Parting tip breakage

Please have a look at around 12m 30s on THIS video and tell me why you think the parting tip broke.

Edited By Neil Wyatt on 30/05/2020 22:02:58

Because it's not a parting tool, but is intended for profiling and grooving. At least that's what I use mine for:

Dunno why he feels the need to part off so far from the chuck. Well I have an idea, but this is a public forum.

Andrew

The way the tool sprang to the left and back looked rather odd. In slow motion it looks like the tool was pointing slightly to the right then twists back square. I suspect the cross/top slide has a lot of play in it. Another possibility is the spindle bearings are worn or the lathe is not rigid enough and the work climbed over the parting tool. Also from the swarf it looks like he was cutting harder when it broke.

Unless of course he was moving the saddle to the left.

Reminds me of trying to part on my worn out 1912 vintage Drummond, I had that climb right over the parting tool and stall on top of it.

Adrian

None of them looked to be cutting well judging by the swarf coming off. I've never snapped one of those inserts but did snap the bottom of the holder off but my fault for only having a short amount of the work in the chuck

Looks to me as if the top slide wasn't locked so any sideways force generated by imperfect cutting would pull the topside through its backlash region. Setting the topside parallel to the bed on a light machine is asking for trouble.

A grooving tool like that is going to be pretty pants at parting off anyway. The shape guarantees some degree of chip crowding as it comes off the work. Piddly little brush will do nowt. Needs full flow or carefully directed mist to come out clean.

Proper parting tool inserts are Vee profile at front and top with two points at the business end. These fold the chips so they re narrower than the parting tool slot allowing them to escape. Must be run at the correct speed and feed otherwise even these will give problems. As usual with modern carbide in relatively benign materials chips should come off in short tight coils.

Parting is enough of a pain at the best of times if you can't run fast with full flood coolant. Why compound the difficulty by buying a cheapskate version of an improper tool. Buy cheap, pay twice. The real this work very well when properly aligned and set up. Much of the advantage of the rear tool post type on a small lathe is that it gets set-up properly and left alone. Not topside to set wrong too.

Clive

Dunno why he feels the need to part off so far from the chuck. Well I have an idea, but this is a public forum.

Well, I’ll be more direct, blunt, cynical, etc than Andrew. I think it was engineered to break - by setting the tool at a slight angle and parting, without support, so far from the chuck. I think the breakage was predictable.

Hi Guys,

That video should be called "How not to part off" !

I thought the MGMN inserts were suitable for parting, ones I have seem to do it OK

Why would you put such rubbish on you tube, oh hold on we aren't meant to criticise.

Tony

I use inserts like that for parting off. Bought the holder and inserts from China, made a holder to suit my back mounted tool post and the whole thing works OK, well most of the time anyway.

Would not ever consider parting off that far from the chuck.

As an aside, my lathe does not like 3 or 4 mm inserts, but seems quite happy with 2mm ones, so I stick with them.

Happy parting off !

Hi Tony,

I agree with you !

If you were going to demonstrate parting off, you would at least attempt to do it properly !

Yes, even the filthy cheap ba****od ones I have work fine in that type of grooving holder, as long as you dont try anything too big.

I recently smashed a couple of inserts and fatally wounded the holder, in exactly the same way as in the video above. Mainly because I was testing to try and find where the horrific banshee wail and chatter was coming from on my WM280, I think I may post a thread about that...

Suffice to say that if it isn't cutting right and you press on regardless then they do break just like that

He is not using power feed. It is alternating between cutting and rubbing so when it goes from rubbing to cutting he gets a dig in with predictable results.

Martin C

Did Neil delete the video lonk from the OP?

Possibly. I’ll send it to you.

As I understand it MGNM was a Koroly own brand style and specification of insert. Other makers seem to make look alike and compatible fit ones these days.

Koroly always seem to have made specific distinction between parting off versions and grooving types. Although the grooving / profiling types are said to be strong against side forces the book illustrations I've seen imply that cutting depth is limited. Ideally the support blade shouldn't enter the cut. Can work your way deeper with profiling of course.

Even the parting types don't seem to be expected to go very deep. But they are said to be for fast turning.

Speed of course being a major issue when it comes to chip evacuation form a narrow parting tool groove. A blue hot, heat softened chip cut at high speed behaving very differently from a relatively cool one taken at lower speeds. As ever the issue is that the chip is wider than the groove and will jam at times unless due precautions are arranged. Carbide tips are generally arranged to cut a Vee shaped chip which is narrower than the groove. Sharp cutting points at the ends of the Vee encourage the chip to fold. Radiused corners make the insert much stronger for profiling duties but the chip doesn't fold so well.

Putting an angle on the end of an HSS blade makes the chip even wider but sets it at an angle across the groove so, theoretically, it twists rather than jams. Lubrication helps as does taking a continuous chip. When I have issues with such its usually when the chip breaks fairly deep in and the new chip doesn't twist sideways cleanly to come out of the groove.

Clive

Watched it twice. Looks very much like the toolpost rotated under pressure. Which would break any tool. But what do I know. I am only a Hammer chewer.

Steve.

Clive, Korloy do indeed say they can be used for parting, in fact they even make L & R hand ones so the pip is left where you want it as well as the usual neutral. I suppose the insert does not know if it is doing a 5mm deep groove in 15mm dia work or 10mm dia work and in the later case would actually be a parting cut. Korloy Cat

They do also say to part near the chuck!

No video link is there a reason for it been removed?

difficult to say with the link removed ... but ... if the crossslide is a degree off perpendicular it'll break parting tips as soon as a certain amount of infeed is made ... ask me how I know