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

[rleete]

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

 

[steamer]

+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

 

[Sparticusrye]

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.

 

[MachineTom]

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.

 

[greenie]

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?

Dave

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

regards greenie

 

[Troutsqueezer]

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.

 

[willburrrr2003]

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.

 

[rake60]

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

 

[greenie]

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

 

[ShedBoy]

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

 

[MachineTom]

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.

 

[rake60]

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

 

[Tin Falcon]

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
.

 

[tattoomike68]

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.

 

[greenie]

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

 

[bronson]

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.

 

[Maryak]

Hey Greenie,

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

Bob

 

[chuck foster]

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

 

[greenie]

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

 

[greenie]

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

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