How to make small rust repair patches, one way

[Flank]

Hi all,
I wanted to show how I make small rust repair patches that can be used in addition to larger repairs. A little background on the car, I am doing a front suspension pan replacement. I already have all the 'store bought' replacement panels and have them fitted to the car, a '74 Carrera. I use 'clecos' to hold the panels in position for the mock up portion of the repair. In these photos, the replacement panels are removed. What I have left is the areas that are rusted and in need of repair before going forward with the final installations of the large pieces. The area of concern is the lower portion of the inner fender, under the battery.
The patches themselves are made from 22ga. steel. I have a small sheet of an automotive grade steel. I was told that it has a larger tin content and makes it easier to cold form, by hand and small hammers.
In the first picture, to get a good idea of what it looks like, is a cutout that was made to allow a filler piece to fit flush in the opening. A larger patch will go over this and be spot welded into place. The smaller filler piece will be spot welded to the larger.




I usually try to put the larger backing piece on the side of the hole that is out of view. In this case it will be on the inside of a longitudinal support.
When making a patch, I try to keep the pieces rectangular. Measure the bad area and come up with a size of the filler piece. Then I make the backing piece about 3/8 of an inch larger all the way around.
By using the thin metal, it is easy to form by hand to the contour of the surrounding area. Then I do the same with the backing piece. To keep the location consistent, I use a cleco to hold the piece in place.
I then spray the area with blue lay-out dye.
In the next picture you'll see two sets of scribe lines. The outer one is to give me a reference as to where to position the filler piece. Of course it has to cover the rusted area. My cut line will be the scribe line for the filler piece.




Then with my high-speed (20,000rpm) grinder that has an 1/8" collet, I use an 1/8" three fluted cutting bit, we called them 'pin' routers. They are like a drywall router bit, but are made for steel. I then start making the cutout, working in a counterclockwise rotation.

[HelmetHead]

Flank,
What brand and where do you get the 3 flute cutters? I've done most of my cutting with cutoff wheels and sometimes they are just to big to get into the small/tight spots.

Thanks for the informative post.

Helmethead

[Flank]

I have been 'burned' before by making a long thread that is too large to upload.
To continue, the picture of the hole being cut out is for a different patch. I had to make three repairs to the inner fender under the battery compartment.
Once the cutout is made, I spend a bit of time 'deburring' the edges. This is important, not only to prevent future rust, but to make everyone happy with the end results. In the next picture, the filler piece has been fitted.




Then I can align up the backing piece with the cleco hole and hold the two pieces together for further contouring of the backing piece. Using clamps and a body hammer, you can make a smooth patch area and fit the backing piece like shown.




I did the same proccess for the other two patches. Finally when all the cutouts made and the filler pieces fitted, I removed everything to prep the bare metal.




I used scotch-brite and cleaned the bare metal the best I could and gave the areas a good coating of Ospho. Then I quit for the night (2:00am).
The next day, I can spray the areas around the patches and the back side of the patches with 'weld-thru primer'. These patches will be held in place by using a large spot welder. A similar repair can be made with a mig welder doing what I call "imitation spot welds".
When done the areas can be smoothed out with the body hammer again and a little dress-up, followed by a little more of the weld-thru primer until the finish painting begins.
I hope you all enjoyed this. This is a typical repair that I do all over the car, when rust is present.
I ran out of space on the camera, but latter I'll post a picture of the few tools used.

Thanks, Flank

[Kemo]

thanks for posting...I would like to see more pictures of how this repair is progressing, if you have them.

thanks again.

[mikeatfhc]

Thank you... very informative, keep it coming.

[haycait911]

Originally Posted by HelmetHead

Flank,
What brand and where do you get the 3 flute cutters? I've done most of my cutting with cutoff wheels and sometimes they are just to big to get into the small/tight spots.

yes please, I've never seen these.

[Walko]

any more pics

Michael

[Flank]

Hi All, thanks for the interest. I welded the patches in the other night using the spot welder.




After the pieces were welded in, I sprayed them one more time with the weld-thru primer just to get something on them.

Here is a picture of my basic hand tools that get used a lot. My main ones are the two hammers. If any of you do a search called 'Flanks Targa' you'll find lots on the work I'm doing on my 71. The work here is on a 74 Carrera.



Here are the parts that are going into the suspension pan replacement. Followed by a picture of the Trammel points used to locate the pan based on the factory dimensions.




and



In the next picture, I'm locating the pieces in place and determining on what side of the piece will the weld go. I'll be using the mig welder and doing my version of an immitation spot weld. In joining two pieces of metal together, I'll drill a 3/16" hole on one of the pieces of metal (marked with paint). Then during the welding process, I'll aim the wire from the gun at the piece behind the hole and give it enough to make a goood weld so that the 'puddle' fills up the drilled area and produces a small 'button'. By painting a spot at each place that I want a weld to go I'll know which of the two parts gets the hole drilled in it. This also helps you know how you are progressing.




Later I'll get the information on the "pin routers" that I used to cut out the metal to be patched. I'll be working on the car a bit during the holidays trying to make its owner happy.




Later, Flank

[preston_brown]

Flank,

When you do those two-part metal patches, do you butt-weld the perimeter of the flush fitting patch from the other side? Or just skim-coat with filler? I'm thinking of moisture getting in between the body and the larger, backing patch piece from the other side.

Just trying to understand, this seems like a great way to get a good fitting patch because of the thinness of the metal, but I've done all my patches in the past with 20ga and butt-welding. Makes for lots of grinding.

-- Preston