Hello, this is Randy. You ask a very good question. This is a long writing to explain, so hang on. What I read from your question is – is it chatter, if so is it the cutter or the part that is causing the chatter of your machining operation? So, the best way to look at this is to determine the frequency of the problem occurring. Is it from the cutter or is it from the part or is it both? This is pretty simple to solve but you will need the proper equipment to derive the answer. What is required to be known are the natural frequency of the cutter at the tool tip and the natural frequency of the part being machined at it’s intervals of machining.
I will try and break it down to understand. Let’s look at chatter from physical aspects first. Everything upon this earth has matter, which has a natural frequency. Ever seen those commercials of a glass breaking with the tone of a person singing? The glass breaks because the frequency of the singer reaches the natural frequency of the glass and shatters it due to matching the natural frequency of the glass, resonance, causing the glass to resonate at it’s natural frequency. You can’t hear it because it is to high a frequency. The glass shakes from this frequency, which is chatter by it’s own natural frequency. How about those guys driving next to you and your car shakes from their sound system in their car? Those are low frequency vibrations, which carry high amplitude, causing your car to shake. This gives you an idea of the force of frequency vibrations.
This is the same property in machining. This is called the Tooth Pass Frequency. The cutter has a natural frequency and the part has a natural frequency, period. The cutter natural frequency does not change but the part frequency will, due to material being machined from it. The more mass of the material the lower the frequency, the less mass of material the higher. Therefore, the more machined of a part say as to make it more thin walled, the higher the natural frequency it will produce. Now, to determine, which is causing the problem. Certain frequencies of the cutter, machine and part could cause resonance, which I do not fully understand. You can be advised from experts in the field at my site.
The easiest way to determine if your cutter or part is causing a problem is to do an impact test. Special equipment is required but you can use this equipment on all your machines, on tools, on parts on the machines themselves. You will need to see my site for these products. Called the MetalMax System, from MLI.
Once you know the natural frequency of the cutter at the tool tip you will be able to determine the proper rpm to run chatter free of the cutter on your machine, the higher you reach the number 1x the deeper you can go. Natural Frequency x 60 divided by number of teeth will be your optimum rpm and depth of cut, divide this by 2 for the next rpm, 3, 4, etc. if your machine tool can not reach a certain rpm. Once you reach the 5x on this calculation it will probably do no good to match this tooth pass frequency. This equipment will also tell you the flexibility of the cutter being examined to tell you the depth of cut, which you can to optimize. It will also tell you the natural frequency of the part to determine which cutter to use by way of frequency analysis.
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