Key Tips for CNC Machining PMMA/Acrylics

1. Tool selection: Because PMMA is a relatively soft material, sharp and carefully selected cutting tools are required to prevent tool wear and breakage. High-speed steel (HSS) tools are usually the best choice for machining PMMA, although carbide and drill-plated tools can also be used. Only use tools specified for plastics machining to cut PMMA. A good rule of thumb is to use a high shear edge geometry (1- or 2-flute tool) with an edge rake angle of approximately 5° and a clearance angle of 2°.

2. Cutting Speed: Due to the relatively low melting point of PMMA, it is critical to use moderate to low cutting speeds when machining this material. Excessive cutting speeds may cause the material to melt or deform, resulting in poor surface quality and tool wear.

3. Feed Rate: Check out this study that shows the effect of feed rate on cut edge quality when machining PMMA. The study shows that a feed rate set at 75% of the tool break rate is optimal for cutting edge quality. A more comprehensive white paper on machining acrylic with diamond micromilling can be found here.

4. Coolant: Due to PMMA‘s low coefficient of thermal expansion, it is a good idea to use coolant when machining this material. Coolants help prevent the material from overheating and improve surface quality. Since PMMA is compatible with a wide variety of solutions, it is not difficult to find a suitable coolant.