Sudden Onset Chatter Issues - riding the struggle bus and need some HELP, please.

[derf]

Raise the tool height...carbide cuts better above center.

 

[MyLilMule]

I appreciate all of the responses so far. A few of you have suggested a different tool.

Perhaps it wasn't obvious, but I have had this lathe working for 3 years. I haven't changed a thing. I tried three different tools (each with a different tool holder, insert holder and different insert geometry). I also tried a different insert with a different coating. Different nose radii. I also tried a HSS tool. Same result.

I also tried different RPMs and feeds. Same result, just different amplitudes.

The tool height is perfect on center. Same way I set up every tool and have never had an issue, until a week ago.

Something is loose or broken, I just can't seem to figure out what. What else can I check short of disassembly of the headstock?

 

[MyLilMule]

Here's a video using a live center in the tail stock. It's "better" but not at the larger diameters. I was taking off a good chunk there for a bit.

The last two cuts were at .050 DOC and .025 DOC and you can see the crappy surface finish. The smaller diameter looked fine.

 

[mattthemuppet2]

that's weird. If it was something loose in the headstock then you would have really heard it when you hit that large depth of cut at the end of the small diameter cutting. Instead it cut quite happily, breaking a nice chip. I was actually wondering what the problem was at that point!

Too me it looks like a speed/feed/DOC issue. I've had that spiral harmonic chatter before. Try increasing the DOC at the same speed and feed or decrease the speed at the same DOC and feed. Does it do the same thing with a sharp insert, like a polished for alu one?

Do you get the same problem hand feeding? What about in other materials (eg alu)?

 

[GT-6 Racer]

I think Matt is right. Speed/feed/doc, material. I’ve had this problem on my SB too. Gummy low carbon steel is the worst. Try a chunk of 1144. See if the issue goes away. I’ve had some steel I had to go to a shear tool to get a finish. On my Monarchs, I just push the feed a little or DOC and the chatter goes away on mild steel. One other thing is chuck jaws. Could they need reground? bellmouthed jaws can allow chatter I understand. Have a collet chuck or maybe try between centers.

 

[piper184]

Check the belt pulley on the motor to see if it is tight. Mine came loose one time and caused all kinds of strange things and noises until I figured it out.
Heck, check all the pulleys to make sure they are tight on the shafts. Also a belt that is missing a chunk or starting to de-laminate can cause all kinds of racket on a car engine, might do something on a lathe too.
The idea of trying it between centers will at least eliminate the chucks, although you said it happens on both the 3 and 4 jaw, so not likely the chuck. Just another thing to eliminate.

What happens if you drop down into back gear? Wouldn't be the proper speed, but it might give you a clue.

 

[MyLilMule]

Here's some brass an aluminum. Brass did not do well, aluminum did better, but surface finish is not what I had been getting before. It was a mirror finish with the same RPM, feed and DOC.

Guys, you're not hearing me, I have machined a part from the EXACT PIECE OF STOCK with the same RPM, tool, insert, feed, depth of cut, etc. THE EXACT SAME PROCESS and did not have this level of chatter.

 

[MyLilMule]

I think I am going to just disassemble the headstock. Pull the spindle and check everything. It's possible a thrust bearing blew up and I just can't see it. - AFTER experimenting with more feeds and speeds.

 

[tq60]

Single or 3 phase?

If 3 phase, VFD, Rotary of Static Converter.

Line frequency is 60 hz, you coukd do some math to determine if related, start with 3600, (60 hz for 1 minute).

Divide by rpm.

See if in a "slice" you have that many bumps around the circumference of the slice.

Single phase motors have more of a tendency to have a rumble due to the way they work, 3 phase is much smoother duty a static converter uses a cap to start the motor and then it runs similar to single phase.

Single phase motor or 3 phase with static converter matched to the wrong material will give you this.

Sent from my SM-G781V using Tapatalk

 

[MyLilMule]

Single or 3 phase?

If 3 phase, VFD, Rotary of Static Converter.

Line frequency is 60 hz, you coukd do some math to determine if related, start with 3600, (60 hz for 1 minute).

Divide by rpm.

See if in a "slice" you have that many bumps around the circumference of the slice.

Single phase motors have more of a tendency to have a rumble due to the way they work, 3 phase is much smoother duty a static converter uses a cap to start the motor and then it runs similar to single phase.

Single phase motor or 3 phase with static converter matched to the wrong material will give you this.

Sent from my SM-G781V using Tapatalk

Single phase. And unless this motor suddenly went bad, it's been fine for 3 years.