severe chatter issues

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jason30809

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Im new to posting but have been lurking about and reading for about a year but I have finally expended every avenue of problem solving I can possibly think of so I bring this question to you guys to see if anyone can help. Thanks in advance for your time and help. I have an atlas 10f lathe with an aloris style QCTP and a 6.5 in 4 jaw chuck and use mostly HSS but have had this problem with both HSS and carbide tooling. Over the past 8 months or so i have been fighting severe chatter while attempting to parts of just about all materials and diameters at just about all feeds and speeds. I have tightened all gibs, disassembled the head stock to check bearings and the spindle and both appear just fine. I have also tightened the pre load on the bearings to the point where run out is minimal while pushing on the chuck but eventually tightened to a point where the motor was working pretty hard to turn the spindle and the belt was wanting to slip so Backed off to as little run out as possible while still allowing the spindle to turn freely. All bolts that mount the feet of the bed have been properly tightened and shimmed 16 gauge sheet metal. This is a problem I didn't have with this lathe the entire time I have owned it but literally one day it was parting smoothly and the next the chatter was so bad it felt like major damage would be done if i continued the cut. The only piece of info they may be helpful to those with alot of experience with these lathes is that when cutting soft stuff like 6061 with say 1.75 in OD, the chatter disappears once i get down to about the last 1 inch of diameter of the parting operation. Guys i appreciate any help anyone can give. Im so frustrated and fed up with this problem that I have thought many times about just getting rid of the machine because if I cant part off then the lathe is pretty much useless for my needs. Its never been crashed while in my possession and no catastrophic event has taken place. I just dont get it and cant figure it out. I have looked for anyone in my area that is proficient with these machines but have come up dry. If a video is necessary i would be more that happy to provide that. Again thanks for your time folks. I forgot to add that the chatter starts only when the tool actually begins to grab the part and really start cutting. You know, the point where there is enough pressure to go from the tool rubbing and making powder chips, to the point where the blade engages the material and begins to produce properly formed chips. when those chips should start, instead the chatter begins forcing me to slow my feed and never be able to actually cut the material or feed the tool properly.
 
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Not sure what is going on but let's start the discussion and the other guys can jump in.

So, if I understand correctly, you are experiencing severe chatter when parting off. The lathe parted well until one day when it didn't. You've adjusted and checked to make sure the machine is tight but it still chatters. The only positive is that when you reach the last inch of material, the chatter disappears. The chatter occurs at all speeds and feeds, which I take to mean you've tried different speeds and are power feeding with the cross slide to part off. Given that the lathe didn't chatter in the past, I assume you know that the tip of the cutter must be on center and that the blade must be perpendicular to the work; you are not a newbie at this parting stuff.

Is that about right?

I'm going to assume that your blade is sharpened correctly, you know to use lubricant and you know how to part on your lathe - sounds like you do.

It seems to me that something is moving. It may be the cross slide, compound, tool post or tool holder but something is moving.
  • I'm wondering if the gibs in the compound or cross slide are okay. Because they're tight doesn't mean the gibs are adjusted evenly along their lengths so maybe check them?
  • Is the tool post solidly mounted to the compound? With wear and tear the surface the post rests on may no longer be flat and that can lead to movement.
  • How well does the tool holder lock into the QCTP? How vertical is the blade in the holder? If it is the type of holder that cants the blade at an angle, the block that locks the blade can tilt the blade so you have to be careful to align the blade vertically.
If all this stuff checks out then I'm not sure what is going on. The fact that chatter resolves might suggest your parting speed is too high. As you get to the inner part of the cut, surface speed slows down and that suggests your speed at the start of the cut may be too high. You can try slowing down and see what happens. You can also try feeding manually to see if that helps; parting should be a smooth operation with a slight resistance to feed. Some guys feel that you should feed with a lot of positive pressure but I've never found that to be necessary when the set up is correct.

One more thing to check is the tool height. It works best when the tool is dead on center. If the tip is too high then you're rubbing; if its too low then you'll dig in. Many guys line up the tip with a tailstock center but that is not accurate enough. Either use a tool height gauge or machinist rule (trap it between the tool and the work and adjust height until the rule is vertical) but the tip needs to be on center.

Okay, maybe some feed back from you and we can narrow it down further.
 
I could have started a couple of radio stations with all the chatter I was getting off my lathe .

Here are a few of my suggestions before we get going off at a tangent & missing simple connected things ..

Think & check every thing through logically in a set order

Make sure your tool is sharp & correctly ground . Cut the eye off a big sharp pointed darning needle . Set it in the chuck . point out to the tail stock , run the lather check it is running true .
Now check the cutting edge of the tool against the point of the needle .. is it accurately set in line ?

It's best to slide the tailstock out the way to the right , remove any tools in it and eyeball it from the tail stock along the center line axis . Not having your eye lined up can give you a lot of error ...I tend to put the cross slide to just past the needle tip looking from above the bed ...head over the axis . Almost make the needle point touch the cutting edge of the tool using the compound or saddle . Then wind the cross slide back till I can see it is aligned from above and along the horizontal axis from the tailstock view turn the chuck by hand 360 & recheck things . It took me a while to realise that I could be a few thou out if I only did it from one axis or was not dead in line with the axis .
I have also checked ( & had to reset ) that the tailstock is dead on the chuck centre by putting a needle in the chuck & the tailstock chuck ... I found it easier than trying to use a steel ruler / scale as I have a busted left shoulder & back problems .

Have you also used engineers blue & the base of the tool post to check that the flat surface it sits on is perfectly flat .....in all directions including caddy corners ( the diagonals ) ?

My new to me lathe had several thou of hump where someone had pulled a hardened bolt up the mounting / Tee slot to secure the old lamp post tool post . When I tried to part or do an internal bore the pressure of the cut was enough to ever so slightly cause the tool post to rotate a few thou or more as well as busting a few parting blade it chattered a lot .
It took a while to find out why it chattered so much , but after I discovered I'd cut cone shaped holes & cured it as above things got better ...much better .

Do you also have enough thread on the anchor bolt to ensure things are fully home when you have tightened the tool post . ie Is the bolt shank is stopping the nut going fully home ?

Tool grabbing into the metal .

My little experience tells me , it is often is the result of cross shaft free play being suddenly taken up usually by the cross gibs not being tight enough & or the saddle gibs being slack .

... Have you checked the ways of the lathe with a decent steel ruler / scale to see if they are badly worn ?

When parting do you lock the saddle to the bed ( you should ) as well as ensuing that the gibs are not slack / too easy to slide ?

When you start the parting always wind the wheel out so the tool cutting edge is a 1/4 " or more away from the work piece then gently start to advance it to the work piece & into it at an even speed , so it takes a thin curl un blued by heat off the piece rather than chipping it off . Use both hands to try & keep the tool moving at an even speed once you get taking material off .
 
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Awsome questions guys, i think i can narrow down a few things that might help yall figure this out. The tool post seems to lock just fine and always has but i have not check with layout fluid i have tightened gibs from the saddle to the compound from being nearly unable to move the saddle cross feed and compound to being easy to turn. I always hand feed in the tool and always lock the carriage im sure if i used powerfeed the tool would definitly catch and either break off or cause the part to ride up on it and stall the machine. I probably shouldnt use the word "chatter" to describe whats happining because that suggest an annoying noise and bad finish. What im dealing with is a horrible vibration that makes you think "something major is about to break". its to the point where yesterday the nut holding the compound handle on vibrated off the machine and onto the floor. I litterarly cannot part anything at all with this thing. Its to the point of feeling dangerous. Something is seriously wrong here and I just dont understand it. Another thing that may help out is when im feeding the tool in, right as it gets to the point were the tool would bite into the material and start producing nicely curled chips, the feeling i have in my hand coming from the cross slide handle, is like the cross slide is kind of floating toward the material. Almost like reverse backlash if that makes sense. At least it seems like im getting that feeling from it but i could be wrong because the vibration is so intense. Like i said earlier, i dont know if its possible to upload videos on here but if that would help i can try to record this massive vibration. Thanks again guys
 
Put your left hand on the front of the compound slide and pull firmly toward you as you advance the cross slide with your right hand. If that changes things, the parting tool is dragging the cross slide forward and itself into the work. There is always some backlash between the cross feed screw and nut. Possible causes are parting tool not on center coupled with gibbs too loose. Parting tool not ground right.
 
as far as parting tool positioning i have tried dead center and a little below and as far as the grind goes i get the same result with standard parting blade ground to about 5 degrees front rake and stoned smooth, an 1/8in ground tool and indexable carbide blade. Something is physically wrong with some part of this machine i.e. something worn, broke or loose or something like that. I know the basics always have to be asked but trust me over the last few months i have tried every form of tool and geometry that has ever been written in just about every book and if the gibs get any tighter i wont be able to turn the knob. something else is going on. Its hard to describe how violent and severe the vibration is. this is really really bad
 
just tried pulling back on the cross slide and no dice. still major vibration.
 
OK, you have to pull back pretty hard for it to make an audible difference. It isn't a practical solution, but when you described the "floating feeling", I realized that I had had a similar problem while trying to use a full 90 degree form tool to put a large radius end on some 1" diameter copper electrical connectors that I was trying to make. The cross feed crank felt just like it does if you have a fair amount of backlash in the cross feed, put the crank into the middle of it, and then rock the crank back and forth. Takes virtually no force. I think that something is different about either your parting tool or how it is being held. But I don't know what.
 
just to see what happens I locked down all gibs pretty much as tight as i could get them including the cross slide and went for a cut in 1.75 in aluminum. This appeared to have made a difference. the vibration was still present about 1/5 of the way into the cut but it was far less severe than it was. The problem is that where i had the gibs tightened to was more of an experimental setting than a functional setting because i really had to tighten then down tight......real tight. I think this takes my worrys out of the head stock and and into the carriage/cross slide/ compound/ QCTP.
 
That sounds like some progress. Hopefully now you can try one, or two at a time and figure out the source of the movement.

One other piece that I have NOT seen mentioned is the spindle speed. There is a HUGE difference between the surface feet per minute at a diameter of 1/8 inch and a diameter of 2". SFPM = dia.[in] /4 *RPM

See my comments here: http://www.hobby-machinist.com/threads/soft-jaws.55689/#post-460870

Please let us know how it goes.

-brino
 
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