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So, for cutting out letters (usually in 20 lb material) and also the release cuts on finished signs - upcut or downcut when cutting HDU? When I cut aluminum I use an upcut Amana single flute bit to get the chips out of the way. But with HDU, does it really matter? I'm not talking about 3D carving, just cutting out letters. How about for PVC in thickness from 1/4" to 1".
Thanks!
I've always down cut with HDU. Creates a cleaner cut. That's my experience.
With low temperature plastics like acrylic and especially PVC, I find the best results are with an upcut single flute running low rpm's and a fast speed. The chips have to be cleanly ejected or they may melt, decreasing the quality of the cut and possibly breaking the bit.
PVC is really soft so I've found it can be cut aggressively and have a nice clean cut.
On PVC I use a "0" flute at low RPMS and cutting aggressively.
I use downcut bits on HDU.