What are Springback or Spring Back Dimple Dies?

Many aircraft builders ask what the difference is between a Springback and regular dimple die. The concept behind springback dies are that the aluminum is slightly "canned" in the opposite direction of the dimple (about 1-1/2 degrees) which allows the aluminum to "Spring back" into a flat sheet around the dimple. A regular dimple die will leave a slight can around the dimple, in the same direction as the dimple. Springback dimple dies were developed by the Aluminum Company of America in 1942 under contract for the National Advisory Committee for Aeronautics. Since that time there are a few tool companies that have the illusion that they invented the springback dimple dies, or that they have improved upon them. We have measured and tested all of them. The bottom line is that the spring back dimple dies work on 1/8" or larger diameter countersink holes, and all of them work the same with no noticeable difference in the finished product. However, technique of dimpling also affects the finished dimple and canned effect. On 3/32" rivets we find that a standard die works as well as the spring back dimple die. Many will argue these points, but they will also say that they invented this 1942 tool. The best dimpled hole is one that is dimpled a second time with the actual rivet that will fill the hole and a dimpling block -- see my May 2, 2006 previous post on this subject.

RV Tool Kits

Many new builder's ask if they need a full tool kit or if it is wise to only get an empennage tool kit to start with. I think that most RV builder's will agree that the tool list on Van's website really does not contain all of the tools needed for the empennage or the full airplane. It's a good start, but many other tools are needed to build the airplane. Most full tool kits provide the necessary tools for the sheet metal work, but many other tools are available to make the building process easier and to do a better quality job on the finished product. When a builder is considering the empennage kit rather than a full tool kit the things to keep in mind are: 1. Do you plan to build the full airplane or are you only building the empennage to see if you are really ready to tackle the airplane. If so, you may want to consider the empennage kit. If you are committed to the whole airplane then start with the full tool kit. 2. Buying the kit piece-meal will most likely cost more money in the long run. Shipping is expensive, often as much as the tool itself if it is a small purchase. These costs will add up and could significantly increase the total cost of the tools. 3. Most full kits are assembled in a way that gives the best price available and gives you a set of matching tools. I believe this is the best way to go if you are committed to building the airplane. Thanks, Glenna

The Best Drill for aluminum sheet metal

What is best in an air drill for aluminum work on an airplane? #1 Speed, #2 User friendly, #3 comfort, #4 quiet, #5 reversible. For aluminum 2000+ RPM is needed. A drill that is user friendly will accept the drill and accessory sizes you need to use and will be easy to change bits/tools. A keyless chuck is the best way to accommodate this. A drill should be comfortable in your hand. A drill should be quiet. Some air drills like the Sioux palm drill are very quiet. Many builders are going to high speed battery operated drills which are also quiet. Reversible -- well, I threw it in but have never owned one myself. That's why it's at the end of the list. I've never seen a worn out reversing trigger on a used drill.

Building the Van's RV Aircraft

If you are considering building a homebuilt airplane then look carefully at a Van's RV aircraft. Some things to consider. Van's has more kits produced and more flying airplanes than any other homebuilt. Accident history of homebuilt aircraft is important to research and understand. Only an aircraft mechanical or performance failure may be reason to shy away from certain aircraft. Most of the Van's aircraft that have been involved in accidents have been the result of pilot error or builder error. Van's aircraft are very high performance and require the right level of pilot experience. If you build one don't fly it yourself unless you have actual stick time in another Van's aircraft or with an experienced RV pilot in your local area. Avoid builder errors by checking and double checking every decision you make at www.vansairforce.net. Other builders will be glad to help you avoid any problems. If something doesn't seem quite right then ask before you build or install that part. Use the very best tools from www.planetools.com so that you can be sure the parts and assemblies you use on your airplane will be right. Take time to do every job correctly. Rework if you need to. This will help you avoid any mistakes during the building process. Ask a fellow EAA RV expert to assist you by reviewing your work and helping guide you in the building process. This is invaluable in that it will help you avoid costly mistakes and rework. In the end you will have a fantastic performing airplane that will take you just about anywhere you want to travel. HAVE FUN. Thanks, Glenna RV8A N220LS (In to tools!).

How long should a rivet be before driving or squeezing?

Several builders and customers of aircraft tools have asked how long a rivet should be before they drive or squeeze the rivet. The simple answer is the shank of the rivet should stick out 1-1/2 times the shank diameter before driving. There is a link to a mil-spec above that has the exact measurements in Table 3. If you follow the 1-1/2 times the shank diameter rule you will always be pretty close. Hope this helps those of you who may not have heard this before. Glenna

Dimpling Block - Setting Perfect AN426 Rivets

I have had several questions on the earlier explaination of making a dimpling block to set AN426 rivets. A couple of photos have been added to this link to show what the dimpling block looks like and how it is used to set near perfect rivets. This process will set the rivet in the skin before actually driving the rivet. The result is that the rivet and skins will fit nicely together. When the rivet is actually driven this will produce the best quality flush rivet.

Pneumatic Rivet Squeezer Set-up

The set up of a pneumatic rivet squeezer is different for riveting and dimpling.

For riveting -- Always start with a gap when the squeezer is fully activated. The initial gap should be the skin thickness plus the length of the "finished" rivet. Once the rivet is squeezed if the butt of the rivet is squeezed too little add shims or fine adjust until the butt of the rivet is the correct size. It is better to have the rivet squeezed too little than to over-squeeze.

For dimpling -- The dimple dies should touch each other without any gap. The male die should be in the fixed part of the yoke and the female in the set holder that moves when the squeezer is activated. When dimpling, place the aluminum over the male set holder and trip the squeezer trigger very fast and at full throttle. This will "slap" the dies together to create a nice crisp dimple.

Caution -- Pneumatic squeezers have enough power to spring a yoke. Most yokes spring a little during dimpling and riveting, but do not operate a squeezer with less than zero clearance in the yoke as this may permanently bend the yoke.

Deburring Rivet Holes

A lot of discussion centers around deburring of rivet holes. After drilling and installing hundreds of thousands, if not a million rivets I can say with some authority you do not need to deburr rivet holes in .020 or .032 aluminum. What is left in the hole is not a burr, but is actually a chip left over from the drilling operation. You can easily remove chips by disassembling the parts, putting on a pair of gloves and lightly running your hand across the drilled sheets. What must be avoided is removing the aluminum material. The holes should be crisp and clean, not deburred by removing material. If you do have an occasional burr (a piece that you cannot remove by rubbing) you can remove it by taking a countersink bit and lightly turning it by hand to remove the burr.