I suppose the reason why some sellers of these holders supply two " blades" confirms what Ketan says about them breaking. Can't say I've damaged my similar type holder yet and am still on the first end of my holder with the "spare" still unused.

It's my reach to parting tool for anything over 12mm, below that Like Ketan I use a HSS Co one particularly on brass/bronze and also have a 1mm wide insert tool that gets used quite a bit on smaller stiff.

Slice of 70mm Cast Iron 1.5mm thick, and another smaller piece 0.5mm thick

Hello All,

I have only ever possessed the NCIH type parting tool (Type 26 x 3mm).

To date it does everything I need it to. It is true, probably, that it takes a bit of getting used to.

Tips do eventually wear out and/or break. But, to me, I still feel that the rapport usage/price is well within reason. As Jason has said, they can be used right up to capacity (80mm mild steel), with some care.

A quantum leap, for myself, was when I switched to parting off under powered cross feed. Tip life increased tenfold !!

ATB

Daniel

Me too! Still my preferred parting-off tool. Impressive when working well but not indestructible. Parting-off demands a lot of the lathe and the tool. Much easier to part-off on a heavy stiff machine than a bendy lightweight.

Two main problems I get.

1. Swarf tends to jamb in the slot and the tool stops cutting, rubs and increases the unwanted forces on the machine that can displace the tool-tip. Aluminium causes most trouble because it's sticky and tends to weld, blunting the tool.
2. The tool and maybe the whole saddle tend to bend slightly dropping the tool-tip and causing dig-ins. Anything that reduces rigidity is bad,, It can happen too fast for the operator to react and some are severe enough to damage the tool.

I've found all parting-off tools perform best with a steady feed when cutting correctly, which means getting the tool height, rpm and feed-rate right. Not too fast, not too slow, and definitely not jerky. Swarf clearance is vital. Proper lubrication helps, and the tool tip should be in good condition. Add it all together and it's not surprising parting-off goes wrong!

Parting off is a balancing act. I found a lot more skill was needed to do it successfully on a Mini-lathe than my WM280, and I imagine anything heavier would be easier again, mainly because big heavy lathes are less likely to flex enough to allow the tool-tip to dip into a dig-in.

What's really annoying is some lucky chaps don't have trouble parting-off. I suspect they have a steady hand, quick reactions and a natural feel for when tools are cutting correctly. The rest of us have to practice and experiment. I no longer expect disaster every time I part-off, but I'm not surprised that it goes wrong every so often.

The design of NCIH holders may be deliberately weak:

I suspect in commercial use where feed-rates are carefully calculated and automated, a dig-in means something really bad is wrong, and the tool is intended to break before the expensive CNC machine does.

Still the best option for parting-off I've tried. Ketan's image shows the maximum parting-off diameter to be rather small: I invariably use the tool to take much deeper cuts than that!

Dave

I have parting blades in 26mm and 32mm size, from 1.6 to 5mm wide. I wouldn't use the wide ones for parting, only grooving as the lathe isn't really stiff enough for parting, especially with steel.

I ruined one end of my Kennametal 26mm by 1.6mm blade when the work moved in a three jaw chuck. A four jaw independent chuck is much more secure.

Remember to check your jibs for tightness, and always lock the saddle when parting.

I made a dedicated rear cut off block to hold 26 and 32 blades which bolts directly to the cross slide, with the blades inverted. I also added a rear saddle lock as the cutting forces are upwards. This is much stiffer than using a normal toolpost. 

I would never part off dry, soluble oil from a squirty bottle for steel, and WD40 or similar for aluminium. 

A great advantage of using the GTN inserts is that they are available from several sources, the best I know of is Korloy. I have some in 1.5, 2 and 3mm wide. 

Edited By old mart on 23/07/2019 14:01:45

Edited By old mart on 23/07/2019 14:09:56

Well I do have a genuine problem. It's cowardice! I can't quite bring myself to try power feeding during parting-off. Now I've admitted the real reason I'll have to try it next time.

Most disasters in the Duffer Workshop can safely be blamed on the operator…

Just to confirm I like these. When I want to make little grooves I use HSS.

In my experience confidence is the best aid to parting, (s)he who hesitates is lost!

Neil

Why not just swap the tips? The ones in the link look an awful lot like gtn3 tips. These are readily available and if you are prepared to wait they can be had for as little as 60p a tip from China.

Those of us lucky enough to have the use of a mill can make their own custom made rear toolposts, and dedicated conventional types.

One of the reasons that I have never gone the QCTP route (apart from the cost), is the slight loss of rigidity as mentioned by Brian G.

It looks like a bent flat head screw driver:

Ketan at ARC.