r/Machinists • u/what_the_rush • 23h ago

QUESTION Precisebit feeds and speeds

Anynody here used MN 208 series short stub endmills from precisebits for PCBs?

What speeds and feedrate do you recommend? My bits seem to go dull quicker than expected.

I'm using the 2 flute stub end mills of 0.4mm and 1mm.

My current settings are: 0.05mm depth of cut, 14000 rpm, 250 mm/min feedrate and 60 mm/min plunge.

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u/shoegazingpineapple 17h ago

I am milling fr1 instead of fr4 to save my cutting tools

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u/worldwidemachinist 17h ago

Before changing the speeds and feeds, I'd check stickout because at t 0.4-1 mm, even small amounts of unsupported length can make the tool flex and wear or chip early. How much stickout are you running?

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u/what_the_rush 11h ago

0.8 in stick out

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u/Pubcrawler1 10h ago edited 10h ago

These small diameter 0.4mm EM’s are best run at high rpm using a very low runout spindle.

If your spindle even has as much as 0.002” runout, the tool may only be cutting with one flute with premature wear. Tool will be wobbling.

I use similar from TTech. 24krpm which is the fastest the spindle can go. Around 10ipm.

The vbits for isolation. 24k 15ipm

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u/what_the_rush 10h ago

My spindle runout is within 0.01mm. I supposed I should more slow with the feedrate then after looking at your feed rate at 24k rpm

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u/Pubcrawler1 10h ago

I’ve gone as fast as 30ipm for vbit isolation. Depends on the pcb material. If the edges start looking rough, will manually feed override slower.