Parting tool trouble

Hi, hope someone can help.

im having a bit of a nightmare using this new parting tool that I bought from arceurotrade.

I haven’t been able to part properly with it yet and have already broke the original blade, good job I ordered a spare with it. I’ve tried all 3 speeds of my Myford ml7 lathe, still without any good results, just keep getting chatter or the chuck stopping and wedging into the tool, thats how I broke the blade that came with it.

as you can see in the photos, the blade is spot on the centre cutting height, it’s an 8mm by 10 tool holder and lines up perfectly, so I can’t understand why it’s not cutting through properly.

hope someone can tell me what I’m doing wrong, would I be better using a Hss parting tool instead.

thanks

chris m…

Edited By JasonB on 03/08/2022 18:22:48

Worn headstock bearings is one thought. Noel.

I would not trust a MT shank held in a 3-jaw to be on ctr height. Put it in the spindle taper or try against the tailstock ctr

Lots of advice already discussed on this forum but are your slides tight and are you using lubrication to start with, need more details.

Tony

Admittedly, in a rear toolpost, but for parting off I rig up a fairly steady gravity fed drip feed of lubricant for my ancient HSS blade.

I tried a carbide parting tip in the front toolpost, and had just the problems that you have, so reverted to the inverted HSS blade in the rear toolpost.. (And the swarf falls out so that bit does not clog)

I made a rear toolpost for my ML7 and then had fewer problems parting off.

A carbide tip SHOULD produce two streams of swarf, from the grooved top, so should not clog.

It works so well for me that I now use PCF (0.0025"/rev ) when parting off, because both are narrower mthan nthe cut.

Daft question, but the tool is square to the axis, so that doesn't rub on the side of the cut?

You do need to keep up a steady feed, so that the tool cuts rather than rub.

May be, being carbide, it needs high speed and feed to generate heat at the cutting edge, to soften the metal.

Don't know what you are cutting, but the swarf looks a bit small for steel, or is it cast iron?

Cast iron can be chilled on the outside, and so, hard, which needs to be driven through to the softer core metal.

Either way, try to learn how to use both hands to apply a stead feed rate.. That is a skill that will stand you in good stead on all jobs.

It may cost you a few tips, but experimenting is how you learn.

Experience allows you to recognise the mistake, the next time that you make it!

Howard

P S

A centre held in a 3 jaw WON'T be on centre, unless myou nhave an exceptional chuck.

It is likely to run out by anything up tom 0.005" on a reasonably good chuck, more non a worn one..

You should set to a centre, located in the 2MT bore, and recently trimmed up.

Use a 2 MT centre, not a parallel one in a 3 jaw!

You would spend time profitably, making a Centre Height Gauge, It would aid setting tools to centre height considerably.

This might be part of your problem! (Looks to be on centre but may not be . If too high will cause problems)

Let us know how you get on

Howard

Edited By Howard Lewis on 03/08/2022 18:43:33

Personally I wouldn't use a tool like that for parting off. They're more of a grooving tool. Carbide parting off inserts will chatter badly if the feedrate is too low. I use power cross feed and a absolute minimum of 4 thou/rev. If you're not confident to let rip then HSS is more forgiving.

Andrew

Although I mostly use mine with a round nosed insert it does get used for parting or grooving sometimes.

Seems OK on the Warco front mounted in a QCTP, 15mm mild steel, 450rpm 0.0025" /rev feed. Nice bright short curly chips rather than long swarf when run at this sort of finer feed rate.

I wonder whether you could put that in a formal letter to Greenwood Tools (RIP) and the Sandvik Corporation Ltd, Inc. LLC, etc. Maybe cc. Messers Iscar, Kennemetal, Korloy, etc.

My Q-cut parting tool, a fine example of a parting tool with a grooved top, has only ever produced a single stream of swarf for in excess of ten years now.

Having now seen your quite astonishing revelation, I feel cheated. Do you think I should demand my money back?

Kindly draw me a picture of how this phenomenon should occur please.

Chris,

I used to have lots of problems when parting off, I tried carbide and HSS but had some expensive foul ups, my conclusion was that model engineers lathes are inherently unstable because they flex too easily when under pressure such as parting off. My approach to reduce the problems that I was having was to check that everything on the lathe was adjusted correctly, that means making sure the gibs are adjusted nice and snug, when you are making the cut make sure you have locked the top slide and the carriage, my carriage lock was useless so l made a new lock which firmly clamps the carriage to the bed. My next idea was to always use lubrication when parting off, it’s surprising how much difference that can make, when cutting make sure that you advance the tool at a constant rate, be sure and firm with your movements. I still have problems if I use carbide tips, it is as though I am not running the lathe fast enough, I chicken out on running fast on parting off so for now the carbide tips are put to one side and I only use HSS, I am surprised at how much easier that the operations are now that I have incorporated the ideas mentioned above, I used to dread parting off and would in preference reach for the hacksaw but now my confidence has been rebuilt and I am using my parting tools again. One point I use as thin an HSS parting tool as I can, I find it is easier and more forgiving. Dave W

Are you hand feeding it or what speed is the power feed running at?

Re set the tool so that it is 5-10 thou above centre. 5 thou should do, but if the tool and compound are dipping with load, the higher amount might be needed. .

This is more important with carbide parting inserts than with HSS. The very last thing you want is for the work to climb over a carbide parting tool. Instant failure.

Check that the tool os running true to the run of the slide. It needs to be like no more than 1 thou or 0.03mm per 20mm of travel. Also assuming that the top slide and the compound slide don't have sloppy gibs. That looks to be the multi direction turning insert, rather than the Parting specific insert. The difference is the the top rake is positive and a sharper front end with a geometry that curls the chips better. As Jason said, a feedrate of about a thou per rev and upto 45mm in diameter under 500 rpm works, but at around 250 rpm, coolant does not go everywhere. It needs plenty of coolant for best results. Parting tools should be on centre to slightly above. The reason for the success of rear parting holders on older machines, is that as the tool tries to lift, the slop in the gib tightens the gap, making it more rigid.

I've got one of these; I've found it to be very fussy about feed and speed. My lathe has variable speed control so I can twiddle the control knob to find a speed that works. The feed needs to be pretty brutal - anything less and it will chatter badly and the swarf comes off as a powder. When you get it right, it works well, but most of the time I find an HSS blade less hassle.

edit: I think the insert on mine is different - it has a shallow groove in the top, which I can't see in your photos, and its single-ended.

Edited By Andy Stopford on 03/08/2022 21:21:52

As Mark Rand says, carbide parting off should be above centre height. I have read the instructions from Kyocera and Kennametal and both state that the tip should be 0.1mm, 0.004" high when parting solid stock.

I never part with anything but carbide inserts and have never seen two streams of swarf coming off. The profile of the tip makes the ribbon curve longitudinally like a length of rainwater gutter which is then narrower than the width of the cut.

Any loosness in gibs or flexibility make parting much more difficult. I have a solid block with inverted blades which bolts directly to the cross slide and together with front and rear saddle locks, is used for the most challenging parting.

A four jaw independent chuck and the minimum work overhang also help.

Edited By old mart on 03/08/2022 21:33:08

Edited By old mart on 03/08/2022 21:33:34

I do parting at 800 RPM, 0.02 mm/rev, use lubrication and the powerfeed. I have 1.2 mm HSS and 2 mm carbide (SP200) parting tools.

I don't part off the last 0.5 mm when parting steel.
I can only do parting on both my lathes when the tool is mounted upside down and the rotation is reversed.
I check the height of the tool by facing an aluminium bar.

The stickout of your parting tool is very long!

The stickout length would be the same with the similar type I use, but mine are 20mm, so the stiffness would be better. The design having a double ended insert makes that type rather long which is unavoidable.

Power crossfeed does help a lot, and makes it easy to apply constant coolant, too.

Could possibly be your three jaw chuck is worn bell-mouthed and allowing the job to move, causing jams. Try on a piece of material held in the four jaw chuck and see if it works better.

From looking at your pic, it may be that your parting tool is not set perfectly square to the lathe axis. Check it with a dial indicator. With a bit of practice you can line the tool up by eye with the edge of the cross slide.

On my ML7 I have found the T section HSS parting tool from Eccentric Engineering works brilliantly and even better mounted upside down in the rear toolpost. It has a nice sharp cutting edge that requires less force and thus creates less flex in these lighweight lathes than a carbide insert tool. See this thread here LINK

Edited By Hopper on 04/08/2022 03:04:02

My lathe is an Emco Compact 8 which is just hobby grade so the power is low. For cutting steel, I could not use carbide parting tools of width more than 1.5 mm but even when the insert is so narrow, I could not part stainless steel until I switched to sharper inserts. The insert I am using now is ground instead of molded.  Yours seems to be molded. Will not work well on my lathe. Tool life of ground inserts is on the short side but given the low price, it's acceptable for me.

Edited By Y C Lui on 04/08/2022 05:26:17

DC31k

Don't demand your money back.

Read the various pieces of advice to grind a V in the top of a HSS tool, or examine your carbide tool.

(I think that either Edgar Westbury, or Arnold Thorp gave this suggestion; so not a new idea. )

By having a V in the top of the tool, it should have, effectively, two cutting edges, and so will produce two streams of swarf, each narrower than the width of the slot that has been cut, so reducing the risk of swarf jamming.

Having had bad experiences with a Garmin tool, I have never plucked up courage to use my Q Cut. I just stick with my 3/32 wide HSS , with no top rake, mounted inverted in the rear toolpost, and increasingly use power feed. .

One bit of information that i do lack is the author of the quotation that "Sarcasm is the lowest form of wit" can you help?

Howard

Edited By Howard Lewis on 04/08/2022 05:20:24