Parting off using a powered cross feed

[Mick B1Participant @mickb1]

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

[HuubParticipant @huub]

Posted by Niels Abildgaard on 24/03/2023 13:34:53:

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

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.

[Howard LewisParticipant @howardlewis46836]

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

[bernard towersParticipant @bernardtowers37738]

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

[JellyParticipant @jelly]

Posted by Mick B1 on 24/03/2023 14:23:48:

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.

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…

[old martParticipant @oldmart]

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

[Mick B1Participant @mickb1]

Posted by Jelly on 24/03/2023 18:50:29:

Posted by Mick B1 on 24/03/2023 14:23:48:

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.

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…

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.

[JasonBModerator @jasonb]

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

[old martParticipant @oldmart]

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.

[Chris GunnParticipant @chrisgunn36534]

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

[Clive FosterParticipant @clivefoster55965]

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

[Anonymous]

Posted by Clive Foster on 24/03/2023 20:57:46:

…insert type tools have concave top, bending the chip to make it narrower than the slot…

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

[old martParticipant @oldmart]

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.

[Anonymous]

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

Andrew

[SillyOldDufferModerator @sillyoldduffer]

Posted by Mick B1 on 24/03/2023 20:01:02:

Posted by Jelly on 24/03/2023 18:50:29:

Posted by Mick B1 on 24/03/2023 14:23:48:

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.

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…

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.

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

[Nick WheelerParticipant @nickwheeler]

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.

[JellyParticipant @jelly]

Posted by Mick B1 on 24/03/2023 20:01:02:

Posted by Jelly on 24/03/2023 18:50:29:

Posted by Mick B1 on 24/03/2023 14:23:48:

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.

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…

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'll give you a very practical example:

Next week a friend is coming over with a short length of 170mm Hastelloy C22 bar, because he wants me to turn him two DN50 blank PN40 flanges.

There's barely enough material to make them and even if I could fit it on my bandsaw it would not cut well or straight, if at all.

So I need to take an 82.5mm deep parting cut through a notoriously awkward nickel-chromium superalloy…

That will stress the lathe enough as is, there's zero chance of me maintaining sufficient or consistent tool pressure and feed rate through a cut that long feeding by hand; at which point Bang! Broken insert, if not broken parting tool, and quite possibly a £900 piece of material ruined.

[Dave HalfordParticipant @davehalford22513]

it's a good thing if you have power Xfeed and it works better than manual otherwise there's no point and it's back to the hacksaw.

It's also a good thing if Xfeed backlash is minimal because if the tool digs in suddenly your 4thou per rev can be 25 thou and everything stops.

[Chris CrewParticipant @chriscrew66644]

it's a good thing if you have power Xfeed and it works better than manual otherwise there's no point and it's back to the hacksaw.

I am assuming that you mean taking a hack saw to the work-piece whilst it is still in the lathe? That to me would be a very big 'no, no'. How many lathes have we seen with hacksaw marks gouged into the bed at the head end because a person was also unskilled in the use of a hacksaw and applied excessive downward pressure causing the blade to crash through the cut and into the lathe bed?

Apologies if my assumption is incorrect.

Edited By Chris Crew on 25/03/2023 08:38:37

[Dave HalfordParticipant @davehalford22513]

Posted by Chris Crew on 25/03/2023 08:37:22:

it's a good thing if you have power Xfeed and it works better than manual otherwise there's no point and it's back to the hacksaw.

I am assuming that you mean taking a hack saw to the work-piece whilst it is still in the lathe? That to me would be a very big 'no, no'. How many lathes have we seen with hacksaw marks gouged into the bed at the head end because a person was also unskilled in the use of a hacksaw and applied excessive downward pressure causing the blade to crash through the cut and into the lathe bed?

Apologies if my assumption is incorrect.

Edited By Chris Crew on 25/03/2023 08:38:37

Exactly Chris, there's lots of them out there. Don't know why a using the bench vice is so un appealing.

[Clive FosterParticipant @clivefoster55965]

Provided you have a sharp tool and sensibly light infeed dig in isn't problem with power feed.

The 'bang, everything stops" experience with power feed is invariably due to chip jamming in the tool slot. Which is why lubrication is desirable and the narrowed chip produced by insert tools so beneficial. As Andrew says a properly set up and properly fed insert tool leaves an excellent finish showing that the chip doesn't significantly touch the sides of the slot. Any contact being so light that the surface is not marked.

In practice we generally have to grind a conventional HSS blade with a flat top. Geo.H Thomas put a Vee top and front on his (how?) but thats for advanced folk only.

Grinding the front at an angle effectively produces a tilted chip that is less likely to jam up as it's already trying to rotate away from the walls of the slot. The top of the tool also needs to be angled for best results as that re-enforces the twisting action. Get the two angles opposed and it will jam! Need to get the speeds and feeds right so a long chip comes out. Unfortunately angling the tip produces a side force on the tool so it rubs disturbing the finish. All too often hobsons choice. Pip on the end of the job or rub marks.

Tight spiral chips on top of the tool indicate incorrect speed and feed combination. High risk of jamming up.

As ever careful set-up and careful work practice will get round these issues but its important to be aware of what can go wrong.

Small lathes have slender feed screws.

Effectively the push force goes through a column the core diameter of the screw. Not very big.

The helix of the thread produces a side force so the unsupported length of screw between the handle bearing and nut has a bowing force imposed. Clearance between nut and thread doesn't help as this provides extra space for any bow.

If the tool stops cutting momentarily the feed forces causes the unsupported part of the screw to bow acting like a stiff spring. Further feed with the tool not cutting increases the bow until the spring force is sufficient to re-start cutting an action whereupon the tool jumps forward. It takes more force to start a cut than it does to keep it going so the restarted cut is even greater than pure geometry predicts. In the worst case the job climbs over the tool or breaks it during the climb process.

Naturally the deeper the parting off slot the longer the unsupported part of the feed screw so the greater the bow tendency. Deeper slot means more chip drag too and thinner part of job remaining makes the whole thing less stable so, if a hand feed job is going to go wrong it always seems to be about 2/3 rds through. Just when you start to relax thinking "Yup, it's going right this time!"

Hence Daves "4 thou cut going to 25 thou and bang" scenario. Most likely with materials that work harden or form built up edges.

Given maliciously careful hand feed its possible to demonstrate this spring action on a slightly loose machine with the slide visibly oscillating as the cut stops and starts. First happened to me with an alloy forming a built up edge leading to regular momentary stops in cutting after the built up edge formed before it broke away as the tool rubbed allowing cutting to resume. Spectacular marks on the cut faces.

Using a rear tool post with a conventional feed screw keeps the screw in tension so there is no bow effect. SouthBend Heavy 10 lathes fitted with a taper turning attachment have the cross feed screw effectively reversed so it pulls from the back operating in tension. Parting off with a taper turning equipped Heavy 10 is noticeably better behaved and generally less fraught than with the non taper turning version with its conventional push feed screw.

Clive

Edited By Clive Foster on 25/03/2023 09:55:16

[Clive FosterParticipant @clivefoster55965]

Sorry double post. Why?

Clive

Edited By Clive Foster on 25/03/2023 09:46:10

[Bob Unitt 1Participant @bobunitt1]

Posted by Chris Crew on 25/03/2023 08:37:22:

it's a good thing if you have power Xfeed and it works better than manual otherwise there's no point and it's back to the hacksaw.

I am assuming that you mean taking a hack saw to the work-piece whilst it is still in the lathe? That to me would be a very big 'no, no'. How many lathes have we seen with hacksaw marks gouged into the bed at the head end because a person was also unskilled in the use of a hacksaw and applied excessive downward pressure causing the blade to crash through the cut and into the lathe bed?

Apologies if my assumption is incorrect.

Edited By Chris Crew on 25/03/2023 08:38:37

I regularly use a hacksaw on chucked-up pieces in the lathe. The cure to the problem you describe is a very simple 2-minute job to make – a piece of wood with 'feet' either side to straddle the lathe bed. I use the same board to protect the bed when changing chucks etc.

[John HaineParticipant @johnhaine32865]

Well the answer is obviously some do, some don't. Personally I'm in the do category, partly because I don't have a cross-feed handwheel any more but mainly because it works so much better (for me anyway).

If you are using HSS parting blades (front or rear TP), you can make a dish in the "top" surface using a round diamond rat-tail file in a few minutes. You can hold the blade in a vice or toolmakers clamp so the faces of the jaws will stop the file sliding off the surface, but once you've made a shallow depression in the right place it's self guiding. I'll try to get a photo of mine.

[John HaineParticipant @johnhaine32865]

Like this.

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