severe chatter issues

Hi everyone, reading through this post and noticed that tool heights mentioned here were set at center. I was taught to set it at 2-4 thou above to counteract spring in the blade and therefore it will sit at center under load. If at center or below, when under load it will definitely chatter as it cuts and springs back up into position. Or starts to rub rather than cut if sufficiently low. Also there is a change in top rake of a few degrees which may have minimal impact depending on the material.

Jason says "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."
My reply to Jason is - this is the window where you have your speed and feed correct.
If you watch a cnc lathe parting off, it speeds up the closer it gets to center. Realistically we cant do this with our machines, we set speed to cover the entire operation and adjust feed to suit.

"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"
This is another issue I have had with apprentices mainly but also tradesmen, they back off their feed when the chattering starts. They should be increasing their feed at this point until they see their little clocksprings coiling up and jumping out.
At the end of the day machinetool rigidity and correct setting of tooling in conjunction with optimum speeds and feeds gets the job done quickly and the nerves are not so shattered.
 
most of the chatter I find is from too much speed. my story is on a 12x36 frejoth lathe. turned my front disc rotors on my lathe and could not stop the chatter at the slowest speed. got it as smooth as possible with emery cloth and thought it would work. so reassembled my brakes and tested them. well they worked too well, almost went through the windshield the first tap.took them back off and re pulleyed my lathe to 30 rpm ( from 60 rpm) and recut them much better, but first I tried all the tricks like wrapping a bicycle inner tube around the part this helped some but not enough. moral to the story doun use disc braked if the surface looks like a fine file bill
 
guys im back. I was never able to find the problem and finally gave up on it. After 5 years of it sitting idle and the work I need to use it for piling up, I decided to do some searching and see if i could find an answer and came across this thread. Does anyone on here live around Augusta ga? I have come to the realization that I need to somebody to see this with their own eyes and you would be surprised at how hard it is to find old school machinist that know these old machines like the back of their hands. If anyone lives around here it would be great if you could take a look. I feel like something is cracked or broken or worn. I really think one of yall would find the problem within minutes. All i know is whats not causing the problem .... its not tool height or feeds or speeds because i have literally tried them all. Geometry of parting tool doesn't matter either because i have tried them all. I have double and triple checked the easy stuff like that. now im convinced something is broke i just can figure out what. Someone mentioned the chatter decreasing as i got closer to the center of the parting operation so they think it could be a feed speed thing... I have tried just about every combo of feed and speed i can think of but something else that happens towards the center of the part being cut off is the force pushing down on the tool also decreases and i think that might have some relationship with why the chatter decreases toward the center of the cut. Anybody that can help would be so greatly appreciated. thanks
 
Hi Jason,

If you cannot find a local, knowledgeable volunteer, perhaps you can take video with your phone and post it here.
I have successfully posted *.mp3 videos to this forum.

Two other things:
1) On my 9" Southbend I initially tried parting with a thin blade(1/16") thinking that the cutting forces would be reduced and it would lessen chatter.
That did NOT work!
I have to use a thicker parting blade(3/32"), and I believe it has to do with the stiffness of the tool.
I was surprised the difference that small looking change made.

2) I have seen once where the t-nut that holds the tool post to the top slide was too thick. It caused the tool post to be able to rock on that small mating surface. Once the t-nut was cut down the problems went away.

-brino

edited to fix widths.
 
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Check your upper compound slide where the tool post mounts. I've seen a couple of these that were cracked in the T-slot area. I finally went to a steel version.
 
Hey brino, 1/16th is smaller than 3/32nd in my book.
Swap your numbers around to prevent confusion mate.
 
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