On the higher quality micrometers (mics) they will often be able to measure to .0001 of an Inch. Where as a regular mic can only read to .001 of an inch. Reading this style of mic takes a certain amount of finesse and experience.
In this photo below you will that on the internal barrel there is an additional scale that runs vertically. This scale is numbered 1 through 0.
On this scale each number represents an .0001 of an Inch. The 1 representing .0001 and the two representing .0002 and so on. This measurement is referred to as ‘tenths” in the machining world. If a person were to say “One and a tenth” they actually mean .0011.
Reading these is accomplished through figuring out which line on the external barrel best lines ups with the internal barrel. In the following photo you can see that the 4 on the external barrel best lines up with 1 on the internal barrel. This results in a measurement of .0001 or 1 tenth.
It is best to take a measurement several times when dealing with this scale. You can literally measure dust thickness which can result in about a half of tenth variance. I always measure three times for consistency.
In the above photo you can begin to see how this becomes subjective. I would call this two tenths because the four on the external barrel lines up better than the three. This is subjective and is the reason why I measure multiple times.
In this photo above it is clearly two tenths. It is important to note that the I am using for lining up with on the external barrel is not relevant. It will change the only thing I am looking for when I measure this way is which two lines match up the best.
This photo above tells us that the measurement is nine tenths.
This photo is hard to tell and I would call it 4.5 tenths. Neither number three or two is exactly matching to the internal barrel and they are equally spaced in my opinion. This happens quite a bit in precision machining and again is the reason that I suggest measuring multiple times.
In this final photo below you can see that the three on the external barrel lines up almost perfectly with the 5 on the internal barrel. This results in the reading being five tenths
The important take away when measuring things this small is to be consistent with the tension you place on the micrometer when closing it. The better quality mics will have a ratcheting tension knob that will give you the same tension every time. In the photo below the tension knob can be seen on the top of this depth mic. Notice that it is smaller diameter than the rest of the external barrel.
Fecke – KJ4ZRZ