Carving in MDF

[hardwoods]

I am new to carving signs and I have one to make for a friend. I am thinking about using Extira. I tried carving a test piece in MDF and many of the letters broke off. I used a 3/8" ball nose bit to clear away the background. I cut it at 3/8" depth. Would I be better off backing the cut depth off to about 1/4" or less? Also will the Extira hold together better?

[bryson]

Dan, You may want to try Medex exterior fiber board. I use it to make casting patterns and do not have any problems with the letters breaking off.
Bryson