3D Printed Sword: Build

Printing

Material

The filament I decided to use was silver Hatchbox PLA.  After printing the coloring of the plastic turned out more of a shiny gray than a silver.  While I knew I was going to paint the sword anyway, I wanted a grayish base color so that the color of the filament wouldn’t show through.  Plus, if the sword ever gets scratched, the dull gray scratch color will look more realistic.

Settings

My biggest concern for the printed parts used for the sword was the strength, specifically the strength between print layers.  This was most critical on the blade of the sword, due to its length and weight providing a lever arm that could cause the prints to snap.  Additionally, due to the way I decided to print out the blade, speed became an issue.  I oriented the sword segments so that the blade was divided along the X-Y plane.  This meant that the longest axis was in the Z direction.  The Z-axis is also commonly the slowest on a 3D printer, mainly because a leadscrew is usually used.  To compensate for all of these design concerns, I tried to find an optimal balance between weight, strength (particularly layer adhesion), and print time.

After reading numerous studies and suggestions, I decided on a layer height of 0.3mm and width of 0.4mm.  I also ran the hotend a little on  the hotter side at 210C.  Because I planned on sanding and finishing, allowing for a little stringing (a common result of too-high hotend temperature) was well worth the added strength and layer adhesion it provided.  I also kept the infill a little low at 10% so the blade wouldn’t be too heavy.

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The 18 50mm segments of the blade are shown above.  They turned out pretty good with minimal stringing.  One noticeable feature on the outside of the blade segments are the vertical lines.  These are caused by interaction between the internal hole perimeters and outside perimeters.  There’s isn’t enough space for both sets of perimeters and so some external artifacts are present on the outside.  Luckily these can be easily hidden by the finishing process.

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The two halves of the pommel didn’t turn out as well as I’d hoped.  Because I printed with the center of the pommel on the bed, there wasn’t enough support for the circular arch that would hold the grip.  This can hopefully be fixed with some sanding and finishing.  Also shown above is the hole that the blade will be glued into.

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Lastly are the grip and pommel.  The grip was printed in two halves and held together by a metal spine.  Three 2mm holes were extended through the length of the grip so the pommel and blade could both be securely attached.

Assembly

The majority of the build time was spent assembling the blade, because it’s the most complex part.  I used cyanoacrylate glue (super glue) due to it’s good adhesion to PLA.  The brand I used was also labeled as “gap filling.”  I figured this would be useful if the tops and bottoms of the blade segments were slightly warped or didn’t match up properly.

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I also used a metal spine to prevent stress on the glue joints and provide additional strength to the blade.  Due to the metal pieces only being 300mm long, I trimmed the rods so that, when transitioning from one rod to another, the joint is in the center of a blade segment.

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I was able to fit three metal spines at the wider base of the blade.

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I cut the metal rods so that a decent portion would protrude from the bottom.  These extra length could then be used to mount the blade to the grip.

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With the pieces all glued together, the next step was coating it!

Finishing

The process of finishing the blade was divided into three main parts, coating, sanding, and painting, with an additional step of leather wrapping the grip.  These steps weren’t terribly difficult, but nevertheless the finishing took a long time, with each step requiring patience.

Epoxy Coating

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The first step in finishing the sword involved coating the plastic in epoxy.  The brand I used was XTC-3D.  It works like most epoxy, involving mixing the two parts together to get a rapidly curing mixture.  I then had about five minutes before the epoxy hardened to brush it on to the plastic.  After this was a four hour wait for the epoxy to finish curing.  Once completely hardened, the epoxy left a hard, clear coat over the plastic.  This had the added benefit of adding more strength to the plastic by holding together the print layers and separate parts.  Because I planned on sanding the pieces anyway, I used an excessive amount of epoxy when coating, as is evident by the visible epoxy drips.

Because I had to apply the coating two each side of the blade separately, I had to wait four hours between each half.  I also wanted to apply three coats to the blade.  What resulted from this was the week long process of coating the blade because I only effectively had time for one half of a coat once I had gotten home from work.

Sanding

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The next step was sanding down the epoxy coating to a smooth, metal-like surface.  This was by far the most tedious process.  I initially bought plain sandpaper and started the process of sanding everything down by hand.  As I soon realized, this was a profoundly terrible idea and would have taken forever.  I shortly gave up and bought a random orbit sander.  The benefit of the “random orbit” was that no directional sanding lines would show up on the finished piece, and so the sword would look uniformly smooth, just like actual steel.

New toy in tow, I forged (pun intended) on with the process of smoothing out the pieces of the sword.  I started out by using 80 grit sandpaper to sand the flat surfaces of the blade entirely flat, and then slowly worked my way through 150, 220, 320, 400, and 600 grit sandpapers.  These left me with an incredibly smooth surface that was ready for painting.

One downside of the sanding that I noticed was that the vibrations caused some of the superglued joints to come undone.  Both the pommel and a piece of the blade had to be reglued.  The blade one actually happened after painting and was difficult to repair.

Painting

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The last step was painting everything.  This was the simplest step, but was still time consuming due to having to wait for each coat to dry before flipping over the sword to paint the other side.  I spray painted each of the pieces separately with silver spray paint, with several coats for each piece.

Leather Wrapping

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As a bonus step, I decided to wrap the hilt in leather to add a nice touch to the finished product.  I cut the leather roughly to size stretched it out a bit, then superglued one edge to the grip.  I specifically left the grip unpainted so that the glue would have a stronger hold on the plastic part.  I then tightly wrapped the leather around the octagonal grip, applying glue on each face.

Failings

While I’m fairly happy with how the finished product turned out, there are two things that didn’t turn out as I’d hoped.  Mainly the stiffness of the blade was lacking and joints between blade segments couldn’t handle the stress of the finishing process.

Stiffness

While the PLA is stiff enough to prevent significant bending, the metal rods have a certain flexibility that allow some give at the inter-blade joints.  As a result, the blade is more flexible than I’d like.  I had to handle the sword very carefully for fear of the joint bending causing the blade to crack or break.  If I attempt a repeat of this project, or something like it, I’ll have to consider a fix for this.

One option would be to use a different type of joint.  The current, flat joint that I’m using allows for some space between the segments where the metal rods can bend.  If I had used some type of overlapping joint it’s possible that the flexibility would have been reduced.

Another alternative would be to use a stiffer material for the blade spine.  Something like carbon fiber rods would be much hopefully be much stiffer.  The only concern with this would be the lack of flexibility putting more strain on the glue joints between segments.

Cracking

The biggest issue I had was with the blade segment joints not being strong enough to withstand the finishing process.  Specifically the vibrations from the sander caused the joint adhesion to fail in one particular spot.

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Near the top of the blade, where the cross section of the blade was small and only one spine held the segments together, the glue joint repeatedly failed.

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At first I reapplied both the glue and the epoxy coating and sanded it down again.  However this caused a second failure, at which point I gave up and just used a lot of super glue and some light sanding.  Fortunately the poor finish isn’t too noticeable at a distance.

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Another part of the blade partially cracked towards the bottom.  Some of the epoxy came out between the blade segments leaving a slight crack.  Because spray paint is so thin, it was unable to hide this defect.

I think the only solution to the strength problem would be to  change the way I’m joining the segments since the superglue doesn’t seem to be strong enough.  Two different methods I could use would be heat or friction welding when using PLA, or solvent welding when using ABS.  These methods would hopefully make the whole blade into one cohesive unit.

Another possible option would be to use a different kind of paint.  I used spray paint which is thin by necessity and has trouble hiding defects.  Using a thicker, brush-on paint would have done a better job hiding the cracks that popped up.

Finished Product

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Despite the issues I had I’m mostly happy with the finished product.  Unfortunately not all projects can be resounding successes, but I learned some new techniques and have a nice decoration for my office now!

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