“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:
“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…
Doug says:
If the machine vibrates without cutting, it could be the gain parameters of the servo motor. If they are not set correct the motor fights itself to hold position. During the cut I would check the spindle taper for wear (bell mouth), and or drawbar tension. Rule out the cutter first.
Noel Deveau says:
In turning, tools being on center is a must to eliminate this type of chatter associated with turning. I have found that there are many other conditions that lead to excessive chatter. As some who was doing a lot of milling in my time I noticed that correct rpm, depth of cut, feed rate, tool diameter and length come before the rigidness of the machine. The biggest factor that I found was tool or work piece rpm. excessive RPM causes chatter. I also found that that in turning the right depth of cut and appropriate tool geometry was critical. Don’t rough with a finishing tool. Machines whether they are small or big are going to have some harmonic issues. Placement and the way they will be secured in place is critical. We typically would create at new pad of concrete which was professionally leveled with anchor bolts secured in the pad. thee machine was leveled and bolted down. chatter can be controlled but its a fine line
speakingofprecision says:
Thanks for sharing your experience Noel.
speakingofprecision says:
Thanks Doug, Your “check the cutter first” sentiment is in agreement with those of this post. thanks for your insights as to what else may be going on.
Dan says:
Our biggest problem with chatter comes from stock removal amounts. With multiple cuts on the same surface, previous cuts taking too much material cause finish cuts to sometimes have chatter, allowing the tool to “skip” on the surface being milled.
Ken DeRoche says:
While we were colleagues many years ago, Bill was just one of my many mentors. He has valid points; primarily that in most cases the machine is not the culprit. In my years I’ve learned that the rest of the “system” has a lot of details that, if not considered, will induce chatter. Some, including machine, are included in the paper found here – http://www.mfg-labs.com/filedownload/Papers_Presentations/Leigh%20AHS%20paper-old%20version.pdf .
speakingofprecision says:
Especially when some work materials work harden. Calculating proper removal rates for sequential operations is an important aspect to assuring operations don’t get ambushed by “glazed” or workhardened surfaces.
Thanks Dan.
Miles
speakingofprecision says:
Thanks for the great link, Ken.
Miles
Jeremy says:
I have to agree the the general consensus here on this blog post. I have been in the machine tool industry for more than 10 years now both hands on and researching them. Checking the cutter first makes sense. I can’t tell you how many times I have seen large machines dismantled only to find that the problem was not in the machine itself, but a minor component of it which could have been repaired without a weeks worth of work and down time.