Machining Acrylic Perfectly: Beginner Guide

Machining Acrylic Perfectly: Beginner Guide

Machining Acrylic Perfectly: Beginner Guide

Acrylic is a versatile material, available in different colors, and provides the physical durability of plastic with the optical properties of glass, making it ideal for various applications.

Machining can be a great way to make intricate cuts on acrylic with high precision and accuracy.

A popular use of acrylic machining is to make signboards and acrylic lights.

This article provides a detailed guide about machining acrylic and discusses the advantages of switching to CNC for machining acrylic products.

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How to Machine Acrylic for a Perfect Cut?

Comgrow ROBO CNC engraving on cast acrylic
Comgrow ROBO machining cast acrylic

Acrylic can be machined with tools such as lathes, mills, and routers. While mills and routers can cut or engrave different patterns, lathes can be used to machine asymmetrical components. A 1-flute or 2-flute end mill with a high helix angle is ideal for machining acrylic.

Apart from that, there are various other factors to consider, such as speeds and feeds, chip load, depth of cut, type of machine, etc., for perfecting the process of machining acrylic.

You can either calculate them by using mathematical formulae or use a calculator such as a chip load calculator, speeds and feeds calculator, etc.

Selecting the Right Machine for the Process

Acrylic is a soft material that generally does not require a strong cutting force to perform the machining operation, and there are various machines that can be used for cutting and shaping acrylic.

Router

Comgrow ROBO
Comgrow ROBO

To get started with machining acrylic on a router, a small-sized desktop CNC router can be used for performing clean cuts with a high surface finish.

However, a capable router with a rigid configuration and higher power output can enhance the quality of cuts by reducing the vibrations and improving the torque delivered for removing the material.

Some capable machines that can be used for machining acrylic include Comgrow ROBO, Zenbot 4896, Shapeoko Pro, Snapmaker 2.0, etc.

Milling Machine

Grizzly G0705 Milling Machine
Grizzly G0705 Milling Machine

Milling machines can be used for performing precision cuts on acrylic workpieces.

Generally, when milling acrylic, it is advised to use cast acrylic instead of extruded acrylic.

This is because, cast acrylic is less prone to developing internal stresses during its manufacturing, and therefore is less prone to breaking or cracking during the milling operation.

Acrylic can be machined with both manual and CNC mills.

Although both have different operational procedures, the optimal parameters of machining will remain the same.

Milling machines such as Harbor Freight mini milling machine, Tormach 1100M, Tormach PCNC 440, etc., can be used for machining acrylic.

Lathe Machine

Eastwood mini metal lathe
Eastwood mini metal lathe

Lathe machines can be used for turning acrylic to produce axisymmetric workpieces with high precision.

Unlike other machines, lathe machines consist of a high-speed rotating chuck that holds the acrylic workpiece while a stationary cutting tool moves along the X and Z axis to perform the machining operation.

The horizontal alignment of the lathe machine and the use of a single-point cutting tool facilitate easy chip clearance, resulting in hassle-free machining of acrylic.

Acrylic, being a soft material, can be machined on either a wood lathe or metal lathe.

While wood lathes use hand-held tools, providing better flexibility to carve complex shapes, metal lathes are best suited for precision machining.

Apart from that, CNC lathes can be used for machining complex geometries with high precision.

Generally, machining acrylic does not require a rigid configuration and a benchtop lathe can be used for producing acrylic parts.

Selecting the Right Cutting Tool for Machining Acrylic

Different types of CNC endmills
Different types of CNC endmills

Acrylic, being a ductile material, produces long chips that are prone to clog the flutes of the cutting tool and this can drastically affect the tool life.

Moreover, poor clearance of chips can result in chip recutting, which results in high frictional heat, thereby melting the workpiece and affecting the quality of the cut.

Unlike lathe turning, milling operation uses a multi-point cutting tool and is prone to accumulation of chips around the cutting area, thereby affecting the quality of machining.

Therefore, it is important to select the appropriate cutting tool for CNC routers and milling machines to produce the best quality cuts.

Although you can use a metal cutting end mill for machining acrylic, it is recommended to select router bits specially made for machining plastic and acrylic.

Based on the Number of Flutes

Number of flutes on a cutting tool
Number of flutes on a cutting tool

To overcome these issues, it is recommended to use an end mill with the least possible flutes.

A 1-flute end mill provides the best chip clearance but can produce burrs along the cut.

Whereas a 2-flute or even 3-flute end mill will provide satisfactory chip clearance with good rigidity, thereby reducing vibrations and enhancing the quality of cut.

However, 3-flute end mills have higher chances of chips getting jammed into the flutes, and might need cleaning, during the machining process, to remove the accumulated chips.

Based on Tool Geometry

When machining acrylic, it is recommended to use a cutting tool with a rake angle of 6° or higher and a significant clearance angle to avoid rubbing of the tool against the material.

Using a cutting tool with no clearance angle can result in the rubbing of material and lead to a foggy finish on the cut edge.

Furthermore, a cutting tool with a higher helix angle (upcut) facilitates easy clearance of the chip, thereby facilitating chip removal and providing the ability to maximize the feed rate.

However, an upcut cutting tool pulls the chip out of the workpiece, and using this type of cutter for machining very thin workpieces can result in the snapping of the workpiece under the pull exerted during cutting.

Therefore, when machining thin workpieces or workpieces that cannot be clamped firmly to the work table, it is recommended to use a downcut tool with a high-pressure CNC cutting fluid supply to facilitate chip clearance.

Based on Tool Material

A diamond-coated cutter is the best choice for producing a glass-like finish when machining acrylic.

However, diamond-coated cutters are very expensive and are generally used in industrial applications where a high surface finish is of utmost importance.

For a typical acrylic machining application, carbide cutters produce excellent cuts with a good surface finish.

Furthermore, you can also use HSS cutting tools, but at the cost of the surface finish of the cut.

HSS cutting tool will produce a frosty finish which can be improved by post processes such as flame polishing the cut edges.

Set Optimal Machining Parameters

Setting the Machining Parameters
Setting the Machining Parameters

Optimal machining parameters depend upon various factors, such as the capability of the CNC machine, type of cutting tool, type of cut being performed, machining technique being used, etc.

Hence, it is always recommended to perform test runs to find the optimal machining parameters for your setup before machining the actual workpiece.

When machining acrylic with a small-sized router, it was observed that using a 20° 0.1 mm tip engraving bit with a spindle speed of 10,000 RPM at 0.02" depth of cut and 5 ipm feed rate produced the best results with minimal vibrations.

Similarly, when machining acrylic by an adaptive cut technique using a 1/8" 2-flute end mill, it is recommended to start your test runs with a spindle speed of around 18,000 RPM at 0.09" DOC, 0.013" optimal load, and a feed rate of around 80 ipm.

However, for operations such as slotting or profiling, where the entire width of the cutter is involved in the cutting process, it is advised to significantly lower the feed and depth of cut.

When performing the CNC machining of acrylic, plunging the tool directly into the workpiece can result in unwanted skipping of steps.

Therefore, it is advised to use CAM software that provides the ability to set a helical or ramp pattern for slowly plunging the tool into the workpiece, allowing for greater depth of cut.

You can also follow a similar ramp path when machining acrylic manually by a hand-held router or milling machine.

Workpiece Holding

Clamping tools for a CNC router
Different workpiece clamping tools for a CNC router

Machining acrylic involves the delivery of a strong cutting force to remove the material from the workpiece.

Although acrylic is relatively easy to machine and does not require strong cutting force, using an upward cutting tool applies a pulling force on the workpiece.

This upward pull can dislodge the workpiece if the clamping used to hold the workpiece is not strong enough.

Furthermore, being a soft material, a weak clamping force can lead to vibration of the workpiece, resulting in scratching of the acrylic surface at the clamping area.

Therefore, it is advised to use a strong clamping technique with rubber pads to eliminate the risk of scratching the workpiece surface.

Lathe machines generally consist of a 3-jaw or 4-jaw chuck that holds the workpiece firmly during the machining process.

However, it is important to ensure the eccentricity of the workpiece because an offset of a few degrees can drastically affect the accuracy of the machining process.

Lubrication

CNC Cutting Fluid
CNC machining with cutting fluid

Machining acrylic does not necessarily require lubrication during the process.

However, using a cutting tool with a 3-flute or higher configuration can result in the accumulation of chips, leading to increased frictional heat.

This heat can melt the acrylic chips and weld them to the workpiece and the cutting tool, thereby degrading the surface finish of the cut and drastically reducing tool life.

Therefore, the need for lubrication arises when machining acrylic using a cutting tool with a greater number of flutes at a high feed rate.

How to Improve the Quality of Acrylic Machining?

Acrylic sign made on a CNC router
Acrylic sign made on a CNC router

Apart from maintaining good process control and setting the right machining parameters, there are certain things that can further improve the quality of your final product.

Prepare a Good Design

Mellowpine design in Illustrator
Preparing "Mellowpine CNC" design in Illustrator

A good design is a crucial element in CNC machining, and there are various aspects to consider when preparing the design.

The general rule of thumb when preparing a design for cutting acrylic is to ensure that each design element has a width greater than or equal to the thickness of the workpiece.

This ensures the structural integrity of the design and prevents it from snapping easily.

When designing, consider the type of cutter that will be used for the machining process.

Rounding the edges of design
Rounding the edges of design

A round cutter cannot be used to cut perfectly square profiles.

Therefore, it is important to fillet the edges of the design in such a way that the fillet radius is greater than or equal to the radius of the cutting tool.

There are various CNC software that can be used for the design and control phase of a CNC manufacturing process.

Set an Appropriate Cutting Direction

The cut direction is the orientation of the rotating tool, i.e., clockwise or anti-clockwise rotation.

When machining soft materials like acrylic and aluminum, it is advised to follow the conventional clockwise rotation of the cutting tool.

Clockwise rotation ensures the best results with a clean cut and smooth surface finish.

Use the Ramp Feature

Path followed by an end mill when using ramp feature
The path followed by an end mill when using the ramp feature

The ramp feature plays an important role in determining the optimal depth of cut and surface finish of the cut.

Instead of plunging the cutting tool into the acrylic workpiece, the ramp feature facilitates a gradual entry of the cutting tool into the workpiece.

This reduces the impact load on the workpiece, thereby allowing for a greater depth of cut.

Generally, when machining acrylic, a ramp of around 4 inches produces the best results.

Advantages of using CNC for Machining Acrylic

Acrylic sign made on Comgrow ROBO CNC
Acrylic sign made on Comgrow ROBO CNC

CNC machining acrylic offers various advantages over traditional machining techniques.

Automation

The ability to automate the machining process makes it highly adaptable for mass production applications.

CNC machining takes in the design file, converts it into appropriate G-codes, and controls the cutting tool to perform the desired machining operation.

Apart from that, a G-code program consists of various other codes like S-codes, N-codes, M-codes, etc., that control other miscellaneous activities like spindle control and cutting fluid delivery.

Thereby reducing the need for human interaction during the process, making it ideal for large-scale production systems where repeated operations are to be performed for producing multiple products.

This automated machining is free from human limitations such as fatigue. Therefore, it can be used to produce acrylic products without frequent halts.

As a result, CNC machining reduces the overall machining time and enhances the productivity of the process.

Accuracy and Precision

Apart from quick cycle time, CNC machining also provides the advantage of producing acrylic parts with high precision and accuracy.

A typical CNC router can produce parts with high accuracy of around 0.001” to 0.005”.

This high accuracy facilitates precise machining of acrylic products with complex geometries.

High-Quality Output

The ability to control various parameters and select different cutting tools makes CNC ideal for machining acrylic stocks of different sizes and qualities.

Using an adaptive tool path and setting optimal machining parameters to ensure clean cuts with minimal scope for errors.

As a result, the quality of acrylic workpieces produced by CNC machining is far superior to other traditional machining processes.

Final Thoughts

Acrylic sign made using Comgrow ROBO CNC
Final Product of machining acrylic on a CNC

Acrylic is a soft material that can be machined with relative ease.

However, it is important to ensure optimal machining parameters and good process control to get a quality output.

Acrylic can be machined using end mills meant for cutting aluminum, however, make sure that the end mill hasn't been previously used for metal cutting applications.

This is because an end mill that was used for machining metals will have blunt edges and this can cause poor surface finish when machining acrylic.

When compared to traditional techniques, CNC maching can be costly, but their high productivity and quick cycle time can overcome the high initial cost in the long run.

Frequently Asked Questions (FAQ)

Can we use CNC machining to produce 3D engravings on acrylic?

Yes, a CNC machine such as a router, can be used for producing 3D engravings on acrylic. However, preparing the design for 3D engravings can be comparatively difficult and require a skilled designer.

Can a CNC machine be used for machining glass?

Yes, a CNC machine can be used for machining glass. However, producing high-quality cuts and engravings in glass requires special cutting tools with high RPM and low feed configuration, making it difficult to use beginner-level routers for machining glass.

Is acrylic a good alternative to glass?

Yes, acrylic is a good alternative to glass. It is a shatterproof material that provides optical properties similar to glass. However, it cannot be used as an alternative to glass for applications that require extremely high-optical properties such as transparency, UV resistance, etc.

About John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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