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GNAL

Free and open source processing system for 16mm and Super8 film

/img/gnal_50ft_v3.png

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What's GNAL? Gnal's Not A Lomo!

GNAL stands for Gnal's Not A Lomo because it isn't. While inspired by a certain motion picture development tank the goal of this project is to create a free, open-source, modification-friendly processing system for small format movie film with the added constraint that it be 3D printable or otherwise able to be fabricated on a small scale. All source code and STL files for printing will be made available in this repository.

GNAL is built using OpenSCAD. OpenSCAD is a free, open-source CAD program that uses scripts to generate objects. Building this project in OpenSCAD serves two purposes: it uses only free and open source software to create the GNAL processing spirals and it future-proofs the design by preserving its dimensions in human-readable text format. Even if OpenSCAD were to disappear tomorrow (and we sincerely hope it doesn't) it would still be possible to recreate the GNAL models in another CAD program just by reading the code and reproducing the measurements.

While the files are all free, open-source and readily available to download; actually printing them can be a challenge. Please read through this README for information about materials, printers and troubleshooting your prints.

Happy processing!

Where's the tank?

Good question!

V3 STL Files

50ft/15m

IMAGE_PLACEHOLDER

All 50ft v3 STL files in a .zip

100ft/30m

IMAGE_PLACEHOLDER

All 100ft v3 STL files in a .zip

V2 STL Files

50ft/15m

IMAGE_PLACEHOLDER

All 50ft v2 STL files in a .zip

100ft/30m

IMAGE_PLACEHOLDER

All 100ft v2 STL files in a .zip

V1 STL Files

50ft/15m

IMAGE_PLACEHOLDER

All 50ft v1 STL files in a .zip

100ft/30m

All 100ft v1 STL files in a .zip

Printers

The diameter of these spiral reels limit the printers that are capable of printing this design. The 50ft/15m model is 225.71mm (8.88in) wide at the base and the 100ft/30m model is 299mm (11.77in) wide.

50ft/15m Capable Printers

100ft/30m Capable Printers

There are people successfully printing spirals in sections on smaller printers, but that is not a recommended use of these files as it requires extreme precision to reconstruct the parts into a reel that will load without problems. Another thing to consider is the longevity of the bond made by the adhesive you choose. Don't let that stop you, though. A multi-part printed reel is just not a priority for this particular project. An enterprising spirit might notice the gnal_50ft_spiral_quarter() and gnal_100ft_spiral_quarter() modules in the V3 OpenSCAD scripts and begin to wonder what is possible.

Material

PETG is currently the recommended plastic for printing the GNAL. Since this is a piece of darkroom processing equipment its exposure to water and photochemistry is inevitable and should be considered primarily. PETG (Polyethylene terephthalate glycol) is PET--which is a plastic that's typically encountered in plastic bottles and food containers--in a copolymer with glycol.

Various manufacturers have published safety data sheets for PETG filament. The only warning about reactivity I have discovered states that a condition to avoid is "strong oxidizing agents" which may include reversal bleaches that contain strong acids. This is not a scientific evaluation and may stand to be corrected.

ABS is a viable option but has a greater tendency to warp on larger prints without proper temperature control around the print bed. Since this model needs to be consistently flat across the bottom of the reel, this is not ideal and will make for a challenging print. ABS is a plastic commonly used in injection molding and is also generally non-reactive with photochemistry.

PLA is not recommended but this doesn't mean you can't get an acceptable result with it. The lack of endorsement comes from mostly anecdotal experience witnessing the wear and tear caused by exposure to water on PLA prints. Biodegradable and porous, PLA will wear down in the weakest parts first and on this model that would be the spiral. If you do not need your processing equipment to last a long time, you may find it acceptable. PLA stands for polylactic acid and is likely the most reactive material to use with photochemistry where pH is vital to maintain for consistent results.

Troubleshooting

Many, many issues were encountered during the development of this tool. Prints came out warped, failed midway during multi-day prints and had other mysterious ailments. I am by no means an expert but have built up months of experience trying to print these models on a variety of machines.

Warping

Fused filament fabrication relies on the behavior of plastics at high heat to create a physical object. If your prints are warping, there are a few things to look at.

  1. Material
  2. Heat
  3. Slicer settings

The first thing to consider when your prints are coming out warped off the print bed is whether or not your material is appropriate for this model. Check the #material section of this README for more information, but theres a chance if you are using PLA or ABS that large flat prints of this size are warping due to limitations with the material you are using. PETG has proven to warp far less in my own anecdotal experience and is the recommended material for this project.

The thermal properties of the material you're printing are what leads to warping, so check if your printer is being set to the recommended temperatures on both the bed and extruder for the material you are using. Warping occurs consistently when a part cools too quickly and contracts while the rest of the part is still being printed. Avoid this by using an enclosure on your open-frame printer or by printing in a space with low air flow but still with appropriate ventilation for the material you use.

The slicer you use and the settings in its configuration will make a lot of difference in how your print comes out. During the development of this project Cura is the slicer used most for test prints, however you might find that different software works best with your machine. The settings are important to test before you commit to a complete print of the spiral part.

Here is an example of the key settings used during development while printing with PETG.

Setting Value
Extruder Temperature 240° C
Bed Temperature 80° C
Generate Supports Yes
Infill 20%
Print Speed 40 mm/s

This is a fraction of the overall settings used by Cura, but they note some of the key features that were changed from the default profile provided by Cura.

Development

This project can be edited with only OpenSCAD and the source files in the scad/*_v1, scad/*_v2 or scad/*_v3 directories which make reference to files from scad/libraries. If you wish to run the development scripts you should install the following dependencies.

With just OpenSCAD, you can use scripts such as scad/50ft_v3/gnal_50ft.scad and export the different modules in OFF, AMF, 3MF, DXF or SVG (drawing) format. The CSG models can be imported into FreeCAD and DXF models should be readable by AutoCAD and QCAD.

Dependencies

Build Scripts

Running any of the build scripts scripts--scripts/v1.sh, scripts/v2.sh or scripts/v3.sh--will start an OpenSCAD build process of all components and will log stats about the resulting files and render times to notes/v1.csv, notes/v2.csv or notes/v3.csv.

Keep in mind that V1 and V2 compile times are extremely long and all scripts will use an entire CPU core at 100% utilization while rendering. It's best to run these scripts in the background on a powerful machine or better yet, not at all. See the stl folder for pre-compiled STL files for 3D printing or the releases page for .zip and .tar.gz archives of all versions.

These scripts will render STL files, PNG images of the files and capture metadata about the render process while doing so.

Benchmarks

The scripts/benchmark.sh script will run various tests on the different approaches to generating spirals in the spiral directory. See notes on the actual results of this script below

Version notes

V1

Intended to be mostly compatible with existing processing spirals with some caveats. A spacer that is typically threaded has been replaced by a friction fit part so they are not interchangeable.

This version is designed to fit in existing tanks and use the same spindle screws.

In the process of building this first version several approaches were evaluated to generate the spiral shape. The first is what's best described as a brute force approach laying out an excessive amount of rectangular facets and unioning them together in such a way that the result would be a single continuous spiral. This took hours to days to render depending on the machine used.

Besides the exhausting render times this approach bugged me for one reason: all facets of the spiral were the same size, meaning that the small diameter inner parts of the spiral were packing in millions of unnecessary polygons to allow for the large diameter parts of the spiral to be smooth. This didn't sit well with me. How many CPU hours are being burned by adding detail to a place that doesn't matter? Answer: a lot.

Finally an external library called path_extrude.scad by @gringer was brought in to handle the complicated spiral extrusion step. A simple function that plots a spiral in Cartesian coordinates is used to draw the path and a 2D triangle is extruded along it by the library. This allowed for the path to be drawn at a consistent "resolution" throughout the entire spiral, so the facets of the outermost and innermost parts were the same or extremely similar.

Here is that function reduced to a single line in order to generate an array of coordinates.

spiralPath = [ for(t = [0 : $fn + 1]) [((d / 2) + (t * increment)) * cos(t * angle_i), ((d / 2) + (t * increment)) * sin(t * angle_i), 0] ];

The experimentation in this version predate this particular git repo and so will not be found in the git history, but you can find the vestigial functions in the spiral directory used for benchmarking different approaches.

Beware

This version of the spiral must be printed with supports. The spirals themselves are suspended over voids and this particular feature is addressed in the later versions.

Rendering

Rendered using OpenSCAD version 2019.05 on a 2.2 GHz Core i7 (I7-4770HQ) chip running macOS 10.14.

Model Size (bytes) Facets Volume (mm3) Render Time (sec)
gnal_50ft_spacer.stl 991452 5736 2888.155029 68
gnal_50ft_top.stl 2132181 12624 57936.746094 233
gnal_50ft_spiral_top.stl 36509561 214404 120299.773438 12249
gnal_50ft_spiral_bottom.stl 36606204 214970 121519.937500 13698
gnal_100ft_spacer.stl 991452 5736 2888.149658 74
gnal_100ft_top.stl 3302563 19552 102590.546875 477
gnal_100ft_spiral_top.stl 92423369 542836 223602.078125 89137
gnal_100ft_spiral_bottom.stl N/A N/A N/A N/A

V2

This version aims to improve printability over the V1 model and reducing render time of the spiral. The biggest change to the physical structure of the design is the removal of overhangs from beneath the spiral film guide.

When printing a model with FFF printing, any piece that overhangs empty space (usually) needs to be supported by a temporary removable structure beneath it otherwise you risk the piece drooping. In the case of V1 model, the spiral was completely suspended by the spokes of the reel with large gaps of empty space. This means there were 90 degree overhangs under the most critical part of this model; the grooves for holding the film in position. Printing and removing support structures from beneath the fragile spiral made post-production dangerous for the piece and time consuming.

The solution to this was to extend the spiral to the bottom of the reel and remove triangular sections from them to allow for a lighter print and better chemistry movement. Most printers should be able to print these structures without any support material or any resulting deformations in the model.

One other change in this version is that it reduces the spiral models to a single one to be duplicated, rather than two distinct top and a bottom pieces that differ in only minor ways. This decision was motivated by an interest in making this design better (cheaper) for injection molding.

A secondary benefit of reducing the spiral to a single model was to immediately cut render times for the entire project nearly in half before any other optimizations were made. The first meaningful code optimization toward this goal was provided by a helpful comment made on a long-forgotten design shared on a 3D printing forum.

@sousvide59 (Les Smith) writes

It may be more efficient to approximate the spiral as a series of arc segments, like this <Github gist>.

Les was right. This reduced the several hours render time to 1-2 hours, which worked for this version. Ideally this will be improved further in future versions. Beyond some explorations into OpenSCAD hacks (rendering each complete rotation of the spiral and stitching all resulting STLs) the next version will incorporate other languages and platforms to find the fastest render time for a GNAL spiral. All previous approaches are being compiled into a suite of tests to benchmark render times.

Rendering

Rendered using OpenSCAD version 2020.01.17 on a 3.2 GHz Core i5 (I5-4460) chip running Ubuntu 18.04.

Model Size (bytes) Facets Volume (mm3) Render Time (sec)
gnal_50ft_spacer.stl 991452 5736 2888.150879 22
gnal_50ft_top.stl 2132181 12624 57937.210938 73
gnal_50ft_spiral.stl 34628449 193450 178181.250000 2341
gnal_50ft_insert_s8.stl 5228272 27230 3493.560303 97
gnal_50ft_insert_16.stl 7922994 41426 4664.952637 155
gnal_50ft_spacer_16.stl 561267 3272 4015.912109 19
gnal_100ft_spacer.stl 991452 5736 2888.152100 23
gnal_100ft_top.stl 3302563 19552 102590.812500 118
gnal_100ft_spiral.stl 59279238 330000 345431.531250 4542
gnal_100ft_insert_s8.stl 5228272 27230 3493.559326 99
gnal_100ft_insert_16.stl 7922994 41426 4664.937500 160
gnal_100ft_spacer_16.stl 535264 3112 3964.118164 17

V3

The goals of V3 are to greatly optimize the spiral generation code for speed and to restore the feature of the V1 spiral which maintains a consistent size of individual facets throughout the spiral even as the diameter changes. This will be considered a stable release candidate for publishing the project.

Since the benchmarking process (see below) was developed between V2 and V3, render times are optimized in this iteration of the project. The success of the [scad/spiral/spiral_3.scad](spiral_3.scad) approach stood out amongst the rest, so it was reworked into what exists in V3.

The spiral itself is plotted in 2D with a relatively simple formula that is expressed in the OpenSCAD script through a number of in-line helper functions. It draws the position of various points along the spiral path and then uses the path_extrude.scad library to extrude a shape along those coordinates. This proves to be fast and efficient while not sacrificing any of the detail in the geometry.

Prior to release a serious flaw was found while printing the V3 design. The attempt to remove the need for supports in V2, actually printing the spiral was creating curious side effects during fabrication. Not having material in the voids below the spiral, it seems, allowed air to cool the part and would consistently cause prints to fail when it reached the actual spiral at the top of the reel. Since this is the most important element of the reel, the triangles have been removed and the design is more similar to V1. Testing continues on this version.

In a compromise to make the process of removing the support material less dangerous to the detail on the top, the spiral itself extends lower than V1 into the space between the spokes of the reel. The spiral is also made thicker and is a multiple of my nozzle diameter (0.4mm). This uses slightly more material but is less fragile than V1 and test prints proved that the supports were less difficult to remove than in the earliest model.

This version will also contain a 4x reel stacking feature so that all models can be stacked with 3 spiral reels and a top piece. That will give 200ft capacity to the 50ft model and 400ft capacity to the 100ft model. A stretch goal for this version is to make a 35mm spacer and spindle set so that movie film in the format can be processed in 100ft lengths.

Beware

This version also requires the use of support material while printing.

Rendering

Rendered using OpenSCAD version 2020.08.18 on a 2.2 GHz Core i7 (I7-4770HQ) chip running macOS 10.14.

Model Size (bytes) Facets Volume (mm3) Render Time (sec)
gnal_50ft_spindle_bottom.stl 3760384 75206 4134.077637 1291
gnal_50ft_spindle_top.stl 6915384 138306 22229.814453 1128
gnal_50ft_spacer.stl 286884 5736 2888.150635 62
gnal_50ft_top.stl 1104884 22096 57933.800781 585
gnal_50ft_spiral.stl 9500384 190006 171712.140625 1111
gnal_50ft_insert_s8.stl 1361584 27230 3493.544922 276
gnal_50ft_insert_16.stl 2071384 41426 4665.019531 439
gnal_50ft_spacer_16.stl 602084 12040 4019.470703 281
gnal_100ft_spindle_bottom.stl 3760384 75206 4134.064941 1275
gnal_100ft_spindle_top.stl 6979184 139582 22229.773438 1139
gnal_100ft_spacer.stl 286884 5736 2888.143555 63
gnal_100ft_top.stl 1620084 32400 102557.437500 998
gnal_100ft_spiral.stl 18364384 367286 326573.812500 3746
gnal_100ft_insert_s8.stl 1361584 27230 3493.548340 272
gnal_100ft_insert_16.stl 2071384 41426 4664.790527 450
gnal_100ft_spacer_16.stl 755684 15112 4019.479248 368

Benchmarks

In the process of publishing this repository I started questioning claims I was making in this README. Throughout the development of this processing reel I've been plagued by long render times. As a sanity check, I went through my personal development history on this project and produced 6 distinct spiral generation scripts that I ran through a series of tests to benchmark the render performance, total volume generated and number of facets produced. Render time was the primary metric that concerned me, but I considered the other important in comparing these different approaches.

This work led to the creation of the approach in spiral_7.scad and was ultimately used in V3.

An example of a single test pulled from the notes/benchmark.csv results. These example results are rendered using OpenSCAD 2020.05.23 on a 2.3 GHz Xeon Gold 6140 chip running Ubuntu 18.04.

Spiral Test Diameter (mm) Rotations $fn Size (bytes) Facets Volume (mm3) Time (sec)
scad/spiral/ 47 10 100 7409653 41064 5391.819336 209
spiral_2.scad 47 10 100 15349620 86646 3639.441162 855
spiral_3.scad 47 10 100 1336635 8004 3589.485596 0
spiral_4.scad 47 10 100 1607691 9624 3830.134521 23
spiral_5.scad 47 10 100 4711486 28188 3602.101562 8
spiral_6.scad 47 10 100 4265376 25396 14337.455078 120
spiral_7.scad 47 10 100 990006 5924 3581.499756 0

As you can see, the different approaches lead to wildly different render times for different tests. If you look at the complete results you will see many tests did not even finish due to exhausting the memory on the machine or the process being killed by

In the scad/spiral directory you will find each individual script in a scad/spiral/spiral_#.scad file. The scripts/benchmark.sh script will render spirals at various resolutions and rotation counts and record the results in notes/benchmark.csv.

Consider this comparison of just the 50ft spirals (top spiral from V1).

# Model Size (bytes) Facets Volume (mm3) Render Time (sec)
V1 gnal_50ft_spiral_top.stl 36509561 214404 120299.773438 12249
V2 gnal_50ft_spiral.stl 34628449 193450 178181.250000 2341
V3 gnal_50ft_spiral.stl 9500384 190006 171712.140625 1111

Render times have gone down dramatically between V1 and V2. Times halved again between V2 and V3. The volume has stayed consistent with major changes in geometry (between V1 and V2). The file size of the V3 spiral has reduced to about 30% of the V1 and V2 spirals and the facet count remains roughly the same throughout (which was a surprise).

Faster render times mean more iteration and less time between tests. The next part of the process to examine is slicing which has primarily been done with Cura, but other engines will be looked at for their speed, efficiency and print quality.

License

MIT License

Copyright (c) 2020 Matt McWilliams

Permission is hereby granted, free of charge, to any person obtaining a copy of this hardware, software, and associated documentation files (the "Product"), to deal in the Product without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Product, and to permit persons to whom the Product is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Product.

THE PRODUCT IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE PRODUCT OR THE USE OR OTHER DEALINGS IN THE PRODUCT.