3D Printing, FDM Technology, Post-Processing

FAQ: Best Practices for Post Processing FDM Parts

By Tommy DuPuy on January 23, 2018

Your part isn't always done after the machine goes quiet. Depending on the intended end-use, some 3D printed parts coming off a Stratasys FDM printer will require post processing. To make this process a little easier, we compiled a list of FAQ about post-processing FDM parts.

Removing Support Material 

How can I speed up the support removal process? 

Speeding up the support removal process comes down to two things: part geometry and materials. Some materials will allow manual support removal to cut the time in the solvent tank (because there is less support on the part). For example, parts in nylon should not have the support removed because the material can be easily damaged during the manual removal process.

Also, part geometry can be a factor because if there is very little model material in areas with lots of support you can risk damaging the part by manually removing the support.

How do I remove support materials from the build tray? 

It is not recommended to reuse trays. Issues such as delamination from the tray can occur. However, you can reuse the tray in an area that has not been printed on yet. Here is an example of print on a reused tray:

Reused Printer Tray
If I have an SST machine, can I break off support material by hand? 

Yes. If you break off as much support material as you can before putting it in the cleaning station, you can speed up the support removal process. This will also help your WaterWorks solution last longer, saving time and money. (Your boss will like this!)

Sanding 

Is it possible to sand FDM parts? 

Yes. Many FDM printers use engineering grade thermoplastics. This means parts printed from these machines are durable and can withstand sanding.

>> Learn more in our blog: How to Finish a 3D Printer Part to Look Like a Production Part

What order of paper grit should I use for a smooth surface? 

150-220, 240, 300- 400. Note: The higher the grit, the smoother the part.

Should I use a block under the sandpaper? 

A block helps in the sanding process to evenly sand a surface rather than bearing down on a particular area. Putting too much pressure on one area could cause too much of the model material to be sanded away adding divots to your part.

Priming & Painting 

Can I paint my parts after they're printed?

Yes. FDM printed parts are completely hard when they come out of the machine. They do not require curing or resins to harden the parts. Sanding will help prep your parts for priming and painting.

Should I use a primer before painting my FDM parts?

For best results, yes. This will allow the paint to adhere better and will provide a smoother finish. Several light coats is key to make sure there are no irregularities.

Which primer works best? 

Automotive grade paints and primers will yield great results. However, they are not always required based on the application or look you are going for. Rattle cans also provide a fine finish. You just need to know some basics on painting to have a great paint job, such as how to manage over spray and even how to make a paint booth to eliminate air particulates such as dust and debris. We have found that PPG OneChoice makes a good plastic adhesion and can improve the bond of primer to the plastic parts.

What type of paint should I use?

Before purchasing any paints, ensure they are compatible with the primers. Our experience is that you get what you pay for. All paints work differently but one thing we have found is to not use bondo. This ends up making a mess if you're trying to use it as a filler. You're better off using Acryl-Green Spot Putty.

It is important to use the same brand for multiple colors on a model. Some paints may react negatively if used with other competitively branded paints.

Should I brush or spray my parts with paint?

Canned spray paint or spray guns tend to give the best end result. For the most professional looking finish it will require several thin coats of primer, followed by paint.

Drilling Holes

Can a drill press be used on FDM parts?

Yes. Standard machine tools also work well, such as a lathe or mill but probably not a shaper. However, make sure the area in which your will be tapping is reinforced with extra contours. If not, you part may split apart.

What about the bit type, length or angle?

Any type, length or angle will work. 

Does layer direction matter?

No. Layer direction has no effect on your ability to drill holes in your printed parts. However, it may influence the strength of the finished part. If parts are to be drilled or machined, select Solid under Model Interior in Catalyst.

We must be mindful that if we drill with the grain, a part can split, especially if you put an insert in the area that can cause force on the part.

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