Rust repair

Classiccanuck

Classiccanuck

Senior Member
I had body sandblasted and epoxy primed, there are a few small pin holes that came up after blasting, I've tried to weld them using a mig welder (I'm a newbe at it) with a bit of success, is there anything else I should try or use?
 
Its tough to weld to something that's not there. You may have to cut back to solid metal and make a patch panel. Practice on some junk and not your project. Search for some posts by Flop, here and on the HAMB, He's had some good ones on some Model A rust repair. Good Luck.
 
Take a piece of copper tubing and flatten it and use it to back up
your weld area so you don't but through. Also use gas shield solid
wire not flux core.

Bob
 
Anything can be welded up with a MIG. But that means you are good with it. trying to fill holes with a welder when you are inexperienced is a formula for disaster most times. If you got some of them filled in, good for you, I mean it. I could weld up any size hole you through at me, but there is a knack. That being said, if the metal around it really worth saving? Can you post a pic? Are you using gas, which is true MIG. There is a material I would use after the holes are gone, but lets go a step at a time, I'd like to see what you have done.
 
You can have patchy areas metal sprayed, but you'll have to pay to have it done.

I had a very rare crankshaft built up in a similar manner, and then reground to original.
 
oxy /acetylene makes too large of a hot spot and will warp panels, mig or tig is the way if mig than use gas as noted above also as bob stated above use copper or brass to back the hole and avoid burn through ( an old brass hinge can work well for this but make sure the surface is flat against the hole you are welding , to do this hold it in place with a strong magnet on top of the brass , the magnet will stick through to the steel below the brass. also a way to make sure you fill the hole in a short burst is to cut a 10 inch piece of the mig wire you are using to use as additional filler wire like you would with torch welding the mig with its feed wire is the heat source like a torch it will be adding to the weld as normal and the filler will guarantee that you have wire in the hole to melt and fill it. Zap it ! count ..one.. two.. three and your hole should be done best of luck
 
Just remember that if the metal has pin holes it very likely is very thin elsewhere in the same spot. You need to consider replacing the area with a new patch panel or it will rear its ugly rust head later thru the new paint. much better to do it the right way now. That's what I think.
 
Pinstripe said:
Just remember that if the metal has pin holes it very likely is very thin elsewhere in the same spot. You need to consider replacing the area with a new patch panel or it will rear its ugly rust head later thru the new paint. much better to do it the right way now. That's what I think.
Click to expand...
Or when your sanding you punch a hole thru the weak steel (one of them self taught life lessons haha:rolleyes:)
 
If you only have a few thin spots you can weld them up.

You will need a ER70-s6 TIG rod (same metal as the MIG wire).

A copper block that matches close enough to the shape of the panel.

The problem with the MIG process is the arc puts a lot of heat in the one spot and burns back the edge of the metal.

So put a piece of copper behind the deep pit. It is not there to prevent shrinkage, it controls melt through and helps with keeping the heat down.

Put the tig filler rod in the hole and start the arc on the TIG rod. Feed the TIG rod while continuing the arc.

This will help you control the heat and fill the hole quickly.

When you are done with the weld you need to correct for the shrinkage caused by the heating of the metal. You need to first level the metal from the weld. I like a flapper disk in a 4" grinder. Then use hammer on dolly hits to get the surface back to the correct level. Use a file to check your work and finish the leveling.
 
Well here is my 2 cents ... If its solid enough to make it through blasting I doubt its going to be seriously thin .If the pin hole takes a weld of any sort its not to thin . If the pin hole opens up into a hole the size of a dime get the hole saw out and replace alot more surrounding metal. The copper piece behind is a crutch in my opinion . It doesnt take heat away. The damaging heat is in the panel way before it gets to the copper. And if you are burning through the metal either you metal is done or your welder needs adjusted .
 
While it is nice to have "all steel" welded in, and I have done it, now with the epoxys that are avaliable glue is a good option, even more so if the metal is straight but a little thin ----welding will cause distortion ---more so if you don't have the experience at minimizing it, if the structure is strong enough the wide flat area is a good place to make up a patch to fit inside and glue it on ---on new cars many parts have more glue than weld
 
Kurt in NJ said:
While it is nice to have "all steel" welded in, and I have done it, now with the epoxys that are avaliable glue is a good option, even more so if the metal is straight but a little thin ----welding will cause distortion ---more so if you don't have the experience at minimizing it, if the structure is strong enough the wide flat area is a good place to make up a patch to fit inside and glue it on ---on new cars many parts have more glue than weld
Click to expand...

I'll agree. If someone is inexperienced, or just flat out doesnt have a welder. Someone could glue a patch on the back side, and lightly fill the outside with bondo, if it is just some tiny rust pin holes. We use some glue at work, that's a 3m product, that you scuff the area with a 36 grit scratch then put the white mesh down, then you squeeze out some glue, and spread it over the mesh with a plastic bondo spreader. Once it's dry, it's stronger than just about anything. Once it's dry, you could go to the outside and grind off any glue that would have come through the rust holes. Then you're ready for bondo. It's similar to the old fiberglass method, but this is a stronger fix. We use it to bond plastic peices like bumpers or fender flares when someone brings them in and they have a slight crack. And if it can hold up to the flex of a plastic bumper, then it'll be fine in a model a. I personally would rather have fresh metal, or fill the holes with a weld, but I'm also not ignorant enough to believe that there's only one way of doing things. I think a fix like this in a small area would be okay. But i would suggest not using the fiberglass method. I'm sure if the rust holes are as small as you're leading on to be, fiberglass would be fine. But if it's a bigger hole, the fiberglass will start to break apart sooner than later. I can't tell you how many cars I've seen with the fiberglass patch panels that have started to splinter and the paint Is popping off. And these are cars that have been restored in the past 10-15 years. One of them was just finished and it's already starting to crack.
 
For larger holes or larger patches, there's "Gorilla Hair". And it's corresponding "Bondo" product. But with MIG you CANNOT weld continuosly. It must be weld in short (1 second) bursts. withg a 2-3 cooling period between bursts. Look at my making a patch panel for the bottom of the RF door in my pics. Go to my profile and go down to "My A".
Terry
 
I just finished three weeks tig welding up hundreds of pin holes in a small sheet metal piece that could not readily be patched due to complexity of its shape. For me, copper backing the piece and a lot of setup time spent for each area was key. I have a lot of copper sheet and will cut and form backup pieces that conform close to the metal repair. As said earlier, it is critical to pull away the heat once melting begins to avoid burnout. Edges are critical to have a larger area of backup to keep air/oxygen away from the melting "Swiss cheese", it is so easy to blow holes in material like that.
 
It must be weld in short (1 second) bursts.
Click to expand...

Maybe not even an entire second Terry :) But you are correct, it's on and off and it's a touch to get it right. I've watched people try and weld a hole and make it worse. I grabbed the torch, same settings and the hole is gone. It's touchy. That being said, your setting do have a lot to do with how a MIG goes. Wire feed is very critical, especially when trying to fill holes.
 
If they are pin holes clean it tin it and solder them closed and sand flush neutralize with baking soda done it lots of times
 
I couldn't agree more! It's practice, practice and then some more Practice! I find the initial "shots" tend to enlarge the hole somewhat. Then the weld builds up into a small lump and the metal can sustain it'self. Then the real business of filling the hole begins. Wire feeds are a critical part of the heat control.
Terry



PetesPonies said:
Maybe not even an entire second Terry :) But you are correct, it's on and off and it's a touch to get it right. I've watched people try and weld a hole and make it worse. I grabbed the torch, same settings and the hole is gone. It's touchy. That being said, your setting do have a lot to do with how a MIG goes. Wire feed is very critical, especially when trying to fill holes.
Click to expand...
 
You must log in or register to reply here.
Back
Top