By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

Parting tip breakage

Was it engineered?

All Topics | Latest Posts

Search for:  in Thread Title in  
not done it yet30/05/2020 18:54:10
4645 forum posts
16 photos

Please have a look at around 12m 30s on THIS video and tell me why you think the parting tip broke.

Edited By Neil Wyatt on 30/05/2020 22:02:58

Andrew Johnston30/05/2020 19:11:50
avatar
5499 forum posts
647 photos

Because it's not a parting tool, but is intended for profiling and grooving. At least that's what I use mine for:

split collet use.jpg

Dunno why he feels the need to part off so far from the chuck. Well I have an idea, but this is a public forum. smile

Andrew

AdrianR30/05/2020 19:17:42
476 forum posts
23 photos

The way the tool sprang to the left and back looked rather odd. In slow motion it looks like the tool was pointing slightly to the right then twists back square. I suspect the cross/top slide has a lot of play in it. Another possibility is the spindle bearings are worn or the lathe is not rigid enough and the work climbed over the parting tool. Also from the swarf it looks like he was cutting harder when it broke.

Unless of course he was moving the saddle to the left.

Reminds me of trying to part on my worn out 1912 vintage Drummond, I had that climb right over the parting tool and stall on top of it.

Adrian

JasonB30/05/2020 19:18:44
avatar
Moderator
18113 forum posts
1995 photos
1 articles

None of them looked to be cutting well judging by the swarf coming off. I've never snapped one of those inserts but did snap the bottom of the holder off but my fault for only having a short amount of the work in the chuck

Clive Foster30/05/2020 19:59:22
2204 forum posts
73 photos

Looks to me as if the top slide wasn't locked so any sideways force generated by imperfect cutting would pull the topside through its backlash region. Setting the topside parallel to the bed on a light machine is asking for trouble.

A grooving tool like that is going to be pretty pants at parting off anyway. The shape guarantees some degree of chip crowding as it comes off the work. Piddly little brush will do nowt. Needs full flow or carefully directed mist to come out clean.

Proper parting tool inserts are Vee profile at front and top with two points at the business end. These fold the chips so they re narrower than the parting tool slot allowing them to escape. Must be run at the correct speed and feed otherwise even these will give problems. As usual with modern carbide in relatively benign materials chips should come off in short tight coils.

Parting is enough of a pain at the best of times if you can't run fast with full flood coolant. Why compound the difficulty by buying a cheapskate version of an improper tool. Buy cheap, pay twice. The real this work very well when properly aligned and set up. Much of the advantage of the rear tool post type on a small lathe is that it gets set-up properly and left alone. Not topside to set wrong too.

Clive

not done it yet30/05/2020 20:08:28
4645 forum posts
16 photos

Dunno why he feels the need to part off so far from the chuck. Well I have an idea, but this is a public forum. smile

Well, I’ll be more direct, blunt, cynical, etc than Andrew. I think it was engineered to break - by setting the tool at a slight angle and parting, without support, so far from the chuck. I think the breakage was predictable.

John Baron30/05/2020 20:10:46
avatar
297 forum posts
122 photos

Hi Guys,

That video should be called "How not to part off" !

JasonB30/05/2020 20:16:06
avatar
Moderator
18113 forum posts
1995 photos
1 articles

I thought the MGMN inserts were suitable for parting, ones I have seem to do it OK

Tony Pratt 130/05/2020 20:33:46
1125 forum posts
5 photos

Why would you put such rubbish on you tube, oh hold on we aren't meant to criticise.

Tony

larry phelan 130/05/2020 20:35:31
719 forum posts
14 photos

I use inserts like that for parting off. Bought the holder and inserts from China, made a holder to suit my back mounted tool post and the whole thing works OK, well most of the time anyway.

Would not ever consider parting off that far from the chuck.

As an aside, my lathe does not like 3 or 4 mm inserts, but seems quite happy with 2mm ones, so I stick with them.

Happy parting off !

John Baron30/05/2020 20:50:45
avatar
297 forum posts
122 photos

Posted by Tony Pratt 1 on 30/05/2020 20:33:46:

Why would you put such rubbish on you tube, oh hold on we aren't meant to criticise.

Tony

Hi Tony,

I agree with you !

If you were going to demonstrate parting off, you would at least attempt to do it properly !

Cabinet Enforcer30/05/2020 21:07:18
73 forum posts
2 photos
Posted by JasonB on 30/05/2020 20:16:06:

I thought the MGMN inserts were suitable for parting, ones I have seem to do it OK

Yes, even the filthy cheap ba****od ones I have work fine in that type of grooving holder, as long as you dont try anything too big.

I recently smashed a couple of inserts and fatally wounded the holder, in exactly the same way as in the video above. Mainly because I was testing to try and find where the horrific banshee wail and chatter was coming from on my WM280, I think I may post a thread about that...

Suffice to say that if it isn't cutting right and you press on regardless then they do break just like that devil

Martin Connelly30/05/2020 21:29:15
avatar
1369 forum posts
159 photos

He is not using power feed. It is alternating between cutting and rubbing so when it goes from rubbing to cutting he gets a dig in with predictable results.

Martin C

Mark Rand30/05/2020 22:23:57
887 forum posts
5 photos

Did Neil delete the video lonk from the OP?

not done it yet30/05/2020 22:41:44
4645 forum posts
16 photos
Posted by Mark Rand on 30/05/2020 22:23:57:

Did Neil delete the video lonk from the OP?

Possibly. I’ll send it to you.

Clive Foster30/05/2020 23:14:08
2204 forum posts
73 photos

As I understand it MGNM was a Koroly own brand style and specification of insert. Other makers seem to make look alike and compatible fit ones these days.

Koroly always seem to have made specific distinction between parting off versions and grooving types. Although the grooving / profiling types are said to be strong against side forces the book illustrations I've seen imply that cutting depth is limited. Ideally the support blade shouldn't enter the cut. Can work your way deeper with profiling of course.

Even the parting types don't seem to be expected to go very deep. But they are said to be for fast turning.

Speed of course being a major issue when it comes to chip evacuation form a narrow parting tool groove. A blue hot, heat softened chip cut at high speed behaving very differently from a relatively cool one taken at lower speeds. As ever the issue is that the chip is wider than the groove and will jam at times unless due precautions are arranged. Carbide tips are generally arranged to cut a Vee shaped chip which is narrower than the groove. Sharp cutting points at the ends of the Vee encourage the chip to fold. Radiused corners make the insert much stronger for profiling duties but the chip doesn't fold so well.

Putting an angle on the end of an HSS blade makes the chip even wider but sets it at an angle across the groove so, theoretically, it twists rather than jams. Lubrication helps as does taking a continuous chip. When I have issues with such its usually when the chip breaks fairly deep in and the new chip doesn't twist sideways cleanly to come out of the groove.

Clive

Steviegtr31/05/2020 01:10:33
avatar
1232 forum posts
115 photos

Watched it twice. Looks very much like the toolpost rotated under pressure. Which would break any tool. But what do I know. I am only a Hammer chewer.

Steve.

JasonB31/05/2020 07:00:31
avatar
Moderator
18113 forum posts
1995 photos
1 articles

Clive, Korloy do indeed say they can be used for parting, in fact they even make L & R hand ones so the pip is left where you want it as well as the usual neutral. I suppose the insert does not know if it is doing a 5mm deep groove in 15mm dia work or 10mm dia work and in the later case would actually be a parting cut. Korloy Cat

They do also say to part near the chuck!

Ron Laden31/05/2020 07:25:45
avatar
1921 forum posts
367 photos

No video link is there a reason for it been removed?

jann west31/05/2020 08:07:20
56 forum posts

difficult to say with the link removed ... but ... if the crossslide is a degree off perpendicular it'll break parting tips as soon as a certain amount of infeed is made ... ask me how I know

All Topics | Latest Posts

This thread is closed.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
emcomachinetools
Eccentric July 5 2018
Warco
Allendale Electronics
ChesterUK
cowells
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest