In our last article we discussed some of the sheet metal tools that are needed to begin a project. In this issue we will explore the tools needed to deburr, countersink, dimple, and rivet sheet metal. As a short review, the following steps are basic to most types of aircraft sheet metal construction.
Obviously, certain types of tools are used for each step. We will begin by investigating tools for deburring holes.
- cut the pieces of metal to size and bend if needed
- drill holes for rivets and cleco each hole
- disassemble the pieces
- deburr the holes
- countersink or dimple the holes
- prime the part -- if required
- reassemble the pieces together using clecos
- rivet the pieces together
Drilling aluminum causes a burr to form on each side of the piece. These burrs must be removed by a process termed “deburring.” Failure to deburr could cause a separation between the two pieces being riveted together or it could cause the rivet to not fit tightly. Special tools are used for the deburring process.
You will want to purchase some sort of deburring tool to deburr both holes that have been drilled along with the edges of metal pieces. Deburring the edges will prevent cutting your hands along with providing a smooth surface.
- The first one is called a speed deburring tool. You simply place the end of the tool inside the hole and twist the handle around a couple of times to remove the burrs. Several of these tools may also be used for countersinking metal.
- Drill bits are often used for deburring. A larger size (than the hole) drill bit can be placed in the hole and then manually turned to remove the burrs.
- Burring cutters are available to place in drill motors and deburr. These cutters are similar to a countersink but they do not have a pilot hole.
- A swivel head deburring tool is very popular. This tool has blades to swivel and follow the contour of the work.
- Double edge deburring tools are handy for deburring the edges of aluminum.
Dimpling and Countersinking
The next step is to countersink or dimple the metal if you are using countersunk rivets. AN426 rivets require a 100-degree countersink. These rivets should fit securely in a recessed hole so they are flush with the surface of the metal. Dimpling is the preferred method of accomplishing the recess over countersinking depending upon metal thickness. Dimpling can only be done on thinner metals -- .040 thickness or less. Special dimpling tools are available that basically consist of a set of dies (male shaped to match the rivet head and female corresponding to the degree of countersink) that are squeezed together with the aluminum in between. This will press the metal surrounding a rivet hole into the proper shape to fit a flush rivet. It is imperative that the rivet fit securely to achieve maximum strength. The metal is stretched somewhat during this procedure usually opening the hole to the proper size without additional drilling. Countersinking is done with a special bit attached to a drill on thicker metals - .040 and thicker.
- One tool that I would recommend you purchase for your sheet metal project is a riveting and dimpling tool. This is a very handy tool that allows you to place the metal into the tool and use a wooden mallet to strike the shaft. This allows you to dimple metal if you have a dimple die in place or rivet if a rivet set is in place. This tool ensures proper alignment with the metal surface.
- Dimple dies—these small machined pieces of metal consist of a male portion and a female portion that when pressed together using a squeezer or the tool mentioned above, will leave the proper shape to fit a flush rivet. Dimple dies are manufactured in sizes corresponding to the rivet size.
- Other types of dimpling tools are vise grip dimplers, made for hard to reach places, and pop rivet dimplers that are used with pop rivet tools.
- Countersinking thicker metals is usually accomplished with a countersink that is placed in a drill motor.
Selection of a rivet gun is important. You will be spending a lot of time with this tool so make the selection carefully. Rivet guns are pneumatic tools and the two most popular for our use are the 2X and 3X guns. The X simply has to do with the length of the gun. A 2X gun is adequate for driving up to 1/8-inch rivets. Above that size you will probably want a 3X gun. A 3X gun basically hits the rivet slower and harder. Make sure when you squeeze the trigger of your rivet gun you can vary the strength of the impact. Try out a rivet gun before purchasing if possible. Squeezing rivets is also an option. Several rivet squeezers are available, both hand squeezers and pneumatic squeezers. Most builders prefer to squeeze a rivet rather than drive it if at all possible. I would recommend that you purchase a good quality hand squeezer and a good quality 2X rivet gun. You will be spending a lot of time with these two tools.
After spending money on your air tools you should keep them in good condition. Pneumatic tools should be oiled daily with a non-detergent type oil. A few drops placed into the air inlet of the tool is all that is necessary.
- Rivet fence—It is actually used during the drilling phase of construction. After you layout the rivets you then mark and drill them.
- Rivet squeezer—you can purchase either a hand squeezer or a pneumatic squeezer. A good quality hand squeezer is usually more than adequate. This tool can be used to dimple (as previously discussed) or squeeze rivets. Rivet squeezers also have different sizes and types of yokes to allow for squeezing rivets that are located further from the edge of the piece of metal.
- Rivet sets—You will need sets for flush rivets and for each of the universal rivet sizes you will be squeezing. These sets must be purchased separately from the squeezer. The flush sets (used for flush head rivets) have a smooth, polished face while the sets used for universal rivets are cupped to fit different size rivets. For universal rivets one set is cupped to fit the rivet head while the other set is smooth and is placed against the shop end of the rivet.
- Take a block of wood and drill holes into the wood that will allow you to place all of your rivet sets into the block. This way you will be able to keep up with these small, expensive pieces of metal. Predrilled blocks are also available to purchase.
- Rivet gun—again, several types are available. For the average builder a 2X gun is adequate. The gun itself should be of high quality. You should be able to tease the trigger throttle for precise control of the riveting pressure.
- Rivet sets—your rivet gun will have to have sets for each type and size rivet. You will need a flush rivet set, for flush head rivets, and a rivet set for each size of universal head rivet you will be driving. Rivet sets come in all shapes and sizes. They are offset, long, short, etc. Start out with the standard, straight sets. You can always purchase additional sets as you find a need for them. Many of the flush rivet sets have a rubber guard on them to help prevent slippage while riveting.
- Retaining springs—Another piece needed for the rivet gun is the retaining spring. You must be able to change out the rivet sets on the gun and the rivet sets must be held in place on the gun. They are held in place with a special type of spring adapted to the gun itself. You can purchase a quick change spring that can be used for both straight and flush rivet sets, a spring for flush sets, and a spring for straight and offset rivet sets only (beehive set).
- Back riveting set—if you plan on “back riveting” flush head rivets you will want to purchase a special set. You will also need a back riveting plate for this operation. The back riveting plate acts as a stationary bucking bar while riveting. In back riveting you actually set the shop head of the rivet rather than the manufacturer’s head. Back riveting is used on RV type aircraft construction.
- Air regulator—this is a need addition to your rivet gun. This will allow you to adjust the air pressure going into the rivet gun for more precise control.
- Bucking bars—these pieces of heat-treated iron are placed against the shop head of the rivet during the rivet installation. They come in all shapes and sizes. Start with a few standard sizes and then purchase additional ones as needed.
- Rivet gauge—these small gauges may be used to check for the minimum height and diameter requirements of the shop head of the rivet after you have it installed. Different gauges for different size rivets.
- Rivet cutter—a rivet cutter is used to cut the length of rivets prior to installing them.
- Blind rivet pullers are used to construct several kit aircraft. These are commonly known as pop rivet pullers. The most common is a hand pop rivet tool that has a swivel head. The rivet is placed in the hole and literally pulls the special type rivet through the metal. Pneumatic rivet pullers are also available.
Safety With Tools
Primary attention must be given to safety during the use of your tools. Eye protection is absolutely essential. Drilling metal, grinding, and other tasks, can create metal shavings that can be thrown into an eye. Be sure to wear adequate eye protection. A full-face shield is recommended when you are using a die grinder (high speed grinder). Metal shavings from the aluminum along with pieces of fiberglass from the cutting wheel are thrown with tremendous speed and impact. A high-speed grinder can be very hazardous if not used properly. Ear protection should be used during several tasks such as riveting and drilling. When drilling, be sure your fingers and hands are not in line with the end of the drill bit. Disconnect the drill from its source of air prior to changing bits. Avoid loose fitting clothing. Disconnect rivet guns from their source of air before changing rivet sets. Avoid operating a rivet gun unless the set is against a piece of wood or a rivet. If you pull the trigger without having the set against an object, the set can become a small missile.
Understand that we have presented the most popular and most used tools for sheet metal construction. The list of additional tools you may purchase is endless. There exists a tool for almost every job. Consult your kit manufacturer for the tools you will need to begin your project.