PDA

View Full Version : Lathe chatter problem



bob ward
10-02-2011, 03:16 PM
I was surprised by a serious chatter problem when turning a length of 57mm 2.25” round on my generic 14 x 40 lathe today. First I have to say I don’t know exactly what I’m turning, but I have a lot of it and use it frequently with good results, its fairly tough, probably somewhere around a 1045.

Usually I just turn short lengths in the headstock, 1200 RPM, 3mm .125” DOC turns beautifully, great finish. Today I had a 450mm 18” long piece in the lathe, and even right at the tailstock I had serious chatter until I backed right off to 300 RPM and .5mm .020” DOC.

I had everything clamped as short and tight as I could, swapped between my live centre and a dead centre, had a 16mm .625” 60° centre hole in the end of the round, mounted the fixed steady, tried different inserts all to no avail, 300 RPM and a light cut was the best I could do.

The questions are:- Is this as good as it gets? Is this a limitation of my lathe? Have I overlooked the obvious?

http://www.machineryhouse.com.au/L179D

Scottike
10-02-2011, 03:36 PM
Mystery metals can be mysterious, most likely you picked up a chunk that became work hardened in a previous life, if you've had success with the material before.
Try a different chunk, or turn that one end for end before you go chasing problems with your setup or lathe that might not be there.
I try to stay away from mysterium type metals just for that reason.

edit: Often the work hardened area is only a few inches long, where a bearing was seated, an area that got hot, etc.

P.A.R.
10-02-2011, 04:09 PM
Hi Bob here is a check list is your machine bolted to the floor,have you checked your jibs.Do you have a heavy live center.Have you tried your four jaw or vise verse.Try your steady at the 1/3,1/2,3/4, points to quell vibration.Use your follow rest in addition to your steady.Try HSS instead of inserts.I have found the steady at the half way point or a clamp on weight(dog) works well.

rohart
10-02-2011, 04:22 PM
You should take notice of the frequency of the chatter. The round you are turning is a pretty hefty piece, so if the work, and parts of what is holding it, are going to vibrate, it will be at a fairly low frequency.

If the chatter frequency is higher, and the same frequency you might get turning something lighter and of a smaller radius, then the play that is causing the chatter is in the tool, and parts of what is holding it, compound etc.

Have you got the ability to jettison the compound and mount the tool directly on a block that is anchored to the cross slide ? If the chatter is the same, that would rule out the tool end of things. If it's different, check out the cross slide and the saddle.

uncle pete
10-02-2011, 05:20 PM
As a general rule for chatter, You increase the feed per revolution and/or drop the speed. That almost always works for me. I think at certain times you get into a situation due to material type, diameter, length, cutting tool type and shape etc that chatter becomes a problem for no apparent reason.

Pete

Doggie
10-02-2011, 09:20 PM
Ah yes, Chatter with lathe work can sometimes be a real challenge and problem. One thing that I have found to be real successful is to install a tool-bit in upside down and run the piece backwards. I know that this sounds stupid, but try it and see if it will help.
Hey man now don't laugh at me for saying this, just try it before you criticize me for saying it. Your friend, Doggie :cool:


This is also a good way to forming type cutter to make a grove, corner radius, big thread on a long screw, ETC

Shuswap Pat
10-02-2011, 10:02 PM
Try to move your tool above center, so the nose rubs a little bit. I used to make edger and gang saw arbors - 6" diameter x 6-8' long - 4340. They were a bit%h to keep straight, true and chatter free. One of my 'european associates' said move the tool above center, and it will eliminate the chatter and it did. The other things you can try are turn the tool upside down, and run the spindle in reverse, use a 4 Jaw ( as already suggested), also paper or light cardboard between the jaws and the work, will dampen vibrations. Interesting - when I taught apprentices at a Polytenic Institute in Western Canada - none of this kind of stuff was in the ciriculum. I had a couple of 4th Year Machinist apprentices that said they knew evrything (in the books), and thought they were God's Gift to the Machining World. Then I also had a few others that showed me they were going to be great tradesmen, but didn't try to tell me how good they were.

Patrick