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Parting off

Correct tooling

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Darren Bingham08/06/2020 17:03:31
8 forum posts

Having a bit of trouble with an eclipse parting off tool

it is very sharp, but I had it jam on me in a mild steel bar.

any help would be appreciated.

are the tipped parting tools better?

larry phelan 108/06/2020 17:13:59
1095 forum posts
14 photos

Not really, I manage to jam those as well ! [and even break them ]

Emgee08/06/2020 17:19:21
2158 forum posts
265 photos


Many things can cause this, most of us have found a few, I suggest you check the tool is at centre height, absolutely square with the lathe axis, front of tool is ground with enough front clearance and square to the work. also ensure the blade is vertical so 1 side doesn't rub/bind on the work.


Edited By Emgee on 08/06/2020 17:22:42


Edited By Emgee on 08/06/2020 17:23:30

Mark Gould 108/06/2020 17:23:42
219 forum posts
130 photos

Is the tool exactly perpendicular to the work? Is the tool height correct? Is the carriage locked? Is the work not spinning too fast? Are you using enough lubricant? Are you feeding the tool at the correct rate?

I am by no means an expert on parting and have had my share of mishaps but these are the questions to answer.

Good luck,


ega08/06/2020 17:30:29
2265 forum posts
188 photos

One potential problem with the vee section Eclipse tool is that if it is ground with top rake the tool will then be narrower at the point and may tend to jam in the cut.

There have been numerous previous threads and posts on this subject.

Mick B108/06/2020 17:33:11
2020 forum posts
117 photos

If there are proper side clearance angles down the blade, the most likely causes are

i) the blade isn't set parallel to the movement of the crossslide. I eye mine up mine against the crossslide T-slots, but not all lathes have those.

ii) The tool or blade isn't vertical with respect to the spindle and bed, so the side clearance angles are defeated.

iii) If top rake has been obtained by grinding a short dip in the upper flat of the blade, when the runout of that dip enters the work, it's likely the tool blade at that point is wider than the cutting face because the latter is lower down the taper.

iv) If the tool cutting face has been ground at an angle, typically to minimise the pip on the parted component, the chips will be wider than the tool, and may jam if there are conditions that rotate them across the slot.

Edited By Mick B1 on 08/06/2020 17:37:50

Martin Laycock 108/06/2020 17:41:59
3 forum posts

Try doing 'one and a half cuts.' Do an extra cut to the left of the first one and alternate between the two as you cut deeper. This ensures a small gap between the tool and material and allows for the slight heat expansion of material and cutter.

AdrianR08/06/2020 17:57:21
540 forum posts
36 photos

I have never been too happy with the standard eclipse parting tool. I know it is not an answer to your problem, but recently I bought a Soba parting tool from Chronos **LINK**

I had seen a few USA people raving about T shaped blades with chip breakers. For some reason, they are hard to get over here.

You still have to take great care to get it at centre height and square, but the swarf is folded in on itself and comes out in a neat curl.

To get mine square, I loosen the tool post and move the carriage so the blade just touches the front face of the chuck. With a bright light under it and a magnifying glass, I can get it perfectly square.

As others say, slow steady and plenty of lube. I use a neat oil soaked toothbrush just above the blade. It catches any swarf stuck in the groove and gets the oil down in the groove.


Clive Brown 108/06/2020 18:01:36
709 forum posts
33 photos

I find that the narrowest, 1/16" Eclipse blades jam readily, especially in mild steel. Soluble oil, just applied with a brush makes a noticeable improvement. The wider blades, 3/32" and 1/8" seem to be less prone to jamming, perhaps due to the chips escaping more easily.

Earlier comments re. geometry and set-up are important of course

Darren Bingham08/06/2020 18:26:14
8 forum posts

Thank you all for your quick replies!
I should have really said....

I'm using plenty of lubricant, not cutting too fast and not turning too quickly.

as someone said, I too have set up the tool by bringing it to the face of the chuck. I thought it was as good as I could get it.
I checked the vertical with a set square.
I will check to see if there is clearance ground on the parting tool.
I had it in the holder as far as possible too!

may well be worth making a second cut as mentioned in one of the replies, especially when using such a narrow tool

colin vercoe08/06/2020 18:50:11
59 forum posts

The tipped parting tools cut much better and are more reliable they are usually made from one piece of material and tend to be more rigid and dont tend to jam as much, the tip geometry is designed to curl the chip and make it leave the groove easier, HSS parting tools are normally in a holder sticking out a long way from and overhanging from the tool post reducing rigidity with minimal side clearance they tend to jam all the time

old mart08/06/2020 20:41:08
3347 forum posts
208 photos

Parting is a dark art, even using modern industrial blades does not guarantee success. Their inserts are tapered and are wider than the holder with much more sophisticated geometry than HSS, but can still crash. I quite often start off with a parting tool and finish with a hacksaw.

Part of the problem is not having enough stiffness in the system. A four jaw independent chuck also holds the work much better than a three jaw. There are lots of pictures posted which show the parting tool hanging in the breeze like a wet noodle.

Edited By old mart on 08/06/2020 20:42:34

old mart08/06/2020 20:51:26
3347 forum posts
208 photos

If anyone is thinking of investing in an indexable system, then have a look at ARC's offering. It is one of the least expensive systems.

NCIH blade

GTN inserts

SLTBN blade holding block

John Haine08/06/2020 21:13:23
4186 forum posts
242 photos

Two things revolutionised parting for me.

One, don't go slow! You need speed between the material and the tool for it to cut. When you run too slow, however careful you are when feeding you can get a dig in because tooth load is too high.

Two, if you have it use power feed to get a uniform feed rate.

The other week I parted 1" steel bar at 200 rpm feeding at 5mm/min (CNC). And two days ago I parted off a piece of 12mm brass bar at the same feed rate and 800 rpm.

I use a Kit_Q_Cut system I got from Greenwood a few years back. I also have an upside-down parting tool in a rear holder from Kirjeng which is good but the usual front holder is easier when using CNC because Mach 3 isn't very good with a rear toolpost.

Andrew Johnston08/06/2020 21:28:33
6278 forum posts
677 photos

Feedrate is the key to parting off. On the centre lathe, with an insert parting blade, I never use less than 4 thou per rev power feed, Parting off is now, almost, a routine operation.

On the repetition lathe, with hand feed and a hand ground HSS steel blade, I've measured the chip thickness as between 8 and 10 thou.

To summarise; don't pussyfoot about!


IanH08/06/2020 21:30:22
104 forum posts
59 photos

I second the use of Greenwood’s Q cut parting system and use this on both my machines. I have been using this tool for years and only resort to HSS if I can’t reach in far enough with the Q cut, and then I only use the HSS tool for the last bit. I work mainly in EN 8, 16 and 24 and don’t slow down to part off. Plenty of lubricant, suds or Rocol, and be bold feeding the tool.


jacques maurel08/06/2020 21:34:55
77 forum posts
18 photos


Have a look at my article in MEW:N°268 & 269 (june and july 2018) "A switch off attachment for parting off safely"

J Maurel

old mart08/06/2020 22:09:56
3347 forum posts
208 photos

I must start using the power cross slide feed when parting off, it would help a lot in keeping the lubrication constant. I already have an ultra stiff rear parting off blade holder and can lock the saddle front and rear as well.

Simon Williams 308/06/2020 22:52:52
605 forum posts
81 photos

I've recently realised that my difficulties with a parting tool are mostly related to using one three jaw chuck. Closer inspection reveals that the jaws are ever so slightly bell mouthed, so I suspect the work is walking in the jaws.

The chuck in question is a Pratt Burnerd 160 mm self centreing three jaw. I bought new jaws for it - not convinced this has cured the problem reliably. I'm using an inserted tool courtesy of Jenny at JB tools, or a standard Eclipse parting tool 3 mm wide with no top rake. The lathe is a Mk 2 Bantam. I even modified the top slide slightly so I can lock the gib nice and solid. As far as I can tell the head stock bearings are adjusted right, though they could be a shade loose as I'm frightened of over cooking it. I don't think the Dickson toolpost is the best tool mounting for a parting tool, but its other advantages go without saying.

I bought a (brand new) 5 inch TOS chuck ages ago, but have hardly used it until buying a backplate recently to adapt it to fit on my Bantam. I just know if I say that this has been the cure for my parting off problems I will regret it, but so far so good.

Very - no extremely - not convinced about using power cross feed, but Andrew is right, you need to keep the tool loaded or it chatters like fun, and yes it's a mistake to slow the revs down more than say one gear (25% or so) to reduce the chatter and the heat on the tool, as the chip load goes up significantly. I part off with one hand on the cross slide dial and the other holding an oily paintbrush in the groove.

Hand number three is hovering over the stop lever.

Best regards


Mike London09/06/2020 00:03:59
26 forum posts
1 photos

I have to agree with the comment about the Chronos "T" shaped parting off blade.
It is now my parting off tool of choice.

The Eclipse blades are a pain. Because you have to grind in a rake it means you are limited to depth of cut before they jam and if you resharpen you then have to reset the height etc.
Inserted tips are good but I have found if I do have a jam it not only takes out the tip but often slightly damages the the tip holding part of the blade as well, so they don't hold a replacement tip so tightly which means you end up with another jam!
For what they are, replacement tip holding blades seem to be disproportionately expensive..

The Chronos "T" shaped blades are extremely rigid. Ensuring they are set square and at centre height and I have parted off 60mm diameter stock like a knife through butter. Just touch up the front face with a diamond hone to resharpen and the contoured top surface just curls the swarf clear.
(No connection with the company other than a very satisfied customer!)
(Anybody want to buy some surplus Eclipse blades?)

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