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

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

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

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 !

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

Did Neil delete the video lonk from the OP?

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

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!

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

[This posting has been removed]

I can see neither a video nor a link to a video in the first or any other post.

Whoops, I've just seen a previous post about it being removed. Why? If the video is unsuitable for some reason that necessitates it's removal, then the thread should also be deleted and replaced with a suitable message.

Edited By Gary Wooding on 31/05/2020 10:02:44