How I engrave my Lowers:
I have a Gorton panto-mill. This is a pantograph milling machine, built during WWII and is designed specifically for engraving. I bought it used for about $500.
Generally these are used to engrave text. A reduction ratio is set on the arms and the text masters are placed in the copy board. Then one traces the letters with the stylus and the cutter cuts the letters in the work piece.
Now to engrave designs, I need a master. First, I printout the design on paper. Then I tape the paper to a piece of UHMW plastic about 1/8" thick. Using an exacto knife, I schrimshaw throught the printed lines into the plastic. After the paper is removed, I rub the plastic with shoe polish to bring up the lines. Then I carefully cut along the lines with a viening tool to make a shallow groove. Now the master is finished. This gets mounted to the copy board, the ratio set and then it is cut in the lower.
I also have a Haas VF-0 cnc milling machine that will engrave text all day long, but for designs it needs a program. Ones and twos are much easier on the Gorton. I know this isn't much help to those of you who don't have a panto-mill, but some engraving (trophy) shops do have panto-mills and if you make the pattern they can cut it for you. Just check first what reduction ratio they have. If they can do 16:1, and your finished lower design is 1-1/2" then your pattern would be 24" which may exceed the reach of their stylus. Little errors in the master dissappear through reduction and you should probably shoot for 4:1 or 8:1 in your master pattern.
Regards, Ray