Chances are, if you do any gunsmithing at home you’ll be drilling and tapping holes sooner or later. Small taps commonly used by gunsmiths such as 6-48 and 6-40 are easily broken and difficult to remove. These tips will help you avoid tap breakage.
1. Keep the tap straight as you start the first few threads. If it’s crooked, it will bind and possibly break. Use a simple tap guide. If you are drilling the hole with a mill or drill press, remove the drill and install a guide in the chuck and tap the hole before you move on to the next one so the tap is in perfect alignment. Tap guides are available from any tool supply and usually fit right in your chuck.
Guides for tapping off the machine are easily made from spare stock. I use aluminum round stock chucked in the lathe and drilled with a hole slightly larger than the tap. This improvised guide will start your tap straight (see gallery below).
2. Use sharp taps. Special taps such as 6-48 used only in the gunsmith trade are expensive and it’s tempting to keep using one even if it is starting get dull. Don’t do it. As you’re trying to remove a broken tap with a carbide end mill, you’ll be kicking yourself for not using a new tap.
3. Use a good lubricant designed for tapping the type of material you’re working with. Tapping lubricants in the small quantities we use are relatively cheap, so don’t skimp on them.
4. Secure the work in a vise or fixture. You don’t want the piece you’re tapping sliding around while you work. Dedicated fixtures are great if you work on the same part a lot.
These tips are really common sense. Good luck and good tapping!