Designing and making etched metal parts

If you look at a high end model kit these days, especially vehicle kits such as model railway engines or rolling stock, or space or military vehicles, you’ll often see a flat sheet of etched metal included in the box. If one isn’t part of the kit you can often buy a third-party etched detail set. For example, Paragrafix in the US sell a wide range of etched superdetailing sets for improving science-fiction themed model kits.

Such sheets, traditionally called frets for some reason, are used for providing higher-quality details than can be made using injection-moulded plastic or cast resin; the usual materials for such kits. They can even be used as the basis for a whole model, such as a railway freight/goods car or whatever, in which the sheets are folded like cardboard boxes.

Etched metal offers the advantage of crisp sharp edges, but has the obvious disadvantage that the sheets are always flat. You can fold up a piece of sheet metal into a box, and you can apply a cylindrical curve to a section of flat material, but you can’t easily make a compound curve, a spherical object or a complex dimensional shape.

Acid etching

The traditional method to etch a sheet of metal is to use highly corrosive acid.

You start by applying some acid-resistant coating to your sheet of metal. The resist is usually precisely applied using a black and white transparent film, which is why the whole process is called photo-etch. You then dip the thing into your strong acid solution, swill or spray the etchant around in a tank to ensure a continual supply of acid over the surface, then remove the metal when the etching is complete. You then wash off all traces of the acid and remove the acid resist, resulting in a lovely etched sheet of metal. This is a subtractive process because you’re taking the metal and removing some bits; in this case by dissolving it.

Photochemical or acid etching techniques can be used on many different types of metal. Thin brass sheets are common, because they hold detail well, etch easily, and are cheap. However other materials, such as steel and nickel-silver, are often used.

This method has been used for centuries in various forms, and can offer extremely precise and high-quality results. Metal plates have been etched throughout history for printmaking purposes, for decorating metalwork, for electronics, and for all kinds of related projects.

Drawbacks of acid etching

The biggest downside, of course, is that the chemicals involved are brutal, both to human beings and the environment. The acids must be handled carefully to avoid injury. They’re messy and difficult to use without a lot of experience and the right equipment. And the used-up solutions, filled with biocidal dissolved heavy metals, must be disposed of with care to avoid poisoning wildlife, especially aquatic creatures.

Another drawback is that the acid eats away at the metal like waves lapping at a shoreline. You can’t get straight and vertical walls to your cuts – there’s always going to be a kind of curvature to the base of the etch. This is particularly apparent with thicker materials.

Consider a project with two square holes in a sheet of metal. If you were to laser the holes you’d probably get something similar to the picture on the left, with one half-cut hole and one through hole. But if you used acid etching you’d end up with something like the picture on the right.

Looking at a cross-section drawing gives perhaps a better idea of what happens.

The left diagram is what a laser could theoretically do – it would just burn a hole straight down through the metal. The right diagram shows the way acid will etch downwards at a slight angle, but at the bottom it doesn’t etch up against the walls, resulting in a curve to the bottom of the half-etched hole. On the right the hole has been etched from both surfaces – top-down and bottom-up – resulting in a little projection all the way around the through hole. The projection is called an etch cusp.

Note that this demonstrates a 50/50 etch process, where half the through etching comes from the top and half from the bottom. It’s possible to etch one side longer than the other, to create different results.

Another drawback of acid etching is that sharp corners, such as the 90° corners for our diagram’s squares, have radiuses or radii, so you get rounded corners and not sharp ones. This is because of the way the used-up acid tends to sit in corners and not wash out as easily. This can be minimized by changing the pattern to have slight bulges in the corners. The radius is related to the thickness of the material, and is roughly half the thickness.

Cost-wise, acid photo-etching has a notable production drawback because the cost involves the creation of a transparency, filmwork, or phototool first. This sheet can be used to produce multiple acid-etched frets. Companies will generally store the film for you, so you can reorder a sheet in the future if you want.

The problem for hobbyists is that if you just need a one-off sheet for a project, like I did, you still have to pay the full pre-production setup costs. You can’t amortize the film expense across producing multiple etched sheets, the way a commercial maker would. This is an area where laser has an advantage.

Partial etches

It’s possible to include simulated engraved lines or recesses in an etched sheet. This involves two rounds of etching – the first etches only halfway (say) through a sheet, and the second round etches all the way through, cutting out the pieces. You can also etch from the underside of the sheet as well, giving you additional layering options.

Engraved nameplates are often done this way. Half-etched lettering is made, then filled in with enamel or lacquer paint for contrast.

Another common use of half etching is for recessed lines for tabs that you want to cut, or for bend lines where you want your sheet metal to be folded or bent.

Making your own etched metal parts

It’s possible to make this stuff at home. But it’s onerous and involves nasty chemicals. I’m not going to go into huge detail here, but basically there seem to be two main approaches.

The traditional approach is to make a black and white transparency of your desired pattern. You coat the metal sheet with UV-sensitive material, and then expose it to UV using your transparency as a mask. This leaves the resist material in black areas of the transparency, and removes the resist in clear areas.

Another approach is to use laser printer toner. This is an iron-on process where you print the design onto special material, and then transfer the adhesive-backed toner (which is basically powdered plastic, heat-fused together) to the metal with a household iron.

Once the sheet has been prepared you then dip it in a solution of powerful etchant. Ferric chloride is commonly used, much as it was used with printed circuit boards. Muriatic acid and hydrogen peroxide are also used as etchants.

I have not tried this process.

I’m not crazy about handling the chemicals involved. And every account I’ve read is that the whole process is a fiddly and onerous process, and it’s difficult to get high quality and consistent results without a lot of work. I just want the final pieces; I don’t want to start up another hobby. Especially a potentially toxic one.

Laser etching

Another process uses focused laser beams to burn through the metal material itself. This requires specific types of lasers capable of cutting through metal. Some aren’t able to do this – the beams of CO2 lasers reflect off the metal, for example. Other lasers aren’t powerful enough to make the cuts unless the metal is really thin. Many affordable home laser cutters, used for cutting materials such as paper or thin plastic, can’t be used for metal etching. However, industrial laser cutters do exist and are improving.

Unlike acid etching, laser etching can produce fairly vertical cuts to your etched walls. Not quite straight, but not as curvy as the edges of acid-etched material.

The main drawbacks with lasers are that the edges of cuts can be rough, since the laser is typically fired in pulses. This may lead to a pitted edge, not smooth like an acid-etched piece. And second, half-etching material often results in a rough and pebbly surface, again unlike the smooth surfaces possible with acid etching. This pebbling can be okay – it might be perfect for engraved text that you plan on filling in with enamel paint for example – but for other purposes can be lousy. The metal can also discolor from the heat of the laser.

In the past it wasn't possible to get fine details from laser etching, but the processes are definitely improving, and you can cut pretty tiny details now. The machine needed to do this kind of work differs from the simpler machines used for laser engraving plaques and whatnot.

My goal

I’m currently working on a model of the EVA pod from 2001: a Space Odyssey. I want it to be the zenith of space pod models, and so I’m spending a stupid amount of money and effort on it.

One of these efforts is to ensure all flat-object details on the model are actually made from etched metal. I’m doing two batches of metal etching – one 0.45mm or 0.5mm thick, and one 0.3mm thick.

I’m using nickel-silver because I want certain objects to be made from actual bare metal, and I want much of the visible metal to match stainless steel in colour. Some nickel-silver (copper, nickel, and zinc) alloys such as NS-106 are fairly close in colour to steel. Brass (copper and zinc) is obviously the wrong colour despite being a bit cheaper. Nickel-silver is also fairly easy to solder, unlike stainless steel.

The first step is going over the 3D model and deciding what parts could benefit from being made from etched metal rather than something else – 3D printed, extruded metal tubing, etc. In the illustration below, the parts I want as etched metal are identified in red.

I then exported each object as flat 2D data and imported it into a drawing program. I started laying out a digital design of all the detail parts on the computer.

After many weeks of messing about, trying to fit as many objects as possible neatly into a rectangular shape, I then sent the design to two etching services.

Creating a digital design for etched metal

You simply need a decent 2D drawing or CAD program to make the diagram for the photographic masks (acid etch) or digital instructions (laser) needed by the etching company.

I used Adobe Illustrator, though not because I particularly enjoy using it. As someone who’s used Illustrator since 1987, it’s painful how Adobe are definitely getting worse and worse and are deeply committed to the enshittification model of software – but it’s adequate and I have a subscription to it for a number of other reasons.

You need to be able to draw lines, Bézier curves or similar splines, and operate in layers.  That’s really it.

I produced one layer of the through-cut designs. Black areas indicate where metal survives; blank areas are where the metal should be removed wholly. I made the design as a large compound path. (ie: holes are cut out within the compound path; not white objects layered over the black) Adobe can handle compound paths moderately well, as has some tools for combining objects mathematically.

The whole thing was super fiddly and really time consuming to get exactly right. Especially since the finished design is a collection of individual objects joined by the thin tabs used to keep the finished etch together as a single sheet.

The second layer was colour-coded red, and showed the areas that are half-cut into the surface of the material. This was a bit complicated sometimes, as you have to sort of think of the reverse of what you might normally expect – you need to consider the cut out bits, not the raised bits.

Here’s an example. Let’s say you want a circular metal disc with a triangular notch cut out of one quarter.

1) This is the end goal. A disc with a Pac-man type notch.

2) You basically need to represent it in 2D like this: a black circle showing where metal is present (ie: fully etched), and a wedge-shaped piece in red showing the area to be half-etched through.

3) But let’s say you want to include thin metal tabs connecting the various parts together into a tree. These tabs ideally should be half thickness, making them easier to cut. So, layered, it looks like this.

4) This is the final way the object is represented as two layers. One layer contains the black circle with the tabs as one object. And the other contains the areas in red where the metal should be half-etched through. Note that the tab areas have curved sides where they join the circle.

In terms of file format, I sent .ai (Adobe Illustrator) files to the shops. PDF was supported as well I think.

Laser etching using Noro Laser

Noro Laser are a company in Santiago de Compostela, northwestern Spain. They do laser-cut metal parts, and sell directly via their own site and via US-based Etsy.

As a test I sent them a design to have laser-etched into 0.5mm thick nickel silver metal. They’re competitively affordable, and that was a huge plus for me. Especially since you can have them cut an arbitrarily sized sheet of material. Their laser is billed as having a kerf (cutting width) of 0.2mm wide, which is pretty decent.

Here are my observations on a product I ordered from this company, which tends to work on jewellery products.

1) They have an online quote system, but it cannot be used for complex designs. My model fret, with a bunch of tiny cuts and multiple pieces, couldn’t be effectively analyzed by their software. They therefore had to examine my file and produce a quote manually. If you do this note that it will be more expensive than the auto-generated quotes. Part of the cost increase is the length of time required for the laser to cut out a really complicated set of parts.

Note also that they charge more if you cut out a bunch of individual and separate parts. To save money I redid my design and made sure joining tabs/sprues were used throughout, ensuring the whole sheet was a single object.

2) One of the big hassles is that you have to provide an overlap to the drawings of half-etched objects, because of the way that their laser works.

In other words, you can’t have a simple red object showing where you want a half-etched section to be cut out. You have to enlarge that red area so that it’s 0.5mm larger than the final cut, on outer edges. This compensates for burring-over of the laser beam cut, since the half-etch is applied to the metal prior to the full cut

All this nonsense was a time-consuming pain for me, since I had to redraw all the half-cut areas. I did so by outlining all the objects with a 0.5mm stroke, using the Outline Stroke function in Illustrator, and then manually removing all the inner stroke lines that weren’t necessary. This took ages.

Here’s an example. On the left is the black circle with the area to be half-etched in red. I had to redo all my graphics such that half-etched areas, where they were over top of a through cut, had to extend further out by 0.5mm.

3) They can only laser-cut fine details on sheets up to 80x80mm in size. This size limit could be a problem for many designs.

I ordered a fret 76mm x 70mm in size, using 0.5mm thick nickel-silver sheet.

4) The sheet took about 2 weeks to be produced and then a little over a week to ship to the UK from Spain. The tracking info on the postal websites was never updated. This was annoying, though not Noro Laser’s fault of course.

5) The biggest flop: the product had about 1/3 failed cut-throughs. In other words, a bunch of components were not properly cut out of the metal sheet. The laser had simply not gone all the way through.

This cut-through failure was a huge pain in the ass for me, because nickel-silver is a resilient metal and not easily cut with eg: a hobby knife. It took a bunch of work to cut out the parts I needed. Small circular parts were more trouble than they were worth to cut out.

Noro declined to recut the sheet, saying I should just cut out the pieces by hand. Not a great answer. I decided not to argue with them about it, since I had decided to abandon their product by that point for a number of reasons.

6) The half-etched layer was not perfectly aligned with the full cut. It was out horizontally by maybe half a millimetre, which would be fine for larger objects. But it meant that smaller objects were visibly misaligned and not usable for me.

7) The laser cutting process resulted in raised burrs all the way around cut edges. These were easily sanded off, but it was a bit inconvenient because you have to be super careful when it comes to sanding something so delicate.

These burrs make this particular process kind of useless for commercial products, to be honest. Unless you do a small run and sand every piece by hand yourself, or else pay Noro to sand and polish the parts. I elected not to do the latter since I wanted to be in control of what my finished parts looked like. I’m not making jewellery here – I need precisely made parts that fit together properly.

8) The final major problem was that half-etched surfaces were quite rough and pebbly, owing to the pulsed nature of the laser. This could be fine for some applications, but for many of my purposes I needed a relatively smooth surface.

Painting didn’t resolve the issue. If I’d needed black objects the this problem might have worked. But the objects had to be white, and white paint made the texturing even more obvious. 

9) The sides of each cut were noticeably rough and took some work to file smooth. This is a byproduct of the pulsed laser cutting process. The vertical edges were also quite black, which could be a problem for jewellery makers. You’d need to sand and polish the edges and sides.

10) The metal surface was noticeably yellowed by the heat of the laser. (look at the photo of the burrs above) In fact, when I received it I thought they’d accidentally used brass. Fortunately sanding off the outer layers of material revealed the untarnished nickel silver underneath.

11) The nickel silver sheet that they used was quite yellow in colour. I was expecting something more silvery in tone – closer to stainless steel. It seems they use something like an NS103 alloy, whereas I would have preferred NS106.

This isn’t their fault, per se, (though I wish they’d specified up-front what alloy they use to avoid doubt) but it’s a problem for me since I need some parts to be bare metal that matches steel in tone. Only parts to be painted would work.

Conclusion:

In the end I can’t use most of the parts produced by Noro Laser. I had to throw most of them away – only a tiny handful were actually usable.

Which is a shame, since they are affordable and I thought it would be a good solution to my problem.

Acid etching using PPD

PPD are a photo-etch producer in Argyll, Scotland. I had intended initially to use the photo-etch service of Arch 60 in London, because I’d spoken to them in person and liked their attitude and they clearly produce excellent work. Unfortunately their services cost a lot more than PPD, so in the end I used the latter. Sorry, Arch 60!

1) Supplying PPD with the Illustrator files was fine. Unlike Noro Laser, I didn’t have to mess around providing half-etch layer drawings that spilled over the edges of the desired cuts.

2) PPD will produce photo-etched parts to specific sheet sizes only, and not to arbitrary sizes. The sizes depend on the metal used.

For nickel-silver and brass they only produce 135x290mm, 290x290mm, 290x440mm, and 290x890mm sheets.

3) The fret took 2 weeks for PPD to produce, and then it was sent first class via Royal Mail to London.

4) Unlike the laser-cut parts there are no areas of heat discoloration.

5) However, there are numerous areas of chemical discoloration across the metalwork, on both sides. These are small yellow-brown patches (see below) of tarnished metal. They sand off easily – I polished it using 1200 grit – but it could be a problem if you want the look of clean raw metal.

In fact, the messy appearance of these marks might be enough for someone mass-producing etched metal sheets to not use PPD’s services, to be frank. If you’re reselling a product to someone else you’d probably want your customers to receive nice clean metal sheets, like all the commercial photoetched products I’ve bought over the years. You certainly don’t want to have to re-sand and polish every metal sheet you send to a customer!

Fortunately in my case it wasn’t a huge deal and relatively cosmetic in nature.

6) The half-etched areas are quite smooth, untextured, and very usable.

6) A few components have chipped or damaged edges. Metal is actually missing from these edges, so this is not something that can easily be fixed. According to PPD the damage is caused by the removal of the UV resist. Not sure what that means. Sloppy use of a knife to cut off the remaining resist, maybe?

This again could be the sort of thing that would be a deal-breaker for many people. Someone reselling etched brass sheets to the public probably wouldn’t accept such nicks and cuts, since you’d get a whole load of customer returns. Fortunately my design deliberately had more parts than I needed, in case of unexpected problems with the etching, so I was able to use the undamaged extra pieces for my project.

7) The etch-through cuts have no raised burring – they’re perfectly smooth and sharp. In fact, you have to be careful handling the metal fret – you really can slice your fingers if you’re not careful!

8) The sides are smooth and continuous. There’s no stairstepping or rough edges like you seem to get with lasers.

However, the inevitable problem of acid-etching is apparent. When viewed in closeup, the vertical etched walls are slightly curved at the base. This is just part of the process as described above. Look closely at the hook-like objects just above the “3Dsf.info” logo shown above. You’ll notice that the circular rings have a thin stepped area, the etch cusp, outlining them.

Or examine the slight dip between the etched-out wall and bottom of the lettering. These are artefacts of the acid-etching process.

Some of these artefacts are unavoidable. Others, such as the slight rounding/radiusing of 90° corners, I could have avoided by designing a slight bulge, or corner relief, in the metal at each corner. This would compensate for the way the acid works. But I didn’t do this. Mainly because figuring out the exact amount of relief into the design would have been an iterative process, and I didn’t want to pay for multiple etch jobs – I wanted to pay for one piece and be done with it!

9) I requested NS106 nickel-silver alloy, and that's what they used. The resultant sheet is a slightly warm silver colour, fairly close to the stainless steel I’m using for other visible metal components. So that’s excellent.

My pod contains some visible aluminium, nickel-silver, and steel pieces, reflecting the specific types of metal used in the full-sized pod sets. I use brass in various places where the metal is needed for support or light-blocking purposes and is going to be painted anyway.

Conclusion:

In short, the PPD etched sheet was close to ideal for my application. It’s not perfect, but given the work that you have to do to make an etched metal piece be usable for a model, it’s absolutely fine.

What about solder stencils?

Manufacturers of PCBs (printed circuit boards) produce SMD (surface mount device) or SMT (surface mount technology) stencils for applying solder to a board. These are very thin metal sheets, usually steel, with teeny tiny holes lasered into them. The sheet is placed over a circuit board, and a flux paste containing ground-up solder is applied. The sheet is lifted, and tiny little blobs of solder paste are left behind in precisely the right spots. Components are positioned over the board, the board is heated, and the paste burns off, leaving the metal solder behind, thus joining the components to the board. This is how reflow soldering is done on extremely tiny modern circuit boards.

Many companies will produce very finely detailed steel sheets for this purpose, and they’re often quite affordable, since many of them are highly efficient giant Chinese factories producing huge quantities of stuff. It’s occurred to me that getting one of these firms to make an SMT stencil that actually is in the shape of parts that I need might be a really cost-effective and interesting approach.

I haven’t tried it yet. PCB makers generally want Gerber format files (from the engineering company founded by American inventor Joseph Gerber; nothing to do with the US maker of baby food or the US maker of combat knives), which are the specific file type used to describe the layout of a circuit board. I don’t have any such tools handy, so I’d probably need to design my layout in a different format and export or convert it to Gerber form. At some point I think it’d be an interesting experiment.

For now I think working with companies like PPD makes sense, since they’re used to producing etched sheets for hobbyists like me, and understand that market. They also etch to a variety of metals, and sometimes to thicker materials than SMT stencils are usually made from. Buying SMT stencils would probably be cheaper, however.

Should you make your own etched metal sheets?

Well, it’s kind of fun and the results are pretty effective. It’s pretty cool that such services are out there, and that it’s a fairly straightforward matter to make your digital designs at home and send them off to be made into a metallic reality. As noted, I have no interest in doing the actual etching work myself, but I do find having certain detail components in thin metal form to be very useful for my model making project.

Laser etching didn’t work for me. It might for you, and it might have been better had Noro Laser produced a higher quality product than they did. The huge number of failed cut-throughs, the pebbly texture to half-etch surfaces, and the misaligned half-etches, were the three reasons why I abandoned the Noro Laser product.

Paying extra for PPD to do traditional chemical etching was definitely worth it for me, though it wasn’t particularly cheap. There are the noticeable etch artefacts and discoloration problems, but I can live with them or work around them in most cases.

Note that I have no idea about what other companies, especially those which operate in other countries, are like. I’ve obviously never used them and so can’t offer any assistance in that regard. I just did this writeup of my experiences in the field in case it’s of value to someone else.

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