Here are a few tricks that may help smooth out your machining operation when it comes to holding a close tolerance.

Setting a Bore Gage
There are many ways to set up a bore gage. All of the different methods have advantages and disadvantages. High quality setting rings are probably the most desirable tools to set up bore gages with, but they are extremely expensive. Using gage blocks stacked up with end plates or jaws to create a required dimension is functional but these tools take time to set up. Probably the fastest way to set up a bore gage is with a micrometer, however, this is the least accurate method. This inaccuracy is caused by the inherant backlash between the screw and the nut of the micrometer. If a micrometer is accurately calibrated, it will read a precise dimension only when there is a certain amount of force applied to the anvils of the micrometer. This is what happens when we actually measure something. The two surfaces of the part being measured allow for the take-up of the backlash between the nut and screw. This backlash is the primary cause of problems when setting bore gages with a micrometer. Dial up a number on a micrometer with nothing but air between the anvils and the distance between the anvils is NOT what you read on the mic.

If you've got a spindle lock on your mic., the solution to setting a bore gage with a micrometer is simple. Let's say you want to set your bore gage at .xxx diameter, find or wring up .xxx gage blocks, then set your micrometer to the gage blocks. Lock down the spindle of the mic before sliding the blocks from your mic. You now have a standard to setup your bore gage. Using this method, you should be able to hold one or two tenth tolerances all day long and it is very fast.

Set Your Z Depth in a Hurry
Have you ever tried to dial up one tenth on a knee mill? Not an easy thing to do, even with a quill mounted dial indicator. Besides being a finicky operation, something gets lost in the translation between the handle, the quill and the indicator. Using the dial on the knee handle is a little more steady but it is difficult to determine exactly how much you have dialed up. Take a look at the picture below. This is the same indicator and mag base I used in the write up about getting an old worn out lathe to cut straight and accurate (July 2003). This is easy to set up and is extremely accurate, need a tenth? Dial it up.

Fine Tune your Surface Gage
I probably use my surface gage more than any other measuring instrument, especially when we are making EZ-TRAM's. The problem that I had with my surface gage is that when I attached an indicator on the spindle, a good distance from the base I lost the ability to accurately dial up anything closer than .0003". To solve the problem, I made a larger diameter adjusting dial and replaced the original smaller diameter dial. Take a look at the photo below. The dial is 2" in diameter and .187 thick and knurled on the O.D. After we made this change, dialing up .000050" is no problem.