Sandvik inserts – parting off

[Richard BrickwoodParticipant @richardbrickwood17062]

Parting Off tools – can anyone tell me where I can get Sandvik inserts (N151.2-250-5E 4125) for my parting off tool – or can recommend a new one capable of parting-off 1.5″ BMS bar please?

[Nigel Graham 2Participant @nigelgraham2]

Try JB Cutting Tools, or Cutwel.

(Not “JB Tools”, unless you are in America – but I don’t know if that firm stocks such items anyway.)

I think you’ll find the inserts themselves are all to industry standards, described by their convoluted letters-and-numbers codes, so needn’t necessarily be made by Sandvik to fit Sandvik holders.

So ask by the holder designation, which Sandvik stamps on its side.

 

Parting-off to 3/4″ depth (the bar radius) in free-cutting mild-steel should not be a problem provided the lathe and setting are sufficiently rigid, and crucially, the tool is set correctly to height and perpendicularly to the axis.

I set mine by ensuring the holder is fully engaged with the tool-post, then gently using the saddle handwheel to pushing its flank lightly against the chuck jaws or tailstock barrel face so they act as a square, while tightening the tool-post clamp-nut.

[Howard LewisParticipant @howardlewis46836]

+1 for NG’s advice.

If it needs to be said, have the minimum “stick out” for the tool, don’t rush, just maintain a slow steady feed.

If possible, use a rear toolpost.  This seems to produce forces which are more easily withstood, and the swarf falls way, rather blocking the cut.

HTH

Howard

[Roderick JenkinsParticipant @roderickjenkins93242]

Richard,

The forum looked into this problem a couple of years ago.  Greenwood tools used to supply these inserts individually but since they ceased trading the tips only seemed to be available in boxes of ten – rather more than most people need at £15 odd each.

However, a quick search shows that Cromwell now seem to sell them individually Cromwell tools

for about £20 each delivered.

ARC Eurotrade sell a similar but much more pocket friendly system that works well ARC Eurotrade

with replacement tips at a couple of quid each ARC GTN 2 tips.

HTH,

Rod

[bernard towersParticipant @bernardtowers37738]

I use a GTN2 tip from JB cutting tools that is for stainless and seems to work much better than the std ones and £20 a tip is B steep!

[ChrisLHParticipant @chrislh]

The illustration of the ARC GTN 2 tips gives the impression that they are rather blunt. If this is indeed the case has anyone tried using a suitable hone (e.g. diamond) on the top surface to produce a keen edge suitable for use with lightly constricted lathes ?

[Nigel Graham 2Participant @nigelgraham2]

Don’t try it! It’s not worth it.

You may be able to recover a large, plain-profile tip with a green grit (silicon-carbide) wheel or a diamond hone for general sliding and surfacing cuts;  but the more sophisticated tips including those for parting are moulded to sophisticated shapes of very high precision and accuracy for repeatable, efficient and high-finish production.

Parting-tool tips are also made with a cutting-edge that should be parallel with the lathe axis with proper machine-setting, and a central, symmetrical Vee-groove that folds the chips inwards to reduce binding and to face the cut surfaces properly.

Once a tungsten-carbide tip loses its edge it is effectively dead. It is not made to be re-ground, though you might be able to recover the front face alone by using a high-grade tool-and-cutter grinder with a diamond or Si-C wheel.  Yes the manufacturers want to sell more tips, but they recognise the short life by stating expected tool lives in their catalogues; though admittedly for high industrial production in optimum conditions  – including the right tool for the metal.

 

A heavy lathe might barge its way with light cuts through small-section material with an imperfect tool, HSS or carbide, if you are not too fussy about dimensions and finish, but the more lightly made machines really do need proper attention to tool geometry and setting for best results within their capacity.

[JasonBModerator @jasonb]

I find the GTN-2 work OK on my lightweight Chinese machine on steel and cast iron. I don’t bother with a rear toolpost and even hang it off the side of my QCTP.

Did part of some 115mm thick wall tube today but just went with a cheap import 1.5mm HSS tool as it saved a bit more material that I may have a use for. Quite happy at 200rpm.

[ChrisLHParticipant @chrislh]

Thanks Nigel and Jason for your responses. I usually use HSS parting tools because they are narrower than the carbide ones (less load on the machine). The attraction of the moulded shape is the edge radii which are very tricky to make on an HSS tool and are essential for turning functional crankshafts if you need them to last.

[Nigel Graham 2Participant @nigelgraham2]

The fillets left in the corners are important, as you say, but are their radii ever so critical?

When I turned my steam-lorry crankshaft I used an HSS tool and simply free-hand rounded its corners- I forget if by grinder or oil-stone. The existence of the fillet being more important than its size.

The pin length is slightly over the journal width, but I also chamfered the journal ends.

If you using a parting-tool to profile a crankshaft, an HSS one would be better because you need traverse it as well as feeding inwards, and indexable parting-tools are not designed for side-loading.

[Nigel Graham 2]

On Nigel Graham 2 Said:

Parting-tool tips are also made with a cutting-edge that should be parallel with the lathe axis with proper machine-setting…

Please note that the ones in the original post are denoted N151.2.

If you look at Sandvik’s literature on the Q-cut system, you find inserts with L151.2 and R151.2 designations.

These do not have a parallel (the N is for neutral) cutting edge and are made specifically to leave the ‘pip’ on either the part being cut off or the part remaining in the spindle. As with the neutral ones, they also curl the chip so it is thinner than the kerf of the tool.

Sophisticated manufacturers offer options.

Your comment about side loading needs deeper consideration. Every insert parting blade you buy will be deeper, and hence stiffer (even in the side direction) than an HSS blade cutting the same kerf. Perhaps you could watch this video on YouTube (https://www.youtube.com/watch?v=c4w-ulo3l3g entitled Tools In Action: GARANT grooving) and write to Mr Hoffman to advise of his mistake.

—

On the thickness issue, 2mm seems to be the minimum that is generally described as ‘parting’. Below that, the tools are known at ‘grooving’ and sometimes ‘parting/grooving’. It is a change in nomenclature.

An economic semi-universal insert of that type is the MGMN insert, which also comes in a semi-circular form fitting the same holder as MRMN (so MGMN300 is 3mm wide and MRMN is 3mm dia semi-circle). The round-ended ones can be used as a smaller diameter continuation of RCMT inserts, which stop at 5mm dia.

[JasonBModerator @jasonb]

I keep a modified GTN-2 insert for crankshafts that has had the middle of the 2.2mm width ground away with a Dremel. The reduced contact reduces the risk of chatter and as it is just used towards the end with small infeeds and a sideways cutting action does not need to cut on the front, Yes they will cut sideways. Not the best photo but hopefully you can see the end is concave.

If it is a smallish crank then the MGEH type inserts and holders are made for sideways as well as plunge cuts, the holders are also a bit stiffer so don’t deflect as much against the interupted cut of a crank web. I do a lot of sideways cutting with mine mostly with a MRMN200 2mm insert which leaves a 1mm radius as well as using the parting type for things like cutting the waist on bearings.

 

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