Anti singing!

[bucketboy]

I was turning a long thin tube of 60mm dural today, no matter what speed, feed, or tool I tried, it started to sing like a demented Canary, at a frequency that was very uncomfortable. I tried with and without lube and even tried to damp the noise with a rag held on the tube, still the same ??? Then I noticed a length of foam pipe insulation laying on the work bench, I cut 50mm lengths off and with a piece of dowel I started to pack the inside. I put the tube back on the lathe and tried again.............. absolutely no noise............no ear ache.............perfect finish...............result ;D

Bb

 

[rake60]

Happy to hear you found the answer BB.

In an industrial setting I have seen large lead balls that would roll freely
in the bore used to dampen the chatter. One guy used a loosely rolled
chunk of rubber mine conveyor belting for that. Yet another would stuff
the the bore with coolant soaked shop rags to eliminate the harmonic
resonance.

I don't think of those things in my home shop.

Thanks for the wake up call! Thm:

Rick

 

[cfellows]

I was turning a long thin tube of 60mm dural today, no matter what speed, feed, or tool I tried, it started to sing like a demented Canary, at a frequency that was very uncomfortable. I tried with and without lube and even tried to damp the noise with a rag held on the tube, still the same ??? Then I noticed a length of foam pipe insulation laying on the work bench, I cut 50mm lengths off and with a piece of dowel I started to pack the inside. I put the tube back on the lathe and tried again.............. absolutely no noise............no ear ache.............perfect finish...............result ;D

Bb

Sounds like an idea for a new music instrument! If it's loud and uncomfortable, the younger generation will love it!

Chuck

 

[Tin Falcon]

Tube and pipe has its own needs when hand forging the end needs to be stuffed with wet rags if not a tube or pipe acts like a chimney and draws the heat right to the ends and you can not touch it without tongs or getting burned.
Tin

 

[BobWarfield]

This is a good post to remind ourselves that chatter is a harmonic or resonance phenomenon.

We always think of it as some weakness in our setup or machine. While that is true in some sense, it misses a larger point. Since we have a resonance, we can try to fix it in two ways.

First, and the obvious approach, is we can focus on making things stiffer so they don't vibrate. This is a pious thought well worth having.

But, don't forget the second possibility, which is that we simply need to move the source of vibration to a frequency outside the resonance. Sometimes this is very easy to accomplish. My lathe has a treadmill motor with speed control knob. Just twisting the knob (first faster, surprisingly, then slower) often knocks out the resonance. Packing material in tubes changes their resonant point. Damping is different than increasing rigidity. I dampened my mill by filling the base and lower column with epoxy granite concrete. There is a measure of improved stiffness, but the damping, or tendency to absorb vibration rather than just not vibration is potent.

Haas CNC mills have a special code that lets them dynamically vary the spindle speed by a small range when dealing with a chatter-prone operation. That's very clever, and I keep waiting to see someone make a little electronic circuit they can switch on to vary their VFD for the same reason.

Lastly, there is a whole body of literature about analyzing a particular machine and tooling combination's chatter characteristics. They put microphones on them, study the frequency of the chatter, and then figure out speed and feed combinations that can be much faster and avoid the chatter. Clever!

Cheers,

BW