Round?

Hi Guy,

It depends on what you want to make. If you just want to learn/practice turning, free-cutting steel is cheap and easy to turn, also free-cutting brass. You may also find free-cutting light alloys.

Thor

Scrap metal

Then you can make a mess and learn at the same time

NOT scrap metal, at least to start with. An absolute beginner has a lot to learn about rpm, tool shape, depth of cut and feed-rate and it's easier to start with known materials. I wasted a lot of time on my mini-lathe discovering that odd bits of metal found in the average home are poo. (Different story if you have access to workshop scrap or someone who knows.)

Problem with scrap recovered from manufactured items is that many alloys do not machine well while some are utterly vile, or need to be softened by heat treatment first. Likewise DIY store metals – their aluminium is sticky and the steel gritty. DIY store brass rod is OK, but not the best. Plastics are often difficult to turn and although the lathe will do it, wood is not ideal on a metal lathe. Cast Iron varies between wonderful and horrible and is always dirty. Some stainless steels machine well, but most are difficult because they work harden. Copper and Lead are too soft to machine well. I'm told Magnesium alloys machine best of all, but are an exciting fire hazard. Avoid steel pipes used for gas and electrical conduit until you have more experience – they come with hard welded seams.

In a mini-lathe, I preferred machining shop bought brass (CZ121), Aluminium (2014), free-cutting mild steel (EN3B) and mild-steel (EN1A) in that order. When actually making things, the other way round! My all-time favourite metal is brass because it cuts easily with a good finish and doesn't need lubrication. The swarf comes off in clean flakes, just don't get it in your eyes. My least favourite is cast iron, it often has a very hard skin and, because it's full of carbon, a black mess goes everywhere. You end up dirtier than a black goat playing with printers ink in a coal mine.

Dave

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BDMS is bright drawn mild steel. Theoretically it should be homogeneous, but does frequently have a sort of skin on it that is more resistant than the material inside. All the metallurgy I can remember reading says that mild steel can't work harden, but I don't think I really believe that. So I think the skin's either from work hardening, or scale that been driven into the surface by the drawing process, or both. It's usually present to some degree, but is not very conspicuous in the best material.

My advice would be to look around local industrial estates and see if you can find a firm who machines round bar.

Then explain what you are doing and ask nicely if they 'scrap bar ends' of free cutting mild steel in their scrap bin.

I find some firms really helpful and let you fetch out what you want from the skip. One firm gave me a goodly bundle of lovely10mm dia bar ends about 200mm long which get used for all sorts of things – machines a dream!

Alloy and plastics can be a bit more difficult to find and are very variable in how they machine so are not so good for a complete beginner. Same approach however will often produce the goods.

Just following up my posting about difficulty in drilling certain spots in EN1A:

I have found this problem twice now – 1/2" square stock EN1A – drilling through to 6mm fine generally, but then on the next hole I hit a very hard spot. Latest occurrence: Centre-punched, centre-drill to a couple of mm, then a 3mm drill bit – worked fine down to about 10mm then stopped! And I really mean I couldn't get any further in. So I flipped the part over and tried from the other side – I could barely mark the surface and the drill just wandered about.

This is really frustrating – particularly when you have a few hours work already into a part.

In something I read, there was talk about normalising stock like this: heating to 800C, then letting the stock air cool.

Is this something one should do as a matter of course?

Edited By Kevin Murrell on 15/09/2018 07:01:36

I have a good relationship with a local steel stockholder who will let me go in and look at the offcuts rack. All steel is correctly marked and of traceable provenance. Just picked up over 4 foot of 1" round EN1A for £10 as a cash sale. OK not as cheap as buying the whole bar but good for home use.

I had the same issue with a bit of 1/2 x 1 EN3 the other day took the edge straight off a brand spanking new 10mm sq HSS with 8% cobalt flycutter bit I had been sent to try out and when I say took the edge off I mean turning it into a round nosed tool not just dulling the edge. 1/4" further along the steel cut perfectly well. I have had it happen about 3 times now and am sure it is the material not the tool bit, machine or methods.

This tool did gave a 90deg corner