Modular 3D Printed Hardbox

This instructable is a 3D printing project that will give you a Pelican-style hard case for photo equipment, a laptop, gun case, tool box, whatever...

If you know 3D printing you'd think this would use a lot of filament, but that depends. By using a relatively small value for the infill (around 20% for me) you can make surprisingly light yet strong pieces. This hollow infill will also make for a crushable area that can further protect the equipment inside from extreme shocks.

I started this design when I still had a small 3D printer with around 4" x 4" x 4" print area. All the pieces can be printed on a printer of this size except for some longer rail pieces. I've included shorter versions of those rails as well.

In this version the panels are 4 x 4 inches, the rails are generally 1 1/2 inches (finished dimension). By varying the number of panels you can get case sizes in factors of 4 inches. The panels come in 2 styles, "male" and "female", with the inner flat area either protruding slightly (approx. 1/16") or recessed the same amount. By using these in opposition you can make the case more stackable, the panels on separate cases can register to each other like Tupperware.

I will be updating and improving the pieces for this case over time, with the project posted here and on Thingiverse. However, with multiple copies of only 7 different pieces you can make the exact case you need.

Step 1: Determine Required Box Size and Pieces to Print

This version of the hardbox files are 4" x 4" panels, and 1 1/2" corners and edges. This will allow for boxes in increments of 7", 11", 15", 19", etc. in each dimension. The box in these photos is 11" x 15" x 5 1/2" deep. The box lid can be thin, as in the instructable, or built as the base with panels on the edges.

The panels are available in "female" and "male" variations, where the inset area in recessed (female) or extends (male). If the boxes built are meant to be stacked, alternating the female and male pieces will let them stack easily. Otherwise either panel type may be used. The male panels will be slightly stronger/thicker than than the female ones.

To make the box in this guide requires 34 pieces. Broken down that's 16 female 4x4 panels, 6 male 4x4 panels, 4 bottom corners, 4 opening corners and 4 shallow lid corners. In addition to box pieces you'll need hinges, handle, handle mounts and latches.

Import the enclosed files to your favorite slicer program (i.e. Cura) and print as needed for the application. A "light" box can use settings of 20% infill, .175mm extrusion and 2 shell layers. Test higher (or lower) numbers to get the right amount of "sturdy". Even though those settings may seem very light, remember that the final case will be glued together with splice pieces in the slots. This construction will make the final case much more sturdy than any single piece right off the printer.

The exception to these settings however is for printing hinges, latches and the handle and its mounts. Print these pieces as strong as possible (100% infill) and positioned so the filament is extruded along the longest length runs, rather than the shortest as the perpendicular angle (to the filament extrusion direction) is weakest. Splice pieces will also benefit from being printed at 100% infill.

This box with the settings described require approximately 1.5 kilos of filament. I printed in PLA, but ABS would work fine and allow for acetone smoothing of the final assembled box. Don't acetone smooth before assembly as acetone vapor treatment shrinks the pieces and could wreck the dimensionality. Once an ABS box is fully assembled a very light touch acetone treatment would help the finish as well as sealing seams and improving the strength of the joints.

Step 2: Test Fit All Pieces

It's important to test fit all pieces before gluing. If a piece is not fitting properly you want to know before your 5-minute epoxy is setting up and the piece won't fit properly. Putting tape with references or witness marks on pieces where and how they join is also a good idea. If not, you may put the pieces together different during glue-up, and then they may not fit as expected.

This test is also good for the desired content that the box is intended for. If the box ends up being too small, print more pieces now before glue up.

Also be aware of the assembly order. It is not hard to get in a situation where pieces are permanently glued together, and that won't allow another piece to slide in place. Assembling the 3 "frames" initially is a good approach.

Step 3: Mix Small Amount of Epoxy to Test and Glue a Few Pieces Together

It is good to know how much you can glue up at any given time. Many epoxy glues will set in only five minutes. You can easily waste glue by mixing up too much than can be used while it's still liquid. More importantly, you don't want to apply more epoxy than you can assemble because if it dries before assembly you'll need to remove dried epoxy for the later glue up. This is not fun, especially on the inside of slots. You may want to consider using epoxy with a longer setup time. Epoxies with 8-10 minutes or even 1-hour setup times are available.

With a small amount mixed start by assembling panel sections with cross braces. Using a popsicle stick dab epoxy into the gutter and inside edges of the panels. When panels are glued up, place on a flat surface to ensure they will be flat when the epoxy cures. Be careful that any glue that drips out can end up gluing the pieces to the surface they are drying on.

If the printed pieces are ABS, you can glue them together with an acetone-ABS slurry made with scrap ABS dissolved in acetone. Just be careful that the minimum amount of acetone is used as ABS parts treated with acetone can change a lot dimensionally.

Step 4: Glue Up Panel Sections

Glue all panel sections together, paying attention to the gender/male/female of panels and gluing the appropriate pieces adjacent to each other.

Make sure to join all panels with the appropriate splice piece, a cross for a spot where 4 panels come together, or a straight splice piece where only 2 panels touch each other. Without a splice piece the glue joint will be very weak, make sure you don't butt join any pieces if possible.

Step 5: Glue Up Rails and Corners

Glue up rails to corners, 2 adjacent corners at a time. Assemble a full "frame" (all rails, all corners) with that side's panel sections. Make sure that corners are square and plumb so their panels can slide in place without binding.

Using a drawing triangle or something guaranteed to be square will help in ensuring square assembly. The banana in the picture is not used for testing square, but for scale only.

Step 6: Complete Box and Lid

Now that you know the nature of your epoxy and how much you can comfortably glue, complete the box and lid.

Step 7: Clean Up Dried Glue

Extra epoxy has likely dripped and dried to some surfaces. using a knife or chisel, clean away the dried drips.

Step 8: Fill Gaps With Epoxy Putty

If the fit has not been perfect and you have gaps between the pieces, an epoxy putty can be mixed and filled into cracks with a putty knife. Force putty into cracks and then scrape excess off before putty dries.

The epoxy putty shown is a "water weld" type, it was all that was available. I'm sure any epoxy putty would suffice. The water weld epoxy was very thick, I'm going to look for putty next time that is softer when mixed, it will make filling cracks much easier.

Step 9: Paint If Desired (or Required)

Painting may be effectively required if like me you printed in multiple colors, or of course if you just want a different color and smoothest possible finish. Paint will also fill small cracks and help in weatherproofing the case. If pieces were printed with excess support or overhang drips, sand to smooth and clean up surfaces.

Be sure to review each piece's overhang settings when printing, so you don't have to do too much post-print cleanup. You'll want something like 80 degrees overhang, with a density around 25%. Step 5 shows overhang settings in Cura that worked well for me.

Step 10: Glue Hinge Halves With Alignment Rod

Using a 3/16 solid metal rod, thread hinge halves onto it in preparation for gluing. Do not attempt to glue hinges without using an alignment rod. They will almost certainly NOT be in perfect alignment, and when attempting to open/close they're liable to break.

The hinge pieces are ambidextrous (I think that's the right term) and mirror each other. For 1 hinge print 2 of the exact same pieces and assemble with a Chicago bolt, also sometimes called screw posts.

Glue hinge halves in place with appropriate spacing, align center of hinge hole with box edge or slightly above. Clamp two hinge halves during gluing to ensure they do not move.

Once one half of the hinge has been glued, assemble the remaining hinge pieces with Chicago bolts. Being very careful to not get any glue in the hinge pivot, glue the remaining hinge pieces in place.

After the glue has cured drill through the hinge pilot holes if bolts are desired. If not, fill hinge bolt holes with epoxy putty.

Step 11: Attach Handle and Latch(es)

Glue hinge pivots in place being very careful to not get any glue on the bearing surfaces so that all the parts that have to move aren't glued together. Repeat with the latch pieces.

Step 12: Cut Foam Layers

The fancy cases have cube-cut foam, where thin cuts allow foam to be removed in small cubes to make space for your items. If you use thin foam sheets, such as 1" or so thickness in multiple layers you'll be able to get a similar effect by cutting each layer for that level. Foam sheets from bed cushions or automotive upholstery "landau" closed cell foam works well.