Lathe turning from the centre outwards

Being somewhat addicted to watching some the very good videos showing amazing feats of engineering skills being carried out in very primitive surroundings I have often noticed that when turning a disc or casting in the 3 jaw the cutter can often be seen to be cutting from the centre outwards. I my home workshop I have always worked from the outside towards the centre and so my question is: What are the advantages if any from working from the centre outwards when turning in the lathe and are there special reasons for working in this manner?

Turning outwards at the final cut allows you to use a little used part of the tool (sharper) and the geometry is changed.

When facing off pipe I always work from the centre outwards, then the burr is easily removed with a file.

Sure fire way to chip an insert unless there is a hole in the middle of the work so you can put on the cut without risk of having the tip beyond ctr and the work coming up as you put on the cut.

Greensands, can you post a link to one or two of the videos you mention showing this? Would be real interested to watch. I find the videos of lathework etc coming out of India, Pakistan and Indonesia, Vietnam etc fascinating because of little snippets like this.

It may be that on a lathe with loose headstock bearings, cutting outward from the centre reduces chatter because the cutting forces are pushing the job away from the tool, not pushing it towards the tool and causing dig-ins/chatter. I will have to try it next time in the shed. (Noting Jason's wise proviso about indexable tips and the need for a centre hole, or use HSS.)

They do seem to do some amazing stuff in some of those videos, once you get past the lack of WHS by our standards and focus on the job in hand. One thing I have noticed though is that 3 foot of pipe on the chuck key seems to be universal standard operating procedure.

I do it sometimes depending on the job, I you want a flat bottomed recess in the end of a part then It's easier to put on the cut in the middle and work out as most boring bars are made that way.

Not India but just my shed, turning into an internal corner, also on large work it saves the cross slide having to be wound right out maybe beyond it's travel

Edited By JasonB on 03/02/2023 07:43:20

Edited By JasonB on 03/02/2023 07:45:07

Depending on the lathe, etc, one disadvantage might be the possibility of damaging the cross feed drive…..

Edited By not done it yet on 03/02/2023 12:27:33

Hopper, Joe Pieczynski (Pie for short) does this frequently.

Example of turning from the centre outwards at 03:20

Martin C

Like Jason, from time to time I use a Boring Bar, fed outwards from a central hole or centre deilling, to produce a flat bottom recess.

Howard

Not sure if this is best practice~ It probably isn't ~

but sometimes i face from edge to centre, then feed the tool in some more for the return journey~ saves time on a job that seems to be taking too long.

Makes the most of all those hand wheel turns.

I've just remembered another reason you might want to face from center outwards~

This may be a small lathe chuck problem rather than a large lathe chuck problem.

I was facing an irregular shape in the 4 jaw, roughly round in center, going out to two long slim 'arms' so a rather interrupted cut.

Facing from outside to center the item kept being knocked out of true as i started the pass.

I got quite frustrated. Then

Working from center to edge cured the problem.

On my South Bend 10K and my Nardini 16 x 40 the power feeds are set up so that when the carriage feed is toward the chuck the cross feed is away from the center. I assume the lathe designers assumed the normal facing direction would be from the center outward. I normally face feeding inward so I have to reverse the feed when facing.

I would feel that the type of tooling being used is a consideration as most HSS have rakes ground such that they essentially cut primarily leftwards or right! Inserts are a different matter as they will be unidirectional.

Samuel's observation about irregular pieces being knocked out of true makes me wonder if either the mounting was inadequate or the initial cuts were too heavy (or a combination), as I can't see any difference between the direction of cut causing the issue - even when working centre outwards you will still experience the same irregular parts that cause vibration etc

I often cut in both directions, but as I use HSS a lot, the outward cut is usually very light, more a case of feeling I am doing something useful whizzing the feed handle around rather than just winding it back!

From all the replies to date, I still don't see a convincing case that it might always be better 'outward'

regards Mike

It's probably safer that way (Myfords do it like that). If you are in parallel turning mode and hit the wrong feed then at least you will not plunge into the work and smash something. Could just be that it requires less gearing too.

regards Martin

Just checked my Warco 290V, when the carriage feed is toward the chuck the cross feed is towards the center. I personally don't think it makes a jot of difference either way, I tend to face inwards and then come out on the same setting, a sort of spring cut I suppose you could call it.

Tony