Jo Block Stacks

The fundamental use of gage blocks in the machine shop involves using them as a stack. That is a collection of gage blocks put together using its natural tendency of surface tension to create a stack a specific length that is accurate to a relatively high level of accuracy.

To start off we must first examine the standard 81 gage block set. We have 4 series of gage block sizes in the set.
  • 9 Blocks from .1001 to .1009 in .0001 steps.
  • 49 Blocks from .101 to .149 in .001 steps.
  • 19 Blocks from .050 to .950 in .050 steps.
  • 4 Blocks from 1.000 to 4.000 in 1.000 steps.
As you can see we are sort of limited in stacking the gage block sets. As we only have one of each. However that may seem as a disadvantage, this one specific set will allow one to reach any size from .100 all the way up to 12.000 in steps of .0001.

See when we stack gage blocks we go backwards from our tenth unit (remember machine shop tenth not normal tenth!) all the way up to our inch unit using as few blocks as possible. Since I can show numbers all day long and it will make some sense to some to others little sense I have prepared a calculator output of pictures showing the steps involved for the visual learners as well.

In my example I am attempting to find the gage block stack up for a 5 inch sine bar that needs to be set to a 60 degree angle. So first you would type in 60 on your calculator:

Now we will press the SIN button on our calculator to find the sine value of a 60 degree angle. Notice how the "sine bar" and the "sine function" is used? Its because our hypotenuse is fixed at 5 inches and we wish to find the opposite side where we will put our stack of gage blocks. Our adjacent side is actually our surface plate, so we do not have the ability to control that side.

Now that we have the conversion factor we can actually multiply by 5 which is the hypotenuse of our triangle we are creating using the sine bar.

Which gives us the stack size of the gage block set that we require:

Now that we have the size we require for our gage block stack, we can get to work and create the
stack. One note before we do, my calculator is set to 4 decimal places with the use of the "FIX"
button, not all calculators have this feature, so remember when using a calculator for figuring out
the height of the gage block set, we only care for up to the 4th decimal place which is our tenths.
Anything smaller then that we cannot measure.

Additionally the tolerances of our sine bar make any more digits unnecessary as most commercially purchased or shop produced sine bars are accurate in sizing to .0002".

So our first job is to eliminate the tenths. Since we have 1 tenth, and our gage black set only has
tenths that are added to a 100 thou (.100) block, we will use the .1001 block to eliminate the tenths.

Which gives us according to the picture to the right of our .1001 input on our calculator a resulting
stack of 4.230 left to account for.

So now we must eliminate the 10s of thousandths of a inch position. This position along with the
thou mark should always be eliminated to either .X00 or .X50, due to the fact we can go to the 2nd series of blocks once we get down to 50 thou.

Since we have 30 thou to eliminate to make the tens of thou position a zero, we will use a block
from the second series, specifically the .130 block to continue.

Which gives us a resulting answer of 4.100 left to go.

Now we will eliminate the hundreds of a thou position. This we can do with a single gage
block, using the .100 gage block.

Now that we have eliminated the hundreds of a thou position. Our resultant is simply 4 inches, which we can use the final gage block required for our set using the 4 inch block from the 4th series of gage blocks in our 81 piece gage block set.

As you can see, we only need 4 gage blocks to form the proper stack of gage blocks, by logically
eliminating our smallest size up to our largest there is no extra gage blocks in our stack. Nor is there any need for borrowing gage blocks from another set to get the stack finished.

See how a seemingly endless job of creating a stack was broken down into a bunch of small easy tasks? Well that is all there is to it really, there are ways to over complicate the building of a stack, but if you follow a logical path to eliminate the size you need down to zero you will in no time at all get good at stacking blocks quickly and effectively.

Dimitrios Simitas