An alternative to parting-off

[jimmy bParticipant @jimmyb]

10"??????

Jim

[Nick HulmeParticipant @nickhulme30114]

Parting off Mr Wolf? Easy on the feed, Lots of Speed, Lots of Lube?

Thank you Morag!

[vintage engineerParticipant @vintageengineer]

You make one! I own several lathes and one of them is a Galileo 330 x 2000 with hydraulic drive.

Posted by ega on 04/11/2018 11:33:27:

Posted by vintage engineer on 04/11/2018 09:41:17:

Never understood why people have problems with parting off. Now we have insert parting tools it's a doddle, as they are made for power feed parting off. I usually set the lathe speed to about 500rpm to 800rpm and a medium speed feed and let it go.

I have happily parted off 10" round bar with no problems.

Where does one obtain a parting off tool with a 5" projection? And what lathe runs it?

Not everybody has power cross feed. CNC apart, how does conventional parting off account for the progressive reduction in surface speed of the cut?

[duncan webster 1Participant @duncanwebster1]

Just had a look at the Aldi advert. It says 0.7 to 2.4 m/sec blade speed. This is 138 to 470 ft/min which seems a bit fast for cutting steel

[JasonBModerator @jasonb]

My Femi does 60 or 80 m/min (1.0 & 1.33m/sec) and goes through steel as if it were butter

[mark costello 1Participant @markcostello1]

In an ancient issue of The Home Shop Machinist or Machinist WorkShop a Chap parted off 18" and 16" bronze.

[BWParticipant @bw]

Does anybody run the carbide parting off tools on older slower lathes ie my 60 year old 9" Hercus would be the equivalent of an American South Bend 9" or just a tadge bigger than the British 7" Myfords – my top speed is 720 rpm.

Have successfully used carbide tool bits at far lower than recommended sfm and have managed to get excellent finish, but would like to know if its commonly done to use the carbide parting tools on the lower powered older slower lathes before splashing some $s on one.

Thanks

Bill

[egaParticipant @ega]

I use an inserted carbide tip parting off tool on my 1960s Willson slant bed whose top speed is 954 rpm, typically parting off at up to half that speed.

I think that speed is only one factor; the topic has been well canvassed here, of course.

Unfortunately, in my experience the pricier tipped tools work better than the budget ones.

[Mark RandParticipant @markrand96270]

The major advantage of the insert parting tools is that the hollowed top folds the chip in to a U shape, so that it is narrower than the slot the tool is cutting. That makes chip ejection far more effective and reduces the jamming that a flat topped HSS tool is prone to. G.H.Thomas recommended that the HSS tools have a groove ground on the top face to achieve the same result.

The carbide tools really cope badly with the tool climbing under the work or the work climbing over the tool, so it's normal practice to tun them just a few thou above centre height.

[egaParticipant @ega]

Posted by Mark Rand on 07/11/2018 12:58:46:

The major advantage of the insert parting tools is that the hollowed top folds the chip in to a U shape, so that it is narrower than the slot the tool is cutting. That makes chip ejection far more effective and reduces the jamming that a flat topped HSS tool is prone to. G.H.Thomas recommended that the HSS tools have a groove ground on the top face to achieve the same result.

The carbide tools really cope badly with the tool climbing under the work or the work climbing over the tool, so it's normal practice to tun them just a few thou above centre height.

If I read you correctly, you would recommend that the rear mounted carbide tool be set below centre?

Can you elaborate on "cope badly"?

Good point about the GHT groove.

[Neil WyattModerator @neilwyatt]

Posted by ega on 07/11/2018 13:52:59:

Posted by Mark Rand on 07/11/2018 12:58:46:

The carbide tools really cope badly with the tool climbing under the work or the work climbing over the tool, so it's normal practice to tun them just a few thou above centre height.

If I read you correctly, you would recommend that the rear mounted carbide tool be set below centre?

Can you elaborate on "cope badly"?

In my experience going too low can pull the insert out or chip it.

Sandvik (at the very least) agree with having the tip a thou or two high.

[Mark RandParticipant @markrand96270]

Posted by ega on 07/11/2018 13:52:59:

If I read you correctly, you would recommend that the rear mounted carbide tool be set below centre?

Can you elaborate on "cope badly"?

Yes, if the tool were rear mounted, it'd want to be physically below centre.

If the work rides over the cutting edge of the insert as the tool gets to the centre of the job, due to flexibility in either work or tool holding, then it puts the cutting edge of the tool in tension rather than compression. It just peels the front off the tool before you can do anything about it.

If the cutting edge is fractionally above centre, it's harder for this to happen and the insert will happily push through the last little bit of stock so long as it's in compression.

Having the tool below centre will cost you an insert per cut .

Edited By Mark Rand on 07/11/2018 15:46:35

[egaParticipant @ega]

Posted by Mark Rand on 07/11/2018 15:45:34:

Posted by ega on 07/11/2018 13:52:59:

If I read you correctly, you would recommend that the rear mounted carbide tool be set below centre?

Can you elaborate on "cope badly"?

Yes, if the tool were rear mounted, it'd want to be physically below centre.

If the work rides over the cutting edge of the insert as the tool gets to the centre of the job, due to flexibility in either work or tool holding, then it puts the cutting edge of the tool in tension rather than compression. It just peels the front off the tool before you can do anything about it.

If the cutting edge is fractionally above centre, it's harder for this to happen and the insert will happily push through the last little bit of stock so long as it's in compression.

Having the tool below centre will cost you an insert per cut .

Edited By Mark Rand on 07/11/2018 15:46:35

Thank you for this cogent explanation. I am going to check the height of my parting tool which is of the tangentially-clamped variety. The makers, ISCAR, claim that the design "Provides a solution to the problem of inserts being pulled out during retraction"; this is not the "diving" effect you have described but the tangential tool does seem to be better able to resist it.

[BWParticipant @bw]

With the height setting at +0.001 being important and the groove in the top of the tool being a feature, what is the reference point for the centre height for setting the tool ?

Bottom of groove or top of groove ? Yes, pedantic, but if it saves ruining a few tips from being torn out then worth asking the question.

[fishy-steveParticipant @fishy-steve]

I'm probably missing something but please tell me how you set a parting tool height 0.001" high of center? I'm not interested in a theoretical way. I would like to know the actual method used to ensure that level of accuracy .

Steve.

[Neil WyattModerator @neilwyatt]

Posted by fishy-steve on 07/11/2018 21:23:10:

I'm probably missing something but please tell me how you set a parting tool height 0.001" high of center? I'm not interested in a theoretical way. I would like to know the actual method used to ensure that level of accuracy .

Steve.

Oh there are many, many people on this forum and out there who have various devices for getting their tools dead on centre height. Best I ever came across was a bar carefully machined and lapped to be cut across at exactly half its diameter – this was then to be held in a self-centring chuck…

But it is easy enough with an accurately set gauge, and that's what they will use in industry.

In practice I set my tools by eye against a centre pip, so I'm just making sure it's fractionally high rather than fractionally low.

[Neil WyattModerator @neilwyatt]

Posted by BW on 07/11/2018 20:34:15:

With the height setting at +0.001 being important and the groove in the top of the tool being a feature, what is the reference point for the centre height for setting the tool ?

Bottom of groove or top of groove ? Yes, pedantic, but if it saves ruining a few tips from being torn out then worth asking the question.

Standard inserts have a flat cutting edge at the front, even though there is a shaped groove behind.

Neil.

[Mark RandParticipant @markrand96270]

And as neil says, it needs to be just high enough to stop it eating inserts. This is going to be different on a Hardinge than an ML7 (mine are , at least!).

Basically, if it's working properly, leave it. If you get a chipped insert at the end of the cut, the solution is to raise the tool an RCH.

[fishy-steveParticipant @fishy-steve]

Posted by Neil Wyatt on 07/11/2018 21:34:47:

Posted by fishy-steve on 07/11/2018 21:23:10:

I'm probably missing something but please tell me how you set a parting tool height 0.001" high of center? I'm not interested in a theoretical way. I would like to know the actual method used to ensure that level of accuracy .

Steve.

Oh there are many, many people on this forum and out there who have various devices for getting their tools dead on centre height. Best I ever came across was a bar carefully machined and lapped to be cut across at exactly half its diameter – this was then to be held in a self-centring chuck…

But it is easy enough with an accurately set gauge, and that's what they will use in industry.

In practice I set my tools by eye against a centre pip, so I'm just making sure it's fractionally high rather than fractionally low.

Hi Neil.

I think that your right. There are probably lots of people on the forum who have made various tools to achieve centre. I have myself. But I wouldn't say, hand on heart, that I can achieve the level of accuracy people are talking about.

As for industry. I have personally never seen a turner set a tool to centre taking the level of care that would be needed to get these results. At work I tend to use a centre in the tailstock and my eye. Similar to your own method.

Steve.

[Neil WyattModerator @neilwyatt]

Posted by fishy-steve on 07/11/2018 22:32:56:

As for industry. I have personally never seen a turner set a tool to centre taking the level of care that would be needed to get these results. At work I tend to use a centre in the tailstock and my eye. Similar to your own method.

Steve.

In some industries, especially CNC production, there are people whose job is tool setting.

A quick google shows a CNC tool setter can earn £25 – £30 a hour, that's nearly £60-K a year before overtime… I bet you have to be within a thou to earn that!

Neil

[not done it yetParticipant @notdoneityet]

Do tell me how many people have a lathe capable of not having a tangible deflection at the parting tip? OK, I usually set tool height by facing to no pip, but that counts for nothing with a length of parting tool hanging out from its holder, let alone the forces on the rest of the machine as it loads up, particularly the older machines such as mine (OK, it’s only 5 decades, or so, since it was made). I can still part off successfully, knowing full well that deflection from a theoretical centre height setting is occurring and changing as the cut continues.

Until there was an extra toolpost, fitted (almost) permanently at the back of the long(er) slotted cross slide on the Raglan 5” (compared to the LJ) I didn’t bother too much with parting off. Yes, sometimes things got difficult but never insurmountable. The biggest advantage of the extra fitted toolpost is that it doesn’t need squaring up as often.

[Bill PudneyParticipant @billpudney37759]

Some time ago I got an optical centre finder, it was on sale at the time. It has many useful functions, two of which are centre finding (that's a surprise!) and tool height setting, simply stick it in the tailstock chuck, and you can see the tool in scary detail. To my mind better than all the gauges, tools etc.

cheers

Bill

[Tony Pratt 1Participant @tonypratt1]

In some industries, especially CNC production, there are people whose job is tool setting.

A quick google shows a CNC tool setter can earn £25 – £30 a hour, that's nearly £60-K a year before overtime… I bet you have to be within a thou to earn that!

Neil

Hi Neil, can you point me in the right direction as a previous job search by myself gets nowhere near that figure.

Tony

[ZanParticipant @zan]

Regarding parting off and centre height, (I haven’t discovered yer how to add a quote) thanks for the explanation, that will explain why I chipped a new tip on first use parting off with a new fixed height toolpost, I discovered the tip was just below centre and it went bang! Now been adjusted with a bonded shim under it to get it to centre height.

I agree about cheeped tips as well, I was having great tifficulty with a the next tip, it grumbled when in use on my S7; a lot of force to get it cutting but then it went ok once cutting started. Close examination revealed the top of the tool was flat so it had no back rake. changing the tip for a top brand and instant success. I’d messed about for an age adjusting the spindle end thrust, (tightened it, but now Iv had to loosen it again, too tight it got hot and squeeaked) and all gibs were adjusted( they didn’t really need it). So with the second new tip things changed to service as normal. I had a back post, but sold it when I got the tipped holder as there was no problem from the front working. I didn’t like the back post, it magde using the die holder difficult, and it needed a lot of care to ensure it was clear of the chuck. And it seemed to add a lot of Xslide handle turning to get it in the correct position but with the fixed post tool changing is fast and easy.

[Neil WyattModerator @neilwyatt]

Posted by Tony Pratt 1 on 08/11/2018 09:03:37:

In some industries, especially CNC production, there are people whose job is tool setting.

A quick google shows a CNC tool setter can earn £25 – £30 a hour, that's nearly £60-K a year before overtime… I bet you have to be within a thou to earn that!

Neil

Hi Neil, can you point me in the right direction as a previous job search by myself gets nowhere near that figure.

Tony

It was on indeed.com, but surprise, surprise, when I looked this morning the job has gone!

Still some at £15 an hour or 'negotiable'.

But my original point wasn't the salary so much as there are plenty of skilled jobs out there setting CNC tools to high levels of accuracy.

Neil

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