brass etching for beginners

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Etching for Beginners

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Nigel Lawton: 3,507 Words Version 5

WARNING: ETCHANT CHEMICALS ARE POISONOUS AND SHOULD ONLY BE USED BY

COMPETENT ADULTS WITH DUE CARE AND NOT USING IMPLIMENTS, VESSELS OR AREAS

NORMALLY USED FOR FOOD PREPARATION

There have been many articles written on this subject covering the process of photo-etching, however I would like to describehow I have made use of a different technique which makes the whole process of home etching a much easier undertaking as does NOT require any photographic steps. The set-up cost for this part of my method is therefore much lower and making myown etching tank from readily available materials has kept the overall costs very low.

The basis of etching is to selectively coat some thin brass or nickel-silver sheet with 'etch resist' then immerse it in a chemicalthat dissolves the exposed metal via a chemical reaction. The parts coated with 'resist' are left un-dissolved. Its a great way producing detailed parts from sheet material with the ability to take designs straight from plans or a computer and transfer theto metal. So the process has essentially two steps: -

1. Apply chemical-resistant 'resist' to sheet brass or nickel silver.2. Immerse in a chemical 'etchant', removing when exposed metal has dissolved.

I will deal with these in two separate sections.The Etch Resist

The method I am using to apply resist is known as the toner transfer method. As many will know, toner is a powdered mediused by standard photocopiers and laser printers. It is deposited on the paper or other substrate material by some magicelectrostatic method and then fixed in place by melting it with a heated roller. It is possible to print patterns of toner on asuitable substrate using a laser printer or toner-using photocopier and transfer these to brass or nickel silver to create a etchresist pattern. The toner is transferred by ironing the printed substrate onto the brass with a domestic iron (like you use to iryour shirts) which re-melts the toner and makes it stick to the brass or nickel silver more than the film.

Initially I used a special coated film substrate which, when printed with a suitable resist pattern using a laser printer or standarphotocopier can be ironed on to brass and peeled away to leave the printed areas behind along with the top layer of the film toform the areas not to be removed when etched. However I later discovered that some laser printer type and inkjet overheadprojector acetates also works, the difference being that the special films coating comes away with the toner whereas usingstandard laser or inkjet acetate just the toner is transferred. The special film is easier to use, but expensive, 15 for 5 sheets the time of writing, whereas you can buy 20 sheets of laser or inkjet acetate for as little as 6. The special film may also limitresolution as the backing tends to bridge small gaps its intended for making tracks on a PCB rather than fine etched detailsa model. No such limitations exist with standard laser or inkjet acetate and if you can print it, you can etch it! Using thesematerials I have made some very tiny nameplates with writing only 2mm high that can be read when etched (although you neea magnifying glass really). Depending on your subject material, pocket and adventurousness you may wish to try the specialcoated film first then graduate to standard acetates as I have done. Not all laser and inkjet acetates work. Some laser acetathold onto the toner and you dont get enough transfer to the metal. Some inkjet acetates may not tolerate the laser printerheater roller temperature, always test a piece with your domestic iron set just below the three blobs mark first. You should lofor acetates of both types that have some sort of coating usually only on one side and print onto this coating. The coatingseems to let go of the toner quite well.

Before you get the iron out you need to develop your artwork, which is the shape of the parts you want to make. Most readerof this article will be familiar with the sort of etched brass and nickel silver 'frets' supplied by various 009 and other modelmanufacturers. Here are some of the important features of etching artwork:-

1. Don't leave large areas of metal exposed, it uses up your chemical etchant faster, just leave about 0.5mm-1mm aroundeach of the parts.

2. Make sure you join your parts to the main part of the fret with thin traces otherwise you'll lose them in the etch tank, thesshould be three times the material thickness wide at least.

3. You should make the parts slightly larger than you want to allow for 'undercut'. This should in theory be about 1/3 thematerial thickness (0.08mm for 0.01/10 thou/0.25mm sheet) however for many items you can ignore this effect as it is vesmall.

Starting with the shape you want to produce you need to draw an artwork which is solid in the solid areas of the shape so for
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example the outline shape of my 009 brake stanchion is shown in figure 1

Figure 1 - Outline shape of item to be made by etching

Figure 2 - Solid shape of item combined with other parts on fret

This is translated into the following solid shape alongside the other parts needed as shown in figure 2.

The parts are joined together by thin areas of brass. Note that the main part of the stanchion is 0.7mm in width, scale 2", andshown larger than life here for clarity. I used Microsoft Word to generate this artwork on my PC; clearly you can use a widrange of PC or MAC programs or a photocopied hand drawing to produce the same result.

In theory you can make etchings with a single artwork etching from one side only, I tried this using electrical insulation tape tomask off the whole of the rear of the brass. This technique could be OK for making nameplates & works plates but has two bdisadvantages if you're trying to make cut-out shapes (even for nameplates). Firstly the amount of 'undercut' is much worse aleads to ragged edges and secondly you can't create detail or fold lines by 'half etching'. To allow you to etch both sides youneed to apply resist to both sides which requires two artworks of course, one being broadly the mirror image of the other. I hacreated pairs of artworks by first making a single artwork with all details on it then mirror imaging it and removing bits from eaccopy as necessary. I did all of this in Microsoft Word . I have added half-etch fold lines to the mirrored version shown infigure 3.

Figure 3 - Version of fret showing half etch fold lines.

When considering two-sided etching I was very concerned that I would not be able to achieved good enough alignment betwe

the two sides of the brass leading to staggered and non-aligned etching from each side. However a useful hint I picked up onthe internet provides a fairly easy and effective way to fix this potential problem. All you need to do is arrange your pairs ofmirrored artworks along a 'fold line' with some cross-hair alignment targets equidistant from this same fold line. You can use talignment tools available in most word processing and drawing packages to make sure everything is correctly aligned andcentred. Figure 4 shows the final artwork to produce 7 sets of brake stanchion parts.


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Figure 4 - 7- up fret with alignment crosses.

The way you use this artwork having printed it on the acetate is to fold it carefully so that the mirrored pairs of artworks aresuperimposed, very carefully align the cross hairs viewing through both thicknesses. If using the special coated film you willneed to hold the two thicknesses of film against a cool light source as it is not clear but translucent, I use a low-powerreplacement light bulb, effectively a fluorescent tube. Once you have perfectly superimposed the two sets of cross-hairs stapthe film in the folded position close to each set of cross-hairs but outside the area of the artwork.

Next you need to select and prepare some brass or nickel silver sheet. I have mainly used K&S Metals 0.01"/10 thou/0.25mm

brass sheet as sold in most model shops. Nickel silver sheet is less commonly available but can be purchased from EileensEmporium and others. You can also use other thicknesses of brass and nickel silver sheet from 0.005" to 0.015"/5 to 15thou/0.13 to 0.38mm, possibly thicker. Brass is usual used for modelling body shells and more cosmetic parts, nickel-silver isonly really used for chassis parts as it is more rigid and harder wearing. The only preparation needed is to cut to size to matcyour artwork (excluding alignment cross hairs!) with tin snips and clean thoroughly with ordinary dry steel wool (do not use Bripads or any other form of impregnated abrasive pad and do not use abrasive paper). The cleaning should be carried outimmediately before applying the etch resist.

Next insert your prepared and suitably sized piece of brass sheet into the pocket formed by the folded film and staples with onedge firmly into the fold in the film. Set the iron to just below three blobs and iron the acetate onto the brass on both sidesbeing careful not to move the artwork around. Let it cool then pull the acetate substrate off (as instructed in the special filminstructions) and you have a prepared brass or nickel silver sheet with resist pattern ready for etching. Etching should becarried out immediately after applying resist otherwise the surface of the brass will oxidize again and become resistant toetching. Figure 5 shows the various stages in this process. I usually cover any remaining areas of un-coated metal with an

etch-resist marker to save my etchant (some laundry and general purpose markers work if you dont have a purpose designedresist pen, these are also available from Maplins).

Figure 5 - Preparation of special film and standard acetate masters and toner transfer to brass sheet.

Etching

WARNING: ETCHANT CHEMICALS ARE POISONOUS AND SHOULD ONLY BE USED BY

COMPETENT ADULTS WITH DUE CARE AND NOT USING IMPLIMENTS, VESSELS OR AREAS

NORMALLY USED FOR FOOD PREPARATION

The next thing you need to do is immerse the selectively resist-coated brass in a suitable chemical etchant. There is more thaone option here however I recommend the use of Ferric Chloride which is sold for this purpose by electronics shops for use inmaking PCBs (printed circuit boards). It is supplied as either crystals or as a pre-dissolved solution; I use crystals because thare cheaper. These should be mixed according to the instructions on the pack and to a volume suited to your etching tank (selater in the article). If buying a ready mixed solution check whether it needs more water to be added before use. I recommenthe use of distilled or de-ionised water as the chemicals added to tap water will react with the etchant partly using it up. De-ionised water can be obtained at car accessory shops.

At this point you may be tempted to think that all you have to do is pour some etchant into a shallow bath and put your brass i


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it. I tried this and the results were discouraging to say the least. The problem seems to be that the chemicals do not get stirreenough (even if you stand there stirring it) to ensure that 'reacted' etchant is carried away from the brass allowing new 'active'etchant to react with the exposed brass. Also metallic iron is generated as a product of the reaction and this can deposit on titem being etched preventing fresh etchant getting to the surface. The result is that you can leave the metal in there overnighwithout it etching properly at which point the resist starts to fall off anyway!

I almost gave up at this point but having done some internet research (try typing 'etch tank' into a search engine) I found thatone popular way of achieving home PCB etching is to use a 'bubble tank'. This is a tank sized to accommodate your item to betched having an arrangement to allow air bubbles to be blown through the etchant in a similar manner to that practiced by m4-6 year old children with Coke and a straw in McDonalds. The bubbles should pass over the surfaces to be etched thus

providing continuous agitation. Of course you can buy such an etch tank for perhaps 100-200 (much less in the USA) whicwas more than I wanted to spend being basically mean minded. My usual approach is, if possible, to make my own fromwhatever I have lying around and commonly available cheap components. This is helped by my tendency to never throwanything away because 'it might come in useful'. I recently made use of a razor carry case which I had kept for about 18 yearThe candidates for re-use this time are an empty toilet cleaner bottle and an old fish tank air pump which had been supercedeby a quieter model. I chose a clear toilet cleaner bottle as it is sturdy and chemical resistant and made a tank of just over 500capacity by cutting it off just below the narrowing section. The air pump could be obtained from an aquarium shop or perhapssecond hand from a local paper classified section where I have often seen such things on sale. You should be able to obtainthe cheapest model new for less than 15. If you have a compressor (e.g. for an airbrush) this could also be used but makesure you throttle it right down to avoid having etchant flying everywhere!

Figure 6 - Home made etch tank with bubble bar, aquarium pump and spotlight heater.

The essential element we now need to add to the tank is a 'bubble bar; you can buy such a thing at an aquarium shop whereyou will find it described as an 'air curtain'. Don't be tempted to try an 'air stone' or similar diffuser, these are attacked by theetchant, will not work and will eventually fall apart, use the type of air curtain which is made from flexible foam rubber as this wgive the most even bubble distribution. The type I use is an Interpret Aqua Air Aquarium Flexible Air Wall and cost a fewpounds. I had to remove its plastic fittings and bendy metal insert (because it would be affected by the etchant) and onlyneeded half of its length. I closed one end up with superglue and found that the fish tank air pipe fitted well inside the otherend. Its worth noting that all items used to make the etch tank or used in the etch tank must be plastic, glass or glazedceramic. Most other things will react with the etchant. Initially I made my own bubble bar by drilling holes in a length of plastrpipe about 4mm diameter. I do not recommend this method as its surprisingly hard to get a consistent hole size so I found it


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difficult to get bubbles to come out evenly along the length of the bar. I did use some plastic tubing with a bend at the end(made using a heat gun) to allow me to position the flexible air curtain tube at the bottom of the tank more easily.

Install your bubble bar into the bottom of the tank, mine was a reasonable side jam fit and I do not recommend permanentlygluing this in place as you really need to remove it after each session and clean it to prevent clogging with precipitated iron. Ikeep mine in water (clear plastic or glass container) and run it in water to make sure its working OK before putting it in the etctank each time. If it seems clogged roll it between your thumb and finger in the affected area whilst its running underwater toclear it.

Fill the tank to the required depth with water, don't use etchant straight away. Its easier to see what's happening with water a

Ferric Chloride etchant is hardly transparent. Connect the air pump to the bubble bar and wind up the pressure until you getsome bubbles then adjust for best results. Ideally you are looking for an even distribution of bubbles throughout the tank or aleast consistent bubble density across a wide enough section to fit your job. Make whatever adjustments seem necessary thewhen you're happy that you'll be able to get the bubbles to cover your brass or nickel silver work piece you're ready to fill thetank with etchant instead of water and have a go at etching! One final and simple suggestion with regard to the tank is that thbubbles create a fine mist of etchant when they pop at the surface, to catch most of this stand the tank in a shallow plastic traI use one of the type in which Chinese takeaways are commonly supplied.

At this point I would like to mention an 'optional extra' which you can fit to your bubble tank. This is a heater to warm theetchant, the fastest etching is supposed to be obtained at temperatures of 25-30C which is warmer than you will get using a taat ambient temperature in most rooms (probably garages). Some commercially available bubble tanks employ an aquariumheater - these are glass and suitable for the purpose. I did not have one of these to hand so I have experimented with lowvoltage 'mat' style heaters. Such mat heaters are commercially available for around 10-15 and typically operated on 12V Ddelivering a few watts (say in the range 3-10W). They are usually self-adhesive and you should fit such a heater to one side

(nominally the back) of your bubble tank at the bottom. Run the heater so that the etchant is around 30C for faster etching.Another method which is simple but effective is to shine a 100W spotlight on the tank from a few inches away. In fact I find ththis is likely to heat up the etchant too much if anything! Figure 6 shows my home made etch tank, bubble generator andspotlight heater with the tank filled with water.

For those who are laughing at my 'Heath Robinson' approach I make no apologies, I believe the British are second to none asimprovisers and am a fan of 'Robot Wars', 'Scrap heap challenge', 'Salvage Squad' and similar TV programs which illustrate thpoint.

Figure 7 Workpiece holder design and photo

One final piece of equipment you need to improvise is something with which to dangle your brass or nickel silver into theetchant. This like everything else needs to be plastic. I made a simple clamp using some acrylic off cuts and two nylon nutsand bolts. The springiness of the acrylic provides the clamping action.

Clearly the clamp should be sized to fit your tank, workpiece and etchant fill level and I have made use of clothes pegs (whichare mainly plastic) to support the clamps on the edge of the tank and provide some adjustment. The pegs metal spring will faapart after a while but I consider these disposable items. Figure 7 shows the design of the clamp and my (rather grubby)example.

Now for the payoff, time to etch! Having made all the necessary preparations you simply switch on the bubbles (and heater ospotlight if used - wait until temperature has reached around 30C) and immerse your resist coated brass or nickel silver. Mak


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sure the bubbles pass on both sides and across the full area of the workpiece as uniformly as possible. Check the workpieceremoving it from the tank every 5 minutes until the first holes appear then every 2 minutes until all the exposed metal has beedissolved. Don't leave it too long! This results in the parts you want to keep being dissolved too! Remove the etched brass onickel silver once complete and wash in water to remove all the etchant. I also give a rinse with some mild household bleach stop any residual etching action. Don't forget to switch off the bubbles (and heater) and cover the tank to reduce evaporation iyou are not using the tank again immediately.

Finally you can remove the etch resist with a solvent, I use etching primer thinners or Finnegans thinners (sold for use withHammerite paints), something stronger than white spirit is needed. You could possibly leave the resist in place or sand it offdepending on what you are making.

Figures 8 shows my homemade etch tank, aquarium air pump and work piece holder in action.


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Figure 9 shows my completed brake stanchion etch on the fret and assembled (the shaft is a length of 0.45mm wire).

brass etching for beginners

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