A dividing plate is very useful for things such as drilling holes 120° apart, milling hex flats, etc. By coincidence I had 2 hard drives fail in the past month, they had been running 7/24 for >6 years. A few minutes with a torx driver and out popped a bunch of shiny discs.

The centre hole is just under 25mm, so a piece of 1” steel was sliced off and step drilled to just under 0.25”. A reamer finished the hole to exactly 0.250. The slice was then placed on an arbor, and the circumference turned down to an exact fit into the platter’s hole.

The Taig group on Yahoo recently had a discussion about making indexing plates. There are several ways to get the 40, 50 and 60 holes located on circles.

• Rotary table
• Direct via template
• Using a pattern such as a gear, circular saw blade etc

Creating a template is straight forward. Print it out, stick on your platter with removable glue and mount on the milling attachment or a piece of angle iron bolted to the cross slide. Loosen the centre bolt, turn to next line, lock, drill, repeat many times. With a bit of care this should be accurate enough for most hobby operations.

Using a pattern such as a gear or saw blade is describe in various places. Monty Remon shows several approaches using gears. Keith Brooke shows another method using a drill press.

Lastly Nick Carter sells 60-50-40 index plates for a reasonable price.

Which brings us to the rotary table. Having just received mine from RDG Tools, I needed no excuse to start using it. I tapped the M6x1 centre hole of the table out to the full length. This enabled a locating pin to be threaded in, which I made exactly 0.250” diameter to match the adapter I made above. I set up a carriage stop so all the holes are a consistent depth, the angle on the #3 centre drill provides a nice chamfer.

Locate the centre drill along the outer circle, lock the vertical and cross slides and start the drill-rotate-drill sequence. 60 holes later, move the cross slide to the next circle and start the 40 hole (9° apart) sequence. The centre drill I used was probably not sharp enough, lots of tear out on the reverse side. 200 twists with a small countersink cleaned up the holes!

I still need to make the block with index pins and a bushing to fit the plate onto the drive pulley but the tedious part is done.