How To Cut, Drill And Weld 3D Printed Plastic ?


3D printing is not a perfect process. It has lower tolerances than other CNC processes like injection molding which give you greater accuracy. 

There are instances where it is necessary to cut away plastic for example to remove supports or any excess material. It could be your design might need to have holes or teeth as when designing a gear for example. 

In cases where you need absolute precision, 3D printing can be a challenge. 3D printing is notorious for not producing the most accurate holes due to the layer-by-layer build process. What do you then do if you need a hole in your design?

A common solution is to drill one. But drilling and cutting into plastic involves a few challenges which we will get into today. In this guide, we go over a few tips that will help you safely cut or drill your 3D prints. 

Can You Cut A 3D Printed Model?

3D models can be cut, however, they do display certain characteristics that make it difficult. Plastic melts when subjected to heat and cutting can produce temperatures high enough to melt a 3D model. This is particularly common when using a machine cutter that works at high speed. The faster it cuts, the more heat it generates. 

For smaller models, cutting away a small area of plastic does not present too much difficulty. For larger builds, the process gets more complicated. Machine cutting is highly likely to produce heat that will warp the plastic. At the same time cutting too slowly will produce a jagged finish along the edges of a print.

One particularly effective trick for cutting plastic is to undercut it. You start off by cutting a little less than you want to take off. Then you remove the rest of the excess by filing down rather than cutting. 

The downside to this method is it might not produce as accurate a part for large models that require a high level of precision. Source

Can A Laser Cutter Cut 3D?

A 2D laser cut will only cut a single side of a design. A 3D laser cut on the other hand can recognize and cut a three dimensional shape. This means it can cut more than just the surface of a design.

Generally, laser cutters only cut the surface of an object. A three-dimensional laser cutter goes beyond just the surface and cuts into the different sides of a sphere or cube for example.

Can You Drill A Hole In 3D Printed Plastic?

Subtractive manufacturing has better tolerances than added manufacturing. This is especially true for drilling threaded holes. While drilling is possible for 3D-printed plastic, it does not produce holes with the same type of accuracy as subtractive manufacturing.

Drilling presents the same challenges for 3D prints as cutting does. It produces heat that can melt the plastic. It can also crack the print. The thicker the print is, the more challenging it is to drill or cut without damaging the print. 

One tip you can use to reduce the likelihood of cracking is to drill across or at a right angle to the layer lines in your print. While this does not eliminate the chance of cracking, drilling along the layer lines or “with the grain” has a higher chance of splitting your print. 

Another way to try to reduce cracking is to start by drilling a smaller hole than you need and then gradually expanding the diameter. Directly drilling a large-diameter hole increases the likelihood of splitting. 

How Do You Cut 3D Printed Parts Together? 

Welding 3D-printed parts together is a useful technique for fixing gaps. A common way to do this is with a power drill. Here the drill pushes plastic which acts as the drill bit into the gap. While the plastic is being pushed in, the friction causes the plastic to heat up, soften and weld into the receiving piece. 

This is a technique borrowed from metalworking but it works just as well for 3D prints. It works best for low-temperature filaments like PLA and is a great alternative to using superglue to join parts together. It’s especially useful for joints that don’t have enough space for glue or for complex shapes.

To weld with a power drill:

  1. Insert a straight piece of filament of between 15 to 30 mm into the drill using a collet. The longer your filament the trickier it is to control. Preheat the filament with a blow dryer to straighten out any curves.
  2. Drill while maintaining a consistent speed that’s not too slow or fast.
  3. Maintain enough pressure to penetrate the plastic.
  4. Move the drill in a clockwise motion into the seam.

We also recommend that you check out our post “Can You Splice 3D Printer Filament? How To Join 3D Filaments!

Does 3D Printing Break Easily?

3D printing is a form of additive manufacturing. This is a process where parts are built in subsequent layers that bond together. Subtractive manufacturing processes start from a solid material from which a part is cut. 

The layer-by-layer construction of 3D printing produces weaker parts with a higher propensity to break compared to the solid block material of subtractive manufacturing. 

3D-printed parts lack the strength, impact, and heat resistance that subtractive manufacturing processes will give you. There is still a substantial gap in achieving the same durability with 3D printing as you will find with subtractive manufacturing.

Which 3D Printing Process Produces Stronger Parts?

Another factor to consider is which 3D printing technology to use. Strength varies with the technology used. 

Fused Deposition Modeling (FDM)

FDM printing uses filament to produce a print. There are two main points to consider when evaluating the strength of FDM printing. Firstly, strength in an FDM print is dependent on the orientation of the build. An FDM print will not be uniformly strong across its X, Y, and Z axis. 

With that said, however, FDM printing has a wide range of strong materials including nylon, polycarbonate, and metal to compensate.

Stereolithography (SLA)

SLA printing uses resin to produce a print. The distinctive edge SLA has over FDM printing is that SLA prints are isotropic. Unlike FDM printed parts strength is independent of the build orientation so it is equal across the X, Y, and Z axis. 

With that said, however, there is no resin that can produce parts with a strength similar to filaments like polycarbonate or composites. 

How To Improve The Strength Of 3D Prints

The first step would be to use a strong filament like polycarbonate or metal. Further steps you can take include:

  1. Print with a higher infill percentage. The fill density determines how hollow or solid your print is. The higher the infill the more solid it is. The more solid your print is the stronger it is. A rule of thumb is to use an infill of 50 percent. Using a higher infill will marginally increase strength but at the expense of using more material and reducing print speed.
  2. Print with thicker walls. Shell thickness is the thickness of the outer walls of a print and also has a bearing on the strength and impact resistance. 
  3. Orient your print correctly. FDM printed parts are strongest when loaded or subjected to mechanical stress along the grain. This is the plane parallel to your print bed. Keeping this in mind when designing and printing improves the strength of your print.

We also recommend that you check out our post “How Much Weight Can A 3D Printed Object Hold? Can You Make It Stronger!” & “How Fragile Are Printers & Prints? Do They Easily Break! (Contributing Factors)

sherifjallad

I am a very well experienced techie civil engineer who's extensively interested in 3D printing technology and even more captivated by the potential of 3D printing livable structures

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