Skill Set: More on Tapping Skills

In response to my post yesterday on tap and die, one of our fave MAKE contributors, Ross Hershberger, posted a set of tips we thought should have its own post. Then, reader johngineer chimed in with his own excellent tips. We love getting this sort of intel from our community. Thanks, guys! First, Ross:

Making threads is a very useful skill. Being able to fasten parts with their own threads can reduce the total parts count and the complexity of a project. When I worked in a tooling shop, I tapped hundreds of holes. Here are some tips:

1) For thick material, where ultimate hold is not necessary, you can use the next size larger drill. This will result in less thread depth but the tap will cut easier. The standard for 1/4″ – 20 is a #7 drill (0.201″). A larger #6 hole (0.204″) or 13/64″ will tap easier because the tap is taking off less material.

2) Definitely back off the tap 1/2 turn for every turn forward in thick material. The swarf must be broken loose or it will jam the tap in the hole. Everyone makes that mistake once and then never forgets the hassle of making the repair.

3) When tapping deep holes, periodically run the tap out, blow it off and blow the swarf out of the hole to prevent jamming.

4) There are different types of taps. The tap shown in the video is for through holes. Taps for blind holes have a squared-off rather than tapered end.

5) If you have to tap a bunch of holes in thin material, you can use the tap in a cordless drill on low speed. This is quick, but be careful because removing a broken tap from a hole is very slow.

6) Tap oil is essential to lubricate the working surfaces. Tap Magic is a good one. ATF (automatic transmission fluid) will work in a pinch, too.

And here is johngineer’s additional tips:

7) Know your material. Aluminum, brass, and steel all behave differently when cut, and each requires its own approach. Steel and brass tend to make chips better, which means a cleaner cut, but also that you need to clean out chips early and often. Aluminum, on the other hand, can be more “gummy,” and requires that you break chips yourself. (Do this by backing out slightly every 1/4 turn, in addition to the backing out you’re already doing to clear chips).

8) A small tap means a small force. The amount of force you should exert on a tap varies in proportion to the size of the tap. This means that the force applied to tap a 1/4″ thread is at least half that required to tap a 1/2″ thread. Smaller taps break much more easily. For holes smaller than about 3/16″, you really need the kid gloves.

9) Know if your material can “hold” the threads. Plastics and soft metals like aluminum don’t hold fine (UNF) threads very well. Stick to coarse threads (UNC) If you’re going to be using them with steel or brass screws, which can easily strip fine threads in soft material.

10) A vertical hand tapping machine can be a godsend. Every metal shop I’ve ever been in has had at least one of these around. Grizzly sells one for about $80. I’ve also heard them referred to as “Lassy Tappers.”

11) (Just to repeat what Ross said) Use Tapping Fluid!. If you don’t have proper tapping fluid, you can get away with WD-40, or even mineral oil in a pinch. I use RapidTap myself.

See our entire Mechanics skills series


Gareth Branwyn is a freelance writer and the former Editorial Director of Maker Media. He is the author or editor of over a dozen books on technology, DIY, and geek culture. He is currently a contributor to Boing Boing, Wink Books, and Wink Fun. And he has a new best-of writing collection and “lazy man’s memoir,” called Borg Like Me.

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