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

[arnoldb]

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

 

[90LX_Notch]

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.

 

[Ken I]

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

 

[metalmad]

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

 

[stevehuckss396]

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.

 

[90LX_Notch]

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

 

[stevehuckss396]

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.

 

[rake60]

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

 

[Mosey]

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;

 

[Mosey]

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

 

[greenie]

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

 

[rake60]

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

 

[tattoomike68]

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:

 

[MachineTom]

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.

 

[rake60]

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

 

[tattoomike68]

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.

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.

 

[Blogwitch]

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

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


John

 

[steamer]

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

 

[MachineTom]

HERE! HERE!! @What he said.

 

[lazylathe]

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