Parting off is chicken soup

[ieezitin]

Hi!

This topic was raised on another forum and this was my advice I gave them. For people who are new to machining this maneuver is hidden with perils and safety should be highlighted.

Parting off should not be a hazardous procedure if all the factors of failure are know.

Most incidences are down to the parting tool not having enough side clearance for the swarf to go; two objects of mass cannot occupy the same space at the same time. A trick here is to whittle away a slot by removing the edges leaving space either side and then going straight down the middle for the parting action.

If a clean square cut is your goal then two important factors must be obtained, the cutting tool should be totally square with the longitudinal axis of the work and tool height should be dead center, assuming your ground profile on the parting tool are correct this should not be a hard procedure, again its down to clearance.

Another main culprit is backlash!. Yep hidden slack or lack of it will snatch your cross-slide forward digging the tool in which in turn sets off a sequence of events and ends up ugly quicker than a 50lb fat naked chicken running away from KFC. Limit this menace
But adjusting saddle cross-slide jib screws and don’t forget the top compound slide, plus another fiend could be the thrust feed screw bearing.

A parting tool should always be working meaning the feed of the tool should not lose contact with the work. The length of the parting tool should be kept to a minimum and should be as close to the chuck/collet as possible. chatter will be the evidence.

Another trick is if you want to part off anything over an inch slip it in back gear and take side cuts as I mentioned previously. If the material has a harsh scale on the surface remove this first giving the parting tool a chance to seat its self without damage.

All in all it is one of the most dangerous of machining set ups but its apart of our machining experience and should be mastered. When you are going to part off think through in detail your moves, how you will stand and how to lubricate while manually making the cut and if something screws up you what your actions will be.

Adhering to all of the above will limit your exposure to something drastically going wrong. don’t fear parting off be in control of it.

Hope this helps. Anthony.

 

[Troutsqueezer]

Because I'm new to this and don't know any better, I use my hacksaw. I set the lathe to run in reverse and hold the hacksaw on the top of the spinning workpiece. Easy schmeasy. Goes fast even with steel. It's not a beautiful cut but I can always finish it on the mill.

-Trout

 

[Maryak]

Because I'm new to this and don't know any better, I use my hacksaw. I set the lathe to run in reverse and hold the hacksaw on the top of the spinning workpiece.

Trout,

Sorry mate but that's a great way to damage both yourself and your lathe. May I suggest that if you hacksaw on the lathe, do it by hand with the machine stopped and locked, use a chuck board in place under the cut to protect the ways when the blade comes through in a bloody great rush you weren't expecting, ( ask me how I know :)

Best Regards
Bob

 

[rake60]

Excellent tutorial on parting Anthony. Thm:

I'd add one comment.

When parting most people are concerned about where that piece is going
to fly when the tool reaches center or the ID diameter, what ever the case may be.

In most cases the piece being parted off will drop straight down.
If the tool grabs or the piece kicks, there is no telling where it may fly to.

There is no good reason to allow that to happen.

If you are parting off a solid part, feed the tool in until the connection between the
part and the parent material can be easily broken off by hand. It will take just a few
passes with a file or emery paper to clean up that little nub that will remain.

If you are parting to an open ID you will hear the material start to crackle when the
tool is about to break through. Stop there! At that point the piece will easily break off
by hand as well.

It is better to deburr a center nub or the corner of a bore, than to be hauled off the
Emergency Room to have that piece removed from your forehead.

Follow Anthony's guidelines and don't go all the way through.
It really is a safe and easily learned operation.

Rick

 

[Troutsqueezer]

Bob, I figured when I posted that comment I would perhaps get responses such as yours, and rightly so. Point taken.

Taking all things into consideration; the small HF mini lathe I'm using, the ease with which I am able to overpower it, the success I've had to date coupled with an unhealthy sense of bravado, I'll probably continue down this dangerous path until the surgeon says he can't sew my fingers back on. *bang*

I've always had a rebellious streak...

For larger lathes, I would be singing a different song.

-Trout

 

[Maryak]

Trout,

It's your bits and pieces, your machine, your choice. I hope it continues to work well for you.

Best Regards,
Bob

 

[Blogwitch]

Anthony,

I have to personally disagree with a lot of what you have said.

Parting off or grooving (same thing but not going all the way thru) is not a dangerous operation at all, unless you make it so.

Where it does come into the chapter on being unhealthy, is when you try to do it to larger material than your machine tool should be asked to cope with.

I can part off 3" diameter with no trouble at all, because I have a machine that can cope with the rigidity required to carry it out.

Now for a mini-lathe, even though people will say it will do a lot more, I would consider 1" diameter to be it's maximum, purely because it isn't made to withstand any larger force. Above that, you are moving into the realms of making the machine do jobs that it wasn't designed to do, THAT is when it becomes dangerous.

In a normal parting situation, you would run the machine at the same speed as you would if you were facing off, and the feed speed would be the same. Slowing down is one of the worst things you can do. The feed rate when running very slowly has to be matched to the rotational rate, but because it is going so slow the feed rate is usually too fast, and that is when you start to dig in and snap off tooling. Because I can, most of my parting is done under power, so my feed rates are very close to being ideal.

The tooling does play a large part in parting and grooving, and for big jobs, you need the tooling to be able to do it.

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

And as you can see, it is designed to take those very large downwards forces. Before these, I had to rely on the bladed toolpost holder with the blade sticking out by up to 2" for large billets.

You mention about side clearances. Whenever I grind my own parting/grooving tools, they are done on my surface grinder, with perfectly parallel sides, and upright side faces, the only clearance angle is on the cutting face and top face if needed. BUT, and a big BUT, no 'near enough' square to the job, it has to be exact. The swarf just curls up into a catherine wheel shape and goes nowhere near the side faces. That is with materials that give curly swarf, for brass, it just piles onto the top, there is no room for it to go down the sides and jam up. You might call it luck, but I can cut off hundreds of parts or do hundreds of grooves and still be left with a tool that will be used again, very rarely do they ever jam up, and if they do, it is usually me doing something silly, which we all do at times.

So basically, parting off is just another machining operation, where in the real world, if it is part of your job, you do it without needing to think. The main mistakes that occur in a home shop are asking too much of your machinery (get your self a small mechanical saw instead) or not having the correct tool and being unable to set set it up correctly.

I started to do an article on John Somers site about parting off, but only got the first part completed before my problems started to occur. One day, when I can get back in my shop, I hope to be able to finish it off, which can then be used as a general reference article. It won't cure all ills, but it will dispel a lot of myths that abound regarding parting off and grooving in the home workshop.

http://start-model-engineering.co.uk/begin-with-bogs/parting-off/


Bogs

 

[Gauge3]

Is that your new Chester Lathe Bogs?

What do you think so far. My old Myford S7 may be due replacement before too long.

And can you provide the detail on that long reach parting tool (sourced from etc)?

Ian

 

[lordedmond]

I use a myford big bore lathe with a back tool post fitted with a ISCAR insert parting blade ( approx. 1/8 wide )


I can part off steel up to 2 inch at 300 rpm under power feed

So my take on the problem is machine setup, using the correct tools for the job and the general condition of the lathe

a bit of cutting oil will help
and above all confidence that you can do it do not chicken out on the job a stead feed is required

Stuart

 

[Blogwitch]

I don't want to divert this thread, as it could become very interesting as people discuss their methods, so this is just to answer Ian's question.

First thing Ian, welcome, I would suggest you introduce yourself so that people know just who you are.

Yes Ian, that is my new (now old) Chester UK Crusader lathe. It was bought before they started to offer the stripped down version, and then almost doubled the price of this one. But I did warn people a while ago that prices would be going up dramatically, but no one would believe me.

The Mircona is in fact one designed for industry, I have both a left and right hand version and can penetrate 40mm depth, so can cut off 80mm diameter bar. There are a range of tips available for them (I do have a few different ones) and they can be used as a universal tool as well, as not only can it part off, but can face, profile and turn left and right handed, with just the one tip.

To buy new would cost somewhere around the cost of a new mini lathe, but I watched for months on eBay before I got the first one and the second came a couple of months later. They were both brand new and I paid 35 squid for each, and I bought a load of tips at 2 squid each from the same vendor when he offered them to me. I searched every day for 'Mircona', and eventually got what I truly wanted.

I think I have shown this before, and it is about CNC machining centres, but it does show what the right tools can really do.

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

There are about 4 or 5 in this series from Mircona, and cover slotting tools on the mill as well. Just search Youtube for 'Mircona'.

I hope this helps you.

Bogs

 

[ieezitin]

Bogs,

I have read your post and I don’t see too much on where you are disagreeing with me.

On reflection of my own post, when I conveyed that the parting tool had to be totally square, I should have emphasized the accuracy of it being square. Also I failed to mention the angle of the cutting face; this is a big part of swarf production and removal process agreed.

You did mention types of material being worked by this process and there’s a world of difference between parting cast iron, steel, and brass etc, swarf wise that is.

I did accentuate the word clearance, maybe I was vague here too, I was relating to the tool geometry as well too the tool doing its work. You stated you can cut hundreds of times with the same tool with very little ware and every time getting the job done safely, I know you can because your tooling is spot on and profiled exact, your machines are mostly of heavy construction and high quality balanced with your years of experience.

Through our discussion here we are exposing and revealing the dos and don’ts of parting off, all inexperienced people should take note on the importance of knowing what your machine is capable of and getting tool geometry and set ups correct. After that its chicken soup. John I think you expressed this better than I.

After 31 years of machining I still have not forgotten my apprentice years and the wealth of experience I soaked up from my teacher. When ever he parted steel over 1 inch he back geared, his mindset was slow speed and coarse cut actually the cut becomes the feed. I have always done this and never got into any trouble. Now the machines and tooling then were 80 odd years old and helped remove Hitler from Germany. Now there are newer more efficient forms of tooling, different materials etc that most likely can speed up the parting process, I I have not been exposed to them and know nothing about them. If really large diameter pieces were to be cut he would place the parting tool opposite to the normal position and turn it 180 deg, his philosophy was gravity would remove the swarf at the same time helping out the headstock, the downward cutting pressure stops the lathe mandrel from lifting in its bearings. This applies to steel only, when it comes to speed brass without a doubt can and should be sped up with ease and not sacrificing safety.

Rake.

I agree with you 100% on leaving the ends on and snapping them off. Nothing wrong with it at all and gives you that little more safety edge.

Trout.

At least you are honest; please keep your fingers as it’s hard to type without them.

All in all I stand by my original post and I think I addressed the key issues on this topic; we all do things different and tend to get the desired results right for what we need. The best thing out of this is the fact we have experienced turners/machinists discussing in front of the public techniques, procedures, views and true life situations all laid out for those who wish to absorb it, most of which this valued information will not come out of a book. After this thread comes finally comes to a close the inexperienced will be able to part off safely and will be loaded down with the knowledge of this is how its done.

Foot note. Do not!!!!! Do not ever part off while machining between centers!!!!!!!!!!!!!. Because if you do you really will be eating chicken soup through a straw in a bed.

Anthony.

 

[Deanofid]

Anthony, I'll add something to this last bit, just so the newer folks will know the "why"
behind the "don't do it" part:

Foot note. Do not!!!!! Do not ever part off while machining between centers!!!!!!!!!!!!!. Because if you do you really will be eating chicken soup through a straw in a bed.

When you attempt something like this, (parting between centers), when the tool comes to the center of the cut, the pressure from the tail stock will push what have now become two pieces toward the center of the cut. That will pinch the parting tool HARD between the two rotating pieces, and the lathe chuck is going to do it's best to roll those pieces up over your tool post.

If you have much power driving the chuck, it will succeed in providing you with the dangerous situation of two pieces of metal climbing up over the tool post, usually yanking the work piece out of the chuck and sending it directly toward the operator, (that's You!).

Parting off is not magic, nor is it an unusual shop practice. Like other regular turning operations, you just have to learn how to do it.

Dean

 

[justlesh]

I've been twisting handles for over a 1/4 century and parting or grooving is not an issue for me at all, but, I have worked with guys that just can't seem to get it down, I have even set them up and got them going only to walk 5 feet and hear everthing go POW. What I have settled on for these hardheaded people is the upside down tool and reverse the spindle. These machines are just like mans best friend. If you listen to them with respect and dilligance you will soon find out all those wild and crazy sounds its making is telling you their unhappy and each sound is a clue for you to understand what it needs to be happy. A well seasoned machinest can diagnose problems from across the shop most times.
But also know, that my cure may not be the same as someone elses.
Sorry for being long winded. I just went thru this parting thing at work with a guy that knows it all. He went thru a whole box of 10 inserts while telling me that this lathe is junk, this toolings junk. Gave the job to a young guy with some real talent and he sailed thru the parts only using 2 inserts and machining WAY more parts than the guy with 10+ yrs more experience.
Les

 

[Blogwitch]

Anthony,

We will have to agree to disagree on certain issues, and as I stated in the reply post to Ian, almost everyone has their own methods. I was brought up with parting is just another standard machining exercise, and nothing to be feared at all.

I think where many people go wrong is in their choice of tooling. Just like any other machining operation, you choose your tooling to carry out a specific job, where parting departs from the norm is that almost each material and diameter requires a different tool to get the job done, whereas most people in the modelling fraternity think there is a 'magical' one that will cure all ills. I do use one tipped one for about 75% of my parting, but most others get a special all to themselves, hence my largish collection of parting tools, it is not a boast, but a necessity.

I too remember the early days of carbon tooling, and having to resharpen after every cut, but with the advent of HSS, if the tooling is sharpened and shaped correctly, it only requires a fine dressing by hand every now and again, plus I also hand lap certain carbide tips as well.

I still think you shouldn't slow down your machine for parting, and a lot of people are expecting too much from their small machines. That is just what I think, if someone else thinks it should be done slowly with large billets on small machines, then good luck to them.

We are only here in an advisory capacity.

Bogs

 

[Dirty_Vinylpusher]

Oh you're gonna love this.....

This is how I used to make sure I got a clean square cut.

I will not be doing that for much longer though as my new toy is in the post.
A little C2 lathe.
;D

 

[jgarrett]

OK, what is the best way to make sure the bit is perfectly square to the work???
I usually loosen the tool post and hold the bit tight against the work but sometimes the work is not flat on the end.
Thanks,
Julian G.

 

[lee9966]

I use the face of the chuck as a reference for setting the parting blade square.

 

[ieezitin]

Julian.

Insert the tooling and leave the tool post loose, wind the saddle towards the chuck end ( head mandrel ) use the flat of the face of the chuck to get square, this is the meat of the chuck not the grip jaws. Or if you have not enough room put a steel rule in the jaws having the flat side of the rule in the horizontal, gently grip the rule and then slightly tap with a mallet to seat against the face of the chuck. Then take you square from the rule edge.

You could put the face plate on and do the same.

Anything that is on the mandrel that has been faced and is known to be square, if you have faced a blank using the cross slide 99% times should be square, if its been faced on the compound make sure your setting was dead on 0.

Put an indicator on the bed and put the tip on the top edge of the tool and run in perpendicular to mandrel axis, I say its tricky though but can be achieved.

After all this its any method you can think of using the head spindle to give you the datum point.

I am sure you will get a surge of ideas from other members with great tips.

Hope this helps. Anthony.

 

[Deanofid]

Probably the easiest way is to start by loosening the tool post so it is barely tight. Put a straight edge
against the chuck face, run the carriage w/tool post up to the straight edge and put a little pressure
against it so the side of the tool is flat against the straight edge, then tighten the tool post. Check it
again against the straight edge to make sure you didn't twist the tool post when you tightened it,
and you're set.

That works for factory ground tools. If you grind your own tools, use one of the factory ground
sides of the tool bit as one edge of your parting tool so you have a true reference.

If you don't have a chuck mounted on the lathe spindle, like when you are using collets, you can
do a similar squaring procedure using a small square against either the work, assuming it is not cut on a
taper, or against a rod mounted in your collet.

Dean

 

[Blogwitch]

I am a great believer in using tools the way they were intended to be used, especially tipped tooling.

The manufacturers of these tool tips go to great lengths to get the cutting angles correct, and the unruly model engineer then thinks he can do better than the tooling designers by swinging the tips to all sorts of angles that the tool was never designed to cope with.

So, unless I am cutting tapers with the topslide (compound) or setting over to cut threads, my toolpost and topslide are always perfectly square to the saddle, and so square to the spindle.

If the tooling is mounted square in its holder, then it should automatically be square to the workpiece. Because I am lucky and can machine grind my own tooling, then they also acts just like a manufactured tool.

There are a couple of ways I mount the tooling. The first way is to clamp it into the toolholder on the lathe and run a dti along the side face of the tool, with the dti stuck to the lathe head and the saddle moved backwards and forwards to take the reading. Once it reads 0-0 along the tool length, then it should be perfectly square to the workpiece.

The second is where I already know my QCTP is perfectly square to the spindle, it is just a matter of laying the tool along a flat surface, dropping the holder over it until it too lays along the flat surface, then tightening up the clamp screws. It is then remounted onto the post and you will find everything is perfectly square to the job.


Bogs