After the interest shown in the articles on the Stirling, I thought it might be a good idea to have a series of articles concentrating a little more on the technical side of workshop practice. There are a number of series in the pipeline and they’ll be published on a monthly basis. The best place to start would no doubt be the common materials used in a workshop and where they can be cheaply found and repurposed. This series will not be bogged down by technical nomenclature and material designations (although I will use the EN designations in brackets for reference), but will be more of a general approach to materials, how to change their characteristics and how or where to use them. So Prof. Meticulous, this is not a series for you!
Unfortunately, there will be no suppliers mentioned in these articles because they tend to come and go in these tumultuous times. I’ve also found the quality and service are variable so I would rather not recommend specific suppliers. Besides, most of the materials in these articles are rather common; I’ve stayed away from the Adamantiums or the Unobtainiums typically specified by Mr. Wiki Engineer. For the more specific materials, it’s worthwhile to download the supplier’s catalog where they normally have a common use section that will generally point you in the right direction.
This series will be a two-part series, with this part concentrating on the ferrous materials i.e. the carbon steels. The second part will be the non-ferrous materials, including the aluminiums, copper alloys and stainless steels and a short section on how to differentiate between the materials.
Low carbon steels (mild steel)
Carbon is the most common alloying element in steel production. By increasing the carbon content of the steel it generally becomes stronger (increases tensile strength) at the expense of ductility. Other alloying elements give the steels specific characteristics, for example, if you add small amounts of lead it increases the machinability of the steel, making free machining steel. Typically when adding carbon and other alloying elements it does decrease the weldability of the steel.
The low carbon steels are the workhorses for the home workshop and are used in a number of applications. With the carbon content typically below 0.25%, it’s not readily heat treated without carburizing. The low carbon steels are easy to weld so they’re good for fabrications. They’re also ductile, making forming easy. If it’s a thicker section, then making it red hot and bending won’t make the steel harder, so subsequent machining and fabrication is not an issue. Sometimes you get steel with the mill scale still on. This helps prevent rust with the steel in storage but it’s not kind to your tools so it’s worthwhile removing before machining. A 50/50 pool acid and water (NB! add the acid to water) makes a good pickling solution to remove any unwanted scale.
Some home workshops battle to get a good surface finish with the low carbon steels. To get a nice looking surface finish your final cut should be done using HSS with a sharp edge, and some cutting fluid.
Some parts need additional surface hardness to prevent wear and cold welding in service. This is where case hardening works well. The basic principle is as follows: the component is heated red hot and surrounded by carbon allowing the carbon to diffuse into the steel. This diffusion is temperature dependent and even at red-hot temperatures, it’s a slow process. If you looking for a very hard, strong part you need to encase the part in carbon (crushed anthracite and 1% soda ash works well) and place it in the fires of Mount Doom. Typically I work on an hour per inch thickness at red-hot temperature and that seems to work.
A quicker and easier case hardening method is to heat the component to red hot and dunk it in some used car oil. The diffusion time is greatly diminished and the depth is rather limited but a small amount of case hardening does take place. The item can be heated and dunked a few times to increase the amount of hardening. This also works well to blacken small items that are not worth painting or to prevent corrosion to homemade tools.
Other than steel merchants a source of smaller shafts can be typically found in items like printers and computers. The roller shafts are free machining steel and are accurately ground to size.
High tensile steels
High tensile steels are typically low – to medium – carbon steels with alloying elements added to increase the strength. They can be heat treated depending on the grade obtained. I normally heat a test piece to red hot and quench it in water. I test the hardness with a file; if the file bites in and removes metal easily it hasn’t been hardened, if it glazes over the material it has been hardened. If the steel has become very hard you might need to temper it by reheating to a golden brown and quenching. This will increase the ductile strength and prevent brittle failures. This can also be done in a commercial oven at around 200°C. For smaller items, old bolts (grade 8.8 or higher) are a good source of high tensile steel, or if you need hex pieces Allen keys work (the black ones).
Generally, I stick to EN8; it’s easily obtainable in a wide range of sizes and machines well. I use it for crankshafts, wheel shafts and any shaft that requires a higher strength than mild steel.
High carbon steels and tool steels
High carbon steels and tool steels can be readily heat treated to increase the material hardness. Silver steel is a common tool steel used to make taps, cutting tools, etc. in the home workshop. The steel is heated in the same fashion and tested for hardness as with the high tensile steels. Typically I temper tool steels in our oven. This gives a little more control, and depending on the material the tool needs to cut, different temper temperatures are selected. The list below gives a guideline for temper temperatures.
Old files, broken taps and drills are a good source of tool steel that can be ground to the shape needed for machining, this saves buying expensive HSS rod. The back end of broken taps, ground flat, makes good square drifts for that odd square hole. I also use taps for small taper reamers by grinding them on the lathe using a fitted micro grinder from Adendorff.
Materials for springs can sometimes be an issue to get, especially in small amounts. Flat springs, or leaf spring material can be made from band saw blades or, at a push, hacksaw blades. I’ve also made leaf springs from high tensile strapping, typically found on crates and the flat coil springs from any appliance with a retractable cord. Our vacuum cleaner suddenly stopped retracting the electrical cord about the time I made the coil springs for my loco. Funny that…
For normal coil springs, music wire will work, and certain sizes are available from a music shop. Just ask for the steel guitar wire. For a wider range of gauge sizes, tracer wire used for fishing will work and it doesn’t rust. All of my steam valves and clacks requiring a spring have tracer wire in and they’re all going strong. For larger gauges SS316 TIG welding wire will do the job.
For all those granddads that want to make little toys for their grandkids, I’ve saved the best for last! Tin-plated steel is a convenient source of the plate to make toy models. It’s easy to bend, cut with tin snips and easy to join using normal electronic or plumbing solder. Food grade tins, like biscuit tins, etc. are normally coated with a thin plastic layer on the silver side and branding paint that needs to be removed before the solder will take. This can be done with a thinners-soaked rag. Just make sure you fold the ends over or go over the ends with fine sandpaper to stop the little ones from cutting their hands.
The simplest is of course a little putt-putt boat, and there are a number of designs on the web. The one below is a very simple one a friend’s laaitie helped me build; an engineer in the making!
If you want a slightly more complex project a simple steam car might be the way to go. This one I made for my nephew…
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