From time to time it is needful to screw something into something else, which may not yet accept a screw. If the something else is metal, screw threads can be cut into it using a handy tool called a tap. (For rods, the screw thread cutting tool is called a die).
For a long time this seemed to me like an esoteric and scary task, but when I had to do it, I discovered that it is not difficult at all. It requires a bit of time, a bit of fiddling, and a tap & die set, but is well within anyone's ability who has full use of their hands. I do not even own this tap & die set, I borrowed it from my cousin! You may have a cousin with a tap & die set too. Many people do.
Cutting oil is available at any hardware store. You can if necessary get away without this but I recommend it. We found, having tried it, that lubrication did two things: it made starting the tap a lot easier, and it made the threads a little tighter so that the screw was not quite as loose in the hole. In fact in a couple cases we needed to use a wrench to get the screw all the way tight! This is not a very big deal either way but I suspect that the tighter screw will last longer.
For a long time this seemed to me like an esoteric and scary task, but when I had to do it, I discovered that it is not difficult at all. It requires a bit of time, a bit of fiddling, and a tap & die set, but is well within anyone's ability who has full use of their hands. I do not even own this tap & die set, I borrowed it from my cousin! You may have a cousin with a tap & die set too. Many people do.
Cutting oil is available at any hardware store. You can if necessary get away without this but I recommend it. We found, having tried it, that lubrication did two things: it made starting the tap a lot easier, and it made the threads a little tighter so that the screw was not quite as loose in the hole. In fact in a couple cases we needed to use a wrench to get the screw all the way tight! This is not a very big deal either way but I suspect that the tighter screw will last longer.
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Screws are labeled by the diameter of the outside of the threads. To make a threaded hole that fits a particular screw size, you need to start with a hole that is slightly smaller: just a bit bigger than the size of the inner core of the screw (as if the threads were all removed). Additionally, threads come in several different gauges, although usually there are only one or two standard options for any given screw diameter.
In our case we had 3/8" screws, and therefore needed to drill holes of 5/16". This information is helpfully printed on the tap itself! The thread gauge for our screw is 16 threads per inch. The tap set had a handy little tool for measuring this, but it is also easily possible to count threads next to a ruler.
In our case we had 3/8" screws, and therefore needed to drill holes of 5/16". This information is helpfully printed on the tap itself! The thread gauge for our screw is 16 threads per inch. The tap set had a handy little tool for measuring this, but it is also easily possible to count threads next to a ruler.
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Regarding step 1, I use a vernier caliper to measure the smaller diameter, in the valleys between threads. Then I choose a drill bit a litlle greater. Theoretically you can use the exact measure, but then will be more difficult to tap it.
Instead of a commercial cutting liquid I use liquid soap or animal grease, satisfactorily. The advantages are: it is cheaper, easier to find, and you don't need to care where you keep it.
http://img143.imageshack.us/img143/4736/pict0105y.jpg
The stainless angle I had problems with is in there too.
I need the proper wrench that holds the tap or die. I have been struggling, even today, using Crescent wrench or Vice Grips.
My problem now is threading really small diameter material, like 1/8".
I have wondered about the cutting fluid - I have just used oil.
Thanks
Bill