- tags: design #Mechanical
- Everything you can make out of cold rolled mild steel sheets should be done that way. Its strong, cheap, easily bendable. most useful sheet thickness are 18 (1.2mm) and 10(3mm) Gauges. Also for stainless a cheap 300 series stainless would work with gauge 18 and guage 12 because its expensive.
- Its useful to stock some stainless steel in spring temper, as it can be used for flexures and springs. eg type 301 full hard steel. The nice thing about the series 300 steel is that you can shear them with a shear, you can bend them if you have to. The much harder 400 series cannot be cut with a shear, not bendable.
As a general purpose spring material store series 300 stainless steel with either a full hard or a 3/4 hard. - Other type of spring temper is a 17-7 stainless steel. It comes annealed, so easily formable, so you can bend it spot weld it and do all operations, then you need to heat cycle it. Once after the heat cycle it becomes the hardest springiest of the stainless steel.
The heat cycle is you heat it up to 800C, let it cool down then you heat it again to about 500C and let it cool down. No quenching, just double heating. - Both steel and stainless come in regular and free machining type. Best to spend a bit extra on free machining as you can save a lot of time. The free machining has some alloying components like lead or sulfur to help machinability. - Aluminum is best for large structures and for heat sinks. Good to store 3mm of 5052 Aluminum. The advantage of 5052 is that it can be bent without cracking. The most common one is the 6061 but they will crack when bent. - Spring wire is useful when making your own springs, stocking a couple of sizes of spring wire give the possibility of making many kind of springs. There are two types, one is the Music wire it is carbon steel, its cheap and easily available, but is not rust proof.
If you need rust proof springs then use the stainless steel alloy 17-7, which is available in wire form and make the spring. It is pretreated so only one heat cycle (480C for 1 hr) is necessary. - Loclite used for gluing parts like bearings to shafts, be careful when using it with some plastics as it may lead to cracking. - Wax Stick useful when cutting aluminum as lubricant. Particularly useful when cutting aluminum with wood working tools, put some wax on table saw to cut sheets, or on a router bit to prevent sticking. - Steel - 20MnCr5 Case hardenable steel used for spindles, toolholders, piston pins. - The only hardenable steel you need to have is air harden able A2 steel. The advantage is there is no need to quench it. Quenching will introduce warps into the steel, and A2 is designed to have very low dimensional variations.
If you take regular or high carbon steel and quench it then it will have high dimensional changes, so you need to oversize it and then grind away the extra
Sometimes you will have to grind the surface when case hardening because the outer layer can De-carburize if it is not treated in an inert atmosphere. The best thing is to wrap it in paper and then stainless foil and seal the foil by spot welding. So when it is heated the paper absorbs the oxygen and carburized before the steel can lose the carbon. - Mild Steel has carbon as the main component.
- [Surgical Stainless steel 440]() Useful when dealing with medical devices, but not as corrosion resistant as the [series 300 stainless steel](), cannot leave it inside the body as implants. - [High speed Steel]() You can make tools from HSS, you cannot anneal it, you can grind it. - [Carbon steel]() Cheapest hardenable steel, but need to quench it, lot more science involved. - [Difference between carbon steels](https://us.misumi-ec.com/blog/what-is-difference-between-carbon-steels-low-medium-high/) | [Various carbon steels](https://matmatch.com/learn/material/carbon-steel) - **How to tell the various steel apart** - Take a piece of the steel, grind it and look at the sparks, - [Mild Steel]() very little spark and don't have a star at the end of the spark - [Carbon steel]() Lot more sparks and at the end of the spark there is a star. - [A2 steel]() Dull sparks and no stars at the end. - [High speed Steel]() No sparks at all and few sparks are red, then white. - [Surgical Stainless steel 440]() No sparks at all, less than HSS. - **How to Harden steel** - The best way is with an oven/Klim, but when its a small piece you can heat it up with a torch as well. - Its best to place the work piece over an insulator like fire brick, because it reflects the heat and work can be done 2X as fast. - For A2 steel its at 950c which is white hot and let it cool down in air. - After hardening it can become very **Brittle**. So we need to **Temper** it. - [Tempering]() is a **trade-off between hardness and toughness.** - Depending on the trade-off you need to heat it to between 220 to 300C. 250C will give you a hardness of Rockwell RC60, which is as hard as you need. But if you need **Impact strength** then you need to heat it to somewhere around 300C then it will have a hardness of RC56 but much higher toughness. - The range is 220-300C every 10C will make a huge difference, you need to be able to judge the temperature based on the colour. Luckily stainless steel has a good colour range.
It goes from Straw colour **(200C) to dark brown, to **dark blue (270C) to light blue (320C) to light grey, which is overheated.
The Tempering range is from straw to dark blue, Straw which is full hardness. - One useful thing to get a Carbide tool is to take a piece of discarded carbide insert and braze it on to the steel, using an brazing alloy, so you can make custom tooling, drills, etc.