centerline depth unpredictable

With no apparent reason, when using Centerline either on a project's top most surface or in a carve region the depth of the letters varies. On any given project that depth will be the same through-out but it may be quite shallow or too deep to read. The 90 degree bit does touch the slap plate ok. Once in a while the machine will say that the depth is not the same as when it first read it but not always. I have noted a rattle type noise starting too be heard before the bit starts to contact and at the end of a carve as the bit leaves the wood, but so far I can't find anything loose. Should I pull the flexible shaft out and check for some abnormality? Even with the noise/rattle the carve looks ok as far as crispness although on feathered areas I'm getting a maybe more roughness.

Depth not matching is a sign that you have something wrong in the Z....

A frozen Z Roller Rail Bearing that is slipping rather than rolling.
A loose Z Roller Rail Bearing.
A dirty Roller Rail with wood sap stuck to it making a speed bump causing touch errors. Especially when doing text with the short bit going into DIRTY rail areas not used for the 1/16th carving bit.
Dirty Z Belt Cogs
Dirty Z Encoder
Loose Z Encoder
A FSC Cable going bad loosing pulses.
A bit slipping in the chuck.
Not watching the touch and missing that is STOPS SHORT of touching.
HEAD LEVEL... Place a wide board and touch the bit to the board on left and right side and read the Z Data numbers for level check.
Or place strip of paper on wide board both sides and tug paper. Loose one side then it is high.
Flex is SAGGING and hitting the black cover.

AL

Most fonts are made up of 2 parallel lines. Centerline uses a midpoint between those lines and plunges the V-bit to a depth to fill up the space between those lines so depth will vary as the space between the lines varies. With some fonts, the lines will almost merge together in some places resulting in a very shallow depth. In other places the lines could be farther apart than the diameter of the bit resulting in a depth that is very deep. Because of this, some fonts carve well and others do not. Try changing fonts to see if there are any differences.