Technical HOW TO protect the bare metal around the hole caused by installing a pop rivet

Good Afternoon ,


https://imgur.com/a/jiPVXJ6

The top of this metal patch (red circle ), the edge is slightly high; it wont bend (as much as I hammered it ), but when I clamp it down its flat flush, so can I just clamp it down and then put in a screw tap?

The blue circle, shows how I bent the metal patch around the original inner fender, I am wondering whether I should cut it or just put the outer skin over it?

BONUS QUESTION: For the self tapping screws should I use washers?

I have to fix the car for my brother who has lymph node cancer, for sentimental reasons.

I would rather be working on a vintage Jag or Mercedes.


Thanks and have a great day!

 

Good Afternoon ,


https://imgur.com/a/jiPVXJ6

The top of this metal patch (red circle ), the edge is slightly high; it wont bend (as much as I hammered it ), but when I clamp it down its flat flush, so can I just clamp it down and then put in a screw tap?

The blue circle, shows how I bent the metal patch around the original inner fender, I am wondering whether I should cut it or just put the outer skin over it?

BONUS QUESTION: For the self tapping screws should I use washers?

I have to fix the car for my brother who has lymph node cancer, for sentimental reasons.

I would rather be working on a vintage Jag or Mercedes.


Thanks and have a great day!

 

Kudos to you for doing this for your bro, carry on sir!

 

I too commend your efforts.
I wish I could actually see this up close and personal.
For the red circle, you can heat up the metal with a Map gas cylinder. It’ll allow for more movement and you can hit it with a hammer while it still clamped. At that point when it’s more flush hold it with a tapping screw after you glue it in place.

On the blue circled area, I’d wrap the outer skin over it.

Washers will hold the screwed area in a larger diameter. I’d use them.

I really wish you were welding this thing.

 

The best process for this is to mark the places you want to add a screw on your patch, then drill a hole slightly larger then the outside of the screw shaft, but smaller then the head of the screw at every point you want to put a screw in, on the patch itself. When your get your holes drilled, the screw should pass through the hole in the patch panel up to where the screw head sits against the patch panel. The tighter the screw fits through the hole (a slight drag, or barely fits is best), the better the screw clamping force will be.
The reason for doing this is because when you use a self tapping screw through 2 pieces of metal, it cut threads into the top piece, then it cuts threads into the bottom piece. Between the two pieces is a gap between the two pieces of metal and a ridge from the top piece that will also hold the two pieces apart. As the screw tightens up, the screw will start to strip the threads in both pieces trying to pull them together. Also, as you apply force for the self tapping screw to cut through both pieces, it tends to walk a bit before it starts to cut. If you have the hole drilled in the patch piece (the outside piece) the self tapping screw doesn't have to cut threads in it, so it will cut faster into the bottom, there won't be a gap or a ridge, and since the screw is only cutting threads into one panel, and only pulling to top piece against the bottom piece, it won't try to strip the threads in the bottom piece. You get a tighter fit with less chance of stripping the screw or the metal. The extra advantage is the hole in the outside piece acts as a guide for the self tapper to align the holes better.

On your red circle, I would put the screw closer to the left top corner, between the clamp and the top left edge of the patch piece. I like to have the screws within a 1/4" of the edge of the patch if possible. I also like to see the screws no more then 3" to 4" apart along a long edge. More screws is probably better then not enough screws, but if you are using panel bond ot fiberglass in addition to the screws, less and farther apart works. Then if you have the holes already in the patch piece, you can hold the patch in place and run that top corner screw in (or which ever screw is nearest the place most critical of positioning the patch in its proper position). If there is no specific hole that positions the patch in place, I would suggest you put the first screws into places that are the hardest to clamp, you may have to force the patch in place to put in that 1st screw. When its tight, you can re-clamp the patch closer to the next screw hole, and run that screw in tight. Keep the patch panel as close to the original piece as you can as you go. Continue one screw at a time with re-positioning the clamp for each screw. The patch will be tighter against the original metal.

The use of washers under the screw heads does spread the clamping force to a larger area then just under the screw head does, but it also provides a larger space to hold water, and makes the screw head stand higher away from the patch panel, making it harder to seal for a long term patch life, if that is important.