Parting off using a powered cross feed

By hand here too - because that's how I was taught in college at the start of my apprenticeship back in 1973!

Fortunately I'm blessed with a steady hand and pretty good "feel" so don't seem to suffer with some of the problems others have described. Think I might have a go with power feed now though particularly as I have been very impressed with the insert parting tool I now have - never too old learn a new trick after all. Having said that I seem to mostly work with stainless or aluminium which often sticks to the tool.

No choice: the ML7 has no power cross feed. The only time I have ever snapped a blade was feeding in hard and fast without stopping, using a non-inverted parting tool. So, back to inverted and backing off regularly to clear the chips and cool the tip. Plenty oil too.

If I recall correctly it is the G H Thomas workshop manual book, where he describes a rear toolpost, that recommends parting off using power feed. Apparently he used to gives demos on a Super7 at exhibitions.

Could something like this be usefull if speed can be regulated on the go?

I've very rarely used power crossfeed when parting off, and only after verifying that I can part manually at a rate exceeding the power feed.

Obviously it's done as a matter of course in industry, chiefly with plugboard capstans, multi-spindle and cam autos as these are used on long runs. But IMO you're unlikely to gain much time-benefit unless other features of your setup are automated too, and you're doing a big enough batch to justify the extra setup work. I think that in Model Engineering it's very unusual to be in that situation.

I actually quite enjoy feeling the tool cut under handwheel control, and like Nigel McBurney above, have never seen manual lathes or capstans in production using powerfed partoff - my suspicion is that it's done mainly for bragging rights by the exponents.

Edited By Mick B1 on 24/03/2023 14:25:12

I would give it a try. You can also use the clutch on the cordless drill for some form of protection. If the bolt on your lathe can be tightened to the max , you can replace the bolt by a hex bolt and use a piece of hex steel to drive the nut.

FWIW, Using an inverted tool in a rear tooolpost made parting off much easier with the ML7 and with it's suddessor a bigger and heavier machine (BL12 -24, a Warco BH600 / Chester Craftsman lookalike ) it was so good that having made a larger gear to halve the feed rate, I took to using power feed, with a drip feed of soluble oil, or brush applied engine oil..

Result?

The slow steady feed gave better resuklts, and not being an excessive feed rate, did not flex the parting tool.

Rear Toolpost? Fittred to Capstan and Turret lathes, and definitely power feed on CNC machines.

Howard

Didn't a lot of capstans use lever feed cut off slides?

That seems like an entirely unnecessary snipe aimed at making yourself feel big by doing others down for their perceived motivations rather than adding anything useful to the discussion...

Entirely possible, provided everything is locked and solid. The advantage is the steady feed rate and the fact that it is easier to provide a constant ammount of coolant. Tooling has to be in top condition as well. And as already mentioned, a rear toolpost will be more rigid and eliminates the compound slide flexibility.

Edited By old mart on 24/03/2023 19:47:06

I'm not bothered by return fire . I can't see a practical role for powered partoff in the sort of quantities typical in model engineering, and where other parts of the cycle aren't also automated.

I suspect that those industrial manual and production lathes had pumped coolant, as I said earlier one reason I do it is that it is difficult to feed constantly with one hand while applying cutting fluid with a small brush, if my coolant was automated them maybe that would help?

I also tend to hold a small cup with the other hand to catch small parts as they are parted of so with one doing the cutting fluid and the other ready to catch the part that leaves me with no habds to turn the handwheel.

Edited By JasonB on 24/03/2023 20:18:59

All of my mishaps when parting off have occurred when parting by hand and never when under power, but that might have been just luck. When I see some peoples pictures of their parting setup looking as stiff as a wet noodle, I find it amazing that they ever manage to part off. When I bought my little 7 X 12, I was amused to find that the guy had been parting off with the HSS tool upside down.

I suspect a lot will depend on the lathe used, I have a Bantam, and use power feed if the work is more than 1" diameter, I use a rear tool post with the inserted tip tool the right way up, and run in reverse and flood with coolant.

I use the second slowest feed. It always works for me, but all easy to do on a Bantam.

Chris Gunn

An oft overlooked gotcha with parting off is that the chip is wider than the groove cut by the tool. So the depth of cut has to be shallow enough that the chip can deflect or bend on its way out. If the chip is too strong it will jam up and, at best, seriously mark the work. At worst a major smash up and "unfortunate" language. An especial issue when the tool is cutting square rather than at an angle.

The insert type tools have concave top, bending the chip to make it narrower than the slot so it falls out easily without marking. Not a universal panacea, as I was reminded a couple of days back when hand parting off the first of several components from 50 mm alloy bar. Got a bit too enthusiastic and, even after bending, the over thick chip was still enough wider than the tool slot to seriously mark the cut faces.

Ooops.

Checking the book and setting power feed to the correct depth of cut I realised I had been feeding about 3 times too fast. Instant disaster on a Myford or smaller machine. My hefty S&B 1024 just shoved the tool through with a complete lack of drama.

Clive

The shape of the swarf from my insert parting tool:

Parting off under power feed gives a very good finish on the part, and on the remaining stock. So no cleaning up is required. One has to look at the whole picture before saying something isn't necessary.

Andrew

That chip shape made by carbide insert parting (which we use 100%) reminds me another advantage of rear toolposts using inverted cutters, the chips have gravity to assist their removal.

I suspect the force on a chip due to gravity is going to be tiny, and for long chipping materials of no consequence.

Andrew

Tut! I guess Mick hasn't read the whole thread! I kicked off with:

'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.'

Nothing to do with bragging rights or production rates. Parting-off under power is just a reduced hassle way of getting the job done. Trust me, it's a good thing.

Dave

Is there a worthwhile time saving parting off under power on a small lathe?

For the actual operation - maybe, although it's pretty small.

But there's a big time saving in having to sharpen the tool less, or replacing it because it's bent or broken. Not to mention the time and material cost from having to remake the part because it was damaged when you broke or bent the parting tool. Having both hands free to either catch the part or add cutting fluid can be a really useful too.

I'll keep parting off under power; it's less hassle.