Ten things to not do when checkering or in-letting a stock;
Work when tired.
Work when you are not paying attention or mind is else where.
Work with dull tools.
Work in poor light.
Work in bad ergonomic position, bent over to be less wordy.
Work with less than perfect means to hold your work.
Work under a deadline when you know there is not enough time to do the job right in such a short time.
Forget to checker or inlet under magnification when possible.
Never checker finer than the wood will allow. Some wood will not hold checkering much finer than 18 LPI.
Don't try to use the electric checkering system on anything finer than 18-20 LPI unless the wood is hard as a rock and straight grained.
Plus as a bonus, always end the night with a good dose of Ibuprofen to ease the aches of being tense over work for so long.
These are rules that I have learned by making the mistake of violating each of them over time. On the bright side, a stock job, that goes off the deep end, does burn quite nicely in the fireplace. Order new cutters and let the job wait until they come.