Things I should know cutting various materials on lathe

[Chris TickTockParticipant @christicktock]

[Chris TickTockParticipant @christicktock]

Hi Guys, Is there anything that it would be better to know before cutting various materials on the Sherline lathe. For instance what problems could one encounter cutting say cast iron, aluminium, plastic and for that matter other materials the more experienced machinist has tried and found issues.

Regards

Chris

[David Standing 1Participant @davidstanding1]

Chris

Buy some reputable books on the subject, and have a read!

I don't mean that facetiously, but look through the 'Workshop Practice' series of books, everything you need is there, start with nos 3, 30, 34, 42 and 45.

[Tim StevensParticipant @timstevens64731]

Lots to learn – but keep at it.

One thing that can catch out a beginner is trying to turn brass with a nice sharp tool. Even a new twist drill. What happens is that the tool digs in and breaks off, or jams the machine, or even bends a shaft (etc). Tools for cutting Brass need no 'back rake' on the cutting edge – without this there is no tendency for the brass to grab, pulling the tool further into the work – a problem especially bad if there is backlash in your tool feed. Which of course there always is.

Cheers, Tim

[Chris TickTockParticipant @christicktock]

Posted by Tim Stevens on 27/08/2019 15:35:19:

Lots to learn – but keep at it.

One thing that can catch out a beginner is trying to turn brass with a nice sharp tool. Even a new twist drill. What happens is that the tool digs in and breaks off, or jams the machine, or even bends a shaft (etc). Tools for cutting Brass need no 'back rake' on the cutting edge – without this there is no tendency for the brass to grab, pulling the tool further into the work – a problem especially bad if there is backlash in your tool feed. Which of course there always is.

Cheers, Tim

Thanks Tim yes have a set of zero rake drills for brass but what are the pitfalls of plastic or aluminium etc?

Regards

chris

[BazParticipant @baz89810]

Agree with David Standing 1, buy the recommended books and they will answer all of your questions.

[Tim StevensParticipant @timstevens64731]

Plastic is a wide description, – not all plastics are anything like the same in machining terms. There are 'brittle' plastics like polystyrene, and 'waxy' plastics like polythene, and 'rubbery' ones like polyurethane, but the nicest to machine include acetal, nylon, and rigid PVC. One problem is the nature of the turnings (which can be really tough) and the low melting points of plastics creating problems when parts rub together in machining, or when your tooling is the wrong shape or blunt.

Pure aluminium is a bit soft – the turning waste (or swarf) tends to push together into lumps, and it sticks to the tool, making a good finish difficult. But there are lots of light-alloys which turn nicely and some which polish nicely too. Just follow the advice – get hold of some reference books, which are often around second-hand or even seriously old (and rather dog-eared) so not very costly – and more recent ones for plastics, of course.

And practice.

Cheers, Tim

[Nick WheelerParticipant @nickwheeler]

You'll find it a lot more efficient to buy a few pieces of the material you're likely to use and just try them on your machine, with your cutting tools. Brass, steel, aluminium and whatever plastic you have in mind of about 25mm diameter won't cost you much. And once you've made a few cuts you'll be able to make something, rather than just worrying about it.

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