Re: 1967 Chevelle frame repair
Folks are right, you can buy the specific washer inserts from UMI, or flat washers from the hardware store will work. I use both, depending upon the severity of surrounding rust and metal thickness. If the rust is serious around the hole, I have machined the larger hardware store washers to correct I.D. and whatever O.D I need to fully clear the rust.
Generally, it's pretty simple/quick.
I use a hole saw on a pneumatic drill. An electric or cordless drill will work, but they generally struggle on metal holes this size.
Weld a tab across the damaged hole, and take your time to locate the original center as best as possible. Drill a small pilot hole, and then go for it with the hole saw.
Below are some pictures. One is a smaller O.D. UMI washer (they laser cut them) and the other is a larger hardware store washer. I use a 2 3/8" hole saw for the UMI. I make the O.D. of the hardware store washers not only clear the rust, but accommodate a common hole saw size.
I weld them in with TIG, using about 95-100 amps. That seems to work the best for me to get full penetration without burning through. MAKE SURE THE METAL IS CLEAN BEFORE WELDING!
NOTE: the last thumbnail shows the underside of completed repair - it will look like it is not fully penetrated in the top of the picture. That is where the frame halves overlap from the assembly process, and the weld generally won't penetrate through both layers of frame material. You can see full penetration where it is only one layer of frame material.