Build - Drill and Tap Index

Drill and Tap Index

[Dec. 21, 2014]

This drill and tap index stores all required taps (bottom, plug, and taper) for common screw sizes from  #4-40 up to 1/4"-32. These are the sizes I most commonly use for home machining. With this index, I can easily select a drill and tap for any of the included screw sizes, for either a 50% thread (steel and other hard metals) or a 75% thread (aluminum, brass, and other soft metals). Also included are drills for close fit and free fit holes.

 Empty Index
 Index with drills and taps

You will note that in some of the holes I have cotton swabs inserted - these are "place-holders" for empty holes where I do not have the required item. I do this to make sure I do not return a used drill or tap to the wrong hole. The template for this index is available at the links below, and includes the following features:

  • all holes have marked centers to aid in drilling out the index
  • holes for bottom plug, and taper taps
  • holes for standard drill sizes for each tap
  • holes for close fit and free fit holes for each screw size
  • all the holes for drill are labeled with drill number and decimal size

Links to the template are below:

Making the Index

I start by gluing together two pieces of painted 3/4" thick finished MDF, cut slightly oversize (in my case I used an old MDF bookshelf board from my scrap pile). I just used a good wood glue, and clamped them together overnight.

Next I attached the template, which was printed in color on full page size label stock.

I trimmed the block to size (on all four sides) on the table saw. Note that the MDF is cut just slightly larger than the "label" - this is to help keep the label from coming loose at the edges.

After cutting to size, I gave the label/top two coatings of clear acrylic enamel; I used Rust-Oleum brand, as shown at left, but pretty much any clear acrylic or clear urethane should work. It is probably best to use a spray type application, so as to avoid disturbing the printed image on the label.

Finally, the holes are drilled (I drilled to 3/4 of the total thickness - about 1-1/8" in my case). I tried to drill a "loose fit" hole for each drill or tap. The plans provided above include a guide showing a suggested drill size for each hole.

After drilling, the holes have a slight burr around them; this was removed by sanding very lightly with 180 grit paper - just enough to remove the burr without scratching the label.

The finished index is shown in the pictures at the top of the page. As previously noted, it is recommended to "fill in" any unused holes with a piece of rod or similar, in order to avoid accidentally replacing a used drill or tap in the wrong hole. You may also note that I used screw machine (short) length drill bits, as I find these more useful on my small mini-mill. By the same token, it is not necessary to fill every hole in the index, if you are never going to use a particular size; for example, I don't recall having ever used a #12-32 tap, but I provided space for one for the future, just in case.