“If you have a flat tire on a car, you fix the tire, you don’t look at the tire balance, vibration of the motor, or the paint job…”

Thoughtful follow up to our post on Vibration, Harmonics and Chatter   from William R. Shaffer,  VP at Conicity Technologies.

Conicity provides specialized edge prep solutions for our industry.

Here’s what Bill had to say:

So should I look at the engine mounts, the shocks and struts, the paint job, or should I just fix the tire?
So should I look at the engine mounts, the shocks and struts, the paint job, or should I just fix the tire?

“Perhaps there is some chatter that is a function of machine harmonics, but I have not seen that as of yet. My feeling is that the machines are designed and built with the high level of technology, much higher than the technology that is associated with the design of the cutting tool.

“Cutting tools used to drive the machine tool industry to higher levels of capability because the capability of the tool always exceeded the machine.  Spindle speeds and rigidity often lagged tool designs and machine tools were not able to take full advantage of tool capability.   That was then. Not today.

“Bottom line, machines have surpassed the tool capability and tools really have not made and significant breakthroughs to push the machine building community.

“I deal with chatter on a daily basis for our customers.

“We have successfully cured severe levels of chatter in metalcutting by addressing the micro-geometry of the cutting tool.

“At the end of the day, vibration starts at the tool because perhaps the tool geometry being suspect, friction, perhaps feed rates combined with tool design, but it starts with the tool.

“If the machine hums and vibrates when it not running a workpiece, then you do have a problem.   If you have a flat tire on a car, you fix the tire, you don’t look at the  tire balance, vibration of the motor, or the paint job…

“So the question I would like to explore is “what do the people that make the machine tools feel about their machines having inherent vibration and harmonics that create issues in machining?”

“What do the folks who make the machines have to say about this?

“Is the picture that many may have in their minds that “the machine has it’s own set of harmonics, so does the material that is being processed, perhaps even the tool,” valid, or not?”

Your comments please…

Sometimes the best information that you can get about your machining process requires your sense of touch to feel the vibration.

In many shops, the definition of a problem is  “something that is not easily seen.”

Unwanted vibration in our machining processes can cause variation, unsatisfactory surface finish, and dimensional variability. Unwanted vibration is not easily seen.

A friend who plays fingerstyle guitar sent me a link to a video that got me to thinking about the role of vibration, harmonics, and chatter in our shop processes. The genius of the video is that it makes something not easily seen- easily seen!

Don't try this with your iPhone in your machines...
Don’t try this with your iPhone in your machines…

The video is convincing  that the sounds we hear are tied to a wave form on the string.

The sounds that we hear from our machining processes similarly are tied to a ‘harmonic’ or standing wave  vibration in the workpiece or in the tool and machine. Sometimes, this sound  is lost beneath the noise of other processes in the shop.

So when a machine operator complains about variation while machining, I ask him to lay his hands on a safe part of the machine and tell me what he feels.

If it is more like a Rock  Concert than a smooth constant vibration punctuated with noticeable jolts from the indexing, I suggest that rather than looking at material, we look at the machine itself and the rigidity of the tooling as the likely cause of the variation being experienced.

  • Mass in machines is used to attenuate this kind of unwanted vibration.
  • Wear in machines or any kind of looseness can decouple the tool from that mass, promoting vibration, and thus variation.

In the guitar photo and video, the displacement of the string appears to be far greater than we could imagine possible.

And it turns out that it is an illusion created by the sampling rate of the CMOS camera ‘shutter’ in the iPhone Camera.

Regardless, it serves us a great picture of the unseen and reminds us that in noisy shops, feeling a vibration on a machine may tell us more about the process than our control charts or reading of the tools.

Link to YouTube Video

Problems with the hole often get machinists to blame the material. In my experience checking the drill and machine run-out will  almost always  show the root cause.
There are many ways that a drill can cause problems for a machinist. Many times we look for evidence on the drill itself- chipped corners, edges, or margins. Sometimes the evidence is on the workpiece. And often that means a call to the material supplier.
 But just because the clues appear on the material doesn’t mean that the material is the cause of the problem. In drilling, there are four clues that say “check drill run-out and toolholder alignment and rigidity.”
Four Clues

  • Vibration
  • Tapered Holes
  • Oversize Holes
  • Eccentric Holes

Drill run-out will cause excess vibration when drilling. Run-out can also affect the concentricity and roundness of the hole.  Run-out can result in the hole becoming elliptical, tapered, and affect tolerances needed. A savvy operator checks drills for run-out before putting them in the machine. And a savvy set up technician always checks for run-out in the toolholder or chuck when starting a job.

Well, it is indicating the drill...

 Toolholder or machine caused
However, the cause of the run-out may not just be a bent drill- the tool holder, chuck or spindle may also be to blame. In addition to indicating the drill bits outside the machine, check that the drill chuck and machine spindle is running true.
Length can be an issue
Finally, make sure that the drill is inserted to the proper depth in the chuck, and that the chuck is not overextended. I went on a claim for steel that would not “drill straight” to find a 3/16” drill held in the biggest Jacobs style chuck I had ever seen being held on a # 4 Morse taper. The entire assembly was nearly the length of my forearm, and swinging around on a short cycle time Acme job, the drill never hit the next part on center due to the vibration and lack of rigidity. A more appropriate chuck installed at a shorter length solved this “material problem.”
When the workpiece shows the evidence of the problem, I humbly suggest checking the drill run-out.
 Photo credit