Spindle Speed Variation Control

[gunda]

Hi guys
Can anyone explain how does the spindle speed variation control actually helps chattering? What I understood from the manual is that it changes the spindle speed with a parametrically designated amount at a parametrically designated increment, but how do we find the correct amounts for the parameters?
Thanks!

[fordav11]

as far as I know changing the chuck speed up and down continually puts additional loading on the tool. the extra load stops the chatter. I don't have that on my machine but when required I do it manually at about 1 second intervals +10% then -10%, continually. Works fine here.

[txcncman]

Spindle speed variation helps reduce chatter due to harmonic vibration. Not sure I can explain it better or more simply than that.

A more advanced explanation would be along the lines of as a part (or tool) is turning, it has a certain vibration resonance. This is a point where it acts like a tuning fork. The closer you are to the resonance RPM, the more chatter can and usually does result. Interestingly, this resonance RPM usually seems to be near the same point where cutting tools leave the best finishes. The purpose of varying the RPM above and below this resonance point is to keep the tool engaged with the material at or near its peak speed, while not allowing the part time to vibrate. Another way to think of this is like a guitar string. At a certain length, the string will naturally vibrate at a certain frequency. If you continue to input other frequencies into the string, those frequencies with clash with the natural vibration frequency, thus canceling each other out. The above also applies to a tool vibrating, even when the part is not.

What are the parameters? Trial and error works best for most people. I am sure there are some formulas to calculate this based on part material, hardness, size, length, and RPM. I have no clue where to find those formulas.

[gunda]

Thanks
I was thinking of something similar and according to some publications found in the web I got similar results, however there was too much physics involved and it had to be very carefully read and understood. I hope I can give it a try tomorrow.
Here is a link to what I read
http://wumrc.engin.umich.edu/junni/p...uppression.pdf

[gunda]

Very good explanation txcncman, exactly what I read!
When using this in Okuma there are 3 parameters (P, Q and R) which the SSV function (M695) uses and I was wandering how to obtain these values to make it work for a particular task

[txcncman]

What do P, Q, and R represent? Maximum, Average, and Minimum surface speed? Actual RPM? Percentage of RPM?

[gunda]

Here is a page from the manual. P, Q and R are found at one of the parameter pages or assignable using VFLTQ, VFLTP and VFLTR

[fordav11]

it sounds just like Okuma (i.e. over engineered and under-tested).
it doesn't need to be that complicated.
you could do the same thing with user task. feed a small amount while speeding up 10%, feed the next small amount while slowing down 10%
the best solution is to fix the root of the vibration problem using machining skill and knowledge, not apply snake oil potions and bandaids to the festering wound.

[txcncman]

Is this another cheat code in the video game of machining?

For most applications of this technique, I think you will find P and R will usually only need to be 2 seconds or less and Q at 20% of less. You mileage may vary.

[Green Button]

This option is very useful. We use it with long boring bars, no vibration

[fordav11]

we just use devibe bars with interchangeable heads. sure they are expensive but they are pure quality and last many many years (we have some that are over 20 years old and still work fine). I rarely use a normal boring bar.... devibe all the way

[gunda]

Green Button, from your practice how do you set the parameters for the spindle speed variation function?