Adventures in 3D Printing
Taulman Nylon 618

Don’t you hate the way your closet’s clothes hanging rod dips in the middle? How your longest garments sweep the floor or cover your shoes?

Well, I did. But now I’ve fixed it.

In February, 2013 I was looking to familiarize myself with OpenSCAD and Makerbot Thingiverse’s Customizer extension by creating a parametric bracket that could stop my closet’s clothes rod from smiling at me ever again.

At the time, I had access to a number of consumer FDM machines my employer Undercurrent was evaluating on behalf of a program we designed for GE. When printed in ABS or PLA, my bracket wasn’t strong enough. I knew next to nothing about mechanical design (I mean, just look at those dopey right angles!)

I had it produced at Shapeways using the SLS process in Nylon. It cost about $40. I installed it and it’s proudly kept the master bedroom’s closet from bowing ever since. The guest room, on the other hand, would have to strain under the weight of winter coats for more than two years. My own adventures in printing in Nylon would have to wait.

At the beginning of 2015, additive design guru Spencer Wright sent me a link to some experimental graphene filament that could be used with our Makerbot Replicator 2. I had long wanted to try and print in conductive filament to produce antenna elements (more on that later). Before checkout, I added a few more materials I had no experience printing with, including Taulman’s Nylon 618.

The Disaster

The first time I attempted to produce a part using the material was printing a part for Spencer’s Public Radio project. Spencer had designed a number of manufacturing jigs and we suspected Nylon might be more durable than PLA upon repeated use. Confident after the printer extruded a few layers, we stepped out of the office. When we returned a few hours later a disaster had occured: the part lifted from the build plate and the extruder block had encased itself completely in Nylon.

I wish I had taken photos. It was a mess.

After pleading and pulling favors at Makerbot, they mailed me a new block. It was months before I attempted to reprint in Nylon.

Climbing Back on the Horse

After I rebuilt the Makerbot, the spool of Nylon filament sneered at me from across the room.

“You’ll never win,” it seemed to say.

One rainy weekend I decided to change all that. I quickly measured the dimensions in the guest closet and designed a primative part. Using the excellent commercial slicing/CAM software Simplify3D, I configured a Nylon 618 material profile from parameters on Taulman’s website:

• Retraction distance: 6.00mm
• Outline/Perimeter Shells: 4
• Infill: 100%
• Extruder Temperature: 245°C
• Default printing speed: 3200.0 mm/min

I enabled a raft and supports and as per Taulman, I printed directly onto blue painter’s tape.

Initially, the raft adhered well to the plate. As the part began to build up and the lower layers cooled, the raft began to lift at the edges. I tried to use additional painters tape to tape down the curling edges of the raft, but to no avail.

My neighbor and 3d printing enthusiast, Chris Zucker, suggested I print my raft directly into Mod Podge adhesive. It helped! I was able to produce this:

The largest cylindrical hanger was so warped it was unusable. But, it was strong!

I consulted with Spencer.

He suggested that if the majority of the cooling stresses were occurring across the length of the part that I try and make those Nylon fibers as short as possible and break up the stem by punching triangular holes in it.

“Like a truss,” I said.

“Like a truss,” he said.

So then I designed and printed this:

Even with the truss, the part still warped. Indeed, it wasn’t appreciably different than the first part. This part, however printed well enough to be tested in the closet.

I installed it and pop! It failed as soon as I started to load the rod.

Upon inspection, it was clear what was going on: the part was weakest where the mechanical force was parallel to the bonded layers of Nylon. The part litterally failed along a seam.

What to do?

The Solution

I needed to print the part so it wouldn’t split the hanger when it was loaded. But doing so would mean that one of the hangers would be oriented 90° the wrong way. What to do?

I live next to the Manhattan bridge, its span supported by great flexible steel cables.

As I travelled across the bridge into the office one morning, I looked at those cables and thought, “what if I could print a cable in Nylon?” Then, I could simply twist one of the hangers into place as I installed it.

I’d be working with the material and its strengths without being hampered by the weaknesses of the process.

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A few days and a few trivial geometry problems later, I had a design. All I needed to do was print it. I wanted to minimize the stress-induced warping as much as I could.

The solution I came up with was to print the part in two stages. First, I spread a layer of undiluted Elmer’s glue directly onto the blue paper tape, printed the raft directly into the glue, and cold paused the print until the glue fully cured. Second, I resumed the print and printed onto this very rigid Nylon raft. It worked like a champ (even if it does cost a full sheet of painter’s tape).

This was the result:

So how strong is this bracket?

The Taulman Nylon 618 material specs give its tensile strength at 4,575 psi when 3D printed. My 3D printed cable is made of 4 elements each with a diameter of 1/8″.

Calculating the yield strength of this part is straightforward:

Surface Area of Cable Assembly = 4*π*(1/8″/2)² = 0.04909 in²

Tensile Strength of Bracket = 4,575 psi * 0.04909 in² = 224.59 lbf

Theoretically that’s nearly 225 pounds of force when this bracket is ideally loaded. Even with a 2X safety factor, the bracket should be able to support more than 100 pounds. Clearly, I’ll have to test it to see if the results are this good.

I bet now you want your own Brooklyn Artisanal closet bracket. Lucky for you, all the design files and instructions are available on Thingiverse. The design has been enabled for use in Thingiverse’s Customizer, so you can tailor it to your own unique needs.

If you print one, please let me know. There’s no greater gratification for a creator than to see somebody use their design.