I'm no expert either , snapped plenty of bits myself, I use 3mm (2 flute) to cut my 4.5mm acrylic as well. Here's the settings gwizard gives me @ 2.25mm per pass its: 20428rpm & 1052 mm per min. (this gives me a nice finished edge hardly needs cleaning up) I have read before that you should only cut at half the depth of cutter width ie: 1.5 with 3mm bit. Here's gwizards settings for 1.5 per pass : 21005rpm & 1273.8 mm per min. These settings are with gwizard set at conservative low.
Hope this helps, good luck , I know how it feels too keep breaking bits, still do while trying too cut 3mm 5005 aluminum sheet it's like bubble gum :-)
Cheers
Riche




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