What is etching and what is spray etching?
Etching is the process of eating away a pattern on a target material by using an etchant liquid that attacks the target material.
The most common target materials are copper and brass. The most common etchant liquids are ferric chloride, ammonium persulphate and cupric chloride
On a hobby scale it is common to submerge the target into a container filled with the etchant. This can be very slow and is often sped up by either mechanical agitation or using an aquarium / fish-tank bubbler. Even with the speed up from sloshing the container around this process can take 10-15 minutes for a PCB or over an hour for a thick brass plate.
The spray etching method uses the same etchant liquid as the submersion method, but instead sprays the liquid onto the target. This can speed up the process by an order of magnitude.
The advantages that spray etching has over the more mundane submersion method of etching is
- Less manually intensive
- More uniform etch
- Produces sharper edges / better detail
Where are spray etchers used?
- Manufacturing PCB (Printed Circuit Boards)
- Etching plates for intaglio printmaking
- Etching brass nameplates / plaques
- Photochemical machining of mechanical parts (often used in model trains)
- Etching jewellery
- Etching stencils (if you can't afford a laser cutter hint hint)
- Automatically generating traffic by showing friendly site logos made from brass
Why a ROTARY spray etcher?
This rotary spray etcher can be built for between $50 and $100, depending on where you need to source your material. This is a lot less than the $300 plus that other spray etching machines would cost. It is also quicker and easier to build as long as someone else has made all the errors along the way FOR you.
Well here is where I get to say "follow me on this remarkable journey of discovery"
Background / Prior Art
Types of spray etchers
There are two main methods of building spray etch machines.
- A pressure pump and nozzles
- Rotary spray etchers that rely on centrifugal force
Pressure Pump Versions
This is the method that commercial PCB manufacturing equipment uses. In an industrial setting where reliability, throughput and lowest level of operator skill are valued over cost and size, it wins hands down.
This method is also fairly well represented in DIY projects on the web with at least three projects showing up with only a cursory search in google.
- Proto Trains design dates from 1996 but first appeared on the web in around 2002.
- Adam Seychell dates from June 2007. (Unfortunately missing in action at the moment and on the way-back machine without pictures.)
- Crreed on Instructables from Instructables dating from 2012
The commercial machines and the three DIY projects all approach the uniformity problem differently. Having some relative movement between the nozzle and target removes problems with high pressure spots. Having the target in a horizontal orientation reduces undercut.
|Proto Trains||Stationary||Moving (rotating)||Vertical|
Rotary Spray Nozzle Versions
Rotary spray etchers are a whole different kettle of fish when it comes to DIY projects. It seems that although newsgroups are littered with people starting a project to build one, only one DIY project seems to have been published on the web to look at. It is also not the easiest thing to find as it is in German and “spray etcher” will not turn it up in a google search.
Spruhatzanlage use google translate or BableFish to make a bit more sense of it
The German site although very professionally done and full of helpful pictures, does not address the pitfalls of building one yourself.
Pressure Pump Vs Rotary
- Can be scaled up
- Can be built with target in horizontal position (reduces undercut)
- Can achieve higher uniformity of etch if either target or nozzle are moving
- Expensive to build (relative to rotary)
- Difficult to find suitable pumps (Seychell recomends against Shurflo)
- Labour intensive to build (relative to rotary)
- Poor uniformity with static nozzle/target
- Risk of hoses coming loose and coating your workshop in etchant with some Spray Etcher designs
- Cheap to build
- Easy to build
- Excellent uniformity over a small area
- Lower risk of accidents spraying etchant around
- Can not be scaled up in size a great deal
- Target can only be vertical
- very difficult to get working well (until now)