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Bluedog
04-02-2012, 08:28 PM
Just learning here, but I've done a good bit of turning and threading on my Grizzly 4003 with good success but everything turned near the headstock. Even good results with 416SS. Now I'm trying to turn a 1" bar of 4140 about 20" long between centers and getting a lot of chatter. I'm using AR Warner HSS inserts, high sulfur cutting oil, and tried it with and without the follow rest. Any suggestions? What speeds and feeds should I be using for this?

Thanks for any help.

RussZHC
04-02-2012, 08:52 PM
Very much learning as well...I did not see a steady rest mentioned, I think I would start there...IIRC the ratio I have seen is 5:1 and 1" diameter and 20" in length is a bunch more than that...if I did my math correctly its not a lot of weight...not all that fast but not threading slow either (I will let others give you numbers, past calculations have been "off" so...) and trying to keep held tight between centers may not be satisfactory.

The other thing that maybe coming into play here is with those sizes, the heat could be making it very tight between centers by the time you are nearing completion and I suppose if it wants to revolve then stop from being too tight... (that's just an opinion with little experience to back it up)

Doozer
04-02-2012, 08:56 PM
I don't know what a Grizzly 4403 is.
Say the size, like 10" x 36" so we know what category of lathe we are talking here.


--Doozer

J Tiers
04-02-2012, 09:31 PM
With the follow rest is best chance at that fairly large length/diameter. Especially between centers, with NO help from part of the work being "swallowed" in a chuck.

if you have got chatter with the follow rest in place then.....

1) The follow rest is not adjusted right

2) you have a lathe where:
a) A slide is simply not fitted well to it's mating part,
b) A slide is not gibbed at right snugness,
c) A slide is extended too far
d) tool is stuck out too far
e) toolpost is not rigid, or is rocking on swarf, non-flat compound etc.

3) something I have not mentioned is amiss (dozens of things).

jkilroy
04-02-2012, 09:44 PM
Ok, what RPM are you turning it? Does it chatter over the entire work piece? Are you turning between a chuck and tailstock center or actually between two centers with a dog to drive it?

If is just chattering in the center and not near the ends then your follow rest is not adjusted tight enough.

If you are turning between actual centers is the tailstock center into the work tight enough? If not the work can push away from the cutting tool causing all sorts of issues.

Is your tool height on center? Above center the tool can rub causing noisy chatter. Below center the tool can push away from the work, similar issue.

Whats your depth of cut? (DOC) Sounds funny but taking too light a cut can cause chatter.

What speed are you feeding the tool? You are cutting towards the headstock?

Dr Stan
04-02-2012, 10:14 PM
As others have already pointed out a follower rest is just about required for your set-up. Make sure it is adjusted properly.

I'd also use a high speed steel turning tool as you can use a much smaller nose radius and thus reduce tool pressure and consequently reduce chatter. You will also need to "get under" the existing chatter otherwise it will just continue.

Since you're turning between centers I guess you need to achieve minimal run out. Is it possible to chuck up on the with about 1/2 of the shaft inside the spindle? You could make a support collar to keep the shaft centered inside the spindle.

Bluedog
04-02-2012, 10:39 PM
More info:

12x36 lathe
Turning between centers with a dog driving it.
RPM: I've had the best results at 360 RPM
DOC doesn't seem to change anything.. tried everything from .002 to .012
Feed rate is .0057
Cutting towards headstock.
Tool is on center.

While I'm not getting a great finish anywhere, the chatter only starts up occasionally, and not always in the same place. This is the first time I've tried using a follow rest.. how is it adjusted properly? Do I really tighten it very tight? I am using AR Warner indexable tooling with HSS inserts. I'll check the gibs, I didn't think of that since this is the first time I've had any problems with chatter, but it is the first time I've tried turning between centers. Sorry for the questions, it's just that I'm approaching my final diameter and I'm running out of things to try to get a good finish.

Thanks.

GadgetBuilder
04-02-2012, 10:51 PM
You might try a vertical shear bit:
http://www.gadgetbuilder.com/VerticalShearBit.html

They provide a good finish on most materials and I haven't had one chatter, although that doesn't mean it cant happen.

John

J Tiers
04-02-2012, 11:30 PM
You might try a vertical shear bit:
http://www.gadgetbuilder.com/VerticalShearBit.html

They provide a good finish on most materials and I haven't had one chatter, although that doesn't mean it cant happen.

John

Plus they give a good finish..... good suggestion.

I'm gonna guess this is a single-phase motor machine...... 3 phase usually responds to changes.

Carld
04-02-2012, 11:37 PM
A shear cutter is fine for finish cuts but won't handle anything over .004" DOC at .004" feed 150 rpm.

Try using a 60 deg V nose HSS cutter with a tip radius if 1/32". Experiment with the rpm starting with the rpm and feed your now using.

Adjusting a follower rest on buggered up metal is a real trick. If the surface is rough forget the follower rest or a steady rest.

Something I do to stop chatter on long work is to lay a 2' long 2x4 on top of the shaft while I hold the extreme end. Don't push down on it, just let it rest on the work. Sometimes it helps to raise your end of it a few inches above the shaft.

I hope your using a live center in the tailstock. Also, as mentioned, the heat will expand the metal so you have to check the tightness of the center often.

Oldbrock
04-02-2012, 11:56 PM
In an emergency such as that I often pick up a hammer and rest it on the shaft changing the harmonics. Works sometimes, but to leave hands free make up a roller that mounts on the toolpost so that it rests on the work could kill the vibration. Also use lots of top rake on the tool to minimise tool pressure. A chunk of lead wired to the toolpost so that it rides on the work could help. I'ts all about changing harmonics. I have lead slugs in a rubber strap that I fasten around auto rotors and drums on my brake lathes and you better not forget it or you get chatter every time. Good luck, Peter

Arthur.Marks
04-02-2012, 11:56 PM
As my recent experiences may attest, I suggest a possible culprit is that he's turning 4140: http://bbs.homeshopmachinist.net/showthread.php?t=53257 4130, 4140, same practical difference. Try turning the rpm up. It may be a simply difficult situation as I found 41XX steels like comparatively higher speed and higher feed and a fair DOC, but you're working with a long length/diameter ratio.

Notes on steady rest - loosen fingers and dab the work and finger tip with a hi-temp grease. Don't press the fingers into the work when setting position. Just lightly come to rest on the work; then tighten. Every time you stop the lathe, dab a little more grease if it looks like it has thinned. To be honest, I have extremely little experience with follower rests, but would suggest the same basic procedure as above. It is not meant to really press against the work so much as "steady" the work when it tries to deflect from cutting forces.

Forrest Addy
04-03-2012, 02:07 AM
Yeah, try the hammer trick. The follow rest should control chatter. Set it so the jaws are bearing just after the tool.

If you still get chatter and it happens only at certain places I wonder if the problem isn't a type of resonance other than tool induced work/tool mass/elasticity excitation - chatter. Is your lathe single phase powered? Does the machine hum or emit a constant note while running. Do tools laying on the machine or in the chip pan sometimes buzz or vibrate?

If you get any yesses, look at vibration originating with the single phase motor. A machine tool is a closed mechanical system. If the motor vibrates, the vibration propagates through the lathe cancelling and reinforcing depending on localized dynamics. Machine borne vibration may be recorded by the tool onto the finish leaving an appearance of the grooved surface of a phonograph record. It's very difficult to make an efficient compact single phase motor without them amplifying the motor's tendancy to vibrate.

If you wish to pursue the motor question, take a spare week-end day and experiment. Loosen the motor bolts and insert isolate the motor with hunks of hose from the lathe itself. Then loosen the belt so it can slip somewhat while still delivering enough oomph for light cuts. Run a few operations past experience has shown to promote chatter. If the problem diminishes but returns when you restore the motor to its original state you can make a good case that there may be a problem with the motor itself.

The cure is a smoother running motor. Many machine tool owners have reported smoother finishes and less chatter when they replaced their single phase motors with DC motors and electronic drive or AC three phase motors and VFD.

BTW I refer to "vibration" knowing confusion may emerge. Vibration comes from many sources. The first that comes to mind is mechanical unbalance of rotating parts. I'm not referring to this; most motors come from the factory in excellent mechanical balance. In an AC motor magnetostrictive vibration is possible. The alternating magnetic fields in the motor causes the iron to very slightly change volume emitting a 60 (or 50) cycle musical hum. This is not the my assertion either. The vibration I refer to is what I have come to call "cogging". A single phase motor has no rotating magnetic field. It's an alternating field that the armature rotated in. When lightly or partly loaded the magnetic field snatches at the armature accellerating to to near sync RPM or maybe over-speeding slightly. The next cycle may even DEcellerate the armature. The result is a semi-chaotic tortional vibration part in the stator and part in the armature kinda like a gasoline engine with an intermittant miss. The RPM may average constant but might err +/-5% for part of a revolution. DC and three phase motor do not have this "cogging" or tortional vibration. The DC motor is smoothly commutated and has armature slots slightly skewed to make its rotation even smoother. A three phase motor has a smoothly rotating magnetic field.

Don't get lost in theoretical considerations or tracking the faults of the motor. If your machine tool motor causes a big enough problem for you, that's enough all by itself. Replace it with a motor featuring smoother power delivery.

Finally, Old Tiffie is absolutely positively forbidden to contribute to this thread. Not one single colored sketch or pages of alleged math. Got that?

rohart
04-03-2012, 07:02 PM
Chatter is a word the describes any kind of vibration whereby the tool and workpiece come together and move apart regularly at some frequency.

If you take note of the frequency, it can be a great help in deciding which components are flexing.

You are machining a fairly heavy chunk of steel. Unless the chatter is of a pretty low frequency, you might find that what is flexing is the tool/compound.

Have you ever heard squeal ? Squeal is a high pitched vibration - 1khz or higher - and is something very light vibrating. Usually it's the tool itself. It can be a thin workpiece.

Keep an open mind. When you get the chatter, start wedging, levering against things. If you lean on something and you take up play, or feel vibration, then what you're leaning on may be the problem. Some solve tool chatter by anchoring a heavy lump of steel or lead as near the tool as possible.

Just some thoughts.

Doozer
04-04-2012, 11:57 AM
If you are using a ball bearing center, try using a dead center and see if chatter goes away.
--Doozer