| Index | Thread | Archive | Mar-2000 | Archive | Send |
 |
  |
  |
   |
|
  |
|
of an old post might be in order. As an issue of clarification, FORCE 12 uses only structural rivets and has NOT made a change in methodology by "going to bolts to replace rivets." We have since day one used bolts where we have layers of aluminum caused by inner and outer sleeving. The use of bolts does augment rivets where needed to accommodate element to boom mounting brackets when used for certain models and wind ratings. Hopefully, this is useful information. Natan W6XR/2 FORCE 12 East Ithaca, NY Regarding aluminum "Pop" rivets: Would like to share a little information, as maybe we have a fair amount of experience in this area. One of Force 12's unique product characteristics is that our elements are riveted (with the exception of larger diameter, thick-wall sections where rivets would not be appropriate). The pre-aligned element-to-boom brackets are also riveted to the boom (except for the large weldments used on 80 mtr Yagis). We have used several hundred thousand rivets in the last 6 years. A quick word about the term, "Pop rivets" first... The name "Pop" is actually a registered trademark of the POP Rivet Company. The generic term for a rivet that has no back washer is "blind rivet". A blind rivet is inserted and handled from one side only on the assembly; therefore, it is a different construction than a regular rivet. On the boxes of POP Brand Rivets, they are actually identified as "Blind Rivets." The term "pop" is so common, that we will probably all continue to use it (just like "Coke" - sorry, Pepsi!!). Rivets of this type come in several varieties. The variables are: shaft diameter (i.e. 1/8". 3/16") head diameter and type rivet material (use aluminum for aluminum tubing!) mandrel material and type (different pulling characteristics) "regular" or "closed end" type construction The most common variety of blind rivet is found at the local hardware store. These are a "regular" type construction. This means that the mandrel (the shaft that is pulled by the tool) goes through the rivet body and is attached to a ball at the far end of the rivet body. This is the end inserted into the hole. When the tool is used, the mandrel is pulled outward, pulling the ball along with it. This ball will mash the part of the rivet body that is inside the hole (inside the tubing) up against the inside wall of the tubing. It will continue to do so until the pulling force is sufficient to dislodge the mandrel from the rivet body. Different mandrel designs will pull the ball into the body and leave the ball filling the hole; another is a pull-through, leaving a clean hole; another will leave a portion inside the body to increase shear strength; another will flare the material; another will fully core and spread out a lage portion of the inner surface. The ones usually found are the type that separate from the ball and leave the ball mashed up inside the rivet body. Sometimes, the ball will fall out and rattle around inside an element, so be sure you tilt an element to clean it before putting it up! Please note that the ball material can be important. If it remains inside the rivet, it is most likely participating in the joint. For elements, if the ball falls out, or rusts away, the joint is probably still intact, as the material has been seated firmly into the hole during assembly. Another type of blind rivet is called a "closed end" rivet. This is what Force 12 uses. They are designed specifically for connections where vibration is a primary concern. The closed end rivet has a hole only going part way into the body. The mandrel is attached to the outside (top - towards the rivet head) of this material. After the rivet is inserted into the tubing, the mandrel is pulled. As the pressure increases, the material completely fills the hole, plus pulling tight against the inside of the tubing. When sufficient force has been applied, the mandrel pulls apart from the body. This leaves a solid "hole" and the mandrel is completely removed from the body. The connection has high shear strength and might even be watertight. The mandrels we use on the closed end rivets are steel. Rivets also come with aluminum mandrels; however, the aluminum mandrel will separate from the body with less force, so the steel mandrel provides a more secure connection. None of the steel mandrel remains inside the rivet. The body length of the rivet relates to it's "grip range", or the thickness of material it is designed to hold securely. The grip range of rivets is shown on the package, so be sure to get the right one. A large head is not desired for tubing, as the head will extend beyond the curvature of the tubing, so select one that is probably not the largest in the selection. The diameter of the rivet body is important, as it also relates to the strength of the connection. For most elements, where shear strength is not a primary concern, 1/8" rivets are excellent. When we do inner liners, they are a combination of 1/8" and 3/16", depending on the application. The riveted element-to-boom brackets are secured with 3/16" rivets (with steel mandrels). One should use a little caution in selecting 3/16" rivets, as the pulling force is substantially higher than a 1/8". Unless you have very strong hands (using a hand blind rivet tool), stick with 1/8". Our production lines do not use hand riveting tools, although I do all the time. The production tools are pneumatic and also pneumatic-hydraulic (new marketing term -->pneudraulic). The pneumatic/hydraulic tools are used for 3/16" rivets. The production tools are also equipped with special nose pieces. We use POP Brand production tools and they are exceptional. All we do is keep them oiled and replace the internal springs and jaws as they wear out. Hand tools have quite a range. For price, the Stanley MR-99 is my personal favorite to recommend to folks. The head can be changed from a right angle to in-line. Otherwise, the one I use is called a "Brute" by Creative Engineering, Inc. in Taunton, MA. There is a construction version that I also use, because it is grey and yellow and looks good at shows! On the this type riveter, there is a coil spring that is normally inserted between the handles to keep the tool open. However.....I remove the spring. This is so that I can insert a rivet into the nose and it will stay there (open the handles a little, insert rivet, and the handles close back together with a little force on the mandrel). With the spring in place, the rivet will fall out. Removing an aluminum rivet is simple. The normal hole for an 1/8" rivet is slightly larger than 1/8", as this allows for a small amount of material to be pulled into the hole. To remove, use an 1/8" bit, seat it into the rivet head (where there is a hole already), run the drill slowly to remove the rivet head, then drill through the body, still running the drill fairly slowly. It is rare to have to run a drill very fast. How many times can you do this? At a convention, I once used the same hole all weekend for all the rivet demos. The better quesiton is how many times are you going to disassemble the antenna?? For DXpeditions, a single rivet per element joint is sufficient and very fast to disassemble - much faster than screws or clamps. If you can't take along a drill, then we do make elements for stainless sheet metal screws. These are drilled differently. The holes are first drilled through both pieces, just like for the rivets; then, the sections are removed and the outer tubing is re-drilled larger, as a clearance hole for the screw. If this is not done, the screw will pull material from the inner tube into the space between the tubes, as well as into the outer tubing hole and the pieces will be very difficult to separate, even being unable to separate. Hope this was useful. Have a good day...................73, Tom, N6BT Force 12 Antennas and Systems -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Submissions: send to Force12Talk@qth.com To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk For problems with the list, contact force12@qth.com |
This Thread
|
This Author (Mar-2000) |