Bicycle Mechanics - How to make a cheap shim?

Just a bit of advice please. My old Schwinn has a 1" seat tube. My front derailler is a lost cause. I have a derailler made for a 1 1/8" seat tube I would like to use. So I need a shim for 25.4 to 28.6 mm. I have found them online but with shipping it would cost me $15 to solve this minor issue. Any ideas on how to make my own cheap?

Thanks

Cut pieces of a beer can. Stack as necessary.

If you have an old inner tube cut it to fit.

If you have an old inner tube cut it to fit.

Exactly. Compresses to fit perfectly, and if applied to a clean frame, will not mar the finish.

Both OK ideas. Macine shops keep "shim stock " on hand. I did in machine shops I had. If you're too random with the material,you could end -up with an impossibly stuck post N/G, we read about that plenty here at the forum. "feathered shim" is N/G either,it's tapered. Shim stock, sumtotal of twelve thousanths will do. Cold -rolled copper tubing is about that thickness,a plummer would have a piece,a can's too thin.

It's been a couple of decades but I think that I remember solving that problem by using Velox handlebar tape. The hardest part was figuring exactly how high the derailleur had to be before wrapping the handlebar tape around the seat tube.