3D Printing larger items often requires the design to be broken into smaller parts to fit on your print bed. Breaking a 3D print into multiple parts can lead to unsightly lines and seams. With this step by step article will help to guide you on how to assemble and finish your own multi-part 3D print.
Why Should I Post Process a 3D Print?
3D printing is an amazing technology that allows for people to rapidly create without the requirements of expensive molds and equipment. This ability does often come with the trade off of visual quality. With injection molding of plastic there are very few lines or deformations, just the small injection points in the mold. For 3D printing material is added one layer at a time which leads to unsightly layer lines in a print. These layer lines are less evident in resin printing but with fused deposition printing they can be quite obvious. In addition 3D printers have a limited volume for a single item that can be created which requires items larger than the build volume to be broken into multiple parts, printed, and then later assembled. This method of construction usually leads to seams and other blemishes on the surface of your print. Post processing of your model is any after printing modification; assembly, sanding, cleaning, or painting are all post processing.
Steps To Assemble Your Print
Step 1. Model Design
Entire Model Design in CAD Software Quadrant Exported as STL Cura Slicer Layer View
Design the part in a way that you can easily break it into smaller parts which will fit together. Remember with 3d printed materials to account for the expansion or contraction of your materials. You may want to break out your smaller areas where the parts connect as a test print to ensure you don’t need to adjust dimensions. For my example shield I decided to just slice it into quarters.
Step 2. Print Your Parts
Looking Good Almost There Done… Now for 3 More
Take your files and slice them for your printer. Keep in mind the orientation this particular part should be in to give it the greatest structural strength. I’m printing my test print on an Ender 3 with a 0.8 nozzle at a 0.4mm layer height. I want them oriented face up to make sure the detail isn’t obscured by the supports. Because the print time on these items is 9hrs I used significant brims to ensure that the part stayed adhered. I’m using Hatchbox White PLA for this print as I’ve had good luck with the consistency of this brand so far.
Step 3. Clean Up Your Print
Remove your supports and clean up the surfaces under them. You should test fit the connection areas and if necessary clean them up further by sanding or cutting away little nubs or extra material to get them to fit. Don’t force things and don’t fully fit your parts yet. All four shield quadrants line up easily and after removing the supports and brims I only needed to hit it with a bit of sandpaper where there were some minor imperfections.
Significant Supports for this Domed Shape, Came Off Nice and Easy Though
I realized at this step that I should have split the shield into five prices along the points of the star, things would have been more even. Too late to go back, Halloween is just around the corner and we have a lot of work to do.
Step 4. Assemble Your Parts
This step will vary based on what you designed and how you broke it into parts. Parts that are designed with screws in mind should have the holes tapped. If your part is designed to snap into each other should then it should be carefully fitted. Parts designed for glue or epoxy should have the bonding surfaces cleaned and then be glued and held in position until it sets.
Cyanoacrylate Glue Works Great Here Remember to Support the Parts Until Dry
The sides of my parts are smooth and have very small gaps to deal with I decided cyanoacrylate glue (super glue) was good enough and a two-part epoxy was not necessary. For parts items that may need to stand up to stress or where there is a groove to hold the adhesive two part epoxy may be a better choice. At this stage don’t worry about perfectly fling gaps, the adhesive is to hold things together. We will deal with those gaps shortly.
Step 5. Fill The Gaps and Layer Lines
There are so many products on the market to act as filler I’m not going to address them all. For very minor gaps or layer lines a high fill primer might work well. This is just a very thick spray paint primer. You spray the item and let it dry then sand down the outer layer leaving only the filled gaps and repeat until smooth. Next we have the thicker fillers such as wood putty and glazing putty. For either or these you spread on a thin layer then sand off the excess. Finally we have two part fillers where you mix the putty with the drying agent and then spread it on and again sand off the excess.
Bondo Two-Part Filler For The Seams Back and Front
For my project I selected bondo two-part compound for filling the large gaps where the parts meet and then bondo glazing putty to coat the whole shield and hide the layer lines. The two-part putty sets very quickly (less than 5 minutes) so work in very small batches.
Bondo Glazing and Spot Putty for Final Finish First Round All Dry First Round Sanded
PLA will soften as it heats from the friction of sanding. Using waterproof sandpaper and wet sanding either under running water or in a bath will help protect your print from warping. In general remember this is plastic, not wood. Even if you are using woodfill PLA which technically contains wood, it’s still 70%+ PLA.
Step 6. Prime Your Print
Spray On Primer After First Round of Filler. Looking Much Better but We Have a Ways to Go
Once you have sanded your first fill layer you should prime it to get a nice uniform base coat. Priming at this step will help highlight the areas which still need some work. Simple spray primer for larger items should be fine. If you are building small resin models then a thinner primer would be a good idea so as not to accidentally fill your fine details.
Step 7. Repeat Steps 5 and 6
Round 2 of Filler and Sanding Round 2 of Primer, We’re Getting There
You are going to go through multiple rounds of applying filler, sanding to remove the excess, and priming. Your goal on each round is to make the part look better, don’t expect perfection on the first try.
Round 3 of Filler and Sanding Round 3 of Primer, That’s What We Are Looking For
Step 8. Mask and Paint
A Classic Choice in Colors Silver Base Coat Masking For Blue Blue Paint Masking For Red Red Paint
You are in the home stretch now. The seams and layer lines are hidden or obscured. Paint your item using either blue painters tape or contact paper to mask out the designs you want. For multi-color paint jobs you’ll need to think through the order of application and when pulling off the tape you might need to go back in with a paint brush and touch up a few spots. Pick your favorite color paint and get going. For my shield I’m aiming for an American theme, it just seems appropriate right?
Step 9. Enjoy Your Finished Item
Finished Product Ready For Fighting Hydra, Or Getting Candy Now For Little Brother
You are done, time to either bask in the glory of your finished item or suit up and go fight some evil!
Hopefully you found this guide informative and helpful. If you have any questions or comments let us know below.
