3D Printing a Better Black and Tan Part 5: Too Fast, Too Furious

After the success of the Mini Siphon Mk I, followed by the surprising failures of the full scale Beer Siphon Mk III, several changes have been made to the design to make it less fragile, less leaky, and hopefully just work.  But would it produce a Black and Tan, or just more heartbreak?

Design:

This design is very similar to the Beer Siphon Mk III, with several notable changes.  As in the Mk III, there is a largish fluid reservoir at the top, that when filled, primes a siphon that will empty the reservoir through pipe leading to the bottom of a pint glass.  A second pipe runs from the middle of the siphon pipe up through the reservoir to allow trapped air to escape, so a second siphon can be started while the pint glass is half full.

Notable changes from the Mk III include moving the vent pipe to the edge of the reservoir for added strength.  Additionally, the inner diameter of the siphon and vent pipes was increased to increase the siphon flow rate.  The inlet of the siphon pipe and the top loop were also offset slightly so the siphon pipe doesn’t pass directly over the inlet.  Finally, the area around the inlet was also flattened slightly so it could more easily be covered, in case the reservoir needed to be patched with paraffin wax.

Cross Sections

Cross sections showing the Beer Siphon Mk IV sitting atop a pint glass.

The 3D model for the Beer Siphon Mk IV is available on Thingiverse.

Slicing & Printing:

In addition to the design changes mentioned above, for the Beer Siphon Mk IV, a variety of different slicing settings were modified to address issues observed in previous prints.

To address the problem of leakage from the reservoir, the shell settings were modified to have a wall line count of 4, top and bottom thicknesses of 3.6mm (6 layers), and the top/bottom/initial layer patterns were all set to concentric.  Since this model was printed inverted, support roofs were enabled to hold up the reservoir floor as it printed.  The roof thickness was set to 1.8mm (3 layers) with a grid pattern and 2.4mm (2 nozzle widths) line distance.  The roof was then supported with with a pattern of lines with a density of 10%.

To address the problem of stringing inside the siphon pipe, combing mode was set to “All”.

As with all previous test prints, the Mk IV was printed on a Lulzbot TAZ6.  Due to printing time constraints, a 1.2mm print nozzle with 0.6mm layer heights was used and the model was inverted.  After the durability issued observed in the Mini MK I and the Mk III, it was decided that a switch back to PLA was warranted, as it seemed to be a sturdier material.

Testing:

The resulting print looked good.  However, many of the seams were very obvious, and there was a bit of ghosting in the lettering.  There is also a slight deformation of the reservoir wall near the lip.

Shows printed siphon atop of pint glass.

The printed Beer Siphon Mk IV ready for testing.

The new location of the vent pipe along the reservoir wall was much studier, and suffered no damage while removing support material.  Unfortunately, the roof supports, that had been enabled during slicing to support the reservoir floor, were too difficult to remove and had to be left in place during testing.

Despite our best efforts to remove them, the roof supports appear to be fused to the siphon pipe and reservoir floor.

During testing, some leakage occured both in the reservoir floor and the siphon pipe.  The reservoir leaks were primarily along the flat bottom and along the edges of the feet.  The siphon pipe primarily leaked where is passed through the bottom of the reservoir.  But the leaking was not nearly as bad as in previous iterations of the beer siphon, and was easily patched with a bit of paraffin wax.  There were also minor leaks between the layers that were small enough as to not interfere with testing, however beer that leaked through those interlayer leaks impart a noticeably grungy appearance in some photos..

Shows paraffin wax patching.

Paraffin wax used to patch leaks in the reservoir floor and siphon pipe.

When a full scale test using Guinness and Bass was performed, the Bass was poured too quickly and foamed over, which caused foam to move into the siphon pipe, breaking the siphon.  When more Bass was slowly added, the Bass flowed through the siphon pipe far too quickly, resulting in turbulence that disrupted the desired layering.  As shown below, a small layer of Bass did form.

Shows "layering" of the initial Mk IV testing.

Results of first test of the Beer Siphon Mk IV with beer.

To reduce the flow rate, the end of a small stir stick was inserted into the siphon inlet.

Shows stir stick partially blocking siphon inlet.

Stir stick partially blocking siphon inlet to reduce turbulent mixing due to excessive flow rate.

With the restricted flow, the results were slightly better, but there was much more mixing than desired.

Shows improved layering, with backlight.

Improved layering resulting from restricting flow at the siphon inlet.

What went wrong:

  1. The support roofs were too well attached to be removed.
  2. The siphon pipe diameter was too large, resulting in turbulent mixing instead of layering.
  3. The thickened shells still leaked enough to require patching.

What went right:

  1. The repositioned vent pipe was much sturdier.
  2. Once patched, siphoning worked better than expected.
  3. Partially blocking the siphon inlet reduced mixing.

Possible Improvements:

  1. Reduce the siphon pipe diameter, thereby reducing the flow rate and minimizing mixing.
  2. Modify the shape of the siphon pipe outlet to reduce turbulence.
  3. Adapt known water tight printing techniques to reduce/eliminate leaking.

Conclusion:

This iteration suffered from some leakage as well as the turbulence at the siphon outlet which disrupted the satisfying layering that is characteristic of a Black and Tan.  However, there is hope that with a few minor modifications to the model design and printing settings that a future iteration will work as intended without the need for patching with wax.

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