DIY Photochemical Machining: Creating Precise Sheet Metal Parts at Home

Summary:

The video demonstrates a detailed DIY photochemical machining process, offering a cost-effective alternative to commercial services for producing precise, fine-featured sheet metal parts for prototyping or low-volume production.
The initial steps involve rigorous cleaning of sheet metal using a hot water bath and a water break test to ensure optimal photoresist adhesion, followed by careful drying with shop towels.
Dry film photoresist is then laminated onto both sides of the cleaned metal using a customized laminator designed to correctly peel off the soft protective layer.
High-contrast photomasks are printed on special transparencies using an inkjet printer with specific ink, and a practical trick is shown for printing on clear film.
Masks are precisely aligned on the metal, ensuring the emulsion side is closest to the panel, and exposed to UV light from a custom rig built for sharp shadow resolution.
After exposure, the protective layers are removed, and the photoresist is developed in a sodium carbonate solution, revealing the pattern.
The metal undergoes spray etching in a custom machine with a high-pressure pneumatic pump and ferric chloride, enabling efficient, faster etching where parts fall freely into a mesh bag.
The final step, though not fully demonstrated, involves stripping the remaining photoresist with a strong basic solution.

Various precise metal parts created using the photochemical machining process, including a ring, a solid circle, a fan-like design, and a multi-fingered component. [ 00:21:27 ]

Introduction to Photochemical Etching [0:00]

The video introduces photochemical machining as a method for creating precise sheet metal parts with features too fine for traditional methods like water jet or laser cutting, or for designs with a high density of holes, such as meshes.

Close-up of a fine mesh pattern on a round metal part with a ruler for scale, demonstrating the precision achievable with photochemical machining. [ 00:00:08 ]

Close-up view of etched metal showing fine lines, illustrating the 0.5mm and 0.25mm feature sizes. [ 00:00:13 ]

A large rectangular metal mesh with intricate, uniform holes, showcasing complex patterns difficult for traditional methods. [ 00:00:18 ]

Problem with Traditional Methods:
- Water jets and laser cutters can distort fine features.
- Large number of holes makes cutting impractical or impossible.
Commercial Vendor Limitations:
- High costs: Approximately $300 setup fee and $600 minimum for 10-20 parts.
- Long lead times and slow iteration process.
Motivation for DIY:
- Cost-effective for prototyping and low-volume production.
- Enables faster design iteration and experimentation.
- Personal interest in tinkering and exploring a potential side business.

Why Use Photochemical Etching? [1:39]

Photochemical etching is crucial for applications requiring very fine or complex features that cannot be achieved by stamping, laser cutting, or water jet cutting.

A close-up of a potentiometer's internal wiper, illustrating a common application for finely etched metal parts. [ 00:01:51 ]

A camera with a finely etched microphone grille, serving as an example of intricate metal components in electronics. [ 00:01:55 ]

A battery door mechanism from a camera, showing a common application for custom sheet metal parts. [ 00:02:00 ]

Common Applications:
- Battery terminals, potentiometer wipers, micro switch spring fingers.
- Grilles for microphones or speakers in electronics.
- Components for battery doors and drone parts.
Limitations of Stamping:
- Primarily suited for high production volumes.
- Expensive for low production volumes or prototyping due to die creation costs.
Unique Capabilities of Photochemical Etching:
- The only viable method for creating custom mesh patterns with specific sizes or opacities.
- Allows for complex, intricate designs that other methods cannot replicate without distortion or immense cost.

Optimizing for Cost and Automation [3:00]

The video proposes strategies to reduce the cost and manual labor associated with photochemical etching, making it more accessible.

A mesh bag containing a metal panel with etched parts, demonstrating the concept of parts falling free during the etching process. [ 00:03:30 ]

A bag labeled "Flip-Pins", showcasing a niche product that benefits from photochemical etching due to low production volume needs. [ 00:04:11 ]

A screenshot of a 3D CAD model being analyzed on a manufacturing website, illustrating an automated artwork upload system for real-time analysis. [ 00:05:01 ]

Automated Part Separation:
- Traditional parts are held by tabs and require manual cutting and deburring.
- Innovation: Etching parts while contained in a mesh bag allows them to fall free from the panel during the etching process.
- Eliminates manual handling, counting, and quality control checks, simplifying the finishing process for the customer.
Automated Artwork Generation:
- Current commercial photochemical suppliers often require emailing artwork, leading to slow back-and-forth with layout engineers.
- Proposal: Implement an automated artwork upload system, similar to CNC machining, multi-layer PCBs, or laser/water jet cutting services.
- This would provide real-time pricing and timelines, saving time for both the business and the customer.
Example: Flip Pins:
- Niche products like "flip pins" (DIP-sized pins for breadboards) are ideally suited for photochemical etching due to their low production volume needs, where stamping would be too expensive.

Sheet Metal Cleaning for Optimal Adhesion [5:37]

Thorough cleaning of the sheet metal is the critical first step to ensure proper adhesion of the photoresist.

A screenshot from McMaster-Carr showing various shim stock options and their prices, indicating the low cost of raw materials. [ 00:05:54 ]

A water break test on a metal sheet, with water beading up, indicating surface contamination before cleaning. [ 00:06:35 ]

A clean sheet of metal undergoing a water break test, with water sheeting off uniformly, confirming a thoroughly cleaned surface. [ 00:07:29 ]

Hands drying a cleaned metal sheet with blue shop towels, emphasizing the importance of a lint-free drying process to prevent re-contamination. [ 00:07:43 ]

Material Cost:
- Sheet metal (e.g., from McMaster-Carr) is a relatively inexpensive component of the process, typically costing $5-10 per sheet.
Cleaning Process:
- Water Break Test: Essential for verifying cleanliness. Water beading up indicates oil contamination; water sheeting off evenly signifies a clean surface.
- Immersion Cleaning: Metal is immersed in a heated solution (e.g., water and alcohol, or sodium hydroxide) using a sous-vide cooker to maintain temperature.
- Rinsing: After cleaning, the metal is thoroughly rinsed with deionized water.
- Drying: The best method is to scrub the metal dry with shop towels, as air drying or compressed air can recontaminate the surface with oil droplets.

Applying Dry Film Photoresist [8:19]

The photoresist, a light-sensitive polymer, is applied to the cleaned metal using a laminator.

A customized laminator with added take-up spools, essential for correctly applying dry film photoresist to metal sheets by peeling off the soft protective layer. [ 00:01:17 ]

Photoresist Composition:
- Dry film photoresist consists of three layers: a soft protective layer, the photoresist itself, and a hard protective layer.
Laminator Modification:
- Cheap commercial laminators are not designed for this.
- The laminator needs modifications (e.g., spring-loaded take-up spools) to peel off the soft protective layer as the photoresist is applied to the metal.
Lamination Settings:
- Temperature: Approximately 110°C.
- Speed: Very slow to ensure proper adhesion and removal of the soft layer.
Result: The metal comes out with photoresist firmly laminated on both sides, protected by the hard outer layers.

Creating High-Contrast Photomasks [10:44]

High-quality photomasks are essential for achieving sharp, high-resolution etched patterns.

A side-by-side comparison of photo masks printed with laser (left) and inkjet (right) printers, clearly showing the superior opacity and detail of inkjet output. [ 00:10:49 ]

A finger demonstrating the emulsion side of a transparency film, which is designed to absorb and hold inkjet ink for high-contrast masks. [ 00:11:22 ]

A computer screen displaying printer settings adjusted to dispense the maximum amount of ink, crucial for achieving dense, high-contrast photomasks. [ 00:11:36 ]

Printer Choice:
- Laser Printers are Unsuitable: They produce toner images with pinholes and insufficient density, leading to poor contrast.
- Inkjet Printers are Recommended: They can achieve superior contrast.
  - Specialized Materials: Use special ink and transparencies with an emulsion coating (e.g., from FilmDirectOnline) that absorbs and holds a large amount of ink without smudging.
Printing Process:
- Printer settings are dialed up to dispense the maximum amount of ink for maximum contrast.
- Dual Masks: Two masks are printed side-by-side on the same sheet. This ensures any minor stretching along the printer rollers affects both masks identically, preserving registration for double-sided etching.
- Printer Quirk Solution: If a printer's optical sensor fails to detect clear transparencies, placing a white piece of paper underneath can trick it into printing.

Precisely Aligning and Exposing the Masks [12:50]

Accurate alignment and controlled exposure are crucial for transferring the design onto the photoresist.

Hands aligning two transparent photo masks with a metal sheet in between, ensuring precise registration for double-sided etching. [ 00:13:16 ]

A custom-built UV exposure rig featuring two 405nm floodlights positioned high above the workstation, designed to create sharper shadows for higher resolution etching. [ 00:14:38 ]

A digital timer displaying the exposure time (2 minutes 40 seconds) and a note detailing measured light intensity, providing specific process parameters. [ 00:15:07 ]

Hands carefully peeling off the hard plastic protective layer from the photoresist, preparing the panel for development. [ 00:15:43 ]

Mask Alignment:
- The two printed masks are aligned precisely, emulsion side facing the metal panel, and secured with double-sided tape.
- "Book" Method Avoidance: A hinged "book" method (tape on one side) is avoided because the thickness of the metal can introduce slight registration errors. Taping both sides ensures consistent, symmetric alignment.
Exposure Setup:
- A custom exposure rig is used, featuring two 150W 405nm floodlights.
- Light Source Distance: Lights are placed far from the artwork to create sharper shadows, preventing UV light from "sneaking" under dark areas and ruining resolution.
Exposure Parameters:
- Measured light intensity: Approximately 0.5 milliwatts per square centimeter (mW/cm²).
- Practical exposure time: 2 minutes 40 seconds.
- Note: Commercial datasheets typically suggest a dose of 60 millijoules per square centimeter (mJ/cm²), which would translate to about 100 seconds, indicating some non-idealities in the DIY setup.
Pre-Development Step: Before developing, the hard plastic protective layers are carefully peeled off the photoresist to expose the light-activated material.

Developing the Photoresist Pattern [16:01]

The exposed photoresist is developed to reveal the etched pattern.

The homemade developer setup, a plastic tub connected to an external pump and control unit, used for processing the photoresist. [ 00:16:03 ]

A hand pouring sodium carbonate into the developer tub, demonstrating the preparation of the photoresist developer solution. [ 00:16:08 ]

A metal panel inside a mesh bag after photoresist development, showing the revealed pattern and good registration. [ 00:16:59 ]

Developer Solution:
- A simple solution of tap water and sodium carbonate.
Development Machine:
- A plastic tub equipped with spinning sprinklers, an external pump, a timer, and a heater to maintain the solution temperature at approximately 28°C.
- The metal panel, now in a mesh bag and loaded into a carrier, is placed in the developer tank.
Development Time:
- Approximately 70 seconds.
Rinsing: After development, the panel is rinsed (typically in a dedicated rinse tank, but a hose was used for demonstration).
Quality Check: The developed pattern is inspected for good registration and resolution, ensuring the photoresist has been properly removed in the unexposed areas.

Etching the Metal with a High-Power System [17:04]

The developed metal is then etched using a powerful spray etcher.

The etching tank with a specialized magnetic holder design, allowing for through-the-wall movement and easy loading/unloading. [ 00:17:27 ]

A close-up of the control box for the linear belt drive actuator, showing the stepper motor driver and Teensy microcontroller for automated etching. [ 00:17:56 ]

The air-powered pump setup located beneath the etching tank, crucial for generating the high pressure and flow rate needed for effective spray etching. [ 00:18:07 ]

A close-up view inside the etching machine, showing the high-pressure spray of etchant actively dissolving the exposed metal, accelerating the process. [ 00:20:25 ]

Etcher Holder Design:
- A specialized holder with rollers and plastic-encased magnets allows for "through-the-wall" movement within the etching tank.
- This design eliminates the need for tank penetrations, simplifies loading/unloading, and keeps the panel in precise registration.
Actuator System:
- A linear belt drive actuator (e.g., from OpenBuilds) powered by a stepper motor and controlled by a Teensy microcontroller, featuring a display and user interface.
- This system also controls the heater and etching time.
Etchant Pump and Flow:
- A high-pressure, high-flow Aro pneumatically powered pump is essential.
- Spray Etching vs. Immersion: Spray etching is about 10 times faster than simple immersion or even stirred etching. The force of the spray efficiently removes etch products, accelerating the process.
- The pump's pulsatile output is cushioned by an "air hammer" mechanism.
Material Compatibility:
- Finding plastics compatible with hot ferric chloride is challenging. Nylon and Delrin are unsuitable, and even polypropylene can fail, leading to dangerous leaks.
Etching in a Mesh Bag: The panel is etched inside a mesh bag, which allows the completed parts to fall freely from the main sheet, streamlining the finishing process.

Stripping the Photoresist [20:40]

The final step involves removing the remaining photoresist from the etched parts.

An etched metal panel still partially covered with photoresist, demonstrating the state of the parts before the final stripping step. [ 00:20:58 ]

Stripping Solution:
- A strong basic solution, such as sodium hydroxide or potassium hydroxide, is used to strip the photoresist.
Mechanism:
- The photoresist does not dissolve but rather comes off in large chunks.
Previous System: A flow cell was previously used to facilitate the removal of these photoresist chips from the mesh bag, but it was not available for the demonstration.

Final Results and Troubleshooting [21:22]

The video concludes with a review of the etched parts and a brief acknowledgment of challenges.

A collection of various precise metal parts created using the photochemical machining process, showcasing the final output. [ 00:21:27 ]

Outcome: The parts turned out "kind of okay," but the presenter notes it wasn't his best work.
Challenges Encountered: A major problem with the etching machine required pausing the process midway, which negatively impacted the final quality. The equipment had not been used recently.