My Endmill ‘screams’

2 minute read


a 2-flute upcut bit for wood I’m working on my first-ever CNC milling project: A spoilboard that offers holes and t-nuts for workholding purposes and that supports an x-y fence and a tool length sensor.

I never used a spiral endmill before, but I bought a 6mm 2-cut upcut solid carbide bit with 21mm working length. And it just sounds awful. On my hand-router, I was exclusively using high-speed steel straight flutes and larger bit diameters. They sounded similar to the router itself, a loud but confident hum when cutting through material.

Beginner’s confusion

With this upcut bit, I followed the manufacturer’s recommendations of feeds and speeds for hard wood on my medium density fiberboard workpiece (depth per pass: 6mm, feed: 3500mm/min speed: 24000rpm). But obviously I do something wrong because there’s a terribly loud, high-pitched, uncomfortable screaming/hissing noise when I cut.

I gradually turned up the feed rate because I was under the impression that screaming bits “are not working at full capacity”. I ended up with 9100mm/min (!) where it was better, but still…

Endmill screams while ploughing through MDF


After the 15min job was finished I touched the endmill - Flutes are as good as new and the bit is barely warm to the touch. Hm. Also the router motor did not sound stressed. My steppers made the machine to literally plough through the MDF (smoothly and without any issue), I even had to turn the extraction up to not drown in dust. Also the result looks good to me; tolerances are tight and the cut is as clean as I’d expect it to be - much better than I could have done by hand.

milling in MDF - spoilboard t-nut slots

Open questions

So what am I doing wrong? Is this sound “normal” for a small spiral flute bit? Does MDF need totally different parameters than hard wood for silent cutting, e.g. much less spindle RPM? Do I need to set a different ploughing strategy in my CAM tool?

Hold on tight, I’ll be checking with a forum to get some advice…

Questions answered

OK, I have an answer from the bit’s manufacturer (in German). This sound is normal for small endmills specialized in cutting wood. Well then. Probaby I should build a housing for my machine and buy some very good earplugs. 😬 Let me quote another tool manufacturer:

“Two-flute cutters are always noisier than single or three-flute cutters of the same size. Their 180° opposing cutting edges lead to additional vibrations of the cutter due to the alternately engaged cutting edges. In return, they offer better wear characteristics than single flute cutters and allow better chip evacuation than triple flute cutters.”

Comparison: Same material, different bit

Here’s a comparison video to judge just how different cutters can sound in the same material: 14mm 3-flute endmill face cutter, 10mm shaft, S5500, F7100, Z0.3, Fside 90%

14mm face cutter calmly levels my spoilboard.

Just to test things, I used a spiral strategy in my CAM tool which takes 50% longer than the typical lawn-mower strategies, but this way there are no visible cutter paths on the finished material.