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Parting tools and inserts

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Alan Bain22/02/2022 18:04:13
11 forum posts

I've been trying to unravel the mystery of the right parting inserts to use; I have a plentiful supply of SP-200 (which I think are same as GTN-2) and a load of Iscar holders with numbers like

SGAHR 10-2

SGTHL 12-2

SGTHR 20-2

Blade SGIH 26-3-70

I get the feeling this may be the wrong insert as they seem to shift and shatter very easily; I think maybe there should be a shoulder to limit the insertion depth of the insert. This would make the insert look like GFN-2. But I confess I'm totally confused....

Edited By Alan Bain on 22/02/2022 18:04:30

Howard Lewis23/02/2022 07:07:00
6113 forum posts
14 photos

My advice would be to change over to a holder that takes a HSS parting blade. It will probably be a good investment.

When I bought my second (at l;east ) hand ML7 in about 1985, I was given a holder (with a used HSS parting blade.

I am still musing it and it is not yet worn out, still about half left.

I made a rear toolpost for the ML7 and when that was replaced the parting tool went into a home made four way rear toolpost..

Tried using an inserted parting tool, but found that despite the vee groove in the top mof the inserts, there were dig ins and jams that eventually damaged the holder. So reverted to the HSS blade.

Am now so confident that I part off under power! Must have saved a fortune by not having to buy new carbide inserts!


not done it yet23/02/2022 08:23:24
6812 forum posts
20 photos

I am in rather complete agreement with Howard. I once had a carbide insert parting tool. I now only use a (likely higher spec) Cobalt HSS material, in a stout holder. Sharpened occasionally with the belt sander, as required, the strip will last me several years - and I have a spare in stock but may never need it.

For hobby machines, a rear tool post is a very good improvement, IMO. I just put my lathe in power feed and let it get on with feeding/cutting - while I apply cutting fluid and get ready for the parted part coming free. I most certainly would not recommend anyone to buy a cheap parting tool, if fitted in a QCTP on a light-weight lathe. Just too much overhang for an easy life.

I expect my parting strip cost no more than a couple of your inserts.🙂


Edited By not done it yet on 23/02/2022 08:24:03

Samsaranda23/02/2022 08:40:39
1430 forum posts
5 photos

Tried using an insert parting tool and had the same problem, now use HSS. Dave W

Neil Lickfold23/02/2022 08:57:23
862 forum posts
195 photos

At the moment, there is a change happening with parting blades and inserts. The change is that instead of the insert having a taper shape to it, the new ones have a negative taper, so are slightly smaller at the front. The holder is now a flexure, and is expanded to take the insert. So in some cases, the replacement inserts are no longer available. That leaves them with buying a new blade or doing some deal with x number of boxes of inserts a discounted blade. I have not seen the free blade offers yet. In the 3mm for sure they are a through coolant design as well as a no coolant models. I have both the 2mm wide insert parting blades a a 1mm wide HSS blade that came with the original Dickson quick change tool post and holder sets. I got a spare HSS blade back in 1987 with the set and have never used it yet.

I really like the insert blades for parting off larger diameter stuff that is near solid or has a larger diameter than 1/2 inch in steel . They work well in most materials. For really small stuff or brass and Ali parts under 3/4 inch that are thin walled or need as sharp an edge as possible after being parted off, I use the HSS. The carbide will often leave a burr or quite an amount that will need to be addressed afterwards. Used carefully the Inserts will last a very long time and you can get a lot of parts parted off or grooved etc.

The insert parting works really well when parting off within 10mm of the chuck, even with 4340 bar.


jann west23/02/2022 10:35:56
98 forum posts

Tip for new players: Carbide insert parting tools which are not held perfectly perpendicular to the axis of rotation of the piece will shatter after a certain amount of infeed with 100% regularity.

Ask me how I know this!

I think my toolpost was left a degree off after cutting some threads - and I wasted 4 inserts before I worked it out. Never making that mistake again!

Vic23/02/2022 10:38:10
3074 forum posts
8 photos

I found insert parting tools rather expensive to use. I switched back to HSS but chose the T shape blades with chip breaker which work extremely well.

Andrew Tinsley23/02/2022 11:55:28
1630 forum posts

I have been using an Arc eurotrade Parting off blade with a GTN2 tip This is mounted in a QCP holder. So far it has done all I have asked of it on my Myford. I also have an HSS parting off tool, which I can use in a front and rear parting off block.

Now I would assume that a GTN2 tip in a QCP would be a good candidate for chatter and digging in. The QCP holder on my Myford is certainly not as rigid as a tool in a 4 way holder or indeed one clamped in the time honoured Myford way. So far both the traditional parting off blade and the insert blade have worked faultlessly.

Maybe it is something to do with locking everything that can move or maybe I have just been lucky?


Andrew Tinsley23/02/2022 11:55:29
1630 forum posts

Double post again!

Edited By Andrew Tinsley on 23/02/2022 11:57:46

A Smith23/02/2022 12:03:47
78 forum posts
4 photos

JB tools GN2 tips work perfectly well on my ML7.

Alan Bain23/02/2022 12:34:24
11 forum posts

JB tools would have been my first port of call but they have vanished; website and phone numbers all not working. If anyone knows what has happened would be good to know as they were very helpful!

I should probably have said that the lathe while very much domesticated is a Hardinge HLV-H and I would normally part off under power feed (it is continuously variable). I used to have no issues while using the tips supplied with the holders but then they broke (due I suspect to off axis feed as jann west points out). I then tried SP-200s and and zero success which is why I wondered what might be up.

Will try arceuro.... Thanks

DMB23/02/2022 13:11:43
1312 forum posts
1 photos

I use a QCTP parting toolholder in the post on my MLS7. Cannot remember suppliers name. Quite a tight fit on the post because the tightening slot lip is thicker than my other toolholders which fit easily. I stop the chuck using the clutch and wind the topside back, slacken the toolpost, wind carriage along to hold tool against the chuck face for alignment, clamp up. Steady indeed with Guy Lautards cutting oil mix, low speed, around half normal turning speed for relevant metal. Works perfectly.

I have George Thomas type rear toolpost iron casting for which I will get a roundtoit some day,then I'll be able to set it up for instant use. All the time current satisfactory arrangement is only used occasionally, little incentive to get a roundtoit......

Andrew Tinsley23/02/2022 13:13:23
1630 forum posts

As far as I know, JB Tools are taking a few months break. They said that they will be back later in the year. I hope so as Jenny Blackwell was an excellent supplier.


David George 123/02/2022 13:43:46
1840 forum posts
503 photos

Hi I have an Iscar parting blade SGIH 19-2 and use tip GTN2 IC354 I use it in my rear toolpost and I have the original tip I installed over 18 months ago and still going strong.


I believe the part off tool needs to be straight and sturdy. I can part off more than 3 inch diamiter with little problems.


Mark Rand23/02/2022 21:46:08
1274 forum posts
28 photos

I'm pretty sure a GTN insert won't work in a GFN blade and vice versa.

For the folks that have problems or have given up with carbide parting inserts:-
The insert should always be at centre height or ,better, two or three thou above it. HSS can, mostly, cope with being driven under the work by deflection of the work of tool, carbide can't.

For Allan:-
I don't suppose you've got Multifix toolholders do you? if you have, PeWe tools do a very nice parting blade holder for them, alwough JB's blades need some minor grinding to fit properly.

Alan Bain23/02/2022 22:50:18
11 forum posts

I am indeed using Multifix holders and that PeWe holder does look nice and what I need.

As I recall the JB blades (SP226) are a bit larger than the old Iscar ones and I wasn't exactly sure of the angles (pretty much nothing is a right angle!) but if I knew the angles I should be able to set them up on the surface grinder and take down a little.


Huub23/02/2022 23:27:46
87 forum posts
13 photos

I used a 1.2 MM HSS parting tool for years on the small lathe. For parting you need rigidity. To avoid the parting tool digging in the workpiece, I place the parting tool upside down and invert the spindle rotation. I also let the tool stickout as small as possible. Since I do it this way, even parting steel is not a problem.

I also made a 2mm insert holder for the small lathe and even that works fine. Only the Nema17 stepper on the X-axis has just to little power and misses steps when parting steel. So I replaced it by a Nema 23 stepper and now that is not a problem any more.

John Reese24/02/2022 00:11:21
1035 forum posts

I have experienced mixed luck when using carbide insert tooling for parting off. I have HSS parting blades for my 10" and 16" lathes. It is nice to be able to take it to the grinder and put a slight angle on the cutting edge to eliminate those nuisance pips from the cutoff part.

not done it yet24/02/2022 10:13:13
6812 forum posts
20 photos
Posted by Alan Bain on 23/02/2022 22:50:18:

I am indeed using Multifix holders and that PeWe holder does look nice and what I need.

As I recall the JB blades (SP226) are a bit larger than the old Iscar ones and I wasn't exactly sure of the angles (pretty much nothing is a right angle!) but if I knew the angles I should be able to set them up on the surface grinder and take down a little.


Keep a new spare cutter and you always have a reference to allow grinding the older, used ones back to the original angles(s). Worked for me when I started regrinding HSS cutters.

Henry Brown24/02/2022 10:23:52
552 forum posts
117 photos
Posted by Alan Bain on 23/02/2022 22:50:18:

I am indeed using Multifix holders and that PeWe holder does look nice and what I need.

As I recall the JB blades (SP226) are a bit larger than the old Iscar ones and I wasn't exactly sure of the angles (pretty much nothing is a right angle!) but if I knew the angles I should be able to set them up on the surface grinder and take down a little.


I use a PeWe parting tool holder on a GH1322 lathe with a slightly modified JB blade and their inserts, it works fine provided I keep the cutting edge of the insert in good condition.

I machined an angle on the bottom of the blade to match that of the toolholder to ensure a snug fit.

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