EPP is rubbery + has memory. The wire pushes into the foam, foam compresses, foam springs back behind the wire and grabs it. You'll see the wire bowing forward as it cuts.
Fixes:
1. Slower feedrate — give the heat time to melt rather than push.
2. Lower temperature — surprisingly. EPP at high temp gets gooey + sticky.
3. Thinner wire — less drag area.
4. Pre-tension the foam — clamp it lightly to a backing board so it can't compress as the wire enters.
Many people just accept that EPP cuts look rougher than EPS and finish with sandpaper after.
Fixes:
1. Slower feedrate — give the heat time to melt rather than push.
2. Lower temperature — surprisingly. EPP at high temp gets gooey + sticky.
3. Thinner wire — less drag area.
4. Pre-tension the foam — clamp it lightly to a backing board so it can't compress as the wire enters.
Many people just accept that EPP cuts look rougher than EPS and finish with sandpaper after.