Live Center / Dead Center?

[British Steel]

Many of us avoid the use of the word "mil" because it can cause confusion. Properly speaking in our field, a mil is 1/1000", but some metric people use the word mil as a short form of millimeter or millionth of a meter (0.001mm). This is actually a micrometer (it used to be called a micron).

Nope, that's a micrometre, a micrometer is one of those fancy G-clamps ;0)

Dave H. (the other one)

 

[T Bredehoft]

Back to indicating chuck and tailstock.
1) normally chucks are expected to be not much closer to zero than .003
2) No indicator should be expected to not react to gravity as it is rotated about a horizontal axis.

Use your indicator without rotating it about a horizontal axis, it will not be accurate if it is rotated about a horizontal axis. To verify this, mount a magnet base on the face of a chuck, put the indicator on the top of the chuck and rotate it 90º.

To align chuck and tail stock, a test bar, center drilled on one end and turned to one diameter for its length, should be used. Mount it in the chuck and check that it is concentric to the spindle, shim the bar or move the chuck until you have zero (or nearly so) runout at the chuck, then engage the live center with enough pressure to turn the center with the chuck, snug but not TIGHT. mounting the indicator on the saddle, and against the test bar, first check the top for parallel the ways. Once this is correct, check the side toward you from end to end. If it is not parallel, adjust the tail stock sideways and check again until there is no runout.
Without a test bar, it can be done by turning a piece between chuck and live center, but it's not as quickly accurate and takes a lot longer.

 

[bfd]

what tom above is referring to is bar sag this occurs because of the indicator weight and any supporting weight that plays on the indicator you can still do it that way aslong as you mount the indicator the exact same way when you test it as to when you use it. take the indicator and mount it on a solid bar 4" pipe works well. zero it on top and rotate the pipe 180 degrees. read the indicator on the bottom say .002" out bar sag is then .oo1" but when you use it you still figure on a .002" reading so if you check your tailstock and you get.002" you are on center. the bar way is much simpler. but I thought I would explain it anyway bill

 

[bfd]

bill I got the lazy comment from an old time machinist I apprenticed to way back when. his saying was necessity is not the mother of invention but laziness is. so he would say we invent our own language cause we are lazy don't want to say 1 tenthousandths when we can say 1 tenth bill

 

[Tozguy]

Use of the word 'lazy' bothers me too. Although 'lazy' is commonly used to mean a variety of things but there are better more accurate descriptives for what drives us towards simplicity and expedience.