for CNC: Decision aid
My Endmill 'screams'
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.
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:
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.
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…
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. 😬
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.
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