# Parting Difficulty



## prasad (May 10, 2015)

I am trying to part an aluminum rod 1.5" diameter using my G4000 9x19 lathe and a 1/8" HSS parting tool. I am getting loud growling sound with heavy vibration. I have tried Re-Li-On cutting oil, WD40. They help a bit but no enough to make the parting smooth. The tool height is adjusted to center height correctly. Varying spindle speed helped a bit but not enough. Any advice? 

Thanks
Prasad


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## Micke S (May 10, 2015)

In case the worpiece protrudes more than a few inches from the chuck it may need support from the tailstock.


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## prasad (May 10, 2015)

The work piece sticks about 2 inches from the jaws and parting tool is about 1 1/4" away from the jaws. I am using 6" 4-jaw chuck.


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## Terrywerm (May 10, 2015)

I used to have trouble with chatter when parting from time to time, but since going from a 1/8" blade to a 3/32" blade the problem rarely occurs any more. Hard to believe that 1/32" in width would make as much difference as it did!


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## higgite (May 10, 2015)

All guessing at this point, but it could be any one or a combination of dull tool, parting too far from the chuck and/or too much tool sticking out of tool holder. I would check all 3. And make sure saddle, cross slide and compound gibs aren't loose. Hope this helps.

Tom

Edit: Terry posted while I was typing and made a very valid point. With 3/4”+ of the parting tool sticking out of the tool holder, a wider parting tool might be the ticket.


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## Karl_T (May 10, 2015)

All good advice. Chatter is your machine saying, "I'm not rigid!"


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## prasad (May 10, 2015)

Thank you guys, I will have to buy a wider parting bit then. I tried it again with live center mounted and at one point I think the parting tool got caught. The lathe clutch acted, workpiece slipped in the chuck and became eccentric. So I stopped the parting process and used a hacksaw to cut the piece off. Not exactly to my desired method. Well I am learning.. Every thing that happens here is gained experience... Tomorrow will be better, ha ha.  

Thank you everyone for sharing your knowledge, everything was useful... 

Prasad


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## brino (May 10, 2015)

Hi Prasad,

No disrespect to you intended, but this recent thread has a lot of good advice.....

http://www.hobby-machinist.com/threads/parting-for-idiots.32938/

-brino


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## higgite (May 10, 2015)

prasad said:


> I tried it again with live center mounted and at one point I think the parting tool got caught.



That's exactly what I would expect to happen. I have seen more than once when someone suggested using a tailstock center to support a long work piece for parting. I haven’t had a need to try it, so I’m working on theory here, but it sounds counter intuitive to me. Seems to me that if you have the work piece pinned at both ends, the side force from the parting tool will tend to bend the work piece into an arc, which would widen the parting groove on the backside and narrow it on the front side, pinching the parting blade. Am I wrong?

Tom


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## coolidge (May 10, 2015)

Part it off with a band saw then face it in a 2nd op.


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## Terrywerm (May 10, 2015)

I am not so sure that going to a wider tool is the answer. A wider tool will offer more turning resistance to the work piece, which in turn creates more downward force on the tool, creating more chance for chatter. A narrower tool would offer less resistance, in turn resulting in less downward force and less flex, provided the tool does not stick out too far. 3/32" is narrower than 1/8", not wider.

The other points that have been brought up are all good also, and gib adjustment on the cross slide and the compound are very important. I had mine where I thought they were tight enough, but I had to snug them up just a bit more for parting to go smoothly. Even then I would still have some trouble, which I was able to virtually eliminate by going to the slightly narrower blade. There are times when I need a wider cutoff tool, but most of the time the 3/32" tool works very well.

One last thing to consider is that after sharpening your cutoff blade on a grinder, it might be a good idea to hone it a bit on a stone to give it a very keen edge.


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## Franko (May 10, 2015)

Karl_T said:


> All good advice. Chatter is your machine saying, "I'm not rigid!"



You might check to see that the dovetails on your saddle and cross slide are properly tight.


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## Micke S (May 10, 2015)

I became interested to check if it is possible to use a wide carbide cutter that I've got. I cant see any big use for it except if the load will be very high so thin inserts may snap. The width of the insert is 5 mm (1/5 inch). The workpiece is a 45 mm (1.8 inch) aluminium T6 rod. The gearbox was set to the strongest torque but w/o activating the back gear, which would have produced a lot more torque. I lubricated with small squirts of WD40 and it worked well with auto feed.


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## eeler1 (May 10, 2015)

Not good to use tailstock support when parting.  Make sure tool is exactly square, perpendicular to the work.  Otherwise the tool binds as you advance it.


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## Micke S (May 10, 2015)

I agree with Terry that a narrower insert will make it easier since the load on the lathe is reduced. I normally use 3 mm (1/8's) so the test with the wide insert was just out of curiosity to see if it would work.


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## JAB (May 10, 2015)

The two problems I usually run into with parting is; turning too fast and (as eeler1 says), make sure you have the tool "exactly perpendicular" to the work. It's not hard to turn a 1.5" work piece way too fast. Start slow and you can always speed up to make the process more efficient. Starting too fast is asking for instant problems. There is virtually no side clearance on a parting tool. So if the tool is not exactly perpendicular to the work turning axis, it very soon starts to drift to one side or the other causing it to make a lot of noise and eventually jam. You might also try grinding a 3 degree clearance to the left side of the cutting point, (slope away from the work being parted). This has worked for me in reducing point chatter to zero. I also use a constant coolant/lubricant flow to cool the blade and work and keep the chips moving out of the groove. As stated by others getting all the turning conditions correct is essential to parting. I would also suggest starting with smaller work pieces to get the feel of it.


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## brino (May 10, 2015)

prasad said:


> I tried it again with live center mounted and at one point I think the parting tool got caught.



Prasad, there's one problem! 
higgite nailed it above -* Never, ever part between centres!!!*

It should only be done with the work mounted in a chuck or collet.



prasad said:


> I will have to buy a wider parting bit then



terrywerm was suggesting a thinner parting blade, as that will mean less cutting force required.

-brino


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## Mark_f (May 10, 2015)

It sounds like you are turning too fast. I part in backgear and at the slowest or next to slowest speed on a larger diameter like that. The larger the diameter the less rpm you need. We are dealing with SFM here.


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## mzayd3 (May 10, 2015)

prasad said:


> The lathe clutch acted, workpiece slipped in the chuck and became eccentric.
> Prasad



This may have been the source of your chatter.


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## randyc (May 10, 2015)

You've received some very good advice: careful tool alignment, slow speed, thin parting tool, lots of coolant and don't pause when feeding into the work.

The best thing that I ever did for my smallest lathe was to add this threaded support to the cross-slide.  Parting with a 3/32 blade in any material (under Rc 30) is never a problem.

The support is threaded into a tapped hole in the cross-slide.  A screwdriver slot was machined into the top of the support for easy removal.  (When the compound-slide is in use, the support is removed.)





Incidentally, QC toolposts are not well-suited for parting due to the long cantilevered distance between the cutting edge of the tool and the surface where the toolpost is actually clamped to the compound.  If you _have_ to use a QCTP, consider supporting the tool with a machinist's jack as I did for the boring tool in the photo below:


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## tomw (May 11, 2015)

Just out of curiosity, when parting piece that far from the chuck can you use a *follower rest* to stabilize the part?

Thanks,

Tom


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## JR49 (May 11, 2015)

tomw said:


> Just out of curiosity, when parting piece that far from the chuck can you use a *follower rest* to stabilize the part?
> 
> Thanks,
> 
> Tom


I would say absolutely yes, in fact it sounds like a great idea. But, as a newbee myself, I look forward to hear what the "pros" say


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## randyc (May 11, 2015)

tomw said:


> Just out of curiosity, when parting piece that far from the chuck can you use a *follower rest* to stabilize the part?



I've never heard of anyone doing it.  Offhand, I'd be worried that if the parting tool started to dig in, the work would start to roll over the tool and be pushed out from under the top jaw of the follower and away from the rear jaw.  Can't think of anything good resulting from that sequence of events, LOL


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## gheumann (May 13, 2015)

Parting is an art. I have parted 2 1/2" aluminum and had many failures early on, until I learned that EVERYTHING has to be right: 

tool on center vertically
tool perpendicular to work
good lubricant (I highly recommend "Tap Magic Aluminum"
proper speed - slower than you think
proper feed - enough to produce a steady chip
interrupt the cut more and more frequently as you get closer to the center, clear the chip, restart
BUT - because I need to do this a lot, I bought a cheap harbor freight metal cutting band saw. I prefer the saw!


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## DavidL (May 14, 2015)

prasad said:


> I am trying to part an aluminum rod 1.5" diameter using my G4000 9x19 lathe and a 1/8" HSS parting tool. I am getting loud growling sound with heavy vibration. I have tried Re-Li-On cutting oil, WD40. They help a bit but no enough to make the parting smooth. The tool height is adjusted to center height correctly. Varying spindle speed helped a bit but not enough. Any advice?
> 
> Thanks
> Prasad


I have a Seig mini lathe and suffered the same problems with parting off.  The mini lathe is just not sufficiently rigid.  I then adopted reverse rotation with an upside down tool and have had no problems since.  Check out this video which demosntrates the technique that overcomes the lack of mini lathe rigidity. https://www.youtube.com/watch?v=-RZRq0olsxM


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## kingmt01 (May 14, 2015)

Thanks for the video. This makes sense now. I have problems parting myself. I'm going to give this a try.


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## Highsider (May 14, 2015)

prasad said:


> I am trying to part an aluminum rod 1.5" diameter using my G4000 9x19 lathe and a 1/8" HSS parting tool. I am getting loud growling sound with heavy vibration. I have tried Re-Li-On cutting oil, WD40. They help a bit but no enough to make the parting smooth. The tool height is adjusted to center height correctly. Varying spindle speed helped a bit but not enough. Any advice?
> 
> Thanks
> Prasad


Hi Prasad,   
The problem you are having may have less to do with what I'm seeing discussed here than simply using the proper cutting fluid on aluminum.  This material has a high propensity for galling between the chip and the work piece.  WD-40 and cutting fluids that might work on other seemingly harder to machine materials are next to useless with aluminum.  Go to your supplier for some cutting/threading fluid specifically designed for aluminum.


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## MetalMuncher (May 14, 2015)

I used to have a very hard time parting 6061 aluminum on my mini lathe. I did not see any mention here of the fix I found (after much research) that makes it so much easier for me, so thought I'd share it here. Profile the top edge of your parting tool. Mine has an aggressive relief curve ground into it. I don't have time to post a photo at the moment, but I use a 1/2" wide, 0.060 thick parting tool blade, and the curve dips maybe 1/16th of an inch, so the curve appears profiled rather like the cross section of an ice cream paddle scoop. Together with the other suggestions of keeping a keen edge, on center, perpendicular, slow rpm, etc. it works very well for me now. Parting off a 2" rod is no problem at all. Hope this helps.


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## MetalMuncher (May 14, 2015)

I found a PDF I made documenting this solution, so here it is. It has a photo of the ground parting tool.


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## kwoodhands (May 14, 2015)

prasad said:


> I am trying to part an aluminum rod 1.5" diameter using my G4000 9x19 lathe and a 1/8" HSS parting tool. I am getting loud growling sound with heavy vibration. I have tried Re-Li-On cutting oil, WD40. They help a bit but no enough to make the parting smooth. The tool height is adjusted to center height correctly. Varying spindle speed helped a bit but not enough. Any advice?
> 
> Thanks
> Prasad



Start your cut, before you get chatter widen the cut to the waste side. This may be only 1/8" or much more depending on the material,diameter,etc. Wd -40 or paint thinner will aid in parting.Hone the parting tool. If you could part 1-1/2" in one setting then the parting tool would have to stick out from the holder 3/4"+. Keep the cutter at about 3/8".When the tool holder gets close then extend the cutter.Check for center height after you extend the blade. I use a 6" metal rule against the work and pinched with the tool.The rule should be vertical,not leaning when the cutter is dead center.Raise the cutter if the top of the rule leans towards you.Lower if the top of the rule leans away.
You only have to widen the cut enough so the cutter won't bind and heat up.Usually .010 / .030 is enough. 
mike


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## Round in circles (May 15, 2015)

coolidge said:


> Part it off with a band saw then face it in a 2nd op.




I'd use one of the parting tools that have a wider top edge of the cutting blade than the bottom edge . Have  the blade as wide as the tool post /holder will accept .

Like  " coolidige " says .. once you have made  a couple parting cuts overlapping side by side to keep the width of the parting clear of swarf ,  once you have gone in a few mm with the wide cut say 8 or so mm  then take the part out the lathe  and cut it with a band or put some gloves on & hack saw off whilst it is in a stationary lathe , reset it back up and face the end

I have an indexable parting tool where the cutter  ( 3 mm.5  at the top edge and 2.5  mm at the bottom) has blade width is about 5/8 of an inch which  can be slide forward to or back  from the work .. anything that sticks out the tool holder more than  3/4 " causes no end of harmonic vibrations & chattering to get going.

One thing that does not seem to have been mentioned is that  it's a very good idea to lock the saddle to the bed , for this is one place that  folk don't often associate with parting chatter and breaking of parting tools as the  unclamped saddle slips & slides around .


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## coolidge (May 15, 2015)

coolidge said:


> Part it off with a band saw then face it in a 2nd op.



And by that I mean take it over to the band saw don't try sawing it on the lathe.


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## eeler1 (May 15, 2015)

> One thing that does not seem to have been mentioned is that  it's a very good idea to lock the saddle to the bed , for this is one place that  folk don't often associate with parting chatter and breaking of parting tools as the  unclamped saddle slips & slides around .



Most excellent point!


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## JAB (May 15, 2015)

I never lock down the saddle and never have a problem. I suspect the gib should be tightened on the saddle. Doming, either left or right, is usually because of a   dull, bent, incorrect sharping, or most often the blade is not set to true perpendicular to the turning axis.


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## eeler1 (May 15, 2015)

JAB said:


> I never lock down the saddle and never have a problem. I suspect the gib should be tightened on the saddle. Doming, either left or right, is usually because of a   dull, bent, incorrect sharping, or most often the blade is not set to true perpendicular to the turning axis.



Cool!  Good for you.  But it's good practice for the rest of us to lock down the carriage when parting.  The OP needs help with good practice, and that one thing that might just be the ticket for him.

Agree with the rest, good points.


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## samthedog (Jun 3, 2015)

coolidge said:


> Part it off with a band saw then face it in a 2nd op.



This is what I do. Unless I am working on a tube that I need to part off, I don't even bother with a parting blade anymore. The bandsaw is faster and wastes less material. It also means I don't need to worry about using a follower rest. Plenty of ways to skin that cat if you have the toys.


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