If you have ever ground hardened tool steel on an automatic surface grinder that uses flood coolant, you probably have noticed that the coolant cools the workpiece to a much lower temperature than the ambient air temperature in the room. This means the workpiece has contracted in size, while your height gage or gage blocks have not.

So, you might think your block is exactly the correct size, but the next day you discover that it has mysteriously grown in size. The bigger the block, the more the size changes.

In the past, I guessed from experience how much change would occur, and this worked OK. But then came to some mold cavity blocks made out of D-2 tool steel. Anyway, you machine this tough stuff, it is a problem. In fact, maybe it should be illegal!

What I started doing with great success, was keeping gage blocks set up next to the workpiece while it was being ground. Obviously, you can’t have the correct amount because you would be grinding them when you got to size. You could always set them far enough away from the grinding, but I think it makes more sense to keep it close for the sake of accuracy.

You then use a very small granite surface plate and your height gage with a dial indicator to physically inspect the height of the workpiece. Keep everything clean, use good practice and you will find this method works very well.

You might also use a magnetic base on the wheel guard with an indicator, but I find the vibration of the machine disturbs my measurement.