Look in alt.binaries.pictures. woodworking for "Arc calculator - Arc height calculation.sxc".
It's a spreadsheet I did for the freeware Open Office suite's Calc spreadsheet program. You can download that Sun Corporation freebie ( a direct alternative to Microsoft Office, it also reads their files, with some exceptions due to different formatting and so on) here if you like:
formatting link
'll do one in Excel if someone requests it. Spreadsheets are not usually compatible, so it will have to be redone. This is a fairly simple one, and I hope it will be of use. just ignore the math in the formulas if you want, but it's not protected if you feel the urge ot look into it.
I divided the half chord into ten parts, but can also redo that if more are needed. This does the calculation knowing the chord half-length, and the height from chord to arc at its center. Calculations are for other heights along the chord to get points on the arc. Just the half is needed for a template, or to transfer directly.
Enjoy!
Bill.