I was inspired to make a Center Finder as I did not want to drive 20 miles or pay extra bucks for a store-bought model.

Upon doing a search, I found https://www.instructables.com/id/Make-a-Center-Finder/ posted by Phil B.

I just like to minimize my time working with metal, so I built a drawing, used MDF (can you imagine?) and cut the pieces out at TechShop in San Jose - www.techshop.ws.

Above, you see what the completed finder looks like...

Step 1: Pick Up the 1/4" MDF...

... and cut it! Here's the Corel Draw file...

... and here's the 1/4" MDF after cutting...

finder v3.cdr
Download

Step 2: Put the Splines In...

This (fuzzy) pic shows a spline on top of the two pieces. The splines get glued-in to the top and bottom "ELLs". They assure alignment and connectify the whole thing together. That's right - I said connectify.

Step 3: Look What You've Done to the MDF...

It's altogether now. (All Together Now!)

Step 4: Try It!

Now we get down to business.

This Center Finder will work with round pieces up to 5" in diameter. The drawing could easily be tweaked to enable larger Center-Finding.

Mark a line along the 45 degree bar. The ELL without the 45 degree bar is on the bottom, and I placed the Center Finder on the round piece.