9X20 Lathe chattering problems

[ccm]

I've got the 9X20 Lathe, from Enco... and I'm having an elusive problem with it recently which is dumbfounding me completely.
I use it regularly, have many many different cutters that I use on it, main use it sees is turning 6061 AL. It had the stock tool post holder up until last week when with the stock holder the chattering issue just seemed to start one day, last time I used it, no chatter. So I machined a block of solid 2.5 X 2.5 X 5" long, to directly mount the Bit holder itself directly to the cross slide. It's mounted down with 4 1/4 grade 8 bolts & nuts now. I took the carriage assy. all apart, cleaned, regreased everything, reset & adjusted the gibs to rule that out. Now it's all back together, there's no play to be found, and I'm still getting a chatter, leaving that wavy look to the finish. There's no play in the chuck spindle, and not a trace of backlash / movement in the cross-slide & toolpost holder. My only guess at this point is that it's either the bits are too dull, or I'm not at the right cut-height. I've tried making passes at dead-center on the work piece, and about 1/16th below.
Any suggestions ? I'm up the creek without a paddle & creek at this point.

thanks,
Art

[mxtras]

Loose gibs on the saddle and/or cross slide. Most likely the slide.

Tighten up a little, would ya?

Scott

[ccm]

ok, so loosen them up....hmm, I wouldn't have thought to do that. come to think of it, prior to pulling it off, there was a few thousandths of play in the cross slide, but logically thinking, I adjusted it out with the gibs. Granted it is alittle tougher to turn the screw, but not by that much. Hell, I'll try anything at this point I'm so frustrated with it, not to mention I've got a couple of jobs that have fallen way behind.

thanks for the " other set of eyes"
sometimes that's all it takes...

-Arthur

[rustyolddo]

Tool bit flex. Tool bits extended too far from the holder.

Improper Tool rake angle, you didn't mention what kind of tooling you are using.

Improper centering of the tool bit. It should be dead center with the center of the stock there are widgets for doing this but you can just use the live center then make a facing cut to be sure there is no tit left in the center of the stock.

Dull tool bits. A test is to drag the cutting edge of a tool bit on you thumbnail, if the edge wants to dig into your nail, it's sharp. If it wants to slide, it's too dull.

Too light of a cut, you should take a heavy enough cut to pressure the carriage to remove any slop in the system. Light cuts can create oscillation & resonance & chatter. With that size lathe & stock, you should be able to take .100" in one pass.

A litle more info about your tooling and perhaps a pic and I could tell a little more.

[Mcgyver]

Originally Posted by ccm ok, so loosen them up....hmm, I wouldn't have thought to do that. -Arthur

and so the comedy of errors starts - mxtras said loose gibs - which I took to mean he's saying loose gibs are your problem, not to loosen the gibs

chatter, as I understand it, is basically a standing wave. Cutting force and rigidity (everything, workpiece, machine, overhang, etc) determine how susceptible you are to chatter.

what determines the cutting force and rigidity? every variable you can think of. many have been mentioned already, and more. a little faster or heavier cut might change the frequency and stop chatter, but I've always found I've got to reduce force and/or increase rigidity - everything mentioned does one of the two.

you don't tell us the size/shape/speed/feed/depth of what you are cutting?

from a practical standpoint if you are using correct tool geometry, like rusty says sharpen the bit then try backing off speed, feed or depth of cut and see what happens

[kong]

Most things seem to be covered, but you may want to try lowering the spindle speed a tad. Too high a speed combined with a light finnishing cut can often cause chatter.

[mxtras]

Oh, my! Yes - I am sorry if I was confusing - I meant that loose gibs were one possibility many folks forget contributes to chatter.

They might be loose. You should check to see if there is play using an indicator and tighten them up if necessary....hence the "tighten up, will ya?" sarcasm/pun.

Scott

[Joey]

Originally Posted by ccm leaving that wavy look to the finish.

I had the same problem on an XYZ lathe and it indeed turned out to be the bearings. Although they seemed fine by levering the chuck with a block of wood
and checking with a clock guage (.001-.002"). If you run the spindle at around 400 rpm and mount an old clock touching the chuck you should see intermittant readings with sudden extra movement.
Ours was a loose fit between bearing OD and Housing. But only in one area of the diameter.

If you mount an `opposite hand` tool upside down in the Toolpost and run the machine in reverse, the load will pull any slide play upwards and stop the bouncing effect on the bed. This will eliminate there being a problem with your gibs etc.
I also use this method for deep grooving.

[haysys]

Hi and yes, I too am having the same or similar problem on my Grizzly 9x20.

A "spiral-chatter" is my way of describing it, though there is no noticable chatter or noise during the cutting process. It appeared rather suddenly after a year of good finish and performance. I too have tightened, sharpened, adjusted cutter height at and below center, and shortened my tool overhang to the point of barely missing moving parts.

Art, have you solved your problem yet? If so, what did you find the solution to be?

Thanks!!

[ViperTX]

Thank God, I bought a Lathemaster instead of the ENCO or Grizzly I was considering.

[underdog]

Joey,

Please give us a little more detail on the "clock gauge" method. I never heard that one.

Also, how did you find out it was the head bearings when the indicator indicated no play?

[underdog]

Haysys, I see you're on. Any luck with your chatter problem?