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There are several satisfactory methods for joining fiberglass tubes together when they are sleeved inside one another (as they are when making a quad spreader.)
One method is to cut a slot in the end of the larger of the two tubes using a hacksaw. The slot should be 2 to 3 inches long, and well centered in the tube. You may then use an all-stainless hose clamp (also called a screw clamp) to fit over the outside of the larger tube and compress the portion with the slot around the smaller tube inside, holding it firmly. This method has the advantage of being easily removable for disassembly if required. A second screw clamp may be used for greater security at the joint.
A second method is to glue the tubes together. You may use epoxy (the 50/50 type....consistency of syrup....not the "filler" types of epoxy which are the consistency of putty.) Note that epoxy adhesives do not want to bend or flex. They get quite rigid, so if you are using the fiberglass in an application where the joint will be subject to bending, epoxy is NOT the best choice. If you have adequate curing time, adhesives such as "Goop" (or the very similar and cheaper "clear elastomeric caulk" ) are sold in paint departments of many stores with the caulking products. A caulking-gun sized tube is usually around $5, and will do a large number of tubes. One other adhesive which works quite well, remains somewhat flexible, is inexpensive, and cures relatively quickly, is the construction adhesive "Liquid Nails". Just smear thinly on the outside of the small tube (as far as you will overlap) before inserting. A little smeared inside the larger tube will help, too. Work quickly, as these products cure fairly quickly in air....but once the joint is together, it will take several days to finish the cure because little air can get in the joint. This is a strong, yet flexible joining method with adequate curing time. . You will have to rip the fiberglass apart to disassemble after curing, so be certain you get lengths correct.
Another adhesive is one called 3M 5200 fast cure. (24 hour cure) Sealant, 3M TM Marine Fast Cure 5200 Adhesive
This is a boat building adhesive rated for above and below waterline work. Rated for constant water contact, fresh or salt. Single part adhesive (no mixing) that comes in a caulk sized tube. Very fiberglass friendly. Fumes are not toxic, either!
Available at boat supply houses, or a web search will turn up many dealers. Sells for around $15 per tube. Just make sure it has not old stock, as it has a limited shelf life. Opened tubes may be capped well and refrigerated for about three months for later use. This adhesive sets in one hour, full cure in 24 hours. Forms a SUPER strong bond. Gives you plenty of working time, unlike epoxies, but will cure with limited air contact.
Note that a standard cure version of 3M 5200 is also available (at Home Depot paint departments with the glues, in a toothpaste-sized tube). This product requires a week to cure but is just as strong as the fast cure version.
A good method of applying all of these adhesives inside tubes is to squirt the adhesive on a dowel or rod of smaller diameter than the inside of the tube to be glued. Roll the dowel around on the inside of the larger tube, evenly spreading the adhesive on the inside wall. This is easily done from both ends of the tube. As soon as adhesive is spread, slide the smaller tube or rod you wish to secure inside the larger tube and allow to cure. Be sure the tube is not bent when curing, or it will set in that form!
The third method is by use of a couple of stainless machine screws which go through both tubes. An illustration of this method is below:
When drilling holes for the machine screws to hold sections together, assemble the spreader joint with the exact overlap in place, and drill all the way through both sides at once (taking care to drill straight through the centerline of the tube, perpendicular to its surface.) This method also allows for disassembly if desired. For additional security, apply a little thread lock or glue to the nuts after tightening.
Max-Gain Systems spreaders (in almost all of our spreader combinations) provide enough extra length to allow some of the smaller tube to be cut off (using a hacksaw or an abrasive blade on a chop saw) and inserted into the bottom end of the larger tube. This doubles the wall thickness at the point of greatest stress, and the point where the U-bolts or screw clamps hold the spreader to the spider hub. When installing this internal reinforcement, one of the adhesive methods should always be used. Always try to keep a passageway clear down the center of the tubes for moisture to drain.
Always allow for moisture to drain through any fiberglass spreader. Any water actually trapped in the spreader can freeze and damage the tube. For our Type 2 spreaders (ONLY), which use the SOLID ½ inch rod as reinforcement for the ¾ inch OD tube (where the U-Bolts clamp the tube), the reinforcement joint must not be completely sealed. A small amount of adhesive on one side only of the solid ½ inch rod before insertion into the ¾ inch OD tube is sufficient to hold it in place. No adhesive at all should be used at the point where the sections are joined together-the machine screw method will do the job!
Any fiberglass, no matter how UV-stabilized, will eventually degrade after prolonged exposure to sunlight. Make your spreaders last many years longer-and decrease their visibility to wife and neighbors-by spray painting them flat black. First clean/degrease them with a good solvent such as acetone or methyl ethyl ketone..."M.E.K." (follow their label directions!) Then use a good primer-allowing it to cure at least two days. Finally, finish with a good top coat of flat black. This paint treatment is suitable for most any fixed-position use of fiberglass tube or solid rod which will not require sleeving movement between sizes. NOTE: We do NOT recommend painting our fiberglass push-up masts, or any application in which the fiberglass tubes will be frequently sleeved inside one another. The inside of the tubes is much more abrasive in nature than the smooth outside, and this abrasive inner surface will quickly scar most paints. Thick or multiple paint coats in sleeving applications will also decrease clearance between the tubes, possibly causing binding. In the case of push-up masts, count on our high percentage of UV stabilizers to provide long useful life.
"Pinning" When attaching antennas, rotors, etc . to fiberglass masts or crossbooms, the following precaution is HIGHLY recommended:
Normally, solid rod is used in these applications, because of its great strength, and resistance to crushing when compressed by U-bolts and mounting clamps . Even though it is very strong, the fiberglass is not as hard as the metal clamps or brackets . As a result, as wind and vibration from antenna rotation act on the point where the clamp and fiberglass meet, the vibration will slowly loosen the clamp by "chewing" on the fiberglass .
The remedy for this is to drill a small hole through the mounting bracket, and about half way into the fiberglass rod . Insert into this hole a TIGHT FITTING stainless machine screw . It does not need to be a large diameter, just a very tight fit in both the metal bracket AND the fiberglass rod .
A few drops of a good strong adhesive in the screw threads or in the hole in the fiberglass will also be helpful . An adhesive should be chosen that would hold tightly, but still allow removal of the screw if desired at a later date .
The goal of this procedure is to prevent ANY motion between the clamp and the fiberglass, therefore preventing any loosening over time . It is well worth the effort .
In order to estimate how far out (measured from the center of the boom) a quad wire of a given length will intersect with a spreader, use this formula:
A far less complex method (with thanks to Ed Niemi, K6EDJ) is to simply take the cosine of one side of the quad loop (.707 times the length of one side of the quad loop) and measure out the sp reader (measure from the center of the boom) to determine the point of wire attachment! The measurement from corner to corner, measuring down one sp reader, through the boom, and up the opposite sp reader, (wire attachment point to wire attachment point) of each quad loop will be 1.414 times the length of one side of the quad loop.
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