Parting off using a powered cross feed

Instead of hijacking the running thread on rear tool posts I have a simple question:

How many people part off on a lathe with the cross feed powered instead of hand operating the feed?

JA

Me, always! Failing to feed steadily is one of the main causes of digging in during parting off. Tentative, uncertain, jerky hand movements are begging for trouble. Power feed does a much better job than I do!

I know it's hard for chaps born with steady hands to comprehend that others might be clumsy, but we are.

Dave

Depends on the job. Small parts hand feed but say 20mm+ then normally power feed. Start by hand to make sure nothing feels untoward and then engage the power feed. This is on a Boxford

All the time for me too, leaves both hand free one to apply a bit of cutting fluid the other to catch the part.

Edited By JasonB on 23/03/2023 12:00:09

Nearly always

Nearly always power feed on the centre lathe, minimum feedrate is 4 thou/rev, and usually 6 to 8 thou/rev. On the repetition lathe parting off is manual. But controlled by a lever not a screw thread and dial. Just pull hard on the lever to ensure a decent cut.

Andrew

Almost always, my lowest available feed rate is 0.03mm/rev, (or 1⅙ thou per rev in old money) so there's never a reason not to.

I will sometimes use manual feed on the first few parts if I'm if I'm making multiples of something small but with a high length to diameter ratio, but that usually means I'm trying to work out how fast I can feed without the part deflecting to select a feed rate.

Edited By Jelly on 23/03/2023 13:04:14

Not something I do a lot of but CNC so always power fed when it is done.

Martin C

Nearly always, rear post 40mm EN1A diameter 800RPM feed 0.05/rev works well if the lube is plentiful. Nervy pussying around is a disaster.

Nearly always on the Willson where this feature is available but never on my pre-PXF Myford.

When hand feeding it is sometimes helpful to use an extended handle for extra leverage and a smoother movement.

Instinctively, I feel that a lever-operated slide would work better than a screw for hand feeding.

Almost always on the BL12 - 24.at 0.0025"/rev mubricated by brushing onand ordinary engine oil or soluble oil controlled feed through a needle valve.

On the mini, it has to be hand feed, but have just made and installed a rear toopost, so hope for betterb things.

Howard

Edited By Howard Lewis on 23/03/2023 18:35:38

The reason I asked is in the past there has been some debate about the practice.

My present largish lathe is the first I have owned with a power cross feed. After I got it I happily used the powered feed for parting off until this was discussed in a forum. The opinion was that the practice was an absolute no-no. So I went back to using a hand feed.

Recently talking to others who know what they are doing I got the universal reply "Why give up using the power feed if you have never had problems".

The more I think about it using a hand feed is a sign of a lack of confidence and a power feed ensures the tool is continuously cutting.

Many thanks, and I am going back to using the power feed. There is always the big red button.

JA

Actually the thing I forgot to mention is matching the parting blade geometry to the material. It's something we think about all the time for other toolbits, but sometimes gets disregarded for parting blades.

I once did a job for a friend which involved lots of parting off in copper and some stringy horrible grade of brass, it was all a bit grabby unless I used a really slow feed, having quite a few to do, I specifically ground a parting tool with a small negative rake, and like magic I could suddenly feed at a much higher rate.

Similarly I have a brazed carbide parting tool which is preserved for stainless which is much wider (about 4.5mm) with a reasonably positive rake and chip breaker ground into the top face of the brazed insert, the shape helps reduce cutting pressure when taking the more aggressive feed rates needed to successfully cut stainless, whilst the thicker tool gives sufficient support for such heavy cutting forces.

An example of why the internet is double-edged, well-meaning folk getting it wrong! Parting-off under power is well over a century old, so any debate must be a recent glitch. As a beginner feeling my way into the hobby, common sense told me it was 'obviously' safer to feed by hand because I could stop at the first sign of trouble. Unlike a stupid machine that would cause terrible damage by ploughing regardless into the wreck. Of course 'common sense' is as thick as two short planks, and I was wrong. (Most of the trouble in my workshop is caused by me.)

I suspect a bunch of newcomers tried to part off at a poorly chosen feed-rate, got into trouble, and blamed the machine rather than the clown driving it! And then compounded the mistake by publishing their incorrect conclusions on the internet so the whole world can benefit from it!

Dave

Power feed (CNC), upside down parting tool and lubrication is my way using a SP200 2 mm wide insert, 800 RPM (max to keep the lubrication on the part) and 0.02 mm/rev.

After parting off years at these conditions on both my lathes, I recently started parting off steel dry to allow higher RPM (higher speed). I am not sure if this is a better condition, will try it for several weeks.

Well I am amazed ! My answer is never -- I always use manual feed and always have, indeed I don't recall any of my mentors or contemporaries in 60's onwards using power cross feed when parting off.

Of course we never had the disposable tipped tooling that's available today and to be honest although I have tried these but I much prefer the standard HSS Eclipse blades. Steady feed, don't allow the tool to dwell when stopping and starting the advance, use plenty of oil or appropriate lube.

Feel I'm out of step !!

John

No you are not. Hand feeding can do the job also and if you are experienced and have good results why not.

Some times I also use a 1.2 mm HSS parting blade in normal position and manual feed. When I have time, I will make a tool holder for a 2 mm HSS Co8 blade that I want to try.

Me too Johnf, always hand feed too. Ashamed to say thats on a DSG too . Will I ever be forgiven....

"The opinion was that the practice was an absolute no-no. So I went back to using a hand feed."

And that's exactly what it was, i.e. someone else's opinion. My own view is that there are no 'absolutes' in the privacy of your own workshop. If a technique works for you and produces a result that is acceptable to you, then you must be doing something right no matter how much 'inspector meticulous' may think otherwise. I have easily parted 5" noggins to make back plates for the Myford.

My own approach to parting-off is to use a combination of both hand and power-feed. I don't have the luxury of choice on the Myford but on the Colchester I use both hand and power feed. I always part from the rear tool-post, which should be as large and rigid as the lathe will permit, I keep the tool kept as sharp as possible and I always pump coolant in to the cut. I accept that some people can't tolerate the thought of something containing water being allowed anywhere near their cherished machines, and I understand that to a certain extent and also that it can be a little messy if the stream hits the chuck, but to me it makes any cut so much smoother and it was standard practice in the machine shop where I was once an apprentice. I use a cheap soluble oil diluted about 25:1 with a squirt of Rocol coolant disinfectant that kills the black algae in the sump when the machines are not used for a while.

While I was at work and later on my visits as a procurement engineer to lots of UK machine shopsI can never recall seeing anyone using power feed to part off on a centre lathe ,and I never do now at home with my Colchester, the Ward capstan lathe where i once worked,never had power feed,and the capstan lathe was a real production machine in days gone by, though I suspect that manual winding of the cross slide was quicker,as the parting tool usually at the rear had to be kept well to the rear in order to clear the tools on the capstan turret,so the operator had to wind the handle quickly up to the work then slow down the hand feeding when actually parting off ,rather than wind fast then stop engage a clutch and part off . Of course at the same time the high volume turret auto lathes were enclosed and cam driven so a cam could drive the parting tool up to the work very quickly and slow automatically for the actual parting, plus the fact they were designed to do that job and were very rigid. and the same can occurr on modern cnc machines where there are no handles to wind. When HSS was in common use the general rule was to reduce cutting speed by half when parting.A pumped flow of coolant helps a lot particularly on steel,