[TowerTalk] Skyhawk/truss clamp

[Jim Thomson]

Date: Tue, 14 Sep 2010 19:58:43 -0400
From: "Roger (K8RI)" <K8RI-on-TowerTalk at tm.net>
Subject: Re: [TowerTalk] Skyhawk


On 9/14/2010 6:17 PM, ac9s at mchsi.com wrote:
> I am a little behind, but I thought I would offer my Skyhawk observations.  I had one for a few years - worked very well, but the boom broke in an ice storm.  I have a 3el Steppir on the ground now for electrical repairs and am considering either a TH7 or Skyhawk in the near future.  If I do the Skyhawk again I am going to put a DX Engineering Boom Truss on it.

##  The DX eng version  uses a 3/16; thick, wrap around, cast AL  irrigation type clamp.....and also a mating SS  lag bolt and nylock..for the assy that goes around the boom.       DX eng has them in only 2  boom  sizes..2"  and also 3" .  
I used the exact same boom  truss assy years ago..and still have it.  [ both 2"  and 3"].   Back in the late 70's... the local supplier of irrigation pipe also had these mating cast AL wrap around clamps.    Back then, they only came with plated  carriage bolts, not SS.   There is 2 x square holes in the  wrap around clamp flanges.....to take the square nut that's built into every carriage bolt.   The assy is simply  slid over the  2"/3" boom, and tightened, once positioned.   A thimble is slid over the SS carriage bolt 1st of course...and 5/32 " or  3/16"  galvanized / SS  winch cable used along with nicropress crimps..or  cable clamps.     If cable clamps used... the saddle  bears on the long end of the cable  [ live end]..and not the short end] .   I use nicropress crimps at both the boom end..and also the mast end..then nothing is going to fail / rust.    I have had cable clamps  that have rusted ..eventually.   

## These wrap around cast AL clamps are ideal for  a boom truss.   They stick like glue with barely any tightening..since they have globs of surface area.   I have given up on U bolts / muffler clamps etc..for the boom truss.   U bolts and muffler clamps have virtually zero contact [ no surface area at all]  and just crush booms. 

## The DX eng assy to terminate the truss  onto the mast is slick.   The plate they have designed, has an offset built into it... such that the actual truss line itself  is dead center in the boom..and not  off to one side.   The off set plate attach's to the mast with a PAIR of  2"  DX eng saddle clamps..which are  SS..and have  5/16" threads.   The pair of mating saddles are SOLID AL..and textured..the same as the typ dx eng saddle clamps.    All you add is either   a pair of turnbuckles, eye bolts or what ever you want.   Their pair of clamps will no way ever slip on the mast.   And the solid, wide, thick AL  wrap around clamps  for the 2/3" boom  will never slide, nor rust,etc.    I have never had a problem since I cooked up the idea back in 1976. They had bins of em back then..and as soon as I saw them, I grabbed a few... for truss line work. 

##  Interesting enough..when I was in the local Home depot a week ago, they had bins of SS  carriage bolts..and had the correct size for  AL wrap around clamps.   The bolts on mine are rusted, so will be replaced.   There is no need to drill holes through the boom either.  That all  got started when folks had trbl with muffler clamps  slipping on the boom, and truss lines going slack.  

Later... Jim   VE7RF     
   

A boom truss is one of the easiest things you can make.  Two saddle 
clamps (plain U-bolts will work)  to fit the boom and one to fit the 
mast. 4 eye bolts (two for the boom and two for the mast) three 
relatively shot pieces of Aluminum angle (2 to fit the boom and one to 
fit the mast), and a cable to use for the truss.  I used Phillystran but 
wire rope would work as well. I do not  trust aluminum tube used in this 
application.

The two pieces of angle for the boom only need be long enough to 
securely fit the U-bolt that goes around the boom.  The center of the 
angle is drilled to take the eye bolt. The angle that goes on the mast 
needs to stick out far enough so the two eye bolts will line up with the 
boom.