Before I post my first message on this forum about the topic I would like to make the comment that now retired and getting set up to resume personal projects [suspended while ‘’life got in the way’’], I have a great deal of respect for the pool of knowledge available here and the veteran folks that have spent a lifetime learning their trade and craft of metalworking – so thank you for taking your time to help foster folks like me.
Although my background is in the furniture design and manufacturing area, and education, from first-hand experience I’ve come to learn there are many basic concepts of materials processing, engineering, assembly, troubleshooting – to name only a few – that are easily transferable to almost any other activity.
To keep my message brief but relevant, troubleshooting as I se it often requires a person to quickly think on their feet by sorting through a vast mental library of successes and failures to conclude what might be the most likely and simplest gremlin in the mix.
I lack the knowledge to chirp in about feed, feed rates, or other likely mechanical problems because at this point I am apprenticing on this forum; however, I agree with XD351 when he says that [paraphrased] ‘’here are possibilities – now you figure it out’’. Also, I believe that HWF offers a very interesting possibility that, because the root cause is virtually invisible, such problems of vibration can easily be overlooked or not even considered at all.
So, what is ‘’transferable’’ [as mentioned above] is the term ‘’resonant frequency’’ or otherwise described pretty much as the frequency at which an object will naturally and inherently vibrate due to its physical properties and certain energy acting upon it. As a stringed instrument player and instrument set-up tech, I’ve had several years in learning about energy/sound/vibration transmission and many of the problems unwanted vibration can create with stringed instruments.
With regards to the second photo showing the ‘’weird wavy pattern’’ I am not necessarily stating that vibration is the culprit but only that it could be a very quick troubleshooting option – that is, try the simplest and least expensive possibility first; then, if not that is a cause, go to the second possibility.
A loose motor, sloppy belt, line surges, lathe connected to the same circuit as a fluorescent light, worn bearing, incorrectly sharpened or positioned cutting tool, wooden floor, floppy metal parts (such as a lathe back panel), lathe with very little mass, etc., etc., could all be contributing factors conducive – each as a singular vibration or when combined as vibration ‘’harmonics’’ – i.e.,, multiple overlapping vibrations, or ‘’beats’’ (also described as ‘’wolf tones’’).
Just saying…… that if Bryanbdo’s ‘’weird wavy pattern’’ is due to vibration sources as explained above, then the face of the bronze turning I a real and actual recording of that vibration in the same way as we know a musical recording to be.
Hopefully this posting may contribute to the forum, to the learnin’ process, and to identify machining problems not easily seen.