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.
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10 thoughts on “Skill Set: More on Tapping Skills”
Nice! I just had to tap some holes to an old motor mount to attach a new motor to a 30’s era printing press over the weekend. We used PB Blaster for our tapping fluid.
I definitely second the use of a low speed cordless drill (or power drill with a good speed control or not much torque) for tapping, even in thick material!
It makes it _much_ easier to stay in line with the drilled hole, producing a much better result, faster and easier.
Backing out often is _extremely_ important in this case, because the drill can easily snap the tap in the hole if it snags… Proceed slowly, it’ll still be quicker than by hand!
I often used this technique for M2 – M5 holes in anything from 2mm to 15mm aluminium, and even for blind holes. I rarely hand tap anymore.
Lubrication is indeed a must, and can easily make the difference between a good part and a broken tap.
If you’re really stuck, storm the kitchen, or even use a dab of saliva (try not to lick the tap though ;) )
Thx for the post, Gar! I hope people aren’t intimidated by this unusual technique. It’s easy to master if you fool around with some scrap to develop a feel for it. Try a slightly oversized hole at first, as the extra slop gives you a more forgiving thread. Tapped holes look classy and can solve fastening problems for you, especially in tight or compact assemblies. My Ace hardware sells taps packaged with the matching size drill. I store them together in the original card so I don’t have to sort drills to find the right one when I want to make a threaded hole.
Ross touched on something of great importance when he said “tapped holes look classy”. Indeed! Tapped holes give you crazy cred! :)
One more thing I forgot from my toolie days. In soft metal the tap will sometimes distort the surface upward at the edge of the hole. If it’s important to preserve the fit of two facing surfaces, before tapping prepare the edge of the drilled hole by cutting a chamfer with a triangular chamfer bit. This conical bevel will keep the distorted metal from rising above the bulk surface. It also makes starting the tap a little easier, as it centers and guides it.
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