Very high frequency tone while cutting

[jessicat (Jess)]

Hi ya’ll. I got some new cutters today and loaded up a test cut for the one I was most excited about - Harvey Tool’s #769116-C8 0.25" Variable Helix Chipbreaker.

I started small with an Adaptive Clearing toolpath at 1400 SFM, 90% WoC, 8.4% DoC, and 0.001" chipload. Compared to Harvey’s recommendation of 0.00551" chipload (which my Nomad can not yet actually go that fast) this seemed very safe to start with.

I hit start and noticed two things

• This was far too safe of a cut and I could feel the bit’s disappointment in me. It may as well been cutting through butter.
• My cats freaked out and hid under my bed as despite the cut generally being incredibly quiet, there was a very prominent high pitched tone.

I recorded this short clip while it was cutting:

Very high frequency tone

I also opened it up in Audacity and you can very clearly see the tone (as well as the spiral toolpath which is pretty neat)

The peak frequency is ~8.3kHz, with it’s 2nd harmonic also being pretty prominent.

The spindle is running at 356.5 Hz. 8.3kHz is not a harmonic of this (its in between the 23rd and 24th). What is causing this? Is something about to explode (other than my cats ear drums)? I’ve not used a variable helix bit before so maybe this isn’t unexpected?

[flynnjs (Jason)]

Might be worth reducing the RPM to get 1000 or 1200 SFM, which is lower than the datasheet presented value but it would give you a better chipload if you are at max feed rate.
Also, try changing the stick-out from the collet slightly to see if that moves a resonance.

I wonder if this is the best cutter for a Nomad. The 1/8th" is suited for the smaller chipload and is cheaper. A two flute would also give you a better chipload.
Also the chipbreaker element is likely to go unused because your DOC is less than 20% and the first breaker notch on the flute is approx that far up.

Having said that, your finish is looking really nice and I need to get a spindle like this for my N3.

[jessicat (Jess)]

@flynnjs

Might be worth reducing the RPM to get 1000 or 1200 SFM, which is lower than the datasheet presented value but it would give you a better chipload if you are at max feed rate.
Also, try changing the stick-out from the collet slightly to see if that moves a resonance.

I’ll try that!

@flynnjs

I wonder if this is the best cutter for a Nomad. The 1/8th" is suited for the smaller chipload and is cheaper. A two flute would also give you a better chipload.

I also bought the 1/8" chipbreaker and 1/4"+1/8" for their 2 and 3 flute high helix cutters

@flynnjs

Also the chipbreaker element is likely to go unused because your DOC is less than 20% and the first breaker notch on the flute is approx that far up.

Yeah I figured, I want to try a full axial engagement cut but wanted to start off simple to avoid immediately snapping the bit in half, which is definitely not something I’ve done multiple times with brand new bits.

Edit: I doubled the chipload to 0.002" and the tone is still there but its quite a bit softer

[jessicat (Jess)]

Whoops I accidentally had the feed rate set to 111%. With 0.002" chipload the tone is (audibly) gone.

No more tone

23rd and 24th harmonic are still standing out enough to notice, but its not that bad sound-wise.

[jessicat (Jess)]

This bit makes an absolute enormous mess, seems to launch chips in a full 360° radius. BUT its insanely quiet with that cut, which had an MMR of 0.61 in³/min and left quite a decent finish for a roughing job. 10/10 highly recommend.