Problem achieving a smooth finish

[Nick Watson 1Participant @nickwatson1]

I am a beginner at lathe work. I have various steel bars of indeterminate quality and have been practicing turning the finishes are ribbed rather than smooth. That is it goes smooth then it is as if the tool digs in and it gives a slightly rough and deeper surface. Is this the steel or could there be a fault with the lathe a mkII colchester student. Any advice would be much appreciated

[Nick Watson 1Participant @nickwatson1]

[Anonymous]

NIck: First, welcome to the forum.

Second, the issue of poor finish crops up on a regular basis on the forum, both for turning and milling. The vast majority of finish issues are cleared up by taking care of two factors; material and tooling.

Material first; all steel is not created equal. Some types are easy to machine and some are difficult, and some manufacturers produce poor quality material of any sort. So stage one would be to dump the indeterminate steel and buy a length of steel of a known grade, preferably EN1A, as that should be easy to machine. It will be cheaper to buy a standard length from a commercial supplier, and there's also a good chance you'll get what you paid for.

As for the tooling you don't say what type you are using, HSS, brazed carbide or carbide inserts? There are two rules for cutting tools, irrespective of the type:

1. Don't bother buying cheap cutting tools, they may be cheap but they are poor value

2. See rule 1

Of course even a decent cutting tool needs to be properly ground, at the correct height and running with appropriate speeds and feedrates.

The problem is unlikely to the lathe itself, although going over to check gibs wouldn't do any harm.

Lastly if we knew roughly where you are based there might be some-one local who could assist.

Regards,

Andrew

[Nick Watson 1Participant @nickwatson1]

Thank you Andrew. The lathe came with a lot of tooling some that could not possibly used with this lathe as it is far too large, hss cobalt a boring bar with carbide inserts lots of inserts with no holders quite a mix. I am slowly working through them. I have found a round nose right handed tool with a brazed tip and on the side it says Novite X37/M16 tried it, it has produced a very smooth finish on some new steel. This steel was purchased after your advice, from Ace Metals in Norwich and I told the seller what I was attempting to make and he supplied suitable steel so thank you again seem to be on the right track now

Nick

[mickParticipant @mick65121]

The problem, as I see it, is that in these days of inserted and pre-ground tooling and charts of cutting speeds and feeds for each style of tooling, everyone expects to achieve a good finish because they have bought the tool for the job, so it should deliver. Back when the world was very young things were completely different, with hand ground HSS every job was different, in fact, after rough turning to 0.020'' over size, a turner would experiment with different speeds and feeds before committing to the finial cut to size, as the same machining conditions couldn't be guaranteed from one work piece to another. Taking onboard all of Andrew's points, I feel its good practice to try different approaches, but for finishing, the general rule of thumb is dead sharp tooling, light depth of cut, experiment with speeds and feeds and use plenty of soluble oil, cutting oil or paste applied with a brush brush if no machine fed coolant is available. To become an all round machinist it was expected to take a five year apprenticeship, so you have only just taken the first steps, but good luck with it all.

[wheeltapperParticipant @wheeltapper]

Nick, I see you have discovered Ace Metals.

Greg has always been very helpful to me. Are you local to Norwich? I live in Spixworth.

Roy.

[Nick Watson 1Participant @nickwatson1]

Mick the approach to turning you describe was the way I was trying. after trying every tool that came with the lathe things wern't going well. After the advice from Andrew and getting better material and finding a rusty tool in the bottom of the box that cleaned up well things have improved and am now on the way to making a sleeve puller for the injector sleeves in the 4JX1 isuzu diesel engine.

Roy I am in Felthorpe and Greg was very helpful when I explained what materials I needed

Nick

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