While the Tap & Die go hand in hand as threading tools, they’re very different in the way they work. There are also different tricks for success. So, let’s talk success tips for making external threads with a die.
The Tap and Die are both cutters for making threads. Taps have teeth on the outside for making threads on the inside. Dies are the opposite with teeth on the inside for making threads on the outside. For typical DIY, taps are much more common, and are easier to use properly. Dies are less used (fortunately), and come to failures more often (unfortunately). Mostly, we buy external threads in the form of a bolt, but there are times when we need to create them, so one way is with a die.
What Is A Die?
Remember this picture? It comes from our article on tapping for internal threads. The long straight parts in this image are taps — for cutting threads on the internal surfaces of a hole. The round cylindrical parts in the image are dies — for cutting threads on the external surfaces of a cylinder.
For reference, the “inside” story on threads — tapping internal threads — is covered in the article “Get Thread Tapping Straight“.
Today, we’re talking about dies, and tricks to making good external threads.
For DIY there are 2 really good uses for dies. The first, for chasing threads; and the second, for creating them. The first, chasing or clearing external threads with a die, is the simpler case, so let’s start there.
Anatomy Of The Tool
A die is a pretty simple looking tool. It’s like a nut, but with interrupted internal threads, the edges of which are the cutting teeth. Thread dies are often round on the outside like in the picture, but they are sometimes hex or other shapes. Just like taps, they come in different configurations like with 3 or 4 or 5 or more columns of threading teeth. While specialty dies come with teeth shapes for cutting particular materials, general purpose dies are usually good enough for DIY.
Thread dies have a front and a back — or more accurately, an entry side and an exit side. You can tell the entry side because it has a relief in the cutting threads — with reduced height teeth for starting the cut. The relief in the entry side also helps center the die on the cylinder to begin the thread.
Clearing External Threads With A Die
Have you ever tried to turn a nut onto a bolt and found there is a burr or something in the threads that makes it difficult or impossible for the nut to pass? There are several ways to conquer this, but one is with a die.
So, I have to caveat this trick with a couple things. First, if the bolt is really hard, like grade 8 or 10.9 or something similar, the die might not want to cut a serious burr. Second, depending on how the bolt threads were created, a die might want to peel the threads all the way down, and that can cause it’s own problems. (When the original external threads are super accurate and “tight” fitting, a general purpose die will cut them less accurate and slightly looser fitting. It’s not often a problem, but it’s worth mentioning.)
Clearing threads with a die is a cool trick, but it doesn’t always work perfect. The ideas is to simply thread the die onto a shaft, just like you would a nut. As you turn the die, it trims off burrs and damage leaving a nice thread again. Obviously it can’t put back material that moved, but it can cut off the burrs to clean it up.
The real trick to success is making sure it goes on straight, and to make sure the die comes nicely into the existing threads. If it doesn’t align right, it will cut new threads on top of the old ones, and that will totally ruin the part. “Cross Threading” Anyway, take some care that things align, then this trick will fix the damaged threads.
Creating New Threads
When we think of a thread die most of the time, we think of cutting new threads. Effectively making a bolt. If that’s what you need, then for sure, the die is a great tool to accomplish it.
The concept is simple — place the die on the end of a shaft, then start turning the die. As the die turns, it cuts new external threads. Right? Yes, that’s the concept. Doing it right is the issue.
The first few times I tried to put threads on a shaft, I ended up with a mess. Turns out it’s really hard to get the die on straight when you’re doing it by hand. I ended up with a new thread that was slightly cattywonkus to the shaft. I don’t have a picture, but imagine the threads going at a slight angle to the shaft — where the further down the shaft the threads get deeper on one side and shallower on the other. Eventually the die won’t turn anymore, and the part ends up as garbage. The unfortunate thing is there is no way to correct the issue once the threads are cutting, and you can’t tell you’ve got it wrong until the threads are there.
The trick is to use something that forces the threads to start straight. Here’s a video of how I do it now.
Video: Cutting New External Threads With A Die
Here’s a quick video showing one technique for using a die for good external threads. Just to make it hard, we show a thin wall stainless steel tube, welded seam. Enjoy the video.
So if you’ve ever had trouble — like I have — with getting a die to start truly straight, that’s a good technique. There are not too many times when a thread die is really needed, but when you do, then it’s sure nice to have one. Like the tube in this video — I did not want pipe threads (and they wouldn’t fit that diameter anyway). So, a thread die does the trick.
Instead Of A Die . . .
While the die is right for many jobs, there are substitutes that can come in handy instead of the die. The first, and most beautiful is a friend with a lathe. While that’s not always available, how about variations of bolts. On many occasions I have cut the heads off bolts to use them for something. Bolts are cheap comparatively, and they’re a bunch stronger than material you can cut threads on. One example is shown in the image. I needed a peg with threads, so I just cut the heads off bolts, then rounded the needed end with an “essential” grinder. Works perfectly.
Other options include using bolts or threaded rod, or something similar. For instance, welding a bolt sticking out of a chunk of tube for a long hollow shaft. The possibilities are endless for substitutes, but now you know a good trick for creating external threads with a die, you don’t always have to find a work-around.
Good Luck With All Your Threading!