in the can and added a couple ounces of water then stirred it up and it was good as new.











I started grinding some of the welds to see how it was looking. In the first picture below you can see a couple pits and undercuts (Circled).
I'll need to reweld and smooth those out but nothing to be concerned about. I'm also getting a lot of spatter and I'm not sure why. I might be too hot but I need the heat to move along at a fairly quick pace. I am using Supermix Argon/ CO2 mix. Probably not ideal for stainless. I'll have a lot of cleanup work to do on this without adding spatter to it if I can avoid it. I think I'll pick up some anti spatter spray.

[Jack 1957]

I went out to see my friend Jim that was welding up the casting flaws on the tail lights. I took the rear bumper with me. Jim's an excellent TIG welder and I have a lot of time into the bumper already. I didn't want to risk making garbage and having to start all over again.

The tail light housings didn't take too much time, but the bumper took most of the day. 10AM to 3PM.



We started the welding process on the outer corners of the center section. I was setting up the heat sink paste and helping with that while Jim did the welding. He would do about a 2 to 3 inch bead, then move to the other end while the first one cooled off. I think he said he was using 308 fill rod.
After each series of 4 beads done in X shape order, I would strip off the heat sink paste, add some water to it and apply it to the next areas moving toward the center.



Once the outer edges were finished we adjusted the gaps between the center panel and the inner curved sections. I tightened them up with a hammer and dolly and he welded them up. Last was the license plate recess. Same process on a smaller scale. Before he started this recess, we discussed the likelihood that the corners would pinch in and between the two of us, we couldn't come up with anything to avoid it that we haven't already done. As anticipated, they did pinch slightly but much, much less than I thought they would. They'll easily bump out from the back side. The heat sink paste really is helpfull. I was putting down strips about 2" wide, 3/8" thick and setting it very close to the weld. Maybe 1/2" away.

Overall, I'm very pleased and relieved with the results. I was having nightmares worrying about what I would do if I screwed this up beyond repair. So, many thanks, Jim. I'll sleep well tonight.
In the pictures below, you can see that there is almost no heat warp or distortion anywhere except the corners of the license plate recess. I can have this smoothed out and ready to grind in a couple hours. I had Jim build all the perimeter welds up proud so I wouldn't be grinding into the sheet to form the radius where the sheet and tubing merge.

There are going to be some parts of a project that a beginner might be nervous about attempting for the first time. The considerations should be; What have I lost if I fail? Is there another way to do it with less risk of catastrophic failure? How deep into it are you (time and expense)? Where can I get good reliable advice? If I do fail, what method would I used when I remake the same part? Can you use that method now? Should I get help and learn from your helper?

If it's a small part, I'd say go ahead and try. But if you have a lot of time and money invested and you won't be able to salvage any of it if you fail at one step, get some help or good advice. Rethink your method. Try what you're thinking of doing on some scrap. Most likely, whatever you're doing has been done by someone else, find him! NEVER GIVE UP!
The decision I made to let an expert welder tackle the riskier part of this was based on the fact that I readily admit that I'm not that good of a welder, I don't have a TIG, and I was heading out to Jim's to pick up my tail light housings anyway.
If you do decide to get help from someone with advanced skills, try to be there for the process to watch what he does and how he does it. Ask questions. There's no shame in getting help when needed.

[Gojeep]

I'm relieved for you Jack and glad it is all working out.

[blue62]

the bumper is looking really nice Jack Bravo
I wasn't expecting anything else though

[Jack 1957]

I cut the casting gates off the tail lights so I could check the fit. They are good so I rough ground the welds and let them set for now. I need to finish the bumper first.





I did the first of many rounds of grinding on the bumper. I knocked the welds down with 40 grit discs and bumped the low spots up. It still looks like dog meat but it's getting there.
There wasn't much planishing to do, it was pretty smooth already.. Next step is to fill in a few low spots (circled) with weld and knock those down, then another round of grinding with 80 grit, and on, and on...

[Steve Hamilton]

Jack the tail lights and bumper look really nice!
Thanks for sharing.

Steve

[123pugsy]

Very nice Jack.

[Jack 1957]

I welded up a few low spots and ground all the welds. Next I used a DA sander with 80 grit to start smoothing things out. I had to bump a few low spots up also.
I still have two larger areas to build up with weld. They're at the outer corners on the bottom where the panels meet the lower tubing. That should be the last of the welding.
By the way, go back to the previous page and look at the second picture in post #1167. What's wrong with that picture???? Why didn't anyone catch it?