Build - Five Block Test Buttons

The Five Block Text for surface grinders is done by placing five small metal blocks (of equal height) at the four corners and center of the grinder magnetic chuck, and then grinding all five blocks to equal height. The blocks are then measured - ideally all of the blocks will have measure equal height to a high degree of accuracy. Generally speaking, the test measures whether parts at all locations on the mag chuck are being ground to equal thickness.

The test can be performed with mild steel blocks, but I wanted to make something a bit better. I made hardened steel "test buttons" from 1" diameter O-1 drill rod. The buttons were made by cutting of 1/2" lengths from the drill rod to make five disks. Each of the disks was stamped with a number, 1 through 5, at four locations equally spaced around the circumference. The numbers make it easier to track the location of each button on the mag chuck, so that measurements made after a test grind can be identified with a specific mag chuck location.

While I was at it, I also made a simple wood box to store the buttons.

After the disks are numbered they need to be given an initial grind on the surface grinder to make them equal in thickness. Before performing this grind, I also ground a chamfer on the top and bottom edges of the disk. There is nothing critical about this chamfer, so I just ground it by hand on my bench grinder.

This picture shows the blocks after the initial grind (three have already been removed from the mag chuck). Note that I actually made two sets of these, so there are ten blocks in the picture.

The blocks were then placed in my heat treating oven, the temperature was raised to 1,485 degrees F, and the parts were soaked for 30 minutes at that temperature. When the 30 minutes were up, the parts were oil quenched, and then tempered in a second oven (a used toaster oven I picked up at a thrift shop) at 450 degrees F for one hour.

Testing my heat treating oven was another goal of this project - this was the first time I actually used the oven for a real project.

After cooling the disks were lightly polished with a scotch-brite pad, and then given a final grind (both sides) on the surface grinder. This picture shows the ten blocks at the start of the final grind. Note that the blocks placed close together for this grind - they are not in the positions they would be when doing a test.

As a final check, I measured all of the blocks on my surface plate. The blocks measured as equal in height to within 0.0002" (two tenths) or better. I used a 0 - 5 thousandths indicator for this check, but a tenths-reading micrometer could have been used as well.