Acrylic is the most rewarding plastic to machine and the least forgiving. Cut correctly it produces edges that can be polished to optical clarity. Cut incorrectly it melts onto the tool, chips at the exit, or develops a fine network of cracks days later when a solvent or a load finds the stress the cutting left behind.
Tooling and speeds
Single flute or double flute cutters with a high rake and a polished flute clear chips before they can re weld to the cut. Speeds are high and feeds are steady, because dwelling in one place melts the material. Climb milling gives a better finish. Sharp tools matter more than in metal, since a dull edge generates heat rather than a chip and heat is the whole problem.
Cast against extruded
Cast acrylic machines and polishes far better, has more consistent thickness and is more resistant to crazing. Extruded acrylic is cheaper, thermoforms more easily and is more prone to chipping and gumming when machined. For machined parts specify cast, because the material cost difference is small compared with the scrap rate difference.
Annealing is not optional on stressed parts
Machining leaves residual stress at the cut surface. Combined with a solvent, an adhesive or a mechanical load, that stress produces crazing, a network of fine cracks that appears hours or days later. Annealing the part in an oven at a controlled temperature and cooling it slowly relieves it, and it is the standard step before bonding or polishing.
Edges and finishing
A well machined edge is already good. Flame polishing gives a clear edge quickly and adds stress, so it is unsuitable before bonding. Buffing or vapour polishing gives a better result. Sanding progressively then polishing is slower and the most controllable. Decide which one the part needs before machining, because it changes how much stock to leave.
Questions people ask about acrylic cnc service
Why is my acrylic edge cloudy?
Usually heat: the tool melted the surface rather than cutting it. Sharper tools, higher speed, steady feed and better chip clearance are the fix.
Cast or extruded acrylic for machining?
Cast. It machines and polishes better, has more consistent thickness and crazes less. Extruded is cheaper and better suited to thermoforming.
What is crazing and how do I prevent it?
A network of fine cracks caused by residual stress meeting a solvent or a load. Annealing after machining and before bonding is the standard prevention.
Can acrylic be laser cut instead?
Yes, and it gives a flame polished edge straight off the machine. It also leaves more stress in the edge, so laser cut parts intended for bonding should be annealed.