crisp parting lines

When adding a splitter board around a plug to create a mold-half, what is the best way to create a really crisp edge?

I use to use clay to fill the gap but my current method is to embed the splitter board into bondo that’s on the plug and let cure and then sand the bondo flat with the board. But this still doesn’t have as crisp of parting line as I would like.

Other suggestions?

This really depends on what you are using for your splitter. I make mine out of plastic and hot glue the back side. I use modeling clay against the plastic and run an exacto knife against both edges and get the lines I am looking for. Sometimes to a fault as the part wants to stick or build an edge in it that is harsh.

I do the bondo thing as you describe as the best results , I accept there is a limit of a reasonability to the perfection of the parting line

Buy or make a set of fillet shapers.

I use plasticine clay or bondo.

When Bondo is newly mixed you can use a flat fillet shaper to create a super clean edge without needing to sand. Come back over the area when it starts to B stage to clean up the rough edges. Finish the edge with sand paper just to knock down rough spots.

I’d post pics if I were home but that wont be for a few days.