# Tool dig in. Part, slide and moral totally shattered.



## Hauk (Sep 11, 2011)

I am repeating myself, but I am a total beginner on the lathe, but I just have to ask anyway...

I was happily machining a little flywheel on my lathe, and things went well till I was going to make a 2-3 mm deep slot into the 25 mm diameter round stock. I had already machined the surface, so everything was nice & concentric. 

The attempted cut was made maybe 25 mm out from the 3-jaw chuck with a 3 mm wide cut-off/slotting tool. Speed around 1500RPM, very slow feed. No center in the tailstock. 

Suddenly the tool dug in, ripping the part from the chuck and locking up the machine. 

Part totally ruined, and some damage to the lathe as well.


As you can see, the groove was not very deep when the dig-in occured:






The damage done: 





The tool with the quick change toolholder: 





This leaves with me with several questions: 

1) How stupid was the operation I tried to perform? Could you expect to pull off something like this?
2) Is that dovetail breakage something to be expected, or an indication of a inferior part?
3) What is the most likely cause for the crash? Lack of rigidity on the tool or/and toolholder, deflection of brass bar? All of the above?
4) Are crashes like this a part of a machinist life, or and indication of a total lack of skill?

Regards, 
Haavard H


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## Tin Falcon (Sep 11, 2011)

Well lesson learned. 
parting and grooving can be tricky . I was professionally trained in the basics of machining and I to have had parts torn from the chuck. I am fortunate no broken lathe parts.
Observations: What I see. 
1) rpm way too fast as chuck pointed out. 
2) tool out probably 25 mm keep tool stick out to an absolute minimum. 
3) part stick out check you look good there. 
4) not a lot of meat on the dovetail weak design.
what I do not see:
5) how was tool height set ? Always set up tool to deflect away from the work. Parting tool should be on center line or slightly below never above center line. 
6) was tool honed honing helps a lot . use dead sharp tools for parting grooving. 

IMHO cause of crash RPM too high poor setup and poor lathe design/weak metal on dovetail.
curious what lathe do you have?

tin


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## Hauk (Sep 11, 2011)

aermotor8  said:
			
		

> sorry to see your lathe broken :'(



Me too, but if that was all the damage done, I sort of consider myself lucky.



> the first thing you mentioned that would cause this to happen is the rpm you were turning the work piece!!!!!!!!!
> 1500 rpm's is waaaay to fast you should be parting off at about 2 or 3 hundred rpm.



Ooops...



> if the part is a flywheel you should have drilled and reamed to hole in the center of the part before you parted it off.
> that way the center hole will be concentric to the o.d. of the flywheel.
> secondly you should always part off as close to the chuck as possible, this helps retain rigidity.



The flywheel was not meant to be center driled, it shold have taps at both ends for small ball bearings, like this: 






. 

Here we can also see the small pulley wheel that was to be fitted to the flywheel. Btw, these parts were made by a very skilled machinist, not me!



> crashes like this do happen but they are not the norm, they are usually caused by poor set up and not having the tool sharp and on center.
> 
> if you were parting off at a much lower rpm chances you would not have broke the cross slide.
> 
> ...



It really does. Thanks for taking the time to answer a complete rookie!

Regards, Haavard H


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## Hauk (Sep 11, 2011)

Tin Falcon  said:
			
		

> IMHO cause of crash RPM too high poor setup and poor lathe design/weak metal on dovetail.



Thanks for the feedback! Much appriciated. 
The major bummer is having to wait for the replacement part. I would like to get back in the saddle as soon as possible!

Regards, 
Haavard H


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## Tin Falcon (Sep 11, 2011)

Another observation is there may have been a sharp score line on the inside corner of the dovetail this would have concentrated the stress along that line and cased a clean break .
when you get the new one make sure there is a smooth radius on that inside corner. 
Tin


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## Blogwitch (Sep 11, 2011)

Hauk,

It looks like the broken bits could be stuck together and measured up OK, and if it was me, I would see about getting someone to knock you up a replacement part out of a normal steel, it's not really a big job.

That really looks to be a very weak spot, and could cause you the same problems in the future. The top part of the unit is much beefier, so shouldn't cause any problems.

I don't know where you are located, but if it is the UK, then contact me and I will make you a new one. I'm sorry, but that offer can't apply if you live outside the UK, it just takes too long and expensive for bits to be shipped back and forth.

If you can't take me up on my offer, maybe someone on here from your part of the world will step in with the offer of help.


John


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## Tin Falcon (Sep 11, 2011)

> As a student I had access to a CNC-milling machine, and every now and then I could make some parts for my engine:



You could consider making a replacement part for the lathe. Make it beefier steel instead of aluminum perhaps and add a radius to the inside even that will add strength. Look at this as a learning opportunity.
Tin


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## kvom (Sep 11, 2011)

What part of the work was chucked? If you were holding by the small diameter opposite the groove then the part was stuck out too far. Given the other gouges that seems likely. For a do-over, chuck on the large diameter, and as said above cut the RPMs way down, and also feed very slowly esp. if you hear chatter.


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## dalem9 (Sep 11, 2011)

If you are in the states pm me and I will see what I can do.Dale


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## mzetati (Sep 12, 2011)

You could probably replace the top slide & dovetailed guide with an equally thick block of metal where You will mount the the QCTP, to make use of the lathe while You're waiting for the replacement part.
That would all add rigidity to the setup, easing the parting jobs.
Marcello


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## Ken I (Sep 12, 2011)

I think I can safely say we have all lost the occasional part out of the chuck - it shouldn't happen but it does.

Apart from damage to component and tooling, damage to the lathe is rare - sorry to see what happened.

Some tips :-

Have at least the length of the chuck jaws clamped in the chuck (ie the chuck jaws bear fully against material - the moment you deviate from this the jaws can start to tilt slightly - so your work is effectively held in a "taper" and can wiggle out) - the same goes for collets. Remember it will wiggle into the side of the part off tool and go bang before you can react to it.

Plan to part off as close to the chuck as possible.

Don't chuck a smaller diameter than you are parting.

If you have to deviate from the above bring a live centre to bear to support the work and prevent walkout. Withraw the centre only for the very last part of the cut. If the setup is dicey - hacksaw through the last bit and face off.
If you have to grip a length shorter than your collet / jaws - put a piece of identical diameter stock at the rear of the jaws / collet to prevent "tiltiing"

Part off tool to be sharp and on centre (or slightly below - never above).

Part off tool stick out from toolpost to be the minimum for the job to hand.

Use the narrowest partoff tool that will do the job.

If you have the facility, part off from a rear toolpost in reverse.

Keep the speed down and the feed rate up.

If it chatters - stop and make sure you are not doing someting wrong. If you are happy your setup is righteous try increacing the feed to stop the chatter.

Regards,
      Ken


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## mzetati (Sep 12, 2011)

- apply cutting fluids copiously: I'm using oil for steel (applied with a toothbrush, with all the bristles rows removed but the central one, held directly into the groove) and petroil with aluminium.
- have the tool perfectly square to the workpiece axis.
- retract the topslide so You will have the tool as near as possible to the pivoting point.
- widen the groove by moving the tool sideways half of the tool thickness, to ease chip clearance.
- retract the tool and clear the groove anytime You see the chips have stopped flowing outside the groove. Changes in the noise produced during the cuts are a good reason to retract and check, too. 
- use T-blades.
- The lathe lowest speed is usually too fast: someday I will make an oversized pulley right for the parting jobs.
- reduce the tool overhang to the minimum: on deep grooves You'll start with the minimum overhang and increase it in steps.
- a dig-in / stall is much likely to have modified the way the workpiece is held in the chuck: re-tighten the jaws, or re-chuck the workpiece.

Marcello


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## Arnak (Sep 12, 2011)

Hi,

Personally I use a TCT parting off tool, one with a replaceable tip.

It is much thinner than the tool you are using so much less cutting force.

You can get them in varying shank sizes from Chronos.

Martin


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## Tin Falcon (Sep 12, 2011)

> - apply cutting fluids copiously



Yes I forgot tat one on my list. 
Tin


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## Hauk (Sep 12, 2011)

Thanks for all the feedback! Almost overwhelming... Especially the offers to make me a part. Unfortunately, I am located in Norway, so I might just have to wait for a replacement from the lathe manufacturer. If it takes too long, I might be able to have the part made locally. 

Btw, what do you consider the best cutting fluid for brass? From what I have read, most people machines brass "dry".

Regards, Haavard H


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## Herbiev (Sep 12, 2011)

A bit hard to tell from the photo but it looks like the rake on the cutting tool is set up for cutting steel instead of brass. And as mentioned use heaps of cutting fluid. Good luck. Its all part of learning curve.


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## lordedmond (Sep 12, 2011)

I will second or third the tool was far to wide try and get one that is no more that 1/16 inch or 1.5 mm

Stuart


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## lensman57 (Sep 12, 2011)

Hi,

Sorry to hear about the misfortune.
If funds allow get a tct tip parting tool, they are not cheap but the price is well worth paying. I used to have a lot of problems parting off even small diameter stock on the little Taig lathe but things are a lot better with the new tool. I got mine from Chronus with a couple of spare tips, 2mm I think.
Make sure your cross slide is trammed and secure, the tool height accuracy is a must, part as close to the chuck as possible, use the right speed for the diameter and material and lock all the gibs that are not required. Rigidity is the name of the game here.

Good luck,

P.S : make sure the tool tip is absolutely perpendicular to the work piece.
A.G


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## dalem9 (Sep 12, 2011)

Try to bolt it back together ,about 10 small screw would hold for light work or until you get a new one.Dale


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## Hauk (Oct 13, 2011)

I finally got a replacement for the broken part. Wabeco sent it to me for free together with a new collett chuck (see separate thread), so I am quite happy with their service. 

A little disencouraging was the fact that I have to enlargen and deepen a hole for an indexing pin in the replacement plate. As you might guess, I am not too eager to screw things up again... 

So any advice on drilling in cast iron? I have a half-decent drillpress and a decent drilling vice. I tried drilling into the the broken part, but was not able to produce chips, only dust. Progress was painfully slow. Should I try to increase or decrease speed? Pilot hole? 

Regards, 
Haavard H.


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## rleete (Oct 13, 2011)

Cast does that. Use some oil (I use Mobil 1 motor oil) and drill away.


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## steamer (Oct 13, 2011)

+1 on the blade being far too wide and sticking out too far, and a very weak design.

Halve the blade width, and less than that on the overhang.

Additionally, I don't put too much rake on my parting tools....like zero.

You REALLY don't want any rake on brass....it can be wise to put negative rake on tools cutting brass.

I also make sure they are sharp and honed. That helps

LOTS of oil while parting.

And the biggest factor on parting I think is overall set up.  EVERYTHING has to be right to make it work.

With big parts, I sometimes do this.  Rough drill the hole in the part.....usually there is a hole in the part...but not always I suppose...anyway, put a small center into the part and then support the far end with a tailstock center.

NOW PAY ATTENTION
part most of the way through....NOT ALL THE WAY.

Stop the lathe

remove the part and saw the rest off.

If you part through with the tailstock center in place you will have a BIG wreck...so don't try....OK?

the biggest thing is to get to know you machine....and the only way to do that is to try it.

Dave


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## Sparticusrye (Oct 14, 2011)

Hauk,

I've been fighting my parting tool as well, as can be seen here:

http://www.homemodelenginemachinist.com/index.php?topic=14214.msg162798#msg162798

After I replaced my parting tool holder, since that's what I ended up breaking, I read your post here and used some of the advice. Having the tool a very small amount below centerline made a huge difference in results for me. I don't have a QCTP so I use shims which makes alignment difficult to say the least.

The lowest speed of my lathe is 115 RPM so that is where I run for parting. I will eventually make a pulley to cut that in half as I don't like doing threading and parting over 80 RPM. The lathe I use at work goes down to 40 RPM which is much better for these types of operations.


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## MachineTom (Dec 15, 2011)

In looking at your setup, it appears the the compound is set 90° to the cross slide, I understand a common practice in EU. Now the design of the dovetail is poor as others have stated, but by positioning the compound as your did, the dovetail which broke had 100% of the lifting force, the inner dovetail closest to the work had on it compression (downforce) which did not strees the dovetail but a small amount, had the compound been at 29° forces would have been split between the two dovetails, and with the longer lenght of compound, lenght vs width of compound, the forces would been spread over a much wider area, and the failure likey would not occur. 

My second opinion is that the dovetail broke first, based on the photo, the tool then tipped into the work, the chatter is the tell. IMO

You may want to rethink the position of the compound for future work.


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## greenie (Jan 20, 2012)

steamer  said:
			
		

> NOW PAY ATTENTION
> part most of the way through....NOT ALL THE WAY.
> Stop the lathe
> remove the part and saw the rest off.
> ...



*Why do you state this, how do you come to this conclusion ?*

regards greenie


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## Troutsqueezer (Jan 20, 2012)

Using a tail stock, the separated workpiece will fall into the cutting area and could pinch metal with a number of side effects, none of them good. With no tail stock, the workpiece tends to fall away from the tool bit. Now, I'm not an expert machinist by any means, but thinking about it logically leads me to this conclusion. Someone correct me if I am mistaken.


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## willburrrr2003 (Jan 20, 2012)

Don't be too hard on yourself, we all have had parts almost finished that have have been ruined...learn from it as we do, and apply that knowledge to future projects.  I was making a spindle encoder, for me a lengthy process of cnc'ing each step, machining each step and killing it on parting off as happened with you.  I finally did make the part right, and am happy with how it turned out now 

Best Regards,

   Will R.


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## rake60 (Jan 20, 2012)

I second the Never Use the Tailstock when parting.

I would never part a solid piece larger than 1/4" the whole way off.
I cut it in to the point where it can be easily broken off by hand.

If you watch the piece that is being parted off, it will wiggle a little when the when 
it has been cut in enough to stop and break it off..

When parting from an OD to a bore, I usually do part it the whole way through, but you don't 
have to. If you listen to the cut, it will start to crackle when it's almost breaking through.
Stop at that point and the part can usually be peeled off with the edge of a thin 6" scale.

Parting off shouldn't mean finished parts flying out of the machine.

Rick


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## greenie (Jan 20, 2012)

rake60  said:
			
		

> Parting off shouldn't mean finished parts flying out of the machine.
> 
> Rick



The absolute quickest way that I know of to get bits flying around the room when parting off, is, NOT use a live centre, pretty well self explanatory there, eh.

Now if the original poster had used a live centre pushed up tight to that bit of brass, then how in the heck, can that bit of brass EVER jump out of the jaws, even abusing it the way he was. 

If millions of machinist around the world, use the live centre every day of their working lives with it pushed up tight to the bit they are parting off, then, - are - they - doing - it - wrong ?

Don't think so.

So, for those that say, DO NOT use a live centre when parting off, then you are in the MINORITY, I personally think you had better take a good look at your own procedure, and see what your doing wrong before ill advising others.

regards greenie


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## ShedBoy (Jan 20, 2012)

I never use a tailstock when parting because of what Trout said. I catch bored parts with a brass drift, or snap off solid bits when they are nearly done. The most important thing I reckon is to get the tool square. Piece of pvc pipe is good for catching also. Tailstock hard up against is pushing the parted piece into the tool then the tool into the still revolving stock. I will stick with what works for me. High speed CNC don't use a tailstock do they? If parts are flying from parting you are doing it wrong, it should drop down onto a swarfy cushion everytime.

Brock


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## MachineTom (Jan 20, 2012)

I've not had an issue of parts flying around even at 1000 rpm, never use the center when parting, although often a piece of round is held in the drill chuck to retain parts that have a bored hole.

It is handy to leave a pile of chips on the cross slide, it often keeps the cutoff from falling into the chip pan.


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## rake60 (Jan 20, 2012)

greenie  said:
			
		

> So, for those that say, DO NOT use a live centre when parting off, then you are in the MINORITY, I personally think you had better take a good look at your own procedure, and see what your doing wrong before ill advising others.



Sorry greenie but this is one I will not bend on.
Parting with a tailstock engaged is damaging at best, dangerous at worst.

Look at the physics of the operation.
With a tailstock supporting the piece being parted off, what is most likely going to happen
when the tool breaks through? 

In this hobby safety is #1

If this process work well for you, that's fine. You have obviously been very lucky to this point.
I can not allow it to be recommended here.

Rick


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## Tin Falcon (Jan 20, 2012)

greenie :
please do not dispense dangerous information. parting with a tail stock in place is the best way to break a parting tool or have it grab. I have seen machining book with a drawing of such activity with the caption how to break a parting tool. 
You may be able to get away with it using a chuck but never never try it across centers with a drive dog. 
we all have different opinions and perspectives. but lets not compromise on safety .Also it is not recommended or wise to countermand the advise of a staff member with many years of machining experience.

This is a an open forum and all are entitled to a respectful expressions of there view. but lines can not be crossed. 
Tin 
 .


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## tattoomike68 (Jan 20, 2012)

I part off big stuff like semi truck drive lines, I sure as hell dont use a center, the parts might be 100 LBS and 7 feet long.

I dont care if you smash tooling or snap the whole headstock of your lathe, its fine with me.

Just dont tell everyone your dumb ideas.


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## greenie (Jan 20, 2012)

tattoomike68  said:
			
		

> I part off big stuff like semi truck drive lines, I sure as hell dont use a center, the parts might be 100 LBS and 7 feet long.
> 
> I dont care if you smash tooling or snap the whole headstock of your lathe, its fine with me.
> 
> Just dont tell everyone your dumb ideas.



Well sir, if you care to trash your machinery by doing it this way, go for it, I shall see you in hospital one day.

If you use the tailstock with a live centre, then as the parting of tool breaks thru, the top of the job is supported by the piece in the jaws, this leaves a small space for the parting of tool tip to be in. The bit that's just been parted of, is held there by the live centre whilst the chuck slows down and the parted of bit CAN NOT escape and do anything dangerous.

Been in quite a few machine shops, and if you DID NOT use the tailstock, then you were shown the door very fast.

So sir, to me your ideas are just plain stupid, for not using the tailstock with a live centre.

If the original poster had used a live centre, then he would still have his lathe in one piece and be merrily machining away today, but alas, he seemed to follow your dumb stupid idea and not use one, well, what is he doing right now ?

regards greenie


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## bronson (Jan 20, 2012)

I am pretty new to machining and always read this forum to find out the best way to do things. I find for parting that i use the slowest speed possible the shortest tool possible lots of cutting oil tighten all gib screws and have had very good luck parting. One time i did do some parting between centres was not thinking what would happen and that drive dog went for a flight. So in my newbie opinion and what works best for me is no tailstock.


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## Maryak (Jan 20, 2012)

Hey Greenie,

Part something off between centres.............might knock some sense into you.

Bob


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## chuck foster (Jan 20, 2012)

greenie, in the 30 years of machining i have never heard of using the tail stock while parting off in the lathe.

now with that said i am open to new or different ideas all the time, so before i draw a conclusion to your idea i am going to try using the tail stock while parting.

i have some brass and steel pieces that i have to make tomorrow and i will try your idea and see how it works for me.

i know the rest of you guys are going to warn me about the problems that i will encounter but rest assured i will be very careful and i will report my findings tomorrow night.
don't worry about my lathe as i will be using the lathe at work, it is much stronger and more ridged than my old south bend.

chuck


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## greenie (Jan 20, 2012)

Maryak  said:
			
		

> Hey Greenie,
> 
> Part something off between centres.............might knock some sense into you.
> 
> Bob



No thanks, I'll leave those stupid ideas for you to do.

regards greenie


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## greenie (Jan 20, 2012)

chuck foster  said:
			
		

> greenie, in the 30 years of machining i have never heard of using the tail stock while parting off in the lathe.
> 
> now with that said i am open to new or different ideas all the time, so before i draw a conclusion to your idea i am going to try using the tail stock while parting.
> 
> ...



OK, someone who has some sense, use a centre drill to put a small pop in the end, then use the live centre in that centre pop.

Please do add a report about how easy it is.

regards greenie


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## arnoldb (Jan 21, 2012)

I'm not a professional, nor even accomplished amateur machinist, but I *strongly* support the point of view of everyone who has stated not to part all the way through with tailstock support.

On one of my earliest parting attempts a couple of years ago I did try to do this; I ended up with a broken parting blade, a ding on my lathe bed that I had to flatten off, and a ruined workpiece. Not to mention the fact that I had to walk very carefully to the bathroom to get rid of the pair of pants I was wearing... Lesson learned.

I am concerned about the way some of the parting advice has been provided through this thread, without addressing the specifics of the parting jobs needing to be done. And different lathes will also behave differently while parting off.

A lot depends on the job in hand, and the size of the workpieces coming off. I often have a need for additional support while parting off - sometimes it's because I have to make a parting cut quite a distance from the chuck, other times it's because there's a fair length of workpiece that would come off while parting and sometimes purely to compensate for wear in my lathe's headstock bearings. 

This is where I feel a bit of "thinking" is actually the first machining operation. Think through the entire operation before actually physically doing it, and then set up the lathe to mitigate any safety issues.

Sometimes it's just plain necessary to do a parting cut part way through with tailstock support, and then finish the cut with a hacksaw. 
If you have a long piece that will come off, it might be the right time to mount up that fixed steady that's been collecting dust in the cupboard to help stabilize workpieces and prevent things bending and whipping around. 
As has been stated, a workpiece with a hole in the center can be captured on a pin or bit of rod in the tailstock. I've used this method with some grease/thick oil smeared on a bit of rod that's a running fit in the workpiece hole to actually provide some rigidity to a parting cut. With this method it's easy to completely part off a workpiece, as it will just end up sitting on the pin.
For solid pieces, a piece of pipe chucked in the tailstock can be used to catch the workpiece and prevent it from flying off or landing in the swarf during a full parting cut.
For small jobs like making nuts where I don't want to damage the threads by using a pin, I regularly use a rattle-can cap to capture the nut when parting it off. Saves a dig through the swarf mountain.

I find some of the earlier posts in this thread bordering on insulting and some demeaning of beginners... Lets keep posts civil Gents. We have members of varying abilities with vastly different selections of tooling available here on HMEM - please keep this in mind when posting advice or comments.

Regards, Arnold


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## 90LX_Notch (Jan 21, 2012)

I say subtract 1 Karma for greenie!

Seriously, shoot a video of you parting something using your method. Make sure it is a decent diameter.


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## Ken I (Jan 21, 2012)

Amen to that Arnold.

I regularly use tailstock support during parting - but not parting OFF - off being the operative word here.

I have accidentally parted off with the tailstock in place a few times with varying results - sometimes nothing but it can force the tool back into the stock and use the centre hole as a lever - loud bang.

Definitely not reccomended.

If the nature of the work (long piece for instance) requires the live centre - then practically by definition you should not part it all the way OFF.

Lets keep the tone civil.

Ken


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## metalmad (Jan 21, 2012)

Hi guys
while Ive never seen the need for using the tailstock in parting off, it seems a no brainer that the live center may apply a bit of push on the part towards the part off tool particularly if the tail stock is over tightend.
Sooner or later that tool will dig in, why risk it ???

Pete 
a novice


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## stevehuckss396 (Jan 21, 2012)

arnoldb  said:
			
		

> I find some of the earlier posts in this thread bordering on insulting and some demeaning of beginners... Lets keep posts civil Gents. We have members of varying abilities with vastly different selections of tooling available here on HMEM - please keep this in mind when posting advice or comments.



I have to agree with Arnold. You might not agree with Greenie but there are ways of expressing your opinion and still maintain respect for one of OUR members. The reason this is a wildly successfully forum is because no matter the topic, respect is always paid to the member who posted. Lets not loose sight of that.


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## 90LX_Notch (Jan 21, 2012)

Steve,

Whole heartily agreed about civility. However, the tone of this thread changed when greenie, after he called Dave out, professed that everyone was wrong for parting without the tailstock.  In my opinion, he failed to use any tact or civility in his posts.

My 2 cents.

Bob


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## stevehuckss396 (Jan 21, 2012)

90LX_Notch  said:
			
		

> the tone of this thread changed when greenie, after he called Dave out, professed that everyone was wrong for parting without the tailstock. In my opinion, he failed to use any tact or civility in his posts.



Greenie was not exempt in my comment. It was a general reminder to all that we could do a little better.


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## rake60 (Jan 21, 2012)

I used to occasionally run an turret lathe at work to make thin wall steel bore repair sleeves.
Cast iron is difficult to get a good weld repair for re-machining so we'd bore the bearing fits oversize
then dowel a press fit steel sleeve into them. The bore of the sleeves was left undersize so it could
be finished to size after being installed in the cast iron casting. 
The sleeves were typically 10 to 16 inches in diameter with a .187 to .250" wall thickness.

One position in the turret had a 3" diameter 12" long piece of brass round stock in it.
I'd run the turret forward to place that brass into the bore of the bushing to catch it 
when parting it off.

If you would allow those bushings to drop to the ways of the lathe, they would spring and go 
out of round. You'd have a terrible time getting them lined up with the bore you were repairing.

When parting off thin wall parts at home I do kind of the same thing on a smaller scale.
A piece of brass round stock in the tailstock drill chuck, smaller than the bore of the part, 
does the same trick.

Rick


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## Mosey (Jan 21, 2012)

John Walker says in red ink in his "Machining Fundamentals" that one should "never attempt to part work that is held in centers"!
See below;


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## Mosey (Jan 21, 2012)

I honestly don't know what is it that you are trying to say?


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## greenie (Jan 21, 2012)

Mosey  said:
			
		

> John Walker says in red ink in his "Machining Fundamentals" that one should "never attempt to part work that is held in centers"!
> See below;



It appears that some persons on this forum have definitely got the WRONG idea about parting of using a live centre.

What you have posted is correct, if anybody attempts to part of BETWEEN CENTRES, then they can expect the worst.

What I am saying is, if the work-piece is held in the chuck jaws, then put a centre pop into the end of work-piece, now bring the tailstock up with a live centre and place the live centre into that centre pop and use the live centre to hold everything straight and steady with the weight supported, then start to part of.
You can watch the parted of piece, just drop onto the the top of the parting of tool, held there by the tit that is left on the back of the piece when you push thru and it will stay there until the lathe has stopped.

Now what's so dangerous about doing it this way ?

How can the work-piece jump out of the jaws, if it's now pushed back in place and held steady by the live centre ? 

Which would you prefer, an unsupported piece flying out of the chuck jaws, breaking bits and heading who knows where, or the work-piece held steady by the live centre. ?

If the original poster, had been informed by the "knowledge-able persons" on this forum, that you can safely do it this way, then he would still have his lathe unbroken, and be using it now.

So why all this miss-information, about never using a live centre in the tailstock to hold the job steady, whilst parting of ?

I think that a lot of people on this forum, should just go out to their lathes and at least try to do it this way, before firing of half cocked again.

regards greenie


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## rake60 (Jan 21, 2012)

I was determined to leave this alone but it's my name on the front shingle.

Please greenie, do a Google search on the term "Parting between centers."
This is the very first page of results that search gave me.






Just read the previews to those search results.

It is a very dangerous method and should never be attempted.

Rick


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## tattoomike68 (Jan 21, 2012)

I worked for years as a machine tool repairman. One screw machine shop would make 30,000 parts by morning break time. A whole lot of parting going on and not one live center in use. 

:big:


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## MachineTom (Jan 21, 2012)

Here's a video of brass part off, 1" brass, 2" protrusion 1500 rpm, .125 width parting tool, hand feed, the part even dropped onto the crosslide and stayed there, no drama.





My first video post, hope it works.


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## rake60 (Jan 21, 2012)

I had posted this video here before.
It was my very first use of the A2Z parting tool in their QCTP.

Again, this is parting from a 1" OD to a 1/2" bore, so I do part it the whole way through.

[ame]http://www.youtube.com/watch?v=sWvOtj3M4sQ[/ame]

If you listen to the cut, you can hear the crackling I had mentioned earlier just before
the part breaks free.

Rick


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## tattoomike68 (Jan 21, 2012)

MachineTom  said:
			
		

> Here's a video of brass part off, 1" brass, 2" protrusion 1500 rpm, .125 width parting tool, hand feed, the part even dropped onto the crosslide and stayed there, no drama.
> 
> 
> 
> ...



looks great, physics says the part will drop down that why screw machine and CNC lathes have part chutes and very rarely will you need to dig parts out of the chip conveyor output.

Well done on the video, play with camera angles and you can get some good ones with a tripod set over the tailstock and looking down at an angle when doing lathe shots.


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## Blogwitch (Jan 21, 2012)

Bits DO NOT fly off when parting is done correctly, they just drop.

[ame]http://www.youtube.com/watch?v=BG4qEw3eMcQ[/ame]


John


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## steamer (Jan 21, 2012)

Ok guys.  

Greenie, 3 pages or so back you asked why I thought is was dangerous.

I'll tell you why.. I did it!

20 years ago when I didn't know any better, I did it and it crashed.

HARD....The part rises up and climbs over the tool, when it does it grabs the parting tool....when it does that....BOOM!

Won't EVER do it again!.....  Don't tell me why its alright....there's no discussion regarding it with me.  

It's Ricks Sandbox.  

Let's stay civil, build some engines and give it a rest. 

Dave


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## MachineTom (Jan 21, 2012)

HERE! HERE!! @What he said.


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## lazylathe (Jan 21, 2012)

Not to throw any more gasoline on the fire...

I have been in a few production shops, manual and CNC.
Not one of them have used a live centre when parting anything off.
A few did use a catcher in the tailstock if the part was bored or a tube.

The machinist that worked in my dad's printing factory regularly used to repair presses.
He would part the rollers off because they were good useable steel when the were done.
They were about 6 inches diameter and he would have them running in a fixed steady rest and part off lengths.
No live centre used here either.

About the only time i saw him use one was when taking long cuts and then it was used in conjunction with either a fixed
or travelling steady rest, depending on the length of the cut.

For me i will stick to the accepted way of parting off here.
Carefully!
I have never had any issues and 9 times out of 10 the part lands on the cross slide.
The other time it will land between the ways, not an issue either.

Set up, a sharp parting blade, lubrication and concentration are paramount to success!
Practice is also a good thing!!

Andrew


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## tattoomike68 (Jan 21, 2012)

lazylathe you make some good points. I agree with what you say.


I found when working and high speed production shops that parting tool with was dependent on the stock , for 6" you want a 1/4" parting tool. too small a tool is as bad as too big.

Parting 4 inch you might want 3/16"

2 inch 1/8" wide tool works good.

For 1 inch or under you can do fine with a 1/16" parting tool.

When I started working fixing screw machines I saw the guys making parting tools on the surface grinder. I thought their tool geometry was way wrong but I was the one who was wrong, so I shut my mouth and watched the tools in action and got an education from some non college guys.

The tools they made left little to no burrs. some guys set up tools that would go way down a bore and put a champher then pull out before the part was parted off. No burr and the internal champher was done.

I learned alot there the boss had 3 nitro funny cars so that ate up half my time, when the car has a parachute you know its not a toy for little boys. It was cool to have a boss make me work on the cars.

I'm rambling but anyway parting can suck, do it as close the the chuck as you can and get it done. its not magic and you dont need a live center.


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## chuck foster (Jan 21, 2012)

well guys as promised i went to work today and tried parting with the use of a live center.

first item to be parted was brass, i set the parting tool on center and used hand feed. all went well until i got right to the center of the
work piece, then the pressure of the live center pushed the piece that i was parting off. now it pushed it into the side of the parting tool which in turn pushed the parting tool into the piece held in the chuck. i then lessened the live center pressure and the results were the same. the brass shaft was 1 1/2" in diameter and spindle speed was 800 rpm with a constant flood of coolant.

the next item to be parted was 1 1/2" diameter steel turning about 400 rpm with coolant...................same results.
i then tried both set ups over several times using cutting oil and power feed, i varied the rpm,s and the feed rate...............no good.

i then tried using a parting tool fed in from the back of the work (tool in a rear mount tool holder) and i got the same results no matter what i tried.

all in all i tried brass,steel,aluminum and bronze. i used no coolant, coolant and 2 kinds of cutting oil, manual feed and power feed (all at various rates) i tried several different ways of sharpening the parting tool i even varied the rpm of the lathe. nothing worked very well. i then went back to the old way of parting and all was well.

so with all that said i learned one of two things. 
1. i don't know how to part using a live center (greenie please post a video showing how you do it)
2. it just isn't a very good way of parting

please note i am not bashing any one i just wanted to know if I could do this and if not i would like some one to show me how.

chuck


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## radish (Jan 21, 2012)

rake60  said:
			
		

> I was determined to leave this alone but it's my name on the front shingle.
> 
> Please greenie, do a Google search on the term "Parting between centers."
> This is the very first page of results that search gave me.
> ...



Hi Rick, I thought I would just cut in here, I normally just lurk in the shadows and soak up any ideas I can.

You are correct, that parting of between centres is dangerous

Now what this other person is advocating, is not that at all.



From what I can read of all this, is that one end of the work-piece is to be held with the jaws of the chuck, he's just using the live centre, as you would on a very long traverse of the carriage to reduce the thickness of a job.

What's with this "fixation" about parting of between centres ?

He has already said, that is a dangerous practice, and yet you seem to be continuing on, with this wild assumption.

WHY ARE YOU ADDING FUEL TO THIS FIRE WITH YOUR WRONG ASSUMPTIONS?


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## tel (Jan 22, 2012)

I don't think anyone is making assumptions, the fact of the matter is that when you are parting off you want the end of the workpiece free and clear, so it can fall away as it should, NOT get impeded with a centre hanging it up, or, worse still, the pressure pushing it onto the tool and thus the rotating stub of the workpiece. It's certainly not good practice at best, and downright dangerous at worst!


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## mcostello (Jan 22, 2012)

It has not been mentioned here since I have been coming here, but now is the time to bring it up. I have a 14" South Bend Lathe which one would suppose is a bigger lathe than a small or Modelers lathe. It is not the most solid machine, which is going against it's size and appearance. I took some advice from another forum and made an upside down parting tool. It works great, with no problems, people with a threaded spindle have to be very careful not to unscrew things. I have a threaded spindle and part carefully and it works.


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## Mike N (Jan 22, 2012)

I have been in the Tool & Die industry since 1971. I have operated metal lathes since I was in High School (1960's). Until I read this thread I have never heard of anyone using a parting tool with a tail stock & live center. This would be equivalent to milling a piece of bar stock in half when its clamped in a milling vise! I use my lathe for making small parts for my model engine hobby. I chuck my stock close to the jaws & part off small pcs. & catch them with my fingers with a light squeeze. Of course I would not do this with large heavy cutoffs! 

I only have the parting tool sticking out a far as needed to make the cut. I use a .040" parting tool for my small work & .093" is the largest parting tool I own. I have Aloris tool post holders on all 3 of my lathes, I have shimmed up 2 of the tool posts so all 3 of my lathes have the same center tool height. I can share all of my tool holders between the lathes without setting the center height every time.


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## MachineTom (Jan 22, 2012)

Where is the OP Hauk, in all this discussion??


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## Hauk (Jan 22, 2012)

MachineTom  said:
			
		

> Where is the OP Hauk, in all this discussion??



Right here!
I have not been able to use my lathe for everal months due to the crash and some anoying delays in getting a replacement part. Wabeco has been very helpful, and has replaced the part without charge, but it has taken a bit too long. 

I have also bought what I hope is a good parting tool

And I am soaking up all the advice I can while mustering the courage to start machining again. 

I Will keep you posted on my progress!


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## stevehuckss396 (Jan 22, 2012)

I have not seen it discussed here but there is a good possibility that the casting failed causing the trouble. If I were you I would consider making a replacement part instead of installing another possible failure. I have in the past done the same thing you have done and the blade snapped long before a casting on the machine.


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## Mike N (Jan 22, 2012)

When taking heavy cuts or using a parting tool if the compound is set parallel with the crossfeed I think there would be less stress on the dovetail. From the first photo it appears the compound was set at 90 degrees to the crossfeed.


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## 90LX_Notch (Jan 22, 2012)

Regarding parting off: I didn't see mention of it (or I missed it), but locking the carriage is key. Another thing that I have found helpful is to pause and let the tool dwell every so often. Also, as mentioned earlier, keeping the tool sharp and on center are also key. 

Regarding part catchers: The red tubes from WD-40 cans are great for this. You can bottom them out in a blind hole and offset them downward in a tailstock mounted drill chuck. This setup causes the part to ride the red tube away from the parent material once it breaks free. You can easily add more tubes to strengthen the setup for heavier parts.

-Bob


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## Hauk (Jan 23, 2012)

stevehuckss396  said:
			
		

> I have not seen it discussed here but there is a good possibility that the casting failed causing the trouble. If I were you I would consider making a replacement part instead of installing another possible failure. I have in the past done the same thing you have done and the blade snapped long before a casting on the machine.



I must admit that I had several minor dig-ins before the big one. So I am absolutely certain this was a an operator error. 

As I am a jack of all trades kind of modeller, I have not been sitting around looking in awe at the lathe all these months. What has delayed the return to machining is a time-consuming effort to master the art of airbrushing brass models. A learning curve just as steep as machining, but fortunately with a much less risk of crashes & damaged equipment. No compressor explosions so far!


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## stevehuckss396 (Jan 23, 2012)

Hauk  said:
			
		

> time-consuming effort to master the art of airbrushing brass models.



I don't know all the rules but using a phrase like this without posting photos has to violate a rule or two. ;D ;D ;D


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## hobby (Jan 29, 2012)

Just to clear up, that the gentleman was trying to make very clear, That a Chuck was used to hold the part steady, while parting off with the tailstock.

Now with all due respect to the gentleman, 
-----------------------------------------------------------


This is intended to be:
@ Hauk, and to other new people to this hobby


Here is a way to look at that controversal situation when trying to do a proper cutoff method.

The workpiece locked into position in the chuck jaws.
Gravity has no effect on this workpiece.

The tailstock live center has its bearing point with due force on the tailside of the workpiece, the workpiece will not feel the effects of this preasure, due to the supporting of the chuck jaws.

As the cutoff tool enters the workpiece, the workpiece is feeling all the effects of the chuck jaws holding it in position, as the blade cuts deeper into the workpiece, there will come a point where the force of the tailstock will begin to start having influence on the tailstock side of the workpiece.
That is not good.

As the blade comes to full depth the chuck jaw side of the workpiece is fully secured, there will not be any drop from its horizontal position, HOWEVER the point that all the professional machinists are trying to convey to you is this,  

It is not the drop of both sides of the workpiece that will cause a problem, since the chuck side stays stationary, they are trying to point out with as much patiance as they can, it is the drop from the horizontal position of the tailstock side of the workpiece, that due to gravity will inherently drop in the direction of the cuttoff tool, because a fulcrum effect is established as a pivot point with the tailstock live center point in a divet in the workpiece

The loose workpiece will drop and wedge with the pivot point at the tailstock holding it..

This workpiece can only go one direction on this pivot, and that is toward the cuttoff tool.

Thats why these professional machinists are against the tailstock method, with or without chuck being used.

Any pivot towards the cutoff tool is not good practice, just as you never cut a 2x4 in half with both sides of the 2x4 supported at each end, unless the area of the cut is well supported too.

Always a cutoff piece of material never should pivot towards the cutting tool.
Its about kickback, or binding, that will occur in most cases.

Maybe this will help clarify what the professional machinists are trying to convey to you and all the new people to this hobby, in this thread.

These machinists are knowledgable as professionals in there field, so they know what there trying to make clear to the original posters, and any one else who is new to machining.

So please all newcomers adhere to the advise given by the people on this board who have the credentials to make the statements they make concerning safety practices in there field of expertise.


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## tel (Jan 30, 2012)

Look Ma! No centre!

Parting off 4" dia bronze in the Myford. This is one of those rare occasions when I had to part from the front.


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## Peter. (Jan 30, 2012)

There's been a lot of heat generated in this thread and some sign of pack-mentality too. I thought better of this place.

Parting with a center isn't the most dangerous thing you can do in your workshop, the OP managed to make quite a wreck without using one, that piece of brass could make quite a dent in your head. Sometimes using one is preferrable to not, like last week when I was parting off spacer rings from a piece of acetal. That piece would certainly have climbed the tool and come out of the chuck but the center held it nicely.

Quite often a person has to modify what they would normally do according to the situation, expecially when limited to home shop equipment. You wouldn't run across a 6-lane motorway at 4 in the afternoon but you could stroll across it at midnight.


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## hobby (Jan 30, 2012)

I am not a machinists, just a home hobbyist.
Therefore my opinions are not professional advice by any means.

However, looking at the logic of the situation, shows that it is a given fact in every construction field, that any material being cut all the way through should always fall away from the cutting tool.

Unless both ends of the material is supported to keep them stationary, never should a loose work piece ever tilt in the direction of its cutter, wether it is a revolving cutter or a stationary cutter, other wise there is a chance of binding or kickback.

*Please understand*:

The professionals on this board are trying to keep the safety standards intact, there are situations for modifications of a method, but should always keep the safety factor top priority in using a modified method.

It seems that a correct way to use a tailstock during parting is:

1. part only part way through using tailstock, then remove tailstock to finish parting through.
2. Use a tailstock chuck to hold the workpiece and part all the way through, that ensures that the workpiece cannot tilt and bind against the cutter.

Please understand, the professionals on this board ,which I am not, are trying to teach the newcomers the correct way to acomplish these things, when a person learns enough about machining methods, then they can modify the correct ways to suit there needs, by that time they will have learned how to modify these methods within the safety limits.


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## coopertje (Jan 30, 2012)

I am in the same situation as Hobby, never had any education in machining at all, just learned by trial and error. I regret to see so much emotion in this tread, it is something that I am luckily not used of this forum. I believe that a good discussion is based on facts and that the emotions should be left at home (even though that can be difficult sometimes). Please, lets not call each other thoughts, ideas or way of working stupid (i believe doing that is stupid : ). Terms like "I strongly disagree", "for me it sounds really dangerous" etc trigger the beginners over here and sound much more friendly. Every body has the right of having his own opinion, that should be treasured over here and not being demotivated. However I really agree although that safety comes first, so in a way I can understand the emotional responses!!! I am not judging over here, if this way of parting off works fine for him its ok with me, however I personally will never try this method because I am scared of it and I prefer that the material falls away from the rotating chuck instead having it pressed towards it. However a video of greenie in action would be nice to see.

Too bad to see your Wabeco brake down Haul, I would expect better from them, they are not cheap machines! Hope to see you back in business soon! By the way, what type do you have? I had a 6000D and was quite satisfied with it. 

Lets all have (save) fun overhere, regards Jeroen


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## tombstone (Jan 30, 2012)

For a tailstock to engage sufficiently with the part it would have to exert pressure on the part thus forcing it on to the tool while still rotating as it nears the end of the cut as Tel said with the chance of it either breaking the tool or forcing it into the bar stock or damaging the part off face of the part. Keeping the part off slot clear as it is created is obviously important as shown by the design of part off inserts ability to reduce the width of the swarf and allow it to drop clear.A common part off procedure with early cnc lathes was to part off down to about ¼ dia at normal speed and feed rates then reduce rpm to 100 with a feed of .001 per rev which let part drop down clear with out rattling round inside the cabinet.Some years later when twin spindle machining centres were developed the manufacturer found that when the 2nd spindle gripped the part in its collet it pushed it onto the part off tool and usually broke it their answer was to grip the part then move the 2nd spindle back .004 before starting the part off sequence this released pressure on the tool and was very successful.Personally I part off with a 3mm Iscar self grip tool mounted upside down in front cross slide at 500RPM and .006 per rev feed for everything and spray WD40 to lube chips for their release the part either falls into a box or pick it off by hand the current range has been 2 S143 stainless and aluminium down to 1/8 in similar and insert lasts a long time so far touch wood. 
Ray


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## chuck foster (Jan 30, 2012)

it would have to exert pressure on the part thus forcing it on to the tool while still rotating as it nears the end of the cut as Tel said with the chance of it either breaking the tool or forcing it into the bar stock or damaging the part off face of the part

wow i never would have thought of that :

chuck the ignored canuck


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## jpeter (Jan 30, 2012)

That tool looks like it might have some "hook" ground into it. The cutting top rake surface ought to be horizontal or ever so slightly negative so it won't grab and pull itself in. There's lots of rpm charts available on the Internet. Generally when parting the spindle rpm is kept well below the recommended turning rpm. When parting on not so ridged lathes it helps to place a small prop under the tool as close to the work as reasonable/possible down to the slide. Use any old piece of scrap cut to the proper length to jamb under the cutter. That takes quite a a bit of load off the slides and firms up the setup. Try it.


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## jpeter (Jan 30, 2012)

If the work piece had any significient length between the parting tool and tail stock and any significient diameter there's no way the piece between the cutter and tail stock wouldn't after partoff jamb between the tail and the spinning piece causing it to fly off into space. Really small diameter pieces might be ok cuz they'd drop off before jambing, maybe.


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## tel (Jan 31, 2012)

Nope, no 'hook' - that is just a piece of 3/16" square HSS, ground only on the sides and face of the tool. Run at the lowest direct speed on the ML7.


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## hobby (Jan 31, 2012)

jpeter  said:
			
		

> When parting on not so ridged lathes it helps to place a small prop under the tool as close to the work as reasonable/possible down to the slide. Use any old piece of scrap cut to the proper length to jamb under the cutter. That takes quite a a bit of load off the slides and firm up the setup. Try it.




Thanks for that good tip.


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## coopertje (Jan 31, 2012)

In addition (maybe completely unnecessary) to explanation of JPeter below some pictures of such a set-up (took the pictures from a workshop practice series book I was reading last week)












Makes sense to me!

Regards Jeroen


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## Hauk (Feb 2, 2012)

coopertje  said:
			
		

> Too bad to see your Wabeco brake down Haul, I would expect better from them, they are not cheap machines! Hope to see you back in business soon! By the way, what type do you have? I had a 6000D and was quite satisfied with it.



I have a 4000D, and I am hesitant to blame the machine for my crash. Wrong tool, far too high RPM and operator inexperince is to blame. 
In the end, I think Wabeco handled the repair of the lathe very satisfactory. I would not hesitate to buy a machine from them again. 

Regards, Hauk


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## purpleknif (Feb 2, 2012)

Once again, as a full time machinist for 30 years I gotta tell you the MOST IMPORTANT thing whether you're boring, turning, fly cutting, or parting off is TOOL CLEARANCE. If you don't believe this try cutting something without it.


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## chrsbrbnk (Feb 2, 2012)

I've also been a tool&die maker for 30-some years( actually I work with Mike N) ,still have all my digits( so does Mike). When parting off I try to use the t style cutoff tool the relieved sides help reduce the drag and heat ot the tool tip. There is a version of these that has a slight vee in the top of the bit this also helps get the chip from dragging on the par. t on brass I try to be at or alittle bit below center line. Using a cutting oil will improve your chance of sucess by like 10x stick to the standrad FPM cutting speeds for the material your cutting.


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## rake60 (Feb 3, 2012)

I remember parting sequences in programs if the CNC turning centers I used to operate.
The program would maintain the programed SFM up to a maximum that you would set in the program.

For a 2" part, we would program it to part down to a 1/8" diameter.
It would be spinning pretty fast by the time it reached that finish size.
Then you could open the machine up and snap the part off with one hand.
A few quick licks with a burr gun and you couldn't even tell it had been parted off from a larger piece
of stock.

I had that go all wrong one day.
I was running an untried program that had been written by the guy on 3ed shift.
Program looked good to me, so I hit the cycle start button. When it reached the parting sequence, all seemed
to be going well. Then an 18" long pin broke loose and almost came through the containment doors of the machine.

It SHOULD have been programed to have the parting tool come in and cut the 1/4"X45° chamfer, the part down to 1/8"
diameter. He had programed it to part down to 1/8" diameter, THEN cut the 1/4"X45° chamfer. That won't work! LOL 

A quick change in the program and I was able to reach in after the program had finished and break the remaining 38 pins
in that order off by hand.

Rick


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## MyfordMan (Feb 9, 2012)

This is my first post and like a lot of people here I wasn't trained as an engineer I have had the trial and error education and like several here are saying parting off isn't the easiest thing to do on a lathe.

if you look a Hauk's original pic of the failed piece you can see in the main groove on the right that chatter has occurred starting with the tool marks close together then gradually getting wider as the chatter worsened and eventually digging in causing the failure to me this looks as though it was due to a lack of lubrication but as others have said the things to remember are:

Sharp tool.
As little overhang as possible.
Cut as close as possible to the chuck
Lubricate
Not to fast

I haven't tried using a live centre to part and to me personally I can't see the logic but as Greener has been so adamant about this then he must be having good results this way so I'm not commenting one way or the other!

Lee


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## Ken I (Feb 10, 2012)

Without reigniting this particular fire, I often bring the live centre in for parting on my mini lathe - It definitely helps with overall rigidity and therefore helps to eliminate chatter.

This is something I would rather not do - but needs must when the devil drives - If I had a more robust lathe I would not need to do this.

That said, I don't part off as its likely to end badly - but instead part almost to off and then remove the centre and either twist the component off, saw it off or complete the part-off depending on circumstances.

Ken


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## hobby (Feb 10, 2012)

Ken I  said:
			
		

> That said, I don't part off as its likely to end badly - but instead part almost to off and then remove the centre and either twist the component off, saw it off or complete the part-off depending on circumstances.
> 
> Ken



I don't think ,using a tailstock to support the workpiece during cutoff, is really the concerned issue, it's using the tailstock to support the workpiece, as it is being completely cut away from the parent material, that seems to be the caution flag for this method.


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## AnneCourtois (Jan 6, 2013)

Also, as a self trained, hobby machinist, if you look at the scrapped part, you can see that before the illfated catch of the tool into the part, there has been multiple bites of the tool into the part, indicative of tool-flex. This happens very quickly because these scenarios develop exponencially. Look at the cut 340° earlier, you have a smooth cut but within 180-270°, critical heat is reached, your tool start to bend and eventually catches. Within 20-30milliseconds. Failure probability = Lack of rigidity X Lack of lubrication. Meaning you could get away without lubrication if your setup is quite rigid and vice-versa; you could lack a bit of rigidity(that happens easily with hobby level machines) but with plenty of lubrication, one could do just fine.


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## dman (Jan 6, 2013)

i once saw a machinist of several years training a new guy on parting. the machine had a 16" swing and he was using a very rigid quick change tool post though it's been so long i forget the size/model. he was explaining that you dont want to let things rub or they harden, heat up, or gall. well it was a 6 inch aluminum bar he was cutting  and quite aggressively to avoid letting it rub. well i guess the tool wasn't too sharp or chip ejection was a problem and the material started to heat up and gall anyway. next thing you know as he was mid sentence probably looking off to the side talking to the new troop there was a crash as the part pulled down on the tool so hard it broke the dovetail from the tool holder! 

the trainer turned red as he stopped the machine and explained " that is what you don't want to do" lol.


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## MuellerNick (Jan 6, 2013)

I have read some quite ... funny tips in this thread!

But first of all, I think that the dovetail broke, and then the rest happened. Brass is very forgiving when you turn it. It is really hard to make something wrong there.

Retract the compound to make it stiffer.
Part off very near the chuck.
Align the tool dead to the X-axis. The fastest way is to push the side of the tool against the chuck's face, then clamp the tool.
Never adjust tool height above center.

Cutting speed:
Brass with HSS is turned with 100120 m/min surface speed. With a diameter of 25 mm, that makes 12701530 RPM.
I do not remember that I ever turned brass with coolant or oil. In fact, I would never use oil on brass to part off. Why? I'll come back to that.

Now the most common error done while parting off is a feed way to low. If you have an automatic feed along X, USE IT! 0.1 mm / revolution almost always works. If you feed manually, feed fast. Most people start very slow, tool will squeek (SP?, you get it by the sound) and they lower the feed. Wrong! Increase the feed and things will get silent and smooth. Watch for the sweet spot of the feed. If it gets to high, you will get a rumbling sound.
Why no oil for brass? That only starts the tool to rub. You feed in, nothing happens. The oil film breaks and the tool starts to cut and digs in.  You then have a sequence of rubbing and digging in.
If you use oil, you should have an automatic feed. Coolant (water/oil) is more forgiving on that.

On my CNC-lathe, I part off at 150 m/min surface speed (1045 AKA C45 etc.) and a feed of 0.1 to 0.15 mm/rev. At 25 mm diameter, the RPM flats out, she only does 2000 RPM. I use coolant.

On aluminium, always use coolant! The deeper the cut, the more necessary it is. Al tends to bind to the tool. One chip that is torn between work and the side of the tool and the disaster starts. You can avoid that with coolant. Plenty of it.


Nick


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## Brian Rupnow (Jan 6, 2013)

After 5 years of parting stuff off, I must admit it still terrifies me . I grind the tool correctly, I retract the top slide to a minimum of overhang, and lock the gib. I lock down the bolt on the cross slide that locks it to the bed. I make sure the tool is on center. I use lots of cutting fluid. I pray. I stand well to one side of the "disaster zone" if anything is going to fly out of the lathe and kill me.  I wear my safety glasses, and sometimes wish I had a full suit of armour like Sir Lancelot had. Sometimes the part turns off cleanly. Sometimes it digs in, gives a large "SNAP" and the whole lathe jumps 3" off the floor and I crap my pants!!! Sometimes I turn untill the cut is about 1/8" deep, then chicken out and take the part over to the bandsaw to finish the cut.


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## MuellerNick (Jan 6, 2013)

> After 5 years of parting stuff off, I must admit it still terrifies me .



Aren't you the one who said: "I turn all my parts with 650 RPM"?


Nick


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## Brian Rupnow (Jan 6, 2013)

MuellerNick said:


> Aren't you the one who said: "I turn all my parts with 650 RPM"?
> 
> 
> Nick


No, not me. There are 2 or 3 other Brians on this forum though. My lathes lowest speed is 115 RPM and thats where I do my "parting off" otherwise it chatters terribly.


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## MuellerNick (Jan 6, 2013)

> No, not me.



I'm sorry, I got the RPM wrong, not your name
"I do most of my aluminum turning at 970 RPM." (Brian Rupnow)


Nick


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## Brian Rupnow (Jan 6, 2013)

MuellerNick said:


> I'm sorry, I got the RPM wrong, not your name
> "I do most of my aluminum turning at 970 RPM." (Brian Rupnow)
> 
> 
> Nick


 
Turning yes, parting off, no. ---Brian


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