Bodywork Questions

[kelseydum]

I've only been doing bodywork for a few months. I read in a magazine just this morning to use etch primer to prevent corrosion. The only thing I've really used the epoxy primer for... and this is kinda cheating but I have a good teacher... is filling small pinholes and actually using it as a sort of bondo. Lay it on thick and block it out. I still need to learn more about all the chemical and the chemistry side of this though. Hope this helps any?

 

[freakdude]

I've only been doing bodywork for a few months. I read in a magazine just this morning to use etch primer to prevent corrosion. The only thing I've really used the epoxy primer for... and this is kinda cheating but I have a good teacher... is filling small pinholes and actually using it as a sort of bondo. Lay it on thick and block it out. I still need to learn more about all the chemical and the chemistry side of this though. Hope this helps any?

Yeah man , thanx!

 

[rustbucket49]

Well, latest update on the grinding operations....

The shrinking disk came in and I've been playing w/ that somewhat.... However the lows still need hammer and dolly work. Will keep farting around with that....

Also, it's amazing how different advise can be from person to person. I was told to stick w/ higher grit (not less than about 60 or 80) when grinding welds somewhere down the line. Other guys (you smart cats on RRR) say 24 or 36 grit or the hard grinding disks. The latter makes more sense to me - courser grit means less time involved working the area which means less heat. I tossed the flap wheels at suggestion of you guys and went w/ the grinding disk - WHAT A DIFFERENCE!!!! You can knock down a weld real quick and w/ minimal effort and minimal heat build up w/ the grinding disk. I plan to finish off w/ the 24 or 36 grit flexible disk and see how that works out. Hopefully that will reduce the freaking warpage.

Live and Learn....

 

[roddguy1]

That's right Rustbucket, it's all about limiting the heat. When it comes to knocking down welds I start with a 24 grit grinding wheel. I never try to get it all at once, but rather moving around taking a bit at a time, and allowing it to cool. I'm also very careful to limit taking any metal from the adjacent metal by staying literally on top of the weld itself. Once I'm happy with that I smooth it with 80 grit on a 6" DA sander and done.

Here is an example of how important it is to limit the grinding heat. I once filled a roof section for a guy on his Dodge coupe that had a sunroof cut into it back in the 80's. It was all in but I only had time to grind down half of it. Which was perfectly smooth and ready for a light filler coat. When I got back two days later the owner had taken it apon himself to grind down the other side. Well what a mess. He heated it up so badly that it had sunk as much as 2" at the worst point. Plus he had taken out so much metal from the surrounding area that it would have cracked had I tried to work it back up. To say the least I was ****ed. So without saying anything at first I asked him to pay me for the work, which he did, and then I told him he was on his own.

I later found out when I went to use my electric grinder again that he had worked it so hard the brushes where burnt out. I can't imagine how hard he must have been pushing to accomplish that.

 

[rustbucket49]

RodGuy, yeah that sunken metal you're talking about is what happened to me - I really didn't think I was getting it that hot, but I must have spent too much time on it too quick.... Now I have to hammer it back out in a few spots..... I was ****ed to say the least too !!!!

So would you happen to have a photo you could post of how the weld looks at the point where you switch over to the 80 grit on DA?? I presume you lose some control staying on the weld itself when you go to the DA??? Is that an air powered sander or electric? -just curious on that..... a picture would be beneficial to me to see how much metal you're taking off before switching over to the finer grit DA.

 

[roddguy1]

I looked through all my build pics and couldn't find anything that would really illustrate what you want to see. So, I'm working on the scuttle top for the MG today and I'll do up a detailed series of pic to help you out.

 

[rustbucket49]

Rodguy, I am officially requesting a name change for you to "RodGod". I am really thankful to you and the other experts on RRR for helping a numby like me. I got through welding up my trunk lid and used a hard grinding wheel on 4.5" grinder to flatten out the welds like you, Superman Hoitink and several other dudes recommended. Then I switched over to an 80 grit on an electric random orbital. HOLY COW!!!! - unfreaking believable!! Smooth as silk!!!! You cannot see or feel the weld bead !!! You build up very little heat w/ the RO sander. I will however need to use a little filler in places because I didn't match the curvature in a few places (plus my welding sucks), but not a lot. I had very little warpage and will only have to do some metal work in a few spots. I can see how a real metal man who knows what the heck he's doing can do this w/ no filler - particularly w/ a TIG or O/A. I am ecstatic how it turned out for a first time attempt.

I will never use one of those flap wheels again - the difference in the method I was using and the method RodGod (and others) proposed is like night and day - works like a champ. Thanks again. I will have more questions I'm sure !!!!!

I plan to post some pictures hopefully tonight of my current progress on my '49 build thread.... A few of welding and post-grind / pre-filler.

 

[Boltbreaker]

I'm still doing some "investigating" into proper grinding on sheetmetal. This thread issuper helpfull. Thanks to everyone for taking the time to explain it.
Now maybe I wont screw up the bed panels I just welded.