I noticed a few sporadic sparks flying when face milling a 20mm wide piece of mild steel plate.
Cutter and setup:
IMG_6429.jpg

From a different angle:
IMG_6431.jpg

The mill is small, Optimum BF20 (DIY LinuxCNC conversion):
IMG_6432.jpg

Surface finish:
IMG_6433.jpg
The surface looks worse than it is, feels very smooth using finger nail.

Using a 50mm insert cutter running at 1600-1700RPM with a feed of 100mm/sec and cutting depth of 0.2mm. Using WD40 as cutting compound.
The mill specification states max cutter size is 63mm, but that's optimistic at best and a blatant lie at worst, the machine really isn't rigid enough for large diameter (>20mm) cutters.

I see a few sporadic sparks during the cut, not many and mainly near the start/end. The sparks are not the star shaped type you see on a grinder, just a single bright orange glowing small blob.
The tramming of the mill is not perfect, but very close.

My questions:
Is this normal? What makes it spark? How can I prevent these sparks?

Any help/opinion/views would be much appreciated.

Thank you for reading my post.
Attached Images




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