CNC: why end mill breaks? why fails?

CNC: why end mill breaks? why fails?
Published on Apr 18, 2021 by Jiaolyulu

I break 2 18 flat end mills

picture of prototype

The first one breaks because when I am doing the contouring of the inner cut, I want to save myself the trouble of tabs, So I just use 18 inch end mill to do all the inner contouring and when it is finishing the hex hole, the inner hex want to come out and this add force to the bit unexpectedly cause it to break.
picture of prototype

The second one breaks when I am running out of my time and makerspace is going to be closed. So I just try to increase the step down value to make it eating wood more aggressively. Then it breaks.
Luckily, I previously bought 2 18 inch end mill so I actually did not break any bits in Makerspace. But I also learned lesson from it.

Why my CNC pocket is not accurate?

I have a struggle time finding all the pocket I got for the oak wood is a little bit smaller than I expected so I took a lot of effort in sanding every gap I have and every hole I pocket. Then I discover it has something to do with the settings of file.

picture of prototype

By default, my pocket setting would left stock to leave checked as shown in the picture. This would make the pocket 0.02 smaller than expected.