I am sure you have heard the old adage “get the right tool for the job.” The more time I spend working on cars and building things from scratch the more I agree that this is completely true. Yes you can drive a bearing on to a shaft with a long pipe and a hammer, but a press is easier on the bearing and quicker, you can remove many nuts and bolts with a crescent wrench but the correctly sized wrench or socket works better and is less likely to round off the hex head, and you can tighten most bolts and nuts by feel, but a torque wrench is far more accurate and consistent. I could go on and on, as there are hundreds of specialty tools available. But what do you do if the tool you need is not commercially available or is so cost prohibitive that you can’t justify buying one because you will only use it once or twice? My solution is to make one.
I have two full drawers in my tool cabinet of “specialty tools” and about half are home made. They include such things as a bolt pattern redrill jig, bolt in coil spring compressor, and coil over shock compressor just to name a few.
Another of my homemade tools that has served me well and is easy to build is a little gem I like to call a “Square Tap”. What is the hardest part about tapping a freshly drilled hole?? For anyone who has ever used a tap and die the answer is “getting the tap started” The problem is that with no existing threads to grab on to, the tap has nothing but your hand to guide it. That means you not only have to make sure it is perfectly perpendicular to the surface of what ever is being tapped, but also a significant amount of pressure needs to be applied to the tool to insure that as the threads start they do not strip out. These two aspects seem to work against each other and usually result in tapping the hole at a slight angle, a tapped hole that the first few threads are poor at best, and or a combination of the two.
A Square Tap is my solution to the problem and consists of a plate that already has threads in it to guide the tap. By attaching the plate to the part that needs to be taped, you can thread the tap into said plate and use it to guide the tap into the new hole. I have found the easiest way to make a Square Tap is to start out with a piece of 1/4” bar stock. The bar needs to be cut and then drilled out with a bit one size smaller than the desired final tap size.
For the sake of this information I am going to building a 3/8” Square tap and with that said a 5/16” hole needs to be drilled in the bar. The next step is to take a nut of the final desired size, 3/8”, and affix it to the bar. By drilling a hole one size smaller, a 5/16” bolt and nut can be used to firmly hold the 3/8” nut to the bar so that it can be welded. For best results use a bolt that is not threaded all the way to the head so that the nut being welded to the bar stock is over the unthreaded part of the bolt. This just helps to center it a little better.
It is important to note that the coating on most nuts will need to be removed before it is welded to the bar. Most nuts are coated with Zink as a rust preventative which is a good thing, however when welding this material can add impurities to the weld, and also as you are welding the coating burns and produces toxic gasses. I like using a deburring wheel to remove the coating.
Once you have the nut welded in to place the 5/16” hole in the bar stock needs to be tapped out. This is as simple as threading the tap in to the nut and then tapping the bar. When doing any tapping lots of cutting oil needs to be used and a back and forth motion needs to be taken, 1/16 of a turn forward 9/16 of a turn backward, then you go forward 9/16 of a turn until the tap grabs and then go 1/16 of a turn further and so on.
This will insure clean threads and result in a perfectly tapped hole. Once the bar has been tapped the tool is basically done and ready to use, however this is a tool that could last for many years and be used thousands of times, so why not protect it. A complete cleaning with either a wire wheel or in a sandblasting cabinet will leave you with a nice finish, but it will still be susceptible to rust.
The solution for rust prevention is black oxide, also known as gun bluing. Caswell makes a kit that can be used to blue hundreds of items. I purchased one for my Jaguar IRS project and will use for many other things as well. If you will not be bluing very many things a $60.00 kit might be overkill. A less expensive option for those that will only be bluing one or two items would be to pick up a bottle of touch up. Most sporting goods stores carry it. Weather you choose the touch up or the caswell kit the process is the same. You make sure the part is clean and free of all dirt, oil, and rust. You then coat it or soak it in the solution until it takes on a nice dark color.
From there it needs to be oiled which results in a nice tool that is relatively rust proof.
There is one down side to bluing the tool and that is in some cases the best way to hold the square tap to the part being tapped is to tack weld it in place, and as with the coating on the nut mentioned earlier the bluing can mess with the welds, not to mention that after the tool is used the tack welds will need to be cleaned up and those areas reblued. This is just something to keep in mind. If you will probably not be welding on the tool than there is no problem with bluing it. The reality is I have used my Square taps many times and seldom if ever need to tack weld them in to place.
Getting the tool lined up for use takes a little bit of practice, so I recommend tapping a few holes in a piece of scrap steel first. As with any tapping, you start by drilling a hole. Once the hole is drilled the square tap needs to be lined up and secured to the piece being tapped and here is where the practice is needed. I have found the best way to line the tool up with the hole is to thread the tap far enough in to the tool so that a little bit of the tip is sticking out the other side of the square tap and can be inserted in to the hole that will be tapped. When doing this, you need to maximize the amount of tap that is being inserted in the hole with out going so far that the tap keeps the square tap from resting completely flush with the part being tapped.
The easiest way to find the balance is to thread the tap far enough out of the square tap so that it will not rest flush on the part to be tapped, and then back the tap out until the square tap is flush with the part being tapped. Once you have the tap depth set correctly the square tap needs to be secured to the part being tapped. A set of vicegrips or a C clamp works very well as long as the part is uniform and you can get to the under side, but if the piece is of irregular shape than as mentioned above you may need to tack weld the tool to the part being tapped.
Once the tool is secured you use the same basic tapping techniques that we used earlier and tap the hole.
With the hole tapped the square tap can be removed and what you are left with is a quality tapped hole with none of the pitfalls of trying to do it by hand with out a guide.
A Square tap can be made for all the sizes you might use and works just as well for both course and fine thread. Many of the units I have made will have the course thread of a specific size on one end and the fine thread of that same size on the other.
As you can see this homemade tool can come in really handy, and I hope this information inspires you to not only make something similar, but to also think about other homemade tools that may help you on future projects. If you think about it, every tool out there started out because someone wanted something “new” to help them work on a project.
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Gydyup - 67 Mustang Coupe
